- Email: [email protected]
Prospects of Power Generation from Low Grade Heat Resources through Trilateral Flash Cycle (TFC) Using Impulse Turbine
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 110 (2017) 352 – 358
1st International Conference on Energy and Power, ICEP2016, 14-16 December 2016, RMIT University, Melbourne, Australia
Prospects of power generation from low grade heat resources through Trilateral Flash Cycle (TFC) using impulse turbine Mahdi Ahmadi*, Abhijit Date, Aliakbar Akbarzadeh, Shahin Heidari, Md Arbab Iqbal, Farah Melhem School of Engineering, RMIT University, Melbourne 3000, Australia
Abstract This paper is an introductory prospect and experiment of generated force measuring of applying two-phase nozzle and an impulse turbine design for trilateral flash cycle heat engine. In this concept of trilateral flash cycle (TFC), pressurized working fluid (Isopentane) being heated by low temperature hot water and pumped through a two-phase nozzle to impact the impulse turbine blade. Then the generated force, measured by a load cell behind the turbine blade and isentropic efficiency of nozzle is discussed. Based on the investigations carried out so far, there is a high potential of power generation from low temperature heat recourses. Further the basic working principles of power generation system are presented followed by of the governing equations and the thermodynamics. The theory of this paper calculates isentropic efficiency of the nozzle based exit speed of the working fluid out of the nozzle and experimentally measured generated force from lab scale test rig. The initial results from experimental test shows, promising isentropic efficiency for the novel system is around 45%. Also it was observed that the trust generated force increased from 2.5N to 5N by increasing the working fluid temperature from 30 ᤪC to 70 ᤪC respectively. © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. Keywords: power generation; renewable energy; trilateral flash cycle; impulse turbine; Nozzle.
* Corresponding author. Tel. +613 9925 2000. E-mail address: [email protected]
1876-6102 © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. doi:10.1016/j.egypro.2017.03.152
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
1. Introduction As world population continue to rise, finding alternative energy sources to meet global energy demands will become necessary. Also the rapid developing economies accreted the global energy consumption to unprecedented levels. Although researchers continue to maximizing efficiency to improve existing sources of electricity generation but search for alternative energy is inevitable and to achieve stable development, renewable energy became a strategic world's option to attack environmental pollution, the energy crisis and fossil fuel consequences [1] [2]. Currently most of produced electricity power generation is from converting fossil fuels energy in thermal power stations[3]. Emission carbon dioxide from ignition of fossil fuels became a global concerns of climate change and long term global experience shows relation between energy use and carbon dioxide emissions[4]. That creates a question about the future consequences of fossil fuel consumption. At present there is a clear consensus on the impact that this overexploitation of resources is having on the fragile ecosystem of our planet, stretching to the limit the possibilities for sustainability the planet can offer. Therefore, this development, which has been and is clearly unsustainable, must become environmentally friendly, understanding as sustainable development that which is able to fulfil our needs without endangering those of future generations [5]. Renewable technologies are considered as clean sources of energy and optimal use of these resources minimize environmental impacts, produce minimum secondary wastes and are sustainable based on current and future economic and social societal needs. Renewable energy technologies provide an excellent opportunity for mitigation of greenhouse gas emission and reducing global warming through substituting conventional energy sources. Renewable energy sources (RES) supply 14% of the total world energy demand [5]. RES includes biomass, hydropower, low temperature solar, wind and marine energies. The renewable are the primary, domestic and clean or inexhaustible energy resources[6] ,[7]. Large-scale hydropower supplies 20 percent of global electricity. Wind power in coastal and other windy regions is promising source of energy [5], [8]. The share of RESs is expected to increase very significantly (30–80% in 2100)[9]. In the last decade it has been shown catastrophic effects of rapid climate change caused by global warming and a consequence increase in awareness about the importance of a sustainable environment[10]. Out of these renewable energy resources, the advantage of low temperature energy is that it can continuously supply energy and can serve as a base power[11]. This paper is motivated by the improvement necessity of current heat recovery technologies and progress to utilization of large amount of solar and geothermal and heat waste of low-grade heat sources. Temperature below 120 ºC is being targeted as low grade heat which is available from variety heat sources such as geothermal, industries waste heat and solar thermal, can be converted into electricity with applying a binary system. A binary system is a close loop cycle and exerts no gas to environment. Organic Rankine cycle (ORC) is one of the most common thermodynamic cycles[12] in low grade heat recovery field. In ORC working fluid gets vaporized in boiler before acting the expander but in trilateral cycle, working fluid spins the expander in form of two phase mixture of vapour and liquid [13]. As a summarised comparison of ORC and TFC cycles in ORC working fluid enters the heater as compressed liquid and exits as saturated or superheated vapour then amount of utilisable heat from source is limited to the vapour temperature. For example temperature different if in and out can be ∆T= 95 ̊C – 90 ̊C=5 C ̊ . but in TFC, working fluid enters the heater as compressed liquid and exits at higher temperature as compressed or saturated liquid. Then amount of utilisable heat from source is more compared to ORC. For example temperature different if in and out can be ∆T= 95̊c -35̊c=60̊c. Also TFC can be applicable for lower temperatures comparing ORC. Mechanical conversion efficiency can be improved with utilisation of impulse turbine binary TFC. Also simplicity of the mechanism leads to lower cost and has the ability to recovering more heat of low-grade resources can increase the power generation with utilisation of the current heat resources. Although there are many examples of operational Organic Cycle Heat Engines around the world and even a Screw Expander Turbine has been applied in Trilateral Flash Cycle to generate electricity [14] but there is a knowledge gap in converging-diverging stationary nozzle application in trilateral flash cycle with impulse turbine and single element working fluid. In this study we are going to focus on stationary nozzle in trilateral flash cycle and impulse turbine. The rotor of an impulse turbine rotates because of a force created by high velocity two phase liquid from a stationary nozzle after pressure drop. Windmills and waterwheels are simple impulse turbine examples[13].
353
354
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
However, there is a need to convert the large thermal heat from TFC by a proper expander. The expander in this research is a stationary two phase converging-diverging nozzle and an impulse turbine. The impulse turbine utilises the available kinetic energy in the working fluid after expansion in the stationary two phase converging-diverging nozzle and able convert it to mechanical power. The change of momentum of the fluid in the nozzle gives rise to force, which causes the rotor to rotate. The system is also applicable to any low-grade heat sources, such as waste heat recovery and solar thermal sources. It is the aim of this project to develop an economically-viable low temperature heat engine system for utilising low temperature hot water. Achievement of this aim would thus open up the exploitation of the low temperature resources that are not currently being utilised, and hence contribute to the national and international efforts to reduce greenhouse gas emissions. Nomenclature
mwater Water mass flow rate (kg/s) miso Isopentane mass flow rate (kg/s) Added heat Q
W h '3 h h fg X '3 x Vj
Vi Zi Zo U g
Added Work Actual enthalpy point 3 (J/kg) Specific enthalpy of working fluid (J/kg) Specific latent heat of evaporation or condensation of working fluid (J/kg) Quality of working liquid at nozzle exit Quality of liquid - vapour mixture Exit velocity Inlet velocity Height of inlet Height of outlet Density Acceleration of gravity
2. The concept of the system As shown in Fig.1. hot water which can be supplied from any low temperature heat resources, introduced through a heat exchanger and heat up the working fluid (Isopentane) comes out from other end of heat exchanger. Pressurised hot Isopentane goes through the nozzles installed in the turbine housing which has atmospheric pressure, and will spin the reaction turbine which is connected to a generator to produce electrical power. Then the working fluid which is cooled to saturated temperature will go into a tank. Vapour will be condensed in the condenser and re-joins liquid phase in tank to start a new cycle in a close loop.
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
Fig. 1. Schematic diagram of proposed TFC binary cycle 3. Methods 3.1. Experimental measurement of trust force of nozzle Based on explained concept of the system above, a test rig has been made in lab scale to measure the generated trust force of nozzle. To be able to measure the trust force, one turbine blade has been mounted on a load cell in front of two phase converging-diverging nozzle, in same position as the turbine. The test rig has been shown in Fig. 2.
Fig. 2. Test rig for trust force measurement
355
356
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
in this setup, expanded working fluid, exits the nuzzle and impinges the turbine blade. Generated force out of this impact, is being measured by the load cell behind the turbine blade. Input hot water temperature to the system to heat up the working fluid, has been changed in 4 different temperature as 40, 50, 60 and 70 centigrade and force has been measured, rest of the variable not changed. Fig. 3 is a schematic view of the nozzle and Pelton turbine blade setup.
Fig. 3. Schematic view of the nozzle and Pelton bucket setup
4. Results and discussion
Below graph is showing the trend of force increase with increase in hot water input temperature to heat up the working fluid.
Fig. 4. Measured force in different hot water input temperature
Designing of this system is based on trilateral flash cycle (TFC) thermodynamics which is explained in introduction section.The working liquid (Isopentane) is getting compressed in a pump and heats up to saturated liquid in heat exchanger. The working fluid will be pressured and heated close to saturation temperature at point2 in Fig.1 before entering the nozzle throat. The working fluid enters the nozzle throat as saturated liquid at high temperature and expands in an isentropic expansion to exit the nozzle, point 3 in Fig.1. On this point, there is a temperature and pressure drop of liquid from high temperature, high pressure to low temperature, low pressure two phase mixture. Ideally, Temperature at point 3 should be same as point 1. Then the working fluid in the condenser undergoes at constant pressure cooling before moving back to point 1. The red point in fig.4 has been taken as sample data, isentropic efficiency of the nozzle can be calculated as below. Table 1 shows the measured values of the test rig in subjective point of the above graph.
357
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358 Table 1. Measured values of the test rig in subjective point of the above graph. measured value
Value
Temperature of Isopentane before nozzle (point 2) ᤪC
64.6ᤪC
Temperature of Isopentane after nozzle (point 3) ᤪC
24.8
Measured Force(N)
3.6
Isopentane flow (lit/min)
3.85
Table 1 shows the measured force at temperature 64.6 ᤪC which is around 3.6N. Sara Vahaji (2014) used the similar set up and achieved the trust force around 2.8 N [15]. In their work they used water as working fluid in vacuum chamber while in the present work Isopentane at atmospheric pressure has been employed. Another significant difference between their set up and ours is the target geometry. As can be seen in Fig. 3 we used a Pelton geometry which reverse the flow by 165 and increases the objective force [16]. Based on values above, exit velocity of the nozzle can be calculated as:
Vj
miso F
97.1m / s
(1)
In order to calculate the actual entropy at nozzle exit, based on the energy balance equation between the inlet nozzle and the outlet nozzle has been used.
Ein
Eout
(2)
§ · § · V2 V2 miso ¨ h2 i U gZi ¸ miso ¨ h '3 J U gZ o ¸ Q W 2 2 © ¹ © ¹
(3)
By assuming that the nozzle is horizontal, negligible inlet velocity, and no work and heat added to nozzle, above equation will be simplified as below:
h '3
h2
VJ 2 2
224.77kj / kg
(4)
Then isentropic efficiency van be obtained as below:
Kisentropic
h2 h3' h2 h3
0.38
(5)
From above measured force inputs, isentropic efficiency of the nozzle can be shown as below graph.
Fig. 5. Calculated isentropic efficiency based on measured force
358
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
5. Conclusion and suggestions for future studies This study has briefly discussed a binary cycle to utilize the application of a stationary converging-diverging nozzle and an impulse turbine. Also shows an experiment of measuring trust force of a stationary converging diverging two phase nozzle. The results has been used to show isentropic efficiency on the nozzle and can be used for further study on mechanical and electricity power generation in a single element working fluid binary system. The study was about the available low temperature geothermal resources but can be applied at any other low grade heat resource. Initial results showed the exit force of the nozzle applied on the Pelton blade geometry increases to 5 N by rising the temperature to 70 ᤪC. An Isentropic efficiency around 45% was obtained for variety of temperature between 30 ᤪC to 70 ᤪC. In this paper feasibility of the concept of use of stationary converging-diverging nozzle in Trilateral Flash Cycle with low temperature heat resource (lower than 70 ᤪC) was proven. As some suggestions for future work we can: x Run experimental investigation with placing impulse turbine in TFC cycle in order to power generation. x Work on nozzle geometry design, aiming to improve efficiency of the system. References [1] He Y, Xu Y, Pang Y, Tian H, Wu R. A regulatory policy to promote renewable energy consumption in China: Review and future evolutionary path. Renewable Energy 2016;89:695-705. [2] Barbier E. Geothermal energy technology and current status: an overview. Renewable Sustainable Energy Rev. 2002;6:3-65. [3] Date A, Alam F, Khaghani A, Akbarzadeh A. Investigate the potential of using trilateral flash cycle for combined desalination and power generation integrated with salinity gradient solar ponds. Procedia Eng. 2012;49:42-49. [4] U.S. EIA. Annual energy outlook 2013. Washington, DC: U.S. Department of Energy; 2013. [5] Schmalensee R, Stoker TM, Judson RA. World carbon dioxide emissions: 1950–2050. Rev. Econ. Stat. 1998;80:15-27. [6] Goldemberg J. World Energy Assessment; Energy and the challenge of sustainability. United Nations Pubns; 2000. [7] Dincer I. Environmental issues: Ii-potential solutions. Energy sources 2001;23:83-92. [8] Yuksel I, Kaygusuz K. Renewable energy sources for clean and sustainable energy policies in Turkey. Renewable Sustainable Energy Rev. 2011;15:4132-4144. [9] Fridleifsson IB. Geothermal energy for the benefit of the people. Renewable Sustainable Energy Rev. 2001;5:299-312. [10] Kralova I, Sjöblom J. Biofuels–renewable energy sources: a review. J. Dispersion Sci. Technol. 2010;31:409-425. [11] Khan M, Iqbal M, Quaicoe J. River current energy conversion systems: Progress, prospects and challenges. Renewable Sustainable Energy Rev. 2008;12:2177-2193. [12] Dai Y, Wang J, Gao L. Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery. Energy Convers. Manage. 2009;50:576-582. [13] Welch P, Boyle P. New turbines to enable efficient geothermal power plants. GRC Trans. 2009;33:765-772. [14] Smith I, Stosic N, Aldis C. Trilateral flash cycle system a high efficiency power plant for liquid resources. In: Proc World Geotherm Congr; 1995. p. 18-31. [15] Vahaji S, Akbarzadeh A, Date A, Cheung S, Tu J. Efficiency of a two-phase nozzle for geothermal power generation. Appl. Therm. Eng. 2014;73:229-237. [16] Dixon SL, Hall C. Fluid mechanics and thermodynamics of turbomachinery. 6th ed. USA: Butterworth-Heinemann, Elsevier Science Boston; 2010.
ScienceDirect Energy Procedia 110 (2017) 352 – 358
1st International Conference on Energy and Power, ICEP2016, 14-16 December 2016, RMIT University, Melbourne, Australia
Prospects of power generation from low grade heat resources through Trilateral Flash Cycle (TFC) using impulse turbine Mahdi Ahmadi*, Abhijit Date, Aliakbar Akbarzadeh, Shahin Heidari, Md Arbab Iqbal, Farah Melhem School of Engineering, RMIT University, Melbourne 3000, Australia
Abstract This paper is an introductory prospect and experiment of generated force measuring of applying two-phase nozzle and an impulse turbine design for trilateral flash cycle heat engine. In this concept of trilateral flash cycle (TFC), pressurized working fluid (Isopentane) being heated by low temperature hot water and pumped through a two-phase nozzle to impact the impulse turbine blade. Then the generated force, measured by a load cell behind the turbine blade and isentropic efficiency of nozzle is discussed. Based on the investigations carried out so far, there is a high potential of power generation from low temperature heat recourses. Further the basic working principles of power generation system are presented followed by of the governing equations and the thermodynamics. The theory of this paper calculates isentropic efficiency of the nozzle based exit speed of the working fluid out of the nozzle and experimentally measured generated force from lab scale test rig. The initial results from experimental test shows, promising isentropic efficiency for the novel system is around 45%. Also it was observed that the trust generated force increased from 2.5N to 5N by increasing the working fluid temperature from 30 ᤪC to 70 ᤪC respectively. © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. Keywords: power generation; renewable energy; trilateral flash cycle; impulse turbine; Nozzle.
* Corresponding author. Tel. +613 9925 2000. E-mail address: [email protected]
1876-6102 © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 1st International Conference on Energy and Power. doi:10.1016/j.egypro.2017.03.152
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
1. Introduction As world population continue to rise, finding alternative energy sources to meet global energy demands will become necessary. Also the rapid developing economies accreted the global energy consumption to unprecedented levels. Although researchers continue to maximizing efficiency to improve existing sources of electricity generation but search for alternative energy is inevitable and to achieve stable development, renewable energy became a strategic world's option to attack environmental pollution, the energy crisis and fossil fuel consequences [1] [2]. Currently most of produced electricity power generation is from converting fossil fuels energy in thermal power stations[3]. Emission carbon dioxide from ignition of fossil fuels became a global concerns of climate change and long term global experience shows relation between energy use and carbon dioxide emissions[4]. That creates a question about the future consequences of fossil fuel consumption. At present there is a clear consensus on the impact that this overexploitation of resources is having on the fragile ecosystem of our planet, stretching to the limit the possibilities for sustainability the planet can offer. Therefore, this development, which has been and is clearly unsustainable, must become environmentally friendly, understanding as sustainable development that which is able to fulfil our needs without endangering those of future generations [5]. Renewable technologies are considered as clean sources of energy and optimal use of these resources minimize environmental impacts, produce minimum secondary wastes and are sustainable based on current and future economic and social societal needs. Renewable energy technologies provide an excellent opportunity for mitigation of greenhouse gas emission and reducing global warming through substituting conventional energy sources. Renewable energy sources (RES) supply 14% of the total world energy demand [5]. RES includes biomass, hydropower, low temperature solar, wind and marine energies. The renewable are the primary, domestic and clean or inexhaustible energy resources[6] ,[7]. Large-scale hydropower supplies 20 percent of global electricity. Wind power in coastal and other windy regions is promising source of energy [5], [8]. The share of RESs is expected to increase very significantly (30–80% in 2100)[9]. In the last decade it has been shown catastrophic effects of rapid climate change caused by global warming and a consequence increase in awareness about the importance of a sustainable environment[10]. Out of these renewable energy resources, the advantage of low temperature energy is that it can continuously supply energy and can serve as a base power[11]. This paper is motivated by the improvement necessity of current heat recovery technologies and progress to utilization of large amount of solar and geothermal and heat waste of low-grade heat sources. Temperature below 120 ºC is being targeted as low grade heat which is available from variety heat sources such as geothermal, industries waste heat and solar thermal, can be converted into electricity with applying a binary system. A binary system is a close loop cycle and exerts no gas to environment. Organic Rankine cycle (ORC) is one of the most common thermodynamic cycles[12] in low grade heat recovery field. In ORC working fluid gets vaporized in boiler before acting the expander but in trilateral cycle, working fluid spins the expander in form of two phase mixture of vapour and liquid [13]. As a summarised comparison of ORC and TFC cycles in ORC working fluid enters the heater as compressed liquid and exits as saturated or superheated vapour then amount of utilisable heat from source is limited to the vapour temperature. For example temperature different if in and out can be ∆T= 95 ̊C – 90 ̊C=5 C ̊ . but in TFC, working fluid enters the heater as compressed liquid and exits at higher temperature as compressed or saturated liquid. Then amount of utilisable heat from source is more compared to ORC. For example temperature different if in and out can be ∆T= 95̊c -35̊c=60̊c. Also TFC can be applicable for lower temperatures comparing ORC. Mechanical conversion efficiency can be improved with utilisation of impulse turbine binary TFC. Also simplicity of the mechanism leads to lower cost and has the ability to recovering more heat of low-grade resources can increase the power generation with utilisation of the current heat resources. Although there are many examples of operational Organic Cycle Heat Engines around the world and even a Screw Expander Turbine has been applied in Trilateral Flash Cycle to generate electricity [14] but there is a knowledge gap in converging-diverging stationary nozzle application in trilateral flash cycle with impulse turbine and single element working fluid. In this study we are going to focus on stationary nozzle in trilateral flash cycle and impulse turbine. The rotor of an impulse turbine rotates because of a force created by high velocity two phase liquid from a stationary nozzle after pressure drop. Windmills and waterwheels are simple impulse turbine examples[13].
353
354
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
However, there is a need to convert the large thermal heat from TFC by a proper expander. The expander in this research is a stationary two phase converging-diverging nozzle and an impulse turbine. The impulse turbine utilises the available kinetic energy in the working fluid after expansion in the stationary two phase converging-diverging nozzle and able convert it to mechanical power. The change of momentum of the fluid in the nozzle gives rise to force, which causes the rotor to rotate. The system is also applicable to any low-grade heat sources, such as waste heat recovery and solar thermal sources. It is the aim of this project to develop an economically-viable low temperature heat engine system for utilising low temperature hot water. Achievement of this aim would thus open up the exploitation of the low temperature resources that are not currently being utilised, and hence contribute to the national and international efforts to reduce greenhouse gas emissions. Nomenclature
mwater Water mass flow rate (kg/s) miso Isopentane mass flow rate (kg/s) Added heat Q
W h '3 h h fg X '3 x Vj
Vi Zi Zo U g
Added Work Actual enthalpy point 3 (J/kg) Specific enthalpy of working fluid (J/kg) Specific latent heat of evaporation or condensation of working fluid (J/kg) Quality of working liquid at nozzle exit Quality of liquid - vapour mixture Exit velocity Inlet velocity Height of inlet Height of outlet Density Acceleration of gravity
2. The concept of the system As shown in Fig.1. hot water which can be supplied from any low temperature heat resources, introduced through a heat exchanger and heat up the working fluid (Isopentane) comes out from other end of heat exchanger. Pressurised hot Isopentane goes through the nozzles installed in the turbine housing which has atmospheric pressure, and will spin the reaction turbine which is connected to a generator to produce electrical power. Then the working fluid which is cooled to saturated temperature will go into a tank. Vapour will be condensed in the condenser and re-joins liquid phase in tank to start a new cycle in a close loop.
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
Fig. 1. Schematic diagram of proposed TFC binary cycle 3. Methods 3.1. Experimental measurement of trust force of nozzle Based on explained concept of the system above, a test rig has been made in lab scale to measure the generated trust force of nozzle. To be able to measure the trust force, one turbine blade has been mounted on a load cell in front of two phase converging-diverging nozzle, in same position as the turbine. The test rig has been shown in Fig. 2.
Fig. 2. Test rig for trust force measurement
355
356
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
in this setup, expanded working fluid, exits the nuzzle and impinges the turbine blade. Generated force out of this impact, is being measured by the load cell behind the turbine blade. Input hot water temperature to the system to heat up the working fluid, has been changed in 4 different temperature as 40, 50, 60 and 70 centigrade and force has been measured, rest of the variable not changed. Fig. 3 is a schematic view of the nozzle and Pelton turbine blade setup.
Fig. 3. Schematic view of the nozzle and Pelton bucket setup
4. Results and discussion
Below graph is showing the trend of force increase with increase in hot water input temperature to heat up the working fluid.
Fig. 4. Measured force in different hot water input temperature
Designing of this system is based on trilateral flash cycle (TFC) thermodynamics which is explained in introduction section.The working liquid (Isopentane) is getting compressed in a pump and heats up to saturated liquid in heat exchanger. The working fluid will be pressured and heated close to saturation temperature at point2 in Fig.1 before entering the nozzle throat. The working fluid enters the nozzle throat as saturated liquid at high temperature and expands in an isentropic expansion to exit the nozzle, point 3 in Fig.1. On this point, there is a temperature and pressure drop of liquid from high temperature, high pressure to low temperature, low pressure two phase mixture. Ideally, Temperature at point 3 should be same as point 1. Then the working fluid in the condenser undergoes at constant pressure cooling before moving back to point 1. The red point in fig.4 has been taken as sample data, isentropic efficiency of the nozzle can be calculated as below. Table 1 shows the measured values of the test rig in subjective point of the above graph.
357
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358 Table 1. Measured values of the test rig in subjective point of the above graph. measured value
Value
Temperature of Isopentane before nozzle (point 2) ᤪC
64.6ᤪC
Temperature of Isopentane after nozzle (point 3) ᤪC
24.8
Measured Force(N)
3.6
Isopentane flow (lit/min)
3.85
Table 1 shows the measured force at temperature 64.6 ᤪC which is around 3.6N. Sara Vahaji (2014) used the similar set up and achieved the trust force around 2.8 N [15]. In their work they used water as working fluid in vacuum chamber while in the present work Isopentane at atmospheric pressure has been employed. Another significant difference between their set up and ours is the target geometry. As can be seen in Fig. 3 we used a Pelton geometry which reverse the flow by 165 and increases the objective force [16]. Based on values above, exit velocity of the nozzle can be calculated as:
Vj
miso F
97.1m / s
(1)
In order to calculate the actual entropy at nozzle exit, based on the energy balance equation between the inlet nozzle and the outlet nozzle has been used.
Ein
Eout
(2)
§ · § · V2 V2 miso ¨ h2 i U gZi ¸ miso ¨ h '3 J U gZ o ¸ Q W 2 2 © ¹ © ¹
(3)
By assuming that the nozzle is horizontal, negligible inlet velocity, and no work and heat added to nozzle, above equation will be simplified as below:
h '3
h2
VJ 2 2
224.77kj / kg
(4)
Then isentropic efficiency van be obtained as below:
Kisentropic
h2 h3' h2 h3
0.38
(5)
From above measured force inputs, isentropic efficiency of the nozzle can be shown as below graph.
Fig. 5. Calculated isentropic efficiency based on measured force
358
Mahdi Ahmadi et al. / Energy Procedia 110 (2017) 352 – 358
5. Conclusion and suggestions for future studies This study has briefly discussed a binary cycle to utilize the application of a stationary converging-diverging nozzle and an impulse turbine. Also shows an experiment of measuring trust force of a stationary converging diverging two phase nozzle. The results has been used to show isentropic efficiency on the nozzle and can be used for further study on mechanical and electricity power generation in a single element working fluid binary system. The study was about the available low temperature geothermal resources but can be applied at any other low grade heat resource. Initial results showed the exit force of the nozzle applied on the Pelton blade geometry increases to 5 N by rising the temperature to 70 ᤪC. An Isentropic efficiency around 45% was obtained for variety of temperature between 30 ᤪC to 70 ᤪC. In this paper feasibility of the concept of use of stationary converging-diverging nozzle in Trilateral Flash Cycle with low temperature heat resource (lower than 70 ᤪC) was proven. As some suggestions for future work we can: x Run experimental investigation with placing impulse turbine in TFC cycle in order to power generation. x Work on nozzle geometry design, aiming to improve efficiency of the system. References [1] He Y, Xu Y, Pang Y, Tian H, Wu R. A regulatory policy to promote renewable energy consumption in China: Review and future evolutionary path. Renewable Energy 2016;89:695-705. [2] Barbier E. Geothermal energy technology and current status: an overview. Renewable Sustainable Energy Rev. 2002;6:3-65. [3] Date A, Alam F, Khaghani A, Akbarzadeh A. Investigate the potential of using trilateral flash cycle for combined desalination and power generation integrated with salinity gradient solar ponds. Procedia Eng. 2012;49:42-49. [4] U.S. EIA. Annual energy outlook 2013. Washington, DC: U.S. Department of Energy; 2013. [5] Schmalensee R, Stoker TM, Judson RA. World carbon dioxide emissions: 1950–2050. Rev. Econ. Stat. 1998;80:15-27. [6] Goldemberg J. World Energy Assessment; Energy and the challenge of sustainability. United Nations Pubns; 2000. [7] Dincer I. Environmental issues: Ii-potential solutions. Energy sources 2001;23:83-92. [8] Yuksel I, Kaygusuz K. Renewable energy sources for clean and sustainable energy policies in Turkey. Renewable Sustainable Energy Rev. 2011;15:4132-4144. [9] Fridleifsson IB. Geothermal energy for the benefit of the people. Renewable Sustainable Energy Rev. 2001;5:299-312. [10] Kralova I, Sjöblom J. Biofuels–renewable energy sources: a review. J. Dispersion Sci. Technol. 2010;31:409-425. [11] Khan M, Iqbal M, Quaicoe J. River current energy conversion systems: Progress, prospects and challenges. Renewable Sustainable Energy Rev. 2008;12:2177-2193. [12] Dai Y, Wang J, Gao L. Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery. Energy Convers. Manage. 2009;50:576-582. [13] Welch P, Boyle P. New turbines to enable efficient geothermal power plants. GRC Trans. 2009;33:765-772. [14] Smith I, Stosic N, Aldis C. Trilateral flash cycle system a high efficiency power plant for liquid resources. In: Proc World Geotherm Congr; 1995. p. 18-31. [15] Vahaji S, Akbarzadeh A, Date A, Cheung S, Tu J. Efficiency of a two-phase nozzle for geothermal power generation. Appl. Therm. Eng. 2014;73:229-237. [16] Dixon SL, Hall C. Fluid mechanics and thermodynamics of turbomachinery. 6th ed. USA: Butterworth-Heinemann, Elsevier Science Boston; 2010.