Experimental investigation of a Cast-Steel based Thermal Energy Storage System

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10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China

Experimental investigation of a Cast-Steel based Thermal Energy The 15th International Symposium on District based Heating and Cooling Energy Experimental investigation of a Cast-Steel Thermal Storage System Storage System Assessing the the heat demand-outdoor a feasibility of using K. Vigneshwarana, Gurpreet Singh Sodhibb, P. Muthukumarb,b,*, V. K. Arvinddd, cV. K. Arvind K. Vigneshwaran , Gurpreet Sodhi d, ,P. Muthukumar , temperature function for Singh add,long-term heat*,demand forecast G. Balamurugan S. Sriram S.district Senthilmurugan d c I. Andrić

a of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, India-781039. Department Centre for Energy, Indian Institute of Technology Guwahati, Guwahati, India -781039. Chemical Engineering, Indian ofofSuperior Technology Guwahati, Guwahati, Department Mechanical Engineering, IndianInstitute Technology Guwahati, Guwahati, India-781039. IN+ Center for Innovation,ofofTechnology and Policy Research -Institute Instituto Técnico, Av. Rovisco PaisIndia-781039. 1, 1049-001 Lisbon, Portugal d b c Mechanical Engineering, Amrita Vidyapeetham, Coimbatore, India-641112. Department of Chemical Engineering, IndianVishwa Institute of Dreyfous Technology Guwahati, India-781039. Veolia Recherche & Innovation, 291 Avenue Daniel, 78520Guwahati, Limay, France d c Mechanical Engineering, Amrita Vishwa-Vidyapeetham, Département Systèmes Énergétiques et Environnement IMT Atlantique,Coimbatore, 4 rue AlfredIndia-641112. Kastler, 44300 Nantes, France b

a

G. Balamurugan , S. Sriram , S. Senthilmurugan *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc

a,b,c b Guwahati, India -781039. c a Centre for Energy,aIndian Institute ofa Technology Guwahati,

b cDepartment

Abstract Abstract Abstract In the present work, the performance of a thermal energy storage module made of cast steel is evaluated using air as the heat In the present work, the performance of aofthermal module made ofiscast steel is with evaluated using as the heat transfer fluid (HTF). A cast steelcommonly module length energy 740 and diameter 267 mm fabricated 19 cylindrical channels of District heating networks are addressed in mm thestorage literature as one of the most effective solutions forair decreasing the transfer fluid (HTF). A cast steel module length 740 mmsystems and diameter mm is fabricated with 19returned cylindrical of diameter 12.7gas mm for HTF flow. The of module charging and discharging performance data areare reported forthrough anchannels operating greenhouse emissions from the building sector. These require267 high investments which the heat The module charging discharging performance data are for an operating diameter 12.7 for393.15 HTF climate flow. temperature range K to 473.15 K andand the building effect and of renovation HTF flow policies, velocities on module performance is could analysed. The sales. Due to mm theofchanged conditions heat demand in reported the future decrease, temperature range ofstorage 393.15 K toperiod. 473.15 and steel the effect of isHTF flow on module performance is analysed. The estimated maximum capacity of theKcast module 13.76 MJ.velocities The charging and discharging temperature profile prolonging the investment return estimated storage of the module isthe 13.76 MJ. and discharging temperature across the maximum module measured heatsteel transfer phenomenon itThe is observed conduction varies predominantly The main scope ofisthis papercapacity istotoanalyse assess the cast feasibility of using heatand demand –charging outdoorthat temperature function for heat profile demand across module is measured to analyse heat transfer phenomenon and is observed that conduction varies predominantly in the the axial there istheminimal variation in the From the results, ofit 665 is forecast. Thedirection, district ofwhereas, Alvalade, located in Lisbon (Portugal), wasradial usedit direction. as a case study. The experimental district is consisted inbuildings the axialthatdirection, whereas, there isperiod minimal in the radial direction. the from experimental itFor is comprehended that charging and discharging ratesvariation are enhanced by weather increasing the HTFFrom velocity 2.5 m/sand toresults, 4.5 m/s. varyboth in both construction and typology. Three scenarios (low, medium, high) three district both charging and discharging rates achieved are enhanced byTo increasing the from 2.5 m/s to 4.5 m/s. For acomprehended velocity of scenarios 4.5that m/s, the average module temperatures at steady state condition forvelocity charging and discharging are 468were K renovation were developed (shallow, intermediate, deep). estimate theHTF error, obtained heat demand values a compared velocity 4.5 results m/s, thefrom average module temperatures achieved at steady state condition for charging discharging are 468 K and 398 Kof respectively. with a dynamic heat demand model, previously developed and validated by theand authors. and 398 K respectively. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications Copyright Elsevier Ltd.was Alllower rights than reserved. (the error©in2018 annual demand 20% for all weather scenarios considered). However, after introducing renovation © 2019 The Authors. Published by Elsevier Ltd. Copyright ©the 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of(depending the scientific committee 10th International Conference on Applied scenarios, error value increased up to 59.5% the weather of andthe renovation scenarios combination considered). This is an open access article under the CC BY-NC-ND license on (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 Energy (ICAE2018). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. Energy (ICAE2018). decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and Keywords: Cast Steel Module, High Temperature, Parametric Sensible Heat Storage (SHS). renovation scenarios considered). On the other hand,Study, function intercept increased for 7.8-12.7% per decade (depending on the Keywords: Cast Steel Module, High Temperature, Parametric Study,toSensible (SHS). coupled scenarios). The values suggested could be used modifyHeat theStorage function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +91 361 2582673; fax: +91-361-2690762.

addresses: [email protected], [email protected] * E-mail Corresponding author. Tel.: +91 361 2582673; fax: +91-361-2690762.(P. Muthukumar) Keywords: Heat demand; Forecast; Climate change E-mail addresses: [email protected], [email protected] (P. Muthukumar) 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility the scientific 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. 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 scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.739

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1. Introduction The energy storage is becoming an important component to provide uninterrupted energy supply from renewable energy sources. In the energy sector, the concept of standalone renewable energy system for larger application is not able to progress much due to high cost. Therefore, many researchers are focused to study and develop the economically viable energy storage solution for different applications [1]. Specifically, further advancements in the installation of large capacity concentrated solar power (CSP) technology is not evolved as predicted and it requires cost-effective energy storage solution. Thermal Energy Storage (TES) systems are being looked upon as a good alternative for meeting the energy expectations from CSP technology [2]. Nomenclature L D ks N Cps ρs NP Dpi Dpos T_avg

length of the storage prototype (m) diameter of the storage prototype (m) thermal conductivity of the storage material (W/mK) number of HTF tubes specific heat of the storage material (J/kgK) density of the storage material (kg/m3) number of tubes in different Pitch Circle Diameters inner Pitch Circle Diameter outer Pitch Circle Diameter Volumetric average temperature (K)

Abbreviation CSP PCM SHS TES

Concentrated Solar Power Phase Change Material Sensible Heat Storage Thermal Energy Storage

Thermal energy storage is possible with help of materials like rocks and oils, phase change materials and through reversible chemical reactions. Sensible heating turns out to be advantageous in terms of low cost, easy availability and reduced thermal stress. Sensible heat transfer takes place by virtue of temperature difference between the storage material and the working fluid. Sensible heat storage (SHS) is proven to work with CSP for many applications [3]. In literature, the following research components are studied in detail to develop the cost-effective TES modules involving the solid mediums and packed beds: the development of mathematical models for SHS systems and its performance analysis for different thermal applications, testing of thermal performance of a hybrid sensible - latent heat storage model using phase change materials (PCM) [4]. It has been observed that the maximum temperature difference in the PCM model is greatly decreased and a uniform distribution of temperature is obtained by the introduction of annular fins. Eslami and Bahrami [5] studied the transient behavior of a rectangular thermal energy storage system with complex fin configuration using a numerical SHS module. The numerical results are found to be in close proximity with analytical theory. Amrouche et al. [6] carried out a critical review on energy storage systems and discussed their relative merits. The systems operational flexibility, ability to mitigate power fluctuations and high storing-dispatching capability are all studied using a basic mat-lab prototype in their work. Some works are done in sensible TES models focused on finding the effect of using nano-fluids on thermal behavior of SHS materials. The effect of sensible heat flux and mass flow rate of the HTF on the overall storage capacity of the system are discussed [7]. Sragovich [8] studied the operational behavior of a tubular type SHS system using a transient numerical model. A huge temperature drop at the model outlet is observed due to shift from laminar to transitional flow and the methodology is further used to design a storage system at operating temperature of 1273 K. An experimental investigation is made on a compact SHS system, wherein, different shapes of concrete material in a packed bed arrangement are analyzed. The performance parameters including flow rate are varied and it is found that the shape and void fraction of material played a significant role in the process of charging/discharging [9]. Dincer et al. [10] reviewed the different parameters affecting the performance of SHS systems. The environmental impacts, criteria for SHS feasibility, energy and exergy analysis are also discussed in detail. Laing et al. [11] conducted a study to integrate cost-effective concrete based heat exchange designs and their application in the medium and hightemperature range up to a maximum temperature of 673 K. A numerical analysis was conducted to study the thermal behavior for different SHS materials. Based on the charging time as an objective function, an optimum number of tubes was selected and it was observed that with an increase in the HTF velocity there was a decrease in the charging

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time [12]. Laing et. al [3] developed a three-part storage system with two sensible storage modules and one PCM module. The sensible models were used for storage up to 1 MWh and for generating superheated steam, whereas PCM module was used for water evaporation. The study concluded that concrete based SHS systems were compatible with very high-temperature applications up to temperature range of 773 K. Selvam and Castro [13] had developed a cylindrical concrete storage system using different fin shapes like rods, plates and discs. Remarkable improvements in heat transfer were reported, where the charging time was reduced to a maximum of 58.6 %. A detailed cost analysis was presented for different combinations of fins. Rao et. al. [14] conducted an experimental study on a sensible TES system with different combinations of storage and HTF tube materials using Hi-tech Therm 60 as the heat transfer fluid. Concrete and cast steel were used as the storage medium. The storage performance was enhanced substantially for materials with a high value of thermal conductivity. Research works carried out till date, discussed the feasibility of various SHS systems and lab-scale prototype developments of sensible heat storage system, whereas minimum work is reported on the parametric studies on cast steel based sensible heat storage system. In the current study, a detailed experimental investigation is done to study the influence of heat transfer fluid velocity on the thermal performance of the cast steel based SHS system. An experimental setup is fabricated and the key performance indicators of a storage system including charging/discharging characteristics, the effect of HTF velocity on the storage characteristics and the axial temperature variation of the storage module along the length are analyzed. The total energy charged and discharged for all HTF flow velocities are discussed in detail. 2. Experimental procedure A cast steel heat exchanger with 19 embedded tubular sections of equal diameter is fabricated and attached to a system. The basic layout is depicted in Fig. 1. The hot air is circulated into the system with the help of a centrifugal blower having a capacity of 120 m3/h through an electrical heating chamber made of nichrome element heaters with a maximum input power of 48 kW. The arrangement of tubes inside the module section is shown in Fig. 2.

Fig. 1. Layout of the cast steel sensible heat storage experimental setup. Table 1. Configuration of cast steel module. SHS Module

L (mm)

D (mm)

N

NP

Dpi (mm)

Dpos (mm)

Cast-Steel

740

267

19

1,6,12

110

220

Due to the higher thermal conductivity and higher specific heat capacity, cast steel is preferred as the SHS material. The module is completely insulated with a 101 mm layer of ceramic wool in order to prevent heat loss to the surroundings. The flow rate of the air is controlled by varying the blower speed with the help of a variable frequency drive. The temperature of the SHS module is measured with the aid of nine K-Type thermocouples. Three thermocouples at different radial depths are placed at each of the axial locations at 22/370/718 mm. The inlet and

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outlet temperature of HTF is also recorded using a data acquisition system. The SHS module is tested for the charging and discharging processes within a temperature range of 393 K - 473 K at different flow velocities. The geometrical details of the cast-steel module are shown in Table 1. The HTF velocity is measured with help of a pitot tube based velocity meter. The properties of the storage medium are described in Table 2. During the charging process, the model is maintained at a temperature of 393 K and air is supplied to the SHS module at a temperature of 473 K and once the module is charged up to a steady state temperature, the conditions are reversed, such that model is maintained at 473 K and it discharges the energy to air which enters the SHS system at 393 K. The experiments are performed at HTF flow rates corresponding to velocities; 2.5 m/s, 3.5 m/s and 4.5 m/s and the corresponding maximum uncertainty in the measurement of flow rate is ± 2%. The HTF flow is assumed to be in the laminar region.

Table 2. Cast steel Properties [15] Material

Ks W/mK)

Cps (J/kgK)

ρs(kg/m3)

Cast steel

40

600

7800

Fig. 2. Tubular Arrangement of cast steel module

3. Results and discussion 3.1. Charging and discharging of the storage module

Fig. 3. Charging time for different HTF velocity

Fig. 4. Discharging time for different HTF velocity

The time taken by the volumetric average temperature of the TES module to reach steady state is said to be the charging time. Figs. 3 and 4 illustrate the charging and discharging behaviors of the heat storage module. The evolution of the HTF inlet/outlet temperatures and the volumetric module average temperature at different velocities are described. The HTF inlet temperature fluctuates within a small range and it is practically not viable to maintain a constant air temperature for a bulk fluid. During charging, the average temperature attained by the storage module after 370 min at HTF velocity of 4.5 m/s is 468 K, whereas, at 2.5 m/s this temperature is 456 K. While discharging, the temperature of storage module after 250 min at the HTF velocity of 4.5 m/s is 398 K, whereas, at the HTF velocity of 2.5 m/s the temperature is 408.5 K. It is observed from the plots that, the time taken for the charging and discharging processes are proportional to the inlet velocity of the air, the increase in which leads to enhancement in the heat transfer rate. For

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the given temperature range, the density of air at discharging temperature is higher than that of charging temperature, due to which the air flow rate during discharging is marginally higher than that during charging. Hence the discharging process is observed to be faster than charging. Once steady state is reached in both charging and discharging, the gap between the HTF inlet and the HTF outlet temperatures reaches to a minimum value owing to lesser heat transfer to the module. This happens because of drop-in heat transfer potential between the module and the air. The rate of heat transfer in the module at HTF velocity of 4.5 m/s is much higher as compared to other velocities. Also, the energy storage rate is dependent upon the HTF velocity, such that there is better heat transfer rate at higher velocity of the HTF. 3.2. Energy storage/discharge rate The total amount of energy stored and discharged from the storage module is proportional to the volumetric average temperature and thermal properties of the module. Figs. 5 and 6 show the energy storage rate and discharge rates from the storage module. The uncertainty analysis is carried out based on the method proposed by Mc Clintock [16] and the maximum uncertainty found out in the estimation of energy storage/discharge is ± 0.33% (estimated based on the mass of the SHS).

Fig. 5. Energy storage rate at different HTF velocity

Fig. 6. Energy discharge rate at different HTF velocity

3.3. Axial variation of temperature

Fig. 7. Axial variation of temperature during charging

Fig. 8. Axial variation of temperature during discharging

The heat transfer rate in the cast steel module varies significantly along the length. The axial length variation during charging and discharging processes are plotted in Figs. 7 and 8. It is observed from both charging and

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discharging processes that, initially, the variation is huge due to the greater temperature difference between HTF and the module, but this variation diminishes as the time progresses. 3.4. Effect of HTF velocity The rate of heat transfer in the module at HTF velocity of 4.5 m/s is higher than that at other velocities. With increase in HTF velocity from 2.5 m/s to 3.5 m/s, the total energy stored has increased by 13 %. But there is no significant improvement (i.e. about 5%) noted when the air flow rate is increased from 3.5 m/s to 4.5 m/s. The similar trend is observed during the energy discharging process. 4. Conclusions In this paper, an experimental investigation of a cast steel based sensible heat storage system performed at different operating conditions using air as a HTF is presented. For different air velocities (2.5 m/s, 3.5 m/s, 4.5 m/s), charging time, discharging time, energy storage rate and discharging rate are found out / estimated. The effect of inlet HTF velocity on the heat transfer rate is discussed in detail. The percentage of reduction in charging time is significant when the velocity is increased from 2.5 m/s to 3.5 m/s, but there is no admirable reduction thereafter. The thermo-physical properties of HTF and SHS materials are a function of the operating temperature range, thus the HTF velocity and the operating temperature are the defining factors for better performance of the sensible heat storage system. This study may be helpful for building an efficient real-time sensible heat storage system for solar power plants, domestic hot water supply, solar drying, etc. Acknowledgements The authors are very much thankful to the Department of Science and Technology (DST), Government of India, for their financial support (Project No: DST/TMD/SERUD12(C)). References [1] Medrano M, Gil A, Martorell I, Potau X, Cabeza LF. State of the art on high-temperature thermal energy storage for power generation. Part 2—Case studies. Renewable and Sustainable Energy Reviews. 2010 Jan 1;14(1):56-72. [2] Gil A, Medrano M, Martorell I, Lázaro A, Dolado P, Zalba B, Cabeza LF. State of the art on high temperature thermal energy storage for power generation. Part 1—Concepts, materials and modellization. Renewable and Sustainable Energy Reviews. 2010 Jan 1;14(1):31-55. [3] Laing D, Bahl C, Bauer T, Lehmann D, Steinmann WD. Thermal energy storage for direct steam generation. Solar Energy. 2011 Apr 1;85(4):627-33. [4] Zauner C, Hengstberger F, Mörzinger B, Hofmann R, Walter H. Experimental characterization and simulation of a hybrid sensible-latent heat storage. Applied energy. 2017 Mar 1; 189:506-19. [5] Eslami M, Bahrami MA. Sensible and latent thermal energy storage with constructal fins. International Journal of Hydrogen Energy. 2017 Jul 13;42(28):17681-91. [6] Amrouche SO, Rekioua D, Rekioua T, Bacha S. Overview of energy storage in renewable energy systems. International Journal of Hydrogen Energy. 2016 Dec 7;41(45):20914-27. [7] El-Kaddadi L, Asbik M, Zegaoui O, Zari N, Bah A. Experimental study of sensible heat storage/retrieval in/from a nanofluid enclosed between concentric annular tubes. Energy Procedia. 2017 Dec 31; 139:73-8. [8] Sragovich D. Transient analysis for designing and predicting operational performance of a high temperature sensible thermal energy storage system. Solar energy. 1989 Jan 1;43(1):7-16. [9] Warkhade GS, Babu AV, Mane S, Ganesh Babu K. Experimental investigation of sensible thermal energy storage in small sized, different shaped concrete material packed bed. World Journal of Engineering. 2016 Oct 3;13(5):386-93. [10] Dincer I, Dost S, Li X. Performance analyses of sensible heat storage systems for thermal applications. International Journal of Energy Research. 1997 Oct 10;21(12):1157-71. [11] Laing D, Steinmann WD, Tamme R. Sensible heat storage for medium and high temperatures. In Proceedings of ISES World Congress 2007 (Vol. I–Vol. V) 2008 (pp. 2731-2735). Springer, Berlin, Heidelberg. [12] Prasad L, Muthukumar P. Design and optimization of lab-scale sensible heat storage prototype for solar thermal power plant application. Solar Energy. 2013 Nov 1; 97:217-29. [13] Selvam RP, Castro M. 3D FEM model to improve the heat transfer in concrete for thermal energy storage in solar power generation. In ASME 2010 4th International Conference on Energy Sustainability 2010 Jan 1 (pp. 699-707). American Society of Mechanical Engineers.

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[14] Rao CR, Niyas H, Muthukumar P. Performance tests on lab–scale sensible heat storage prototypes. Applied Thermal Engineering. 2018 Jan 25; 129:953-67. [15] Pilkington Solar International, GmbH. Survey of thermal storage for parabolic trough power plants. National Renewable Energy Laboratory; 2000 [SR-550-27925]. [16] Holman JP, Gajda WJ. Experimental methods for engineers. New York: McGraw-Hill; 2001.