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Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS)
Engineering Science and Technology, an International Journal xxx (xxxx) xxx
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Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS) Devendra Kumar Gupta a,⇑, Rajesh Kumar b, Naveen Kumar b a b
Department of Mechanical Engineering, Inderprastha Engineering College, Ghaziabad, UP 201010, India Department of Mechanical Engineering, Delhi Technological University (Government of NCT of Delhi), Bawana Road, Delhi 110042, India
a r t i c l e
i n f o
Article history: Received 20 July 2018 Revised 20 April 2019 Accepted 23 April 2019 Available online xxxx Keywords: Ejector Triple pressure level absorption system Solar energy Parabolic trough collector Thermal energy storage Organic Rankine cycle
a b s t r a c t The Proposed system consists of an ejector organic Rankine cycle (EORC) integrated with a triple pressure level absorption system (TPAS) based on parabolic trough collector (PTC) solar field. This system produces power and refrigeration output at two different temperatures simultaneously. A thermodynamic analysis is conducted to discover the effect of various design parameters such as solar beam radiation (SBR), turbine inlet pressure (TIP), turbine extraction pressure (TEP), and ejector evaporator temperature (EET) on the performance of the proposed system (EORTPAS). It is found that with the addition of TPAS in EORC, the energy efficiency of EORTPAS increases considerably but exergy efficiency decreases. It has also been observed that energy efficiency increases with the increase in TIP, TEP and, EET while decreases with the increase in SBR for both the systems. On the other hand, the exergy efficiency of both the systems increases with increase in SBR or TIP and with the decrease in TEP. It is also noticed that there is a slight decrease in exergy efficiency of both the systems with the increase in EET. Ó 2019 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction The rigorous use of natural fossil fuel has created a havoc of global warming that produces deadly greenhouse gases like- CO2, CO, NOx, etc. More woes are being added by our conventional cooling systems which emit refrigerant gases like CFCs which are high in GWP (Global warming potential) & ODP (Ozone depletion potential). Since the last few decades, scientists did carry out enormous research on the alternative technologies which can be a simile to our natural fossil fuels and also cut down on greenhouse effect by actually reducing the carbon emission. Solar energy also affects the convective ambience creating currents that fuel the air to be wind; hence the wind energy is a derivative of crude solar energy. Not only on winds, but it also affects the formation of tides and we could then materialize the energy as tidal energy [17]. Presently concentrated solar power (CSP) technologies gaining the interest to be used in solar thermal power plants. Major applications of PTC can be found in power plants of southern California known
⇑ Corresponding author. E-mail address: [email protected] (D.K. Gupta). Peer review under responsibility of Karabuk University.
as solar electric generating systems (SEGS) has an installed capacity of 354 MW [15]. For experimental purposes, an installed capacity of power 1.2 MW by the collector has been installed at Plataforma Solar de Almeria (PSA) in Southern Spain [11]. Mokheimer et al. [18] developed a simulation model to evaluate the optical and thermal efficiencies of PTC solar field and also carried out the cost analysis. Their findings showed that the maximum optical efficiency that can be reached is 73.5% in Dhahran and the specific cost for a PTC field per unit aperture area can be reduced by approximately 46%. Barberz et al. [3] presented a new approach for the prediction of thermal efficiency in solar receivers. Two simplifications can be made based on this approach to obtain much simpler equations that describe collector performance for the majority of solar technologies. Tyagi et al. [23] conducted the exergy analysis of PTC for different mass flow rates of heat transfer fluid. Their result shows that for a given value of solar intensity, the exergy output, exergetic and thermal efficiencies had been found to be the increasing function of mass flow rates. An analysis of exergy has been presented in Padilla et al. [19], which shows that the intensity of solar radiation has a high impact on the role of PTC. The exergy efficiency has a relation with the temperature of the HTF leaving the receiver. If the temperature of heat transfer is enhanced, then there will be an improvement of exergy efficiency but a decrease in
https://doi.org/10.1016/j.jestch.2019.04.008 2215-0986/Ó 2019 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
Nomenclature Ap ABS ARC C E EET EJ G1 G2 Gb h HE HTF HTV LTV P PTC R s EORC EORTPAS T TET Tin
Aperture area (m2) Absorber Absorption refrigeration cycle Condenser Evaporator Ejector evaporator temperature Ejector Heat recovery vapor generator (HRVG) Generator of TPAS Solar beam radiation (SBR) (kWm2) Specific enthalpy (kJ kg1) Heat exchanger Heat transfer fluid (Therminol VP1) High temperature vessel Low temperature vessel Pressure (MPa) Parabolic trough collector Extraction ratio Specific entropy (kJ kg1K1) Ejector Organic Rankine cycle (EORC) EORC integrated with a triple pressure level absorption system Absolute temperature (K) Turbine extraction temperature Inlet temperature of HTF to PTC field (°C)
energy efficiency. The performance of CSP varies heavily on the intensity of solar radiation throughout the day; it will be good in a clear bright sky but could hamper the performance during overcast situations. So with the above limitations, it is not feasible to use CSP alone for running of the power plants. Thermal energy storage (TES) systems facilitate to enhance the working of CSP technology. Amalgamating the CSP with the TES is a new face for the present scenario and helping us to penetrate the global market with higher power outputs and efficiencies [8,9,22]. Properly designed combination of CSP and TES can demonstrate the working of the system continuously for 24 h allowing short transient buffers to longer-term night time storage [4]. A feasibility study of using storage tank contains molten salt for parabolic trough solar plants are shown in Herrmann et al. [13]. Their finding predominantly states that for the uninterrupted supply to the cycle, TES could actually reduce the cost of electricity. Analysis of the PTC coupled with an organic Rankine cycle being done to optimize the system in terms of energy and finances in Tzivanidis et al. [24]. Their studies reveal the suitability of cyclohexane to operate PTC to produce 1 MW. To promote sustainability of CSP technologies combined power and cooling cycles have been explored which produces power and cooling simultaneously. Ejector based cooling system is attractive technology due to the absence of mechanical compressor and CFC which leads to energy efficient and environment friendly production of cooling from solar energy [5,6,10]. A computer program has also been generated by Alexis [2] that analyzes the performance parameters of combined cycles. Ejector system has been found to be more feasible economically than the vapor absorption machine. A combined power and ejector refrigeration cycle was analyzed by [27] using R245fa as the working fluid. The analysis shows that while we increase the temperatures of the generator from 335 K to 415 K, the energy efficiency is found to increase from 15.8% to 38% and on the other side the exergy efficiency increased
Tout TPAS TV E_ X_ Q_ _ net W _ m
Outlet temperature of HTF from PTC field (°C) Triple pressure level absorption system Throttle valve Energy rate (kW) Exergy rate (kW) Heat transfer rate (kW) Work output (kW) Mass flow rate (kg s1)
Greek symbols l Entrainment ratio h Incidence angle e Work to refrigeration ratio ex Work to exergetic refrigeration ratio gE Energy efficiency (%) gx Exergy efficiency (%) Subscript X e1 e2 P T 1, 2, 3
Exergy Evaporator 1 Evaporator 2 Pump Turbine state points
from 45.2 to 57.2%. The generating temperature generally kept in the permissible limit as it requires big turbine. Rashidi et al. [21] write the computer code for a power and ejector refrigeration cycle for R123 which is used as working fluid and studied the effects of various dependent parameters on the outcome of the cycle. Results demonstrate that both operating efficiencies (1st and 2nd law) are improved at higher evaporator temperature, while boiler and ejectors experienced maximum exergy loss. It is also observed that at a high inlet pressure of turbine, 1st law efficiency is favorable but 2nd law efficiency is reduced. Thermodynamic analysis of combined power and ejector refrigeration cycles [1,7,12,16,26] demonstrates that the highest irreversibility occurs in heat addition process followed by the ejector and turbine. To enhance the performance of combined power and ejector refrigeration cycle, triple pressure level absorption system (TPAS) is integrated with this combined cycle. Hong et al. [14] studied a new triple pressure level absorption refrigeration cycle. Their results have shown that the COP of the proposed cycle is 30% more than that of a single effect absorption refrigeration cycle (ARC) for specific conditions. Verda et al. [25] develop a mathematical model of a triple pressure level ARC using ammonia-lithium nitrate solution as working fluid. Simulation results concluded that with the use of the ejector, the absorption pressure becomes higher than the evaporation pressure and increase the cooling capacity. Therefore, the efforts carried out in this study is to propose a multi-generation cycle which produces power and refrigeration at two different temperatures simultaneously, using solar thermal energy as a heat source. The proposed multi-generation cycle is the integration of triple pressure level absorption system (TPAS) with ejector organic Rankine cycle (EORC), which meets out the demand of electricity, space air-conditioning and preservation of fruits & vegetables in cold storage. The performance of EORC and the proposed multi-generation cycle is also compared on the basis of energy and exergy approach.
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx Table 1 Main constraints considered for the investigation.
2. Description of working These systems comprise of ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS) based on PTC solar field are shown in Figs. 1a and 2a respectively. Solar thermal energy flux is utilized for the heating of the HTF (1) with the aid of PTC solar field. HTF after passing through HRVG (1–2), where it superheats the high-pressure refrigerant, enters the TPAS generator (G2) to desorb the water vapor from LiBr-H2O solution and then to the PTC solar field for heating (16). The superheated vapor expands (4–5) up to the extraction pressure (Pext) and enters the convergent-divergent nozzle of the ejector. Refrigerant vapor from the nozzle entrains the secondary refrigerant (13) and the mixture is passed through the mixing chamber of the ejector1 (EJ1). The refrigerant stream (6) and turbine exhaust stream (14) combines at (7) and then it is cooled to (8) by transferring the heat to the refrigerant (15-3) in the heat exchanger1 (HE1). Saturated liquid refrigerant from the condenser (9) enters into throttle valve (TV1) (11) and pump (P3) (10). The high-pressure liquid refrigerant (15) from pump (P3) flows into the heat exchanger (HE1) (15-3) is preheated and then converted into superheated refrigerant vapor (4) in the heat recovery vapor generator (G1). The saturated liquid refrigerant (11) expands to the evaporator pressure (11–12) in the throttle valve (TV1) and vaporized in the evaporator (E1) (12–13) to produce refrigeration effect. The water vapor (23) leaving from the TPAS generator (G2) is condensed in the condenser (C2) and leaves as saturated water (24) which further cools in the liquidvapor heat exchanger (HE3) (24–25) then it throttles (25–26) to evaporator2 (E2) (26–27) to produce refrigeration effect. The refrigerant water vapor coming from the evaporator (E2) is preheated in the HE3 (27–28). The LiBr-H2O solution (20) from the TPAS generator (G2) enters into the heat exchanger (HE2) and cools to (21). The solution (21) enters to ejector and entrains water vapor (28) from the heat exchanger3 (HE3) and this mixture flows to the absorber (ABS) (22–17), and then pump (P5) (17–18) to heat exchanger (HE2) (18–19) and ultimately reaches the TPAS generator (G2). Both the systems have a fixed mass flow rate of HTF. Also, the exit temperature of HTF from PTC at given SBR is considered to be the same. For the thermodynamic investigation, the constraints deliberated for the process of the proposed system are depicted in Table 1. The p-h diagrams corresponding to ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS) are also drawn and shown in Figs. 1b and 2b respectively.
Ambient temperature (°C)
25
Ambient pressure (MPa) Turbine Inlet pressure (MPa) Extraction pressure of Turbine (MPa) Extraction ratio Isentropic turbine efficiency (%) Isentropic pump efficiency (%) Mass flow rate of HTF (kg/s) Tracking mode for PTC field
0.101325 1.1 0.4 0.3 85 80 22 Focal axis N-S horizontal and E-W tracking 100
Inlet temperature of HTF in PTC for EORC (°C) Inlet temperature of HTF in PTC for ORTPAS (°C) Pinch point temperature difference (°C) Ejector evaporator temperature (°C) Condenser temperature (°C) Solar beam radiation (W/m2) Aperture Area (m2) TPAS evaporator temperature (°C) TPAS generator temperature (°C)
90 10 5 36 600 10,000 10 85
3. Thermodynamic analysis In order to simulate the performance of the proposed system, the principle of mass and energy conservation are used. The mass and energy balance for a general steady flow system was given as
X
_ ¼ m
in
X
_ m
ð1Þ
out
P P _ is the rate of mass transfer into the system and out m _ where in m is the rate of mass transfer out of the system.
E_ in ¼ E_ out
ð2Þ
X _ in þ _ h þ C2 =2 þ gz Q_ in þ W m in
_ out þ ¼ Q_ out þ W
X
_ h þ C2 =2 þ gz m
ð3Þ
out
The rate of exergy change within the system during a process is given by
X_ heat X_ work þ X_ mass;in X_ mass;out X_ d ¼ DX_ X_ heat ¼
X T0 _ 1 Q T
ð4Þ ð4aÞ
Fig. 1a. Process diagram of ejector organic Rankine cycle (EORC).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
3.1. Energy analysis Solar energy received from the Sun
Q_ Solar ¼ Gb Ap
ð5cÞ
where Gb = I Cosh = Solar beam radiation, I = DNI (W/m2), Ap = Aperture area (m2), h = Incidence angle. Heat gain in the PTC field for ejector organic Rankine cycle (EORC)
_ 1 ðh1 h2 Þ ¼ gE;PTC Gb Ap ¼ m _ 4 ðh4 h3 Þ Q_ gain ¼ m
ð6Þ
where gE;PTC ¼ EnergyefficiencyofPTCfield
gE;PTC
" # Tm T0 ðTm T0 Þ2 c ¼ab Gb Gb
ð7Þ
a = optical efficiency of PTC field = 0.7, b = first order loss coefficient of PTC field = 0.1, c = second order loss coefficient of PTC field = 0, Tm = {(Tin + Tout)/2} = mean HTF temperature. The energy efficiency of the EORC (gE1 ) can be characterized as _ net ) and refrigeration outthe proportion of the network output (W put in the ejector evaporator (Q_ e1 ) to the solar energy input (Q_ Solar ).
_ net þ Q_ e =Q_ Solar gE1 ¼ W 1 Fig. 1b. p-h diagram of ejector organic Rankine cycle.
ð8Þ
_ T¼m _ 4 ðh4 h5 Þ þ m _ 4 ð1 RÞðh5 h14 Þ W
ð8aÞ
_ p dV X_ work ¼ W 0
ð4bÞ
_ 5 =m _4 R¼m
ð8bÞ
_ ½ðh h0 Þ T0 ðs s0 Þ X_ mass ¼ m
ð4cÞ
_ P¼m _ 4 ðh15 h10 Þ W
ð8cÞ
Fig. 2a. Process diagram of ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
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Fig. 2b. p-h diagram of ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system.
_ net ¼ W _ TW _P W
ð8dÞ
_ 5 l1 ðh13 h12 Þð8eÞ Q_ e1 ¼ m
3.2. Exergy analysis Exergy efficiency of PTC field is given by
gx;PTC ¼ fm_ ðh1 h16 Þ T0 ðs1 s16 Þg=Gb Ap
Work to refrigeration ratio for EORC
_ net =Q_ e e1 ¼ W 1
ð9Þ
ð13Þ
Useful work obtainable from solar radiation (£) is given by Petela [20]
4 4 T0 1 T0 þ 3 Tsolar 3 Tsolar
Heat gain in the PTC field for ejector organic Rankine cycle integrated with triple pressure level vapour absorption system (EORTPAS)
¼1
_ 1 ðh1 h16 Þ ¼ gE;PTC Gb Ap Q_ gain ¼ m
The exergy efficiency (gx1 ) and (gx2 ) of EORC, EORTPAS may be reported as
ð10Þ
_ 23 h23 þ m _ 20 h20 m _ 19 h19 Q_ gain ¼ m_ 4 ðh4 h3 Þ þ m
ð10aÞ
The energy efficiency (gE2 ) of the EORTPAS characterized as the
_ net ) and total proportion of summation of the network output (W refrigeration output in the ejector evaporator E1 (Q_ ) and TPAS evaporator E2 (Q_ e2 ) to the solar energy input (Q_ Solar ).
_ net þ Q_ e þ Q_ e =Q_ Solar gE2 ¼ W 1 2 _ 26 ðh27 h26 Þ Q_ e2 ¼ m
e1
ð11Þ ð11aÞ
Work to refrigeration ratio for EORTPAS
_ net = Q_ e þ Q_ e e2 ¼ W 1 2
_ net þ X_ e =X_ Solar gx1 ¼ W 1
_ net þ X_ e þ X_ e =X_ Solar gx2 ¼ W 1 2
ð13aÞ
ð14Þ ð15Þ
where, X_ Solar is exergy associated with solar radiation, X_ e1 X_ e2 is the exergy associate with refrigeration in the evaporators 1, 2.
X_ e1 ¼ Q_ e1 ðT0 =Te1 Þ 1
ð15aÞ
X_ e2 ¼ Q_ e2 ðT0 =Te2 Þ 1 ð15bÞ X_ Solar ¼ Gb Ap
ð15cÞ
Work to exergetic refrigeration ratio for EORC, 2
ð12Þ
l1 ¼ m_ 13 =m_ 5
ð12aÞ
l2 ¼ m_ 28 =m_ 21
ð12bÞ
_ net =X_ e ex1 ¼ W 1
_ net = X_ e þ X_ e ex2 ¼ W 1 2
ð16Þ
ð17Þ
where TSolar is the Apparent Sun Temperature = 5800 K
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
Table 2 Results of simulation for EORC. State points
P (kPa)
T (°C)
_ m(kg/s)
h (kJ/kg)
s (kJ/kgK)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1500 1400 1100 1100 400 116.1 116.1 116.1 116.1 116.1 116.1 22.28 22.28 116.1 1100
172 100 82.83 162 127.8 108.7 98.08 36 36 36 36 5 5 92.77 37.05
22 22 15.77 15.77 4.731 5.479 16.52 16.52 16.52 15.77 0.7484 0.7484 0.7484 11.04 15.77
443.9 258 139.4 398.7 375.8 362.9 353.6 298.3 80.31 80.31 80.31 80.31 273.8 348.9 81.55
22.74 12.71 0.473 1.128 1.138 1.19 1.165 1.001 0.2962 0.2962 0.2962 0.3085 1.03 1.152 0.3002
Table 3 Results of simulation for EORTPAS. State points
P (kPa)
T (0C)
_ m(kg/s)
h (kJ/kg)
s (kJ/kgK)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
1500 1400 1100 1100 400 116.1 116.1 116.1 116.1 116.1 116.1 22.28 22.28 116.1 1100 1300 1.474 5.945 5.945 5.945 5.945 1.474 5.945 5.945 5.945 1.228 1.228 1.228
162.2 100 75.52 152.2 117.6 99.58 88.35 36 36 36 36 5 5 82.71 37.05 90 36 36 70.41 85 35.81 57.71 85 36 24 10 10 36.82
22 22 13.66 13.66 4.098 4.736 14.3 14.3 14.3 13.66 0.6381 0.6381 0.6381 9.563 13.66 22 1.137 1.137 1.137 0.9347 0.9347 1.137 0.2026 0.2026 0.2026 0.2026 0.2026 0.2026
418.5 258 130 388.5 366.3 354.9 345.1 298.9 80.31 80.31 80.31 80.31 273.8 340.3 81.55 232.2 75.83 75.83 150.7 214.2 123.1 558.9 2659 150.8 100.5 100.5 2519 2569
21.47 12.71 0.4464 1.104 1.114 1.169 1.142 1.003 0.2962 0.2962 0.2962 0.3085 1.03 1.128 0.3002 11.17 0.2474 0.2474 0.4765 0.4664 0.1925 0.3182 8.61 0.5185 0.3527 0.3577 8.899 9.064
4. Result and discussion In this paper, performance analysis of PTC field based ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a TPAS (EORTPAS) have been carried out. A theoretical investigation is conducted to discover the influence of
various design parameters such as SBR, turbine inlet pressure (TIP), turbine extraction pressure (TEP), and ejector evaporator temperature (EET) on the performance of EORC & EORTPAS. In this analysis, where a thermodynamic parameter is varied, the other parameters are kept constant as mentioned in Table 1. Tables 2 and 3 show the thermodynamic state of each point for EORC & EORTPAS. Also, Tables 4 and 5 show the distribution of energy & exergy in various components of EORC and EORTPAS.
4.1. Effect of solar beam radiation (SBR) The variation of energy and exergy efficiencies of PTC field for EORC and EORTPAS with the change in SBR is shown in Fig. 3. It is evident from Fig. 3 and Eqs. ((7) and (13)) that the energy and exergy efficiencies of PTC field increases with increase in the value of SBR for both the systems because the outlet temperature of HTF (Tout) from PTC field and the amount of heat transferred to the HTF increases at fixed mass flow rate and inlet temperature of HTF (Tin) to the PTC field. It is clear from Eq. (7) that the mean temperature of HTF (Tm) for EORC is higher than EORTPAS, therefore the energy efficiency for EORTPAS is greater than for that of EORC at the same SBR. It is also clear that the exergy efficiency of EORC is more as that of EORTPAS because the mean temperature of heat addition is greater so the exergy efficiency is greater. The variation of energy and exergy efficiencies for EORC and EORTPAS with SBR is shown in Fig. 4. As SBR increases, the turbine inlet temperature increases which results in greater work output. Also, the temperature of working fluid at the extraction point (5) of the turbine is higher at higher SBR which results in entrainment of more refrigerant from ejector evaporator (13). This leads to greater refrigeration output at the evaporator of the ejector. So, this increase in work output and refrigeration output increases both the efficiencies of EORC at higher SBR. It is also found that with the addition of TPAS in EORC, the energy efficiency of EORTPAS increases considerably but decreases with the increase in SBR. This is due to the fact that with the increase in SBR, work output, ejector refrigeration output increases, and TPAS refrigeration output remain constant but solar energy input increases significantly. This leads to a decrease in the energy efficiency of EORTPAS with an increase in SBR. The exergy efficiency of EORTPAS is lesser than that of EORC due to the reduction of work output at the same SBR. The exergy efficiency of EORTPAS increases because the work output & exergy of ejector refrigeration output increases, while exergy of TPAS refrigeration output remains constant with increase in SBR. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with SBR is shown in Fig. 5 for EORC and EORTPAS. Both work to refrigeration ratio and work to exergetic refrigeration ratio increases with an increase in SBR as the enhancement of work output is better than that of both the refrigeration and exergetic refrigeration output for EORC and EORTPAS.
Table 4 The distribution of energy in various components of EORC and EORTPAS. Term
Input energy from Sun Turbine output Pump input Ejector refrigeration output TPAS refrigeration output Work output Energy output Energy loss
Ejector organic Rankine cycle (EORC)
Ejector organic Rankine cycle integrated with a triple pressure level absorption system (EORTPAS)
Input energy (kW)
% of Input energy from Sun
Input energy (kW)
% of Input energy from Sun
6000 658 19.5 144.8 – 638.5 783.3 5506.3
100 10.9 0.3 2.4 – 10.6 13 91.8
6000 550.9 16.93 120 492 534 1146 6078
100 9.18 0.28 2 8.2 8.9 19.1 101.3
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx Table 5 The distribution of exergy in various components of EORC and EORTPAS. Ejector organic Rankine cycle (EORC)
Exergy destruction/losses in components (i) HRVG (ii) Turbine (iii) Ejector 1 (iv) Condenser 1 (v) Pump (vi) Heat exchanger (vii) Throttle valve (viii) Evaporator 1 (ix) TPAS Generator (x) Condenser 2 (xi) Absorber (xii) PTC Total Exergy destruction/loss
Amount (kW)
% of exergy input
Amount (kW)
% of exergy input
5589
100
5589
100
638.5 16.2 – 654.7
11.42 0.29 – 11.71
534.5 13.81 26.23 574.54
9.56 0.25 0.47 10.28
139.7 100.6 122.96 12.58 16.41 16.41 2.7 1.09 – – – 4521.85 4934.3
2.5 1.8 2.2 0.22 0.3 0.3 0.05 0.02 – – – 80.9 88.29
94.8 83.37 95.98 11.47 16.21 15.47 2.73 2.07 103.58 20.24 19.14 4549.4 5014.46
1.7 1.5 1.7 0.21 0.29 0.28 0.05 0.04 1.85 0.36 0.34 81.4 89.72
Work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) at the same SBR for EORC is higher than that of EORTPAS because of the enhancement of refrigeration output (Qe1 + Qe2) & exergetic refrigeration output (Xe1 + Xe2) and reduction in work output. Work to refrigeration ratio (e) varies from 4.2 to 4.5 for EORC and 0.53 to 1.04 for EORTPAS and work to exergetic refrigeration ratio (ex) varies from 37.6 to 40.3 for EORC and 8.7 to 15.4 for EORTPAS with the SBR variation from 400 to 700 W/m2. The variation of entrainment ratio (l1) with SBR is shown in Fig. 6 for EORC and EORTPAS. As SBR increases, the turbine inlet temperature increases resulting in the increase in the temperature of working fluid at the extraction point (5) of the turbine. This increases the exit velocity of working fluid from the ejector nozzle which leads to the entrainment of more refrigerant from ejector evaporator. Therefore entrainment ratio for EORC and EORTPAS increases with increase in SBR. Entrainment ratio for EORC is higher than that of EORTPAS because turbine inlet temperature is more in EORC as compared to EORTPAS. 4.2. Effect of turbine inlet pressure (TIP)
21 68.4
16 ηE1,PTC ηE2,PTC
67.6 67.2
11 6
ηx1,PTC ηx2,PTC
400
500 600 Solar beam radiation (W/m2)
700
1
Exergy efficiency (%)
Energy efficiency (%)
The trend of efficiencies as the TIP varies is shown in Fig. 7 for EORC and EORTPAS. An increasing trend of work output with increasing of turbine inlet pressure is perceived because of high
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Ejector organic Rankine cycle integrated with a triple pressure level absorption system (EORTPAS)
Fig. 3. Variation of energy and exergy efficiencies of PTC field for EORC and EORCTPAS with SBR.
enthalpy drop for high pressure ratio. This also results in low turbine extraction temperature (5) and consequently low primary stream velocity and low entrainment of secondary vapor which reduces the cooling capacity of ejector evaporator (Qe1). The refrigeration output at TPAS does not change because of the same working conditions across TPAS with variation in with turbine inlet pressure. The combined effect of work output and refrigeration output (s) on the performance of EORC and EORTPAS is to increase in energy efficiency with turbine inlet pressure. The similar increment is obtained for exergy efficiency. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with turbine inlet pressure is shown in Fig. 8 for EORC and EORTPAS. As can be seen from Fig. 8 that the work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) showing an increasing trend with increasing of turbine inlet pressure as work output increases, ejector refrigeration output decreases and TPAS refrigeration output remains same at high turbine inlet pressure. The change of entrainment ratio (l1) with turbine inlet pressure is shown in Fig. 9 for EORC and EORTPAS. Increase in TIP causes a decrease in TET. This low TET stream (5) works as a primary flow for ejector which reduces the primary stream velocity and entrainment of secondary vapor from the ejector evaporator. Therefore, the entrainment ratio for EORC and EORTPAS decreases at a high
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Fig. 4. Variation of energy and exergy efficiencies of EORC and EORCTPAS with SBR.
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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Fig. 6. Variation of entrainment ratio of EORC and EORCTPAS with SBR.
inlet pressure of the turbine. As the turbine inlet temperature for EORC is more than that of EORTPAS, therefore, the entrainment ratio for EORC is higher than that of EORTPAS. 4.3. Effect of turbine extraction pressure (TEP)
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The variation of energy and exergy efficiencies with turbine extraction pressure (TEP) for EORC and EORTPAS is shown in Fig. 10. It is evident that as the TEP increases, work output decreases. It is also observed that the ejector refrigeration output increases with the increase in TEP. The reason for this is that the increase in TEP increases the pressure and temperature of the primary flow entering the ejector which in turn increases the entrainment of secondary vapor. The effect of change in turbine extraction pressure is insignificant on the temperature of HTF at the exit of HRVG. Therefore, refrigeration output at the evaporator of the TPAS
Fig. 7. Variation of energy and exergy efficiencies of EORC and EORCTPAS with TIP.
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Fig. 8. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with TIP.
remains the same. As the increase in ejector refrigeration output dominates over the decrease in work output which results in the increase in the energy efficiency of both the systems with an increase in TEP. The exergy efficiency of the EORC and EORTPAS decreases with increase in TEP because the amount of increase in exergy associated with the ejector refrigeration output (Xe1) is much less than the amount of reduction in works output. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with turbine extraction pressure is shown in Fig. 11 for EORC and EORTPAS. It is evident from the Fig. 11 that the e and ex for both the systems decreases as work output decreases and ejector refrigeration output increases at high turbine extraction pressure. The entrainment ratio (l1) for both the system also changes with TEP. Fig. 12 depicts the rise of entrainment ratio for both the systems at elevated turbine extraction pressure because of the gain in pressure and temperature of the primary flow entering the ejector resulting in which in more entrainment of secondary vapor. The slightly higher entrainment ratio for EORC relative to that of EORTPAS is due to high turbine inlet temperature in EORC as compared to that of EORTPAS. 4.4. Effect of ejector evaporator temperature (EET) The variation of energy and exergy efficiencies with ejector evaporator temperature (EET) for both the systems is shown in Fig. 13. A constant value of work and refrigeration output of the TPAS (Qe2) with the change in evaporator1 temperature (Te1) because their inlet and exit states do not change. As the ejector evaporator temperature increases, the evaporator pressure increases, which increase in the mass flow rate of refrigerant through the ejector evaporator resulting in an increase in ejector
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
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Fig. 9. Variation of entrainment ratio of EORC and EORCTPAS with TIP.
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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Fig. 14. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with EET.
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Fig. 11. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with TEP.
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Fig. 13. Variation of energy and exergy efficiencies of EORC and EORCTPAS with EET.
Fig. 12. Variation of entrainment ratio of EORC and EORCTPAS with TEP.
refrigeration output (Qe1). Therefore energy efficiency increases at higher values of evaporator1 temperature (Te1) for both the systems. The exergy efficiency for both the systems varies insignificantly because the amount of the variation of exergy of ejector refrigeration outputs is insignificant in comparison to the energy associated with the ejector refrigeration output. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with ejector evaporator temperature (EET) for both the systems is shown in Fig. 14. It is apparent from the Fig. 14 that the e and ex for both the systems decreases with increase in evaporator temperature as work and TPAS (Qe2) output remains constant whereas ejector refrigeration output (Qe1) is
Entrainment ratio (μ1, EORC )
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Fig. 10. Variation of energy and exergy efficiencies of EORC and EORCTPAS with TEP.
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Ejector evaporator temperature (K) Fig. 15. Variation of entrainment ratio of EORC and EORCTPAS with EET.
increased at higher evaporator1 temperature (Te1). Work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) at the same ejector evaporator temperature for EORC is higher than that of EORTPAS because of the enhancement of refrigeration output (Qe1 + Qe2) & exergetic refrigeration output (Xe1 + Xe2). The variation of entrainment ratio (l1) with ejector evaporator temperature (EET) is shown in Fig. 15 for EORC and EORTPAS. As the ejector evaporator temperature increases, the ejector evaporator pressure increases, resulting in an increase in the mass flow rate of refrigerant through the ejector evaporator. Therefore, the entrainment ratio for EORC and EORTPAS is higher at elevated evaporator1 temperature (Te1). The entrainment ratio for EORC is
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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slightly higher than that of the EORTPAS because turbine inlet temperature is more in EORC as compared to EORTPAS. 5. Conclusion The proposed system produces power and refrigeration output at different temperatures simultaneously. The thermodynamic analysis was conducted to investigate the effect of various design parameters such as SBR, TIP, TEP, and EET on the performance of proposed system EORTPAS and also compared with the performance of EORC. The conclusions drawn are summarized as: It is evident that the EORTPAS has higher refrigeration output, exergetic refrigeration output, and energy efficiency than that of the EORC. The various thermodynamic parameters such as SBR, turbine inlet pressure, turbine extraction pressure, and ejector evaporator temperature have a significant influence on the work output, refrigeration output, work to refrigeration ratio, work to exergetic refrigeration ratio and entrainment ratio of the proposed system. The energy efficiency for EORC increases from 12.0% to 13.9% and for EORTPAS increases from 18.2% to 19.8%, whereas exergy efficiency increases from 10.4% to 12.8% and 9.2% to 11.1% for EORC and EORTPAS respectively with the increase of turbine inlet pressure from 0.8 MPa to 1.6 MPa. The energy efficiency for EORC and EORTPAS increases marginally with an increase in extraction pressure and ejector evaporator temperature. The exergy efficiency for EORC and EORTPAS decreases marginally with an increase in extraction pressure and ejector evaporator temperature. References [1] B.K. Agrawal, M.N. Karimi, Parametric, exergy and energy analysis of low grade energy and ejector refrigeration cycle, Int. J. Sustain. Build. Technol. Urban Dev. 4 (2) (2013) 170–176. [2] G.K. Alexis, Performance parameters for the design of a combined refrigeration and electrical power cogeneration system, Int. J. Refrig. 30 (2007) 1097–1103. [3] R. Barberz, A. Rovira, M.J. Montes, J.M.M. Val, A new approach for the prediction of thermal efficiency in solar receivers, Energy Convers. Manage. 123 (2016) 498–511. [4] D. Barlev, R. Vidu, P. Stroeve, Innovation in concentrated solar power, Sol. Energy Mater. Sol. Cells 95 (2011) 2703–2725. [5] G. Besagni, R. Mereu, F. Inzoli, Ejector refrigeration: a comprehensive review, Renew. Sustain. Energy Rev. 53 (2016) 373–407.
[6] X. Chen, S. Omer, M. Worall, S. Riffat, Recent developments in ejector refrigeration technologies, Renew. Sustain. Energy Rev. 19 (2013) 629–651. [7] Y. Dai, J. Wang, L. Gao, Exergy analysis, parametric analysis and optimization for a novel combined power and ejector refrigeration cycle, Appl. Therm. Eng. 29 (2009) 1983–1990. [8] P. Denholm, E. Ela, B. Kirby, M. Milligan, The role of Energy Storage with Renewable Electricity Generation. NREL/TP-6A2-47187, National Renewable Energy Laboratory, 2010. [9] P. Denholm, M. Hand, Grid flexibility and storage required to achieve very high penetration of variable renewable electricity, Energy Policy 39 (18) (2011) 17– 30. [10] S. Elbel, N. Lawrence, Review of recent developments in advanced ejector technology, Int. J. Refrig 62 (2016) 1–18. [11] W. Grase, Solar PACES Annual Report, DLR, Germany, 1995. [12] D.K. Gupta, R. Kumar, N. Kumar, First and second law analysis of solar operated combined Rankine and ejector refrigeration cycle, Appl. Solar Energy 50 (2) (2014) 113–121. [13] U. Herrmann, B. Kelly, H. Price, Two tank molten salt storage for parabolic trough solar power plants, Energy 29 (2004) 883–893. [14] D. Hong, G. Chen, L. Tang, Y. He, A novel ejector-absorption combined refrigeration cycle, Int. J. Refrig. 34 (2011) 1596–1603. [15] D.W. Kearney, H.W. Price, Solar thermal plants-LUZ concepts (current status of the SEGS plants). Proceedings of the Second Renewable Energy Congress, Reading UK, 2, 1992, pp. 582–588. [16] A. Khaliq, Energetic and exergetic performance investigation of a solar based integrated system for cogeneration of power and cooling, Appl. Therm. Eng. 112 (2017) 1305–1316. [17] F. Kreith, J.F. Kereider, Principles of Solar Engineering, Mcgraw-Hill, New York, 1978. [18] E.M.A. Mokheimer, Y.N. Dabwan, M.A. Habib, S.A.M. Said, F.A. Al-Sulaiman, Techno-economic performance analysis of parabolic trough collector in Dhahran, Saudi Arbia, Energy Convers. Manage. 86 (2014) 622–633. [19] R.V. Padilla, A. Fontalvo, G. Demirkaya, A. Mrtinez, A.G. Quiroga, Exergy analysis of parabolic trough solar receiver, Appl. Therm. Eng. 67 (2014) 579– 586. [20] R. Petela, Exergy of undiluted thermal radiation, Sol. Energy 74 (6) (2003) 469– 488. [21] M.M. Rashidi, O.A. Beg, A. Aghagoli, Utilization of waste heat in combined power and ejector refrigeration for a solar energy source, Int. J. Appl. Math Mech. 8 (17) (2012) 1–16. [22] R. Sioshansi, P. Denholm, The Value of Concentrating Solar Power and Thermal Energy Storage. NREL-TP-6A2-45833, National Renewable Energy Laboratory, 2010. [23] S.K. Tyagi, S. Wang, M.K. Singhal, S.C. Kaushik, S.R. Park, Exergy analysis and parametric study of concentrating type solar collectors, Int. J. Therm. Sci. 46 (2007) 1304–1310. [24] C. Tzivanidis, E. Bellos, K.A. Antonopoulos, Energetic and financial investigation of a stand-alone solar-thermal organic rankine cycle power plant, Energy Convers. Manage. 126 (2016) 421–433. [25] C. Verda, R. Ventas, A. Lecuona, R. Lopez, Single effect refrigeration cycle boosted with an ejector-adiabatic absorber using a single solution pump, Int. J. Refrig. 38 (2014) 22–29. [26] J. Wang, Y. Dai, L. Gao, Parametric analysis and optimization for a combined power and refrigeration cycle, Appl. Energy 85 (2008) 1071–1085. [27] B. Zheng, Y.W. Weng, A combined power and ejector refrigeration cycle for low temperature heat sources, Sol. Energy 12 (5) (2010) 784–791.
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS) Devendra Kumar Gupta a,⇑, Rajesh Kumar b, Naveen Kumar b a b
Department of Mechanical Engineering, Inderprastha Engineering College, Ghaziabad, UP 201010, India Department of Mechanical Engineering, Delhi Technological University (Government of NCT of Delhi), Bawana Road, Delhi 110042, India
a r t i c l e
i n f o
Article history: Received 20 July 2018 Revised 20 April 2019 Accepted 23 April 2019 Available online xxxx Keywords: Ejector Triple pressure level absorption system Solar energy Parabolic trough collector Thermal energy storage Organic Rankine cycle
a b s t r a c t The Proposed system consists of an ejector organic Rankine cycle (EORC) integrated with a triple pressure level absorption system (TPAS) based on parabolic trough collector (PTC) solar field. This system produces power and refrigeration output at two different temperatures simultaneously. A thermodynamic analysis is conducted to discover the effect of various design parameters such as solar beam radiation (SBR), turbine inlet pressure (TIP), turbine extraction pressure (TEP), and ejector evaporator temperature (EET) on the performance of the proposed system (EORTPAS). It is found that with the addition of TPAS in EORC, the energy efficiency of EORTPAS increases considerably but exergy efficiency decreases. It has also been observed that energy efficiency increases with the increase in TIP, TEP and, EET while decreases with the increase in SBR for both the systems. On the other hand, the exergy efficiency of both the systems increases with increase in SBR or TIP and with the decrease in TEP. It is also noticed that there is a slight decrease in exergy efficiency of both the systems with the increase in EET. Ó 2019 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction The rigorous use of natural fossil fuel has created a havoc of global warming that produces deadly greenhouse gases like- CO2, CO, NOx, etc. More woes are being added by our conventional cooling systems which emit refrigerant gases like CFCs which are high in GWP (Global warming potential) & ODP (Ozone depletion potential). Since the last few decades, scientists did carry out enormous research on the alternative technologies which can be a simile to our natural fossil fuels and also cut down on greenhouse effect by actually reducing the carbon emission. Solar energy also affects the convective ambience creating currents that fuel the air to be wind; hence the wind energy is a derivative of crude solar energy. Not only on winds, but it also affects the formation of tides and we could then materialize the energy as tidal energy [17]. Presently concentrated solar power (CSP) technologies gaining the interest to be used in solar thermal power plants. Major applications of PTC can be found in power plants of southern California known
⇑ Corresponding author. E-mail address: [email protected] (D.K. Gupta). Peer review under responsibility of Karabuk University.
as solar electric generating systems (SEGS) has an installed capacity of 354 MW [15]. For experimental purposes, an installed capacity of power 1.2 MW by the collector has been installed at Plataforma Solar de Almeria (PSA) in Southern Spain [11]. Mokheimer et al. [18] developed a simulation model to evaluate the optical and thermal efficiencies of PTC solar field and also carried out the cost analysis. Their findings showed that the maximum optical efficiency that can be reached is 73.5% in Dhahran and the specific cost for a PTC field per unit aperture area can be reduced by approximately 46%. Barberz et al. [3] presented a new approach for the prediction of thermal efficiency in solar receivers. Two simplifications can be made based on this approach to obtain much simpler equations that describe collector performance for the majority of solar technologies. Tyagi et al. [23] conducted the exergy analysis of PTC for different mass flow rates of heat transfer fluid. Their result shows that for a given value of solar intensity, the exergy output, exergetic and thermal efficiencies had been found to be the increasing function of mass flow rates. An analysis of exergy has been presented in Padilla et al. [19], which shows that the intensity of solar radiation has a high impact on the role of PTC. The exergy efficiency has a relation with the temperature of the HTF leaving the receiver. If the temperature of heat transfer is enhanced, then there will be an improvement of exergy efficiency but a decrease in
https://doi.org/10.1016/j.jestch.2019.04.008 2215-0986/Ó 2019 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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Nomenclature Ap ABS ARC C E EET EJ G1 G2 Gb h HE HTF HTV LTV P PTC R s EORC EORTPAS T TET Tin
Aperture area (m2) Absorber Absorption refrigeration cycle Condenser Evaporator Ejector evaporator temperature Ejector Heat recovery vapor generator (HRVG) Generator of TPAS Solar beam radiation (SBR) (kWm2) Specific enthalpy (kJ kg1) Heat exchanger Heat transfer fluid (Therminol VP1) High temperature vessel Low temperature vessel Pressure (MPa) Parabolic trough collector Extraction ratio Specific entropy (kJ kg1K1) Ejector Organic Rankine cycle (EORC) EORC integrated with a triple pressure level absorption system Absolute temperature (K) Turbine extraction temperature Inlet temperature of HTF to PTC field (°C)
energy efficiency. The performance of CSP varies heavily on the intensity of solar radiation throughout the day; it will be good in a clear bright sky but could hamper the performance during overcast situations. So with the above limitations, it is not feasible to use CSP alone for running of the power plants. Thermal energy storage (TES) systems facilitate to enhance the working of CSP technology. Amalgamating the CSP with the TES is a new face for the present scenario and helping us to penetrate the global market with higher power outputs and efficiencies [8,9,22]. Properly designed combination of CSP and TES can demonstrate the working of the system continuously for 24 h allowing short transient buffers to longer-term night time storage [4]. A feasibility study of using storage tank contains molten salt for parabolic trough solar plants are shown in Herrmann et al. [13]. Their finding predominantly states that for the uninterrupted supply to the cycle, TES could actually reduce the cost of electricity. Analysis of the PTC coupled with an organic Rankine cycle being done to optimize the system in terms of energy and finances in Tzivanidis et al. [24]. Their studies reveal the suitability of cyclohexane to operate PTC to produce 1 MW. To promote sustainability of CSP technologies combined power and cooling cycles have been explored which produces power and cooling simultaneously. Ejector based cooling system is attractive technology due to the absence of mechanical compressor and CFC which leads to energy efficient and environment friendly production of cooling from solar energy [5,6,10]. A computer program has also been generated by Alexis [2] that analyzes the performance parameters of combined cycles. Ejector system has been found to be more feasible economically than the vapor absorption machine. A combined power and ejector refrigeration cycle was analyzed by [27] using R245fa as the working fluid. The analysis shows that while we increase the temperatures of the generator from 335 K to 415 K, the energy efficiency is found to increase from 15.8% to 38% and on the other side the exergy efficiency increased
Tout TPAS TV E_ X_ Q_ _ net W _ m
Outlet temperature of HTF from PTC field (°C) Triple pressure level absorption system Throttle valve Energy rate (kW) Exergy rate (kW) Heat transfer rate (kW) Work output (kW) Mass flow rate (kg s1)
Greek symbols l Entrainment ratio h Incidence angle e Work to refrigeration ratio ex Work to exergetic refrigeration ratio gE Energy efficiency (%) gx Exergy efficiency (%) Subscript X e1 e2 P T 1, 2, 3
Exergy Evaporator 1 Evaporator 2 Pump Turbine state points
from 45.2 to 57.2%. The generating temperature generally kept in the permissible limit as it requires big turbine. Rashidi et al. [21] write the computer code for a power and ejector refrigeration cycle for R123 which is used as working fluid and studied the effects of various dependent parameters on the outcome of the cycle. Results demonstrate that both operating efficiencies (1st and 2nd law) are improved at higher evaporator temperature, while boiler and ejectors experienced maximum exergy loss. It is also observed that at a high inlet pressure of turbine, 1st law efficiency is favorable but 2nd law efficiency is reduced. Thermodynamic analysis of combined power and ejector refrigeration cycles [1,7,12,16,26] demonstrates that the highest irreversibility occurs in heat addition process followed by the ejector and turbine. To enhance the performance of combined power and ejector refrigeration cycle, triple pressure level absorption system (TPAS) is integrated with this combined cycle. Hong et al. [14] studied a new triple pressure level absorption refrigeration cycle. Their results have shown that the COP of the proposed cycle is 30% more than that of a single effect absorption refrigeration cycle (ARC) for specific conditions. Verda et al. [25] develop a mathematical model of a triple pressure level ARC using ammonia-lithium nitrate solution as working fluid. Simulation results concluded that with the use of the ejector, the absorption pressure becomes higher than the evaporation pressure and increase the cooling capacity. Therefore, the efforts carried out in this study is to propose a multi-generation cycle which produces power and refrigeration at two different temperatures simultaneously, using solar thermal energy as a heat source. The proposed multi-generation cycle is the integration of triple pressure level absorption system (TPAS) with ejector organic Rankine cycle (EORC), which meets out the demand of electricity, space air-conditioning and preservation of fruits & vegetables in cold storage. The performance of EORC and the proposed multi-generation cycle is also compared on the basis of energy and exergy approach.
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx Table 1 Main constraints considered for the investigation.
2. Description of working These systems comprise of ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS) based on PTC solar field are shown in Figs. 1a and 2a respectively. Solar thermal energy flux is utilized for the heating of the HTF (1) with the aid of PTC solar field. HTF after passing through HRVG (1–2), where it superheats the high-pressure refrigerant, enters the TPAS generator (G2) to desorb the water vapor from LiBr-H2O solution and then to the PTC solar field for heating (16). The superheated vapor expands (4–5) up to the extraction pressure (Pext) and enters the convergent-divergent nozzle of the ejector. Refrigerant vapor from the nozzle entrains the secondary refrigerant (13) and the mixture is passed through the mixing chamber of the ejector1 (EJ1). The refrigerant stream (6) and turbine exhaust stream (14) combines at (7) and then it is cooled to (8) by transferring the heat to the refrigerant (15-3) in the heat exchanger1 (HE1). Saturated liquid refrigerant from the condenser (9) enters into throttle valve (TV1) (11) and pump (P3) (10). The high-pressure liquid refrigerant (15) from pump (P3) flows into the heat exchanger (HE1) (15-3) is preheated and then converted into superheated refrigerant vapor (4) in the heat recovery vapor generator (G1). The saturated liquid refrigerant (11) expands to the evaporator pressure (11–12) in the throttle valve (TV1) and vaporized in the evaporator (E1) (12–13) to produce refrigeration effect. The water vapor (23) leaving from the TPAS generator (G2) is condensed in the condenser (C2) and leaves as saturated water (24) which further cools in the liquidvapor heat exchanger (HE3) (24–25) then it throttles (25–26) to evaporator2 (E2) (26–27) to produce refrigeration effect. The refrigerant water vapor coming from the evaporator (E2) is preheated in the HE3 (27–28). The LiBr-H2O solution (20) from the TPAS generator (G2) enters into the heat exchanger (HE2) and cools to (21). The solution (21) enters to ejector and entrains water vapor (28) from the heat exchanger3 (HE3) and this mixture flows to the absorber (ABS) (22–17), and then pump (P5) (17–18) to heat exchanger (HE2) (18–19) and ultimately reaches the TPAS generator (G2). Both the systems have a fixed mass flow rate of HTF. Also, the exit temperature of HTF from PTC at given SBR is considered to be the same. For the thermodynamic investigation, the constraints deliberated for the process of the proposed system are depicted in Table 1. The p-h diagrams corresponding to ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS) are also drawn and shown in Figs. 1b and 2b respectively.
Ambient temperature (°C)
25
Ambient pressure (MPa) Turbine Inlet pressure (MPa) Extraction pressure of Turbine (MPa) Extraction ratio Isentropic turbine efficiency (%) Isentropic pump efficiency (%) Mass flow rate of HTF (kg/s) Tracking mode for PTC field
0.101325 1.1 0.4 0.3 85 80 22 Focal axis N-S horizontal and E-W tracking 100
Inlet temperature of HTF in PTC for EORC (°C) Inlet temperature of HTF in PTC for ORTPAS (°C) Pinch point temperature difference (°C) Ejector evaporator temperature (°C) Condenser temperature (°C) Solar beam radiation (W/m2) Aperture Area (m2) TPAS evaporator temperature (°C) TPAS generator temperature (°C)
90 10 5 36 600 10,000 10 85
3. Thermodynamic analysis In order to simulate the performance of the proposed system, the principle of mass and energy conservation are used. The mass and energy balance for a general steady flow system was given as
X
_ ¼ m
in
X
_ m
ð1Þ
out
P P _ is the rate of mass transfer into the system and out m _ where in m is the rate of mass transfer out of the system.
E_ in ¼ E_ out
ð2Þ
X _ in þ _ h þ C2 =2 þ gz Q_ in þ W m in
_ out þ ¼ Q_ out þ W
X
_ h þ C2 =2 þ gz m
ð3Þ
out
The rate of exergy change within the system during a process is given by
X_ heat X_ work þ X_ mass;in X_ mass;out X_ d ¼ DX_ X_ heat ¼
X T0 _ 1 Q T
ð4Þ ð4aÞ
Fig. 1a. Process diagram of ejector organic Rankine cycle (EORC).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
3.1. Energy analysis Solar energy received from the Sun
Q_ Solar ¼ Gb Ap
ð5cÞ
where Gb = I Cosh = Solar beam radiation, I = DNI (W/m2), Ap = Aperture area (m2), h = Incidence angle. Heat gain in the PTC field for ejector organic Rankine cycle (EORC)
_ 1 ðh1 h2 Þ ¼ gE;PTC Gb Ap ¼ m _ 4 ðh4 h3 Þ Q_ gain ¼ m
ð6Þ
where gE;PTC ¼ EnergyefficiencyofPTCfield
gE;PTC
" # Tm T0 ðTm T0 Þ2 c ¼ab Gb Gb
ð7Þ
a = optical efficiency of PTC field = 0.7, b = first order loss coefficient of PTC field = 0.1, c = second order loss coefficient of PTC field = 0, Tm = {(Tin + Tout)/2} = mean HTF temperature. The energy efficiency of the EORC (gE1 ) can be characterized as _ net ) and refrigeration outthe proportion of the network output (W put in the ejector evaporator (Q_ e1 ) to the solar energy input (Q_ Solar ).
_ net þ Q_ e =Q_ Solar gE1 ¼ W 1 Fig. 1b. p-h diagram of ejector organic Rankine cycle.
ð8Þ
_ T¼m _ 4 ðh4 h5 Þ þ m _ 4 ð1 RÞðh5 h14 Þ W
ð8aÞ
_ p dV X_ work ¼ W 0
ð4bÞ
_ 5 =m _4 R¼m
ð8bÞ
_ ½ðh h0 Þ T0 ðs s0 Þ X_ mass ¼ m
ð4cÞ
_ P¼m _ 4 ðh15 h10 Þ W
ð8cÞ
Fig. 2a. Process diagram of ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system (EORTPAS).
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
5
Fig. 2b. p-h diagram of ejector organic Rankine cycle integrated with a triple pressure level vapour absorption system.
_ net ¼ W _ TW _P W
ð8dÞ
_ 5 l1 ðh13 h12 Þð8eÞ Q_ e1 ¼ m
3.2. Exergy analysis Exergy efficiency of PTC field is given by
gx;PTC ¼ fm_ ðh1 h16 Þ T0 ðs1 s16 Þg=Gb Ap
Work to refrigeration ratio for EORC
_ net =Q_ e e1 ¼ W 1
ð9Þ
ð13Þ
Useful work obtainable from solar radiation (£) is given by Petela [20]
4 4 T0 1 T0 þ 3 Tsolar 3 Tsolar
Heat gain in the PTC field for ejector organic Rankine cycle integrated with triple pressure level vapour absorption system (EORTPAS)
¼1
_ 1 ðh1 h16 Þ ¼ gE;PTC Gb Ap Q_ gain ¼ m
The exergy efficiency (gx1 ) and (gx2 ) of EORC, EORTPAS may be reported as
ð10Þ
_ 23 h23 þ m _ 20 h20 m _ 19 h19 Q_ gain ¼ m_ 4 ðh4 h3 Þ þ m
ð10aÞ
The energy efficiency (gE2 ) of the EORTPAS characterized as the
_ net ) and total proportion of summation of the network output (W refrigeration output in the ejector evaporator E1 (Q_ ) and TPAS evaporator E2 (Q_ e2 ) to the solar energy input (Q_ Solar ).
_ net þ Q_ e þ Q_ e =Q_ Solar gE2 ¼ W 1 2 _ 26 ðh27 h26 Þ Q_ e2 ¼ m
e1
ð11Þ ð11aÞ
Work to refrigeration ratio for EORTPAS
_ net = Q_ e þ Q_ e e2 ¼ W 1 2
_ net þ X_ e =X_ Solar gx1 ¼ W 1
_ net þ X_ e þ X_ e =X_ Solar gx2 ¼ W 1 2
ð13aÞ
ð14Þ ð15Þ
where, X_ Solar is exergy associated with solar radiation, X_ e1 X_ e2 is the exergy associate with refrigeration in the evaporators 1, 2.
X_ e1 ¼ Q_ e1 ðT0 =Te1 Þ 1
ð15aÞ
X_ e2 ¼ Q_ e2 ðT0 =Te2 Þ 1 ð15bÞ X_ Solar ¼ Gb Ap
ð15cÞ
Work to exergetic refrigeration ratio for EORC, 2
ð12Þ
l1 ¼ m_ 13 =m_ 5
ð12aÞ
l2 ¼ m_ 28 =m_ 21
ð12bÞ
_ net =X_ e ex1 ¼ W 1
_ net = X_ e þ X_ e ex2 ¼ W 1 2
ð16Þ
ð17Þ
where TSolar is the Apparent Sun Temperature = 5800 K
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
Table 2 Results of simulation for EORC. State points
P (kPa)
T (°C)
_ m(kg/s)
h (kJ/kg)
s (kJ/kgK)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1500 1400 1100 1100 400 116.1 116.1 116.1 116.1 116.1 116.1 22.28 22.28 116.1 1100
172 100 82.83 162 127.8 108.7 98.08 36 36 36 36 5 5 92.77 37.05
22 22 15.77 15.77 4.731 5.479 16.52 16.52 16.52 15.77 0.7484 0.7484 0.7484 11.04 15.77
443.9 258 139.4 398.7 375.8 362.9 353.6 298.3 80.31 80.31 80.31 80.31 273.8 348.9 81.55
22.74 12.71 0.473 1.128 1.138 1.19 1.165 1.001 0.2962 0.2962 0.2962 0.3085 1.03 1.152 0.3002
Table 3 Results of simulation for EORTPAS. State points
P (kPa)
T (0C)
_ m(kg/s)
h (kJ/kg)
s (kJ/kgK)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
1500 1400 1100 1100 400 116.1 116.1 116.1 116.1 116.1 116.1 22.28 22.28 116.1 1100 1300 1.474 5.945 5.945 5.945 5.945 1.474 5.945 5.945 5.945 1.228 1.228 1.228
162.2 100 75.52 152.2 117.6 99.58 88.35 36 36 36 36 5 5 82.71 37.05 90 36 36 70.41 85 35.81 57.71 85 36 24 10 10 36.82
22 22 13.66 13.66 4.098 4.736 14.3 14.3 14.3 13.66 0.6381 0.6381 0.6381 9.563 13.66 22 1.137 1.137 1.137 0.9347 0.9347 1.137 0.2026 0.2026 0.2026 0.2026 0.2026 0.2026
418.5 258 130 388.5 366.3 354.9 345.1 298.9 80.31 80.31 80.31 80.31 273.8 340.3 81.55 232.2 75.83 75.83 150.7 214.2 123.1 558.9 2659 150.8 100.5 100.5 2519 2569
21.47 12.71 0.4464 1.104 1.114 1.169 1.142 1.003 0.2962 0.2962 0.2962 0.3085 1.03 1.128 0.3002 11.17 0.2474 0.2474 0.4765 0.4664 0.1925 0.3182 8.61 0.5185 0.3527 0.3577 8.899 9.064
4. Result and discussion In this paper, performance analysis of PTC field based ejector organic Rankine cycle (EORC), and ejector organic Rankine cycle integrated with a TPAS (EORTPAS) have been carried out. A theoretical investigation is conducted to discover the influence of
various design parameters such as SBR, turbine inlet pressure (TIP), turbine extraction pressure (TEP), and ejector evaporator temperature (EET) on the performance of EORC & EORTPAS. In this analysis, where a thermodynamic parameter is varied, the other parameters are kept constant as mentioned in Table 1. Tables 2 and 3 show the thermodynamic state of each point for EORC & EORTPAS. Also, Tables 4 and 5 show the distribution of energy & exergy in various components of EORC and EORTPAS.
4.1. Effect of solar beam radiation (SBR) The variation of energy and exergy efficiencies of PTC field for EORC and EORTPAS with the change in SBR is shown in Fig. 3. It is evident from Fig. 3 and Eqs. ((7) and (13)) that the energy and exergy efficiencies of PTC field increases with increase in the value of SBR for both the systems because the outlet temperature of HTF (Tout) from PTC field and the amount of heat transferred to the HTF increases at fixed mass flow rate and inlet temperature of HTF (Tin) to the PTC field. It is clear from Eq. (7) that the mean temperature of HTF (Tm) for EORC is higher than EORTPAS, therefore the energy efficiency for EORTPAS is greater than for that of EORC at the same SBR. It is also clear that the exergy efficiency of EORC is more as that of EORTPAS because the mean temperature of heat addition is greater so the exergy efficiency is greater. The variation of energy and exergy efficiencies for EORC and EORTPAS with SBR is shown in Fig. 4. As SBR increases, the turbine inlet temperature increases which results in greater work output. Also, the temperature of working fluid at the extraction point (5) of the turbine is higher at higher SBR which results in entrainment of more refrigerant from ejector evaporator (13). This leads to greater refrigeration output at the evaporator of the ejector. So, this increase in work output and refrigeration output increases both the efficiencies of EORC at higher SBR. It is also found that with the addition of TPAS in EORC, the energy efficiency of EORTPAS increases considerably but decreases with the increase in SBR. This is due to the fact that with the increase in SBR, work output, ejector refrigeration output increases, and TPAS refrigeration output remain constant but solar energy input increases significantly. This leads to a decrease in the energy efficiency of EORTPAS with an increase in SBR. The exergy efficiency of EORTPAS is lesser than that of EORC due to the reduction of work output at the same SBR. The exergy efficiency of EORTPAS increases because the work output & exergy of ejector refrigeration output increases, while exergy of TPAS refrigeration output remains constant with increase in SBR. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with SBR is shown in Fig. 5 for EORC and EORTPAS. Both work to refrigeration ratio and work to exergetic refrigeration ratio increases with an increase in SBR as the enhancement of work output is better than that of both the refrigeration and exergetic refrigeration output for EORC and EORTPAS.
Table 4 The distribution of energy in various components of EORC and EORTPAS. Term
Input energy from Sun Turbine output Pump input Ejector refrigeration output TPAS refrigeration output Work output Energy output Energy loss
Ejector organic Rankine cycle (EORC)
Ejector organic Rankine cycle integrated with a triple pressure level absorption system (EORTPAS)
Input energy (kW)
% of Input energy from Sun
Input energy (kW)
% of Input energy from Sun
6000 658 19.5 144.8 – 638.5 783.3 5506.3
100 10.9 0.3 2.4 – 10.6 13 91.8
6000 550.9 16.93 120 492 534 1146 6078
100 9.18 0.28 2 8.2 8.9 19.1 101.3
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx Table 5 The distribution of exergy in various components of EORC and EORTPAS. Ejector organic Rankine cycle (EORC)
Exergy destruction/losses in components (i) HRVG (ii) Turbine (iii) Ejector 1 (iv) Condenser 1 (v) Pump (vi) Heat exchanger (vii) Throttle valve (viii) Evaporator 1 (ix) TPAS Generator (x) Condenser 2 (xi) Absorber (xii) PTC Total Exergy destruction/loss
Amount (kW)
% of exergy input
Amount (kW)
% of exergy input
5589
100
5589
100
638.5 16.2 – 654.7
11.42 0.29 – 11.71
534.5 13.81 26.23 574.54
9.56 0.25 0.47 10.28
139.7 100.6 122.96 12.58 16.41 16.41 2.7 1.09 – – – 4521.85 4934.3
2.5 1.8 2.2 0.22 0.3 0.3 0.05 0.02 – – – 80.9 88.29
94.8 83.37 95.98 11.47 16.21 15.47 2.73 2.07 103.58 20.24 19.14 4549.4 5014.46
1.7 1.5 1.7 0.21 0.29 0.28 0.05 0.04 1.85 0.36 0.34 81.4 89.72
Work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) at the same SBR for EORC is higher than that of EORTPAS because of the enhancement of refrigeration output (Qe1 + Qe2) & exergetic refrigeration output (Xe1 + Xe2) and reduction in work output. Work to refrigeration ratio (e) varies from 4.2 to 4.5 for EORC and 0.53 to 1.04 for EORTPAS and work to exergetic refrigeration ratio (ex) varies from 37.6 to 40.3 for EORC and 8.7 to 15.4 for EORTPAS with the SBR variation from 400 to 700 W/m2. The variation of entrainment ratio (l1) with SBR is shown in Fig. 6 for EORC and EORTPAS. As SBR increases, the turbine inlet temperature increases resulting in the increase in the temperature of working fluid at the extraction point (5) of the turbine. This increases the exit velocity of working fluid from the ejector nozzle which leads to the entrainment of more refrigerant from ejector evaporator. Therefore entrainment ratio for EORC and EORTPAS increases with increase in SBR. Entrainment ratio for EORC is higher than that of EORTPAS because turbine inlet temperature is more in EORC as compared to EORTPAS. 4.2. Effect of turbine inlet pressure (TIP)
21 68.4
16 ηE1,PTC ηE2,PTC
67.6 67.2
11 6
ηx1,PTC ηx2,PTC
400
500 600 Solar beam radiation (W/m2)
700
1
Exergy efficiency (%)
Energy efficiency (%)
The trend of efficiencies as the TIP varies is shown in Fig. 7 for EORC and EORTPAS. An increasing trend of work output with increasing of turbine inlet pressure is perceived because of high
68
Ejector organic Rankine cycle integrated with a triple pressure level absorption system (EORTPAS)
Fig. 3. Variation of energy and exergy efficiencies of PTC field for EORC and EORCTPAS with SBR.
enthalpy drop for high pressure ratio. This also results in low turbine extraction temperature (5) and consequently low primary stream velocity and low entrainment of secondary vapor which reduces the cooling capacity of ejector evaporator (Qe1). The refrigeration output at TPAS does not change because of the same working conditions across TPAS with variation in with turbine inlet pressure. The combined effect of work output and refrigeration output (s) on the performance of EORC and EORTPAS is to increase in energy efficiency with turbine inlet pressure. The similar increment is obtained for exergy efficiency. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with turbine inlet pressure is shown in Fig. 8 for EORC and EORTPAS. As can be seen from Fig. 8 that the work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) showing an increasing trend with increasing of turbine inlet pressure as work output increases, ejector refrigeration output decreases and TPAS refrigeration output remains same at high turbine inlet pressure. The change of entrainment ratio (l1) with turbine inlet pressure is shown in Fig. 9 for EORC and EORTPAS. Increase in TIP causes a decrease in TET. This low TET stream (5) works as a primary flow for ejector which reduces the primary stream velocity and entrainment of secondary vapor from the ejector evaporator. Therefore, the entrainment ratio for EORC and EORTPAS decreases at a high
31
13
26
ηE1 ηx1
21
9
ηE2 ηx2
5
16 11
400
500 600 Solar beam radiation (W/m2)
700
1
Exergy efficiency (%)
Exergy input Exergy output (i) Work output (ii) Ejector exergetic refrigeration output (iii) TPAS exergetic refrigeration output Total exergy output
Energy efficiency (%)
Term
Fig. 4. Variation of energy and exergy efficiencies of EORC and EORCTPAS with SBR.
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40
3
ε1
ε2
30
2
εx1
εx2
20
1 0
10 400
500 600 Solar beam radiation (W/m2)
700
0
Entrainment ratio (μ1)
Fig. 5. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with SBR.
0.162 0.16 0.158 0.156 0.154 0.152 0.15 0.148 0.146
μ1,EORC μ1, EORCTPAS
400
500 600 Solar beam radiation (W/m2)
700
Fig. 6. Variation of entrainment ratio of EORC and EORCTPAS with SBR.
inlet pressure of the turbine. As the turbine inlet temperature for EORC is more than that of EORTPAS, therefore, the entrainment ratio for EORC is higher than that of EORTPAS. 4.3. Effect of turbine extraction pressure (TEP)
26
13
22
9
18 14 10
0.8
ηE1
ηE2
ηx1
ηx2
1 1.2 1.4 Turbine inlet pressure (MPa)
5
1.6
1
Exergy efficiency (%)
Energy efficiency (%)
The variation of energy and exergy efficiencies with turbine extraction pressure (TEP) for EORC and EORTPAS is shown in Fig. 10. It is evident that as the TEP increases, work output decreases. It is also observed that the ejector refrigeration output increases with the increase in TEP. The reason for this is that the increase in TEP increases the pressure and temperature of the primary flow entering the ejector which in turn increases the entrainment of secondary vapor. The effect of change in turbine extraction pressure is insignificant on the temperature of HTF at the exit of HRVG. Therefore, refrigeration output at the evaporator of the TPAS
Fig. 7. Variation of energy and exergy efficiencies of EORC and EORCTPAS with TIP.
6
50
5
40
4 3 2
ε1
ε2
30
εx1
εx2
20 10
1 0
0.8
1 1.2 1.4 1.6 Turbine inlet pressure (MPa)
0
Work to exergetic refrigeration ratio (εx)
4
Work to refrigeration ratio (ε)
50
Fig. 8. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with TIP.
remains the same. As the increase in ejector refrigeration output dominates over the decrease in work output which results in the increase in the energy efficiency of both the systems with an increase in TEP. The exergy efficiency of the EORC and EORTPAS decreases with increase in TEP because the amount of increase in exergy associated with the ejector refrigeration output (Xe1) is much less than the amount of reduction in works output. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with turbine extraction pressure is shown in Fig. 11 for EORC and EORTPAS. It is evident from the Fig. 11 that the e and ex for both the systems decreases as work output decreases and ejector refrigeration output increases at high turbine extraction pressure. The entrainment ratio (l1) for both the system also changes with TEP. Fig. 12 depicts the rise of entrainment ratio for both the systems at elevated turbine extraction pressure because of the gain in pressure and temperature of the primary flow entering the ejector resulting in which in more entrainment of secondary vapor. The slightly higher entrainment ratio for EORC relative to that of EORTPAS is due to high turbine inlet temperature in EORC as compared to that of EORTPAS. 4.4. Effect of ejector evaporator temperature (EET) The variation of energy and exergy efficiencies with ejector evaporator temperature (EET) for both the systems is shown in Fig. 13. A constant value of work and refrigeration output of the TPAS (Qe2) with the change in evaporator1 temperature (Te1) because their inlet and exit states do not change. As the ejector evaporator temperature increases, the evaporator pressure increases, which increase in the mass flow rate of refrigerant through the ejector evaporator resulting in an increase in ejector
Entrainment ratio (μ1)
5
Work to exergetic refrigeration ratio (εx)
D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
Work to refrigeration ratio (ε)
8
0.162
μ1, EORC
0.16
μ1, EORCTPAS
0.158 0.156 0.154 0.152 0.15
0.8
1 1.2 1.4 Turbine inlet pressure (MPa)
1.6
Fig. 9. Variation of entrainment ratio of EORC and EORCTPAS with TIP.
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9
ηE1 ηx1
15 10
0.3
0.35
0.4
ηE2 ηx2
0.45
5
0.5
1
25
8
ε2
εx1
εx2
56
6
42
4
28
2
14
0
0
0.3
0.35 0.4 0.45 Extraction pressure (MPa)
0.5
0.19
μ1, EORCTPAS
0.17 0.15 0.13 0.11 0.09 0.07
0.3
0.35 0.4 0.45 0.5 Extraction pressure (MPa)
0.25 0.23 0.21 0.19 0.17 0.15 0.13 0.11 0.09
10
15
9 260 262 264 266 268 270 272 274 Ejector evaporator temperature (K)
10
50 40
8 ε1 εx1
6
ε2 εx2
30
4
20
2
10
0
260 262 264 266 268 270 272 274
0
8
Fig. 14. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with EET.
0.21 Entrainment ratio (μ1, EORCTPAS )
Entrainment ratio (μ1, EORC )
μ1, EORC
11
Ejector evaporator temperature (K)
Fig. 11. Variation of work to refrigeration ratio and work to exergetic refrigeration ratio of EORC and EORCTPAS with TEP.
0.21
Work to refrigeration ratio (ε)
70 ε1
ηx2
Fig. 13. Variation of energy and exergy efficiencies of EORC and EORCTPAS with EET.
Fig. 12. Variation of entrainment ratio of EORC and EORCTPAS with TEP.
refrigeration output (Qe1). Therefore energy efficiency increases at higher values of evaporator1 temperature (Te1) for both the systems. The exergy efficiency for both the systems varies insignificantly because the amount of the variation of exergy of ejector refrigeration outputs is insignificant in comparison to the energy associated with the ejector refrigeration output. The variation of work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) with ejector evaporator temperature (EET) for both the systems is shown in Fig. 14. It is apparent from the Fig. 14 that the e and ex for both the systems decreases with increase in evaporator temperature as work and TPAS (Qe2) output remains constant whereas ejector refrigeration output (Qe1) is
Entrainment ratio (μ1, EORC )
Work to refrigeration ratio (ε)
10
Work to exergetic refrigeration ratio (εx)
Fig. 10. Variation of energy and exergy efficiencies of EORC and EORCTPAS with TEP.
ηE2
ηx1
20
10
Extraction pressure (MPa)
ηE1
Exergy efficiency (%)
9
12
Work to exergetic refrigeration ratio (εx)
20
30
0.19 0.17
μ1, EORC μ1, EORCTPAS
0.15 0.13 0.11 0.09
260 262 264 266 268 270 272 274
0.24 0.22 0.2 0.18 0.16 0.14 0.12 0.1
Entrainment ratio (μ1, EORCTPAS )
13
Energy efficiency (%)
25
Exergy efficiency (%)
Energy efficiency (%)
D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
Ejector evaporator temperature (K) Fig. 15. Variation of entrainment ratio of EORC and EORCTPAS with EET.
increased at higher evaporator1 temperature (Te1). Work to refrigeration ratio (e) and work to exergetic refrigeration ratio (ex) at the same ejector evaporator temperature for EORC is higher than that of EORTPAS because of the enhancement of refrigeration output (Qe1 + Qe2) & exergetic refrigeration output (Xe1 + Xe2). The variation of entrainment ratio (l1) with ejector evaporator temperature (EET) is shown in Fig. 15 for EORC and EORTPAS. As the ejector evaporator temperature increases, the ejector evaporator pressure increases, resulting in an increase in the mass flow rate of refrigerant through the ejector evaporator. Therefore, the entrainment ratio for EORC and EORTPAS is higher at elevated evaporator1 temperature (Te1). The entrainment ratio for EORC is
Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008
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D.K. Gupta et al. / Engineering Science and Technology, an International Journal xxx (xxxx) xxx
slightly higher than that of the EORTPAS because turbine inlet temperature is more in EORC as compared to EORTPAS. 5. Conclusion The proposed system produces power and refrigeration output at different temperatures simultaneously. The thermodynamic analysis was conducted to investigate the effect of various design parameters such as SBR, TIP, TEP, and EET on the performance of proposed system EORTPAS and also compared with the performance of EORC. The conclusions drawn are summarized as: It is evident that the EORTPAS has higher refrigeration output, exergetic refrigeration output, and energy efficiency than that of the EORC. The various thermodynamic parameters such as SBR, turbine inlet pressure, turbine extraction pressure, and ejector evaporator temperature have a significant influence on the work output, refrigeration output, work to refrigeration ratio, work to exergetic refrigeration ratio and entrainment ratio of the proposed system. The energy efficiency for EORC increases from 12.0% to 13.9% and for EORTPAS increases from 18.2% to 19.8%, whereas exergy efficiency increases from 10.4% to 12.8% and 9.2% to 11.1% for EORC and EORTPAS respectively with the increase of turbine inlet pressure from 0.8 MPa to 1.6 MPa. The energy efficiency for EORC and EORTPAS increases marginally with an increase in extraction pressure and ejector evaporator temperature. The exergy efficiency for EORC and EORTPAS decreases marginally with an increase in extraction pressure and ejector evaporator temperature. References [1] B.K. Agrawal, M.N. Karimi, Parametric, exergy and energy analysis of low grade energy and ejector refrigeration cycle, Int. J. Sustain. Build. Technol. Urban Dev. 4 (2) (2013) 170–176. [2] G.K. Alexis, Performance parameters for the design of a combined refrigeration and electrical power cogeneration system, Int. J. Refrig. 30 (2007) 1097–1103. [3] R. Barberz, A. Rovira, M.J. Montes, J.M.M. Val, A new approach for the prediction of thermal efficiency in solar receivers, Energy Convers. Manage. 123 (2016) 498–511. [4] D. Barlev, R. Vidu, P. Stroeve, Innovation in concentrated solar power, Sol. Energy Mater. Sol. Cells 95 (2011) 2703–2725. [5] G. Besagni, R. Mereu, F. Inzoli, Ejector refrigeration: a comprehensive review, Renew. Sustain. Energy Rev. 53 (2016) 373–407.
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Please cite this article as: D. K. Gupta, R. Kumar and N. Kumar, Performance analysis of PTC field based ejector organic Rankine cycle integrated with a triple pressure level vapor absorption system (EORTPAS), Engineering Science and Technology, an International Journal, https://doi.org/10.1016/j. jestch.2019.04.008