Vol. 1 No. 1 2015

Chandigarh University Journal of Undergraduate Research and Innovation

A REVIEW ON PACKED BED SOLAR ENERGY STORAGE SYSTEM Pardeep Singh B Tech Student, Department of Mechanical Engineering, Chandigarh University, Gharuan, Punjab Abstract- Now a day‟s thermal energy storage become most popular ways to store solar energy due to it periodical nature. Packed bed storage system is generally recommended for thermal energy storage in solar air heaters. The porous media come out by packing of materials in vessels help in achieving packing bed. There have been various studies on packed beds for their performance analysis and investigation. These studies also include the design of packed beds, materials used for storage, enhancement of the heat transfer and pressure drop in packed beds. The objective of this paper is to review the research work done so far on packed beds systems. It is concluded that materials other than rocks, pebbles and glass have been studied in a few studies. The physical properties, size and shape of the materials are factors that influence the performance of the storage system so they have to be taken into account for any performance study and evaluation.

energy resource. The energy from sun has intermittent nature this makes the energy storage critically important. The continuous usage of solar energy can be done by storage of energy during availability of solar energy. The aim of the present paper is to review the research work done so far on packed beds storage system. Packed beds are most efficient for storing of air based solar energy system as shown in fig 1. The loosely packed material used to circulate the heat transportation in packed bed. The fluid after heating passes through solar collectors into a bed to transfer thermal energy is during the passage of phase change. Thermal energy stored in bed is recovered by circulating air from bottom to top. The heat can be transfer quickly form air to solid by using the high heat transfer coefficient. During initial heating affect is significant only entry but rest of portion does not under go any further change. With the passage of time heating zone also rise near the exit also. After fully charging temperature is uniformly distributed throughout. But in actual practice packed bed does not work on constant temperature. The environment condition such as day, night, rainy seasoned also affect the performance of packed bed in solar system.

Keywords: Packed bed, Renewable energy source. Introduction Solar energy is thermal energy receive from the sun and can be properly utilize by using solar technologies such as solar photovoltaic cell, solar architecture etc. Solar energy is a time dependent

The optimum size of the packed bed for storage system depends on the particular application concerned and numerous process parameters such

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Vol. 1 No. 1 2015

Chandigarh University Journal of Undergraduate Research and Innovation as temperature reading, material, losses of heat, heat rate storage heat losses, sky conditions etc. collector area, efficiency, solar fraction of the total heat load etc.

precisely required. Solid as well as molten industrial wastes like copper slag, iron slag; aluminum slag etc. could be used as storage materials for thermal energy storage. Riaz (1978) analyzed a frame model for various fluid convective motion, the air-rock heat interaction, axial as well as linear bed conduction and internal as well as external particle conduction. The analytical solutions have been carried out for different temperatures at inlet of storage bed for single-phase conductivity model of packed bed material. Maaliiou& McCoy (1985) have represented upgraded model of various design parameters for different packed bed storage systems. It has been concluded from the above study that the difference between the economic value of stored heat energy and also by adding two cost factors such as capital cost and the operating costs to the above value is equal to the net income. The pressure drop in the bed material also affects the operation cost of pump which is used in the setup. Aly and El-Sharkawy (1990) analyzed that the physical as well as chemical properties of solid phase can be used as storage material for energy which affects the design of solid packed bed system. The steel packed beds have shown high storage rate and also higher thermal capacity than the particular rock bed storage system. It was also analyzed experimentally that during the first 6 hours of charging of the aluminum bed, shows a superior storage capacity as compared with that of rock and other materials. Stuginsky& Ismail(1999) reported that rising of particle diameter of rocks decreases pressure drop throughout the bed. It was concluded that the fluids with higher thermal capacities are very much able of exchanging and delivers large amounts of stored energy. Also with the reduction in the void fraction in the microstructure leads to significant increase in the mass of particle size present in the bed which results to increase in thermal storage capacity of the bed. Thacher and Crandall (2004) reported during the experimental investigation that the packed beds have higher degree of stratification. Stratification in a rock bed decreases considerably during the later part of the day, with a small decrease in solar insulation and also there is a significant decrease in the collector outlet temperature. They also concluded that segmentation of the bed can improve the stratification.

Fig 1: Schematic of a packed bed energy storage system ANALYTICAL STUDIES The transfer of heat either from a flowing fluid to a packed bed or from packed bed to flowing fluid has been studied in many theoretical and practical investigation since Schumann‟s original work. Schumann (1929) studied two phase model for packed bed storage system in one dimension by avoiding the axial conduction in the fluid, heat capacity of the fluid and bed material. Fath (1998), Hasnain (1998) and Atear (2006) conducted various studies used in sensible heat storage systems on various solar energy storage techniques and materials applications. They concluded that the material selection depends upon the temperature level of application. They also analyzed that water was the best sensible heat storage liquid because of its abundance, and has a very high specific heat value as compared to other fluids. But above 100 degree centigrade, the storage tank must be able to contain water in liquid form at its vapor pressure. By reserving thermal energy as sensible heat in solids, it is possible that the scarcity of vapor pressure of water and the limitations of other liquids can be excluded by this method. Keeping thermal energy in rock bed material is very common these days because of its cheapness and easy availability. The small cylindrical shape can be used for storage of thermal energy by using another solid material. The storage of sensible heat can be efficient done by using water at high pressure and liquid metals at medium and high temperatures. The metal media is also an alternative where high thermal conductivity is

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Chandigarh University Journal of Undergraduate Research and Innovation The application of rock as a storage material was narrated. The maximum temperature gained during process helps in recovering the energy stored. Ammar and Ghoneim (1991) reported by conducting experimental investigation that the rock beds have slightly more heat storage than in Tafla. It was also analyzed that there is a large degree of stratification in bed part and noticed precisely which are caused by the particles with higher and intermitted values of inter phase surface area per unit volume.

EXPERIMENTAL WORK The Furnas (1930) made an attempt to find relationship between heat transfer coefficient and gas velocity. The experiment result showed a straight line relationship between above said two parameters. The result showed that resistance of fluid flow significant affected by degree of packing in packed bed. The heat transfer coefficient is inversely related with particle diameter. Colburn (1931) conducted an experimental study on heat transfer rate between air flowing through a filled tube with different granular materials and concluded that the heat transfer coefficient is purely dependent on the mass flow rate of air and their respective particles to the tube diameter ratio. Standish and Drinkwater (1970) analyzed that the shape of packing is a important factor in flooding. It was also concluded that besides the size distribution, the particle shape of respective materials which are used is most common factor to affect the different type packing structure and their respective properties.

Audi (1992) tested experimentally the stability analysis of small sized rocks as compared to large sized and their possible use as different energy storage materials. Jordian Basalt and Limestone demonstrated excellent the stability of rocks during the various tests and their storage capacities were widely acceptable.

Sagara and Nakahara (1991) analyzed that the temperature gradient inside the solid cannot be ignored especially in case of large sized materials. It was concluded that the larger sized materials like bricks & concrete blocks have very poor thermal performance but certainly less power supply is required to run the fans. In a solar heating system with a heat pump the small as well as the large size materials have almost the same thermal performance. Large size packed materials may be more favorable as storage materials than the small sized because of the greater fan energy of large bed size as compared to small ones.

Chandra and Willits (1981) did experimental studies and found that the pressure drop through packed bed depend upon not only on rock size but also depends on bed porosity of the material and the airflow rate through them. Also the Coefficient of heat transfer was found to be depended on rock size material and the flow rate of heat. They have also concluded that the air inlet temperature or the initial rock bed temperature has very negligible influence on heat transfer rate. Arber and Courtier (1982) concluded that the rock beds are the most suitable storage units for air-based solar system. Clark and Beasley (1984) concluded that there is significant influence on the dynamic response of both fluid and solid temperature space related variations in the void fraction mainly. Hollands and Sullivan (1984) carried out study on unwashed rocks and concluded that the unwashed rocks so called the fines i.e. very small particles including dust on them consistently increase the pressure drop across the particulate bed material. The density of the unwashed rocks becomes lower than the rocks which have high value of density as compared and the result is that the dust increases the pressure drop. Waked (1986) made an effort for evaluation of the storage material. It was recommended that selection of storage material depends upon many factors such as application, material characteristics and space area and capital.

Ghoneim&Kassaby (1993) analyzed and concluded that the natural soil available in Jordan for air and water based system in their respective forms can be used in the sensible heat storage system. They have studied that an additional area must be provided to them if soil as storage material is used instead of water. The are some problems occurred if water system is used as heat capacity medium but on the other hand the heat capacity of these systems gives better results if we can use them. Nimr et.al. (1996) mentioned in the study that the inlet fluid temperature was not varied with respect to time in the earlier models of packed beds which were used during the experiments. And also they are based on number of assumptions. With the variable range of inlet fluid temperature the packed bed system receives the energy from a heat source

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Chandigarh University Journal of Undergraduate Research and Innovation during charging. So finally in their experimental works to store sensible heat with water as heat transfer fluid they used different rocks as storage material.

the height of the tank, the charging energy efficiency, the stratification number, Reynolds number and Richardson number that signifies heat stratification in a pebble-bed storage system of thermal energy. These all above parameters are investigated experimentally and very precisely under six analogous charging conditions. They concluded that the charging energy efficiency and

Jalalzadeh et.al. (1997) studied heat capacity performance of the different storage materials. On the same time they ignored some parameters like stability aspects which are also very important especially for high temperature applications and also previously they should not be taken into consideration. The performance of zirconium material was much satisfactory as compared to salt/ceramic composite which shows poor physical stability. It was also noticed that on an equal volume basis zirconium medium gives better performance over the other composite materials.

The relation between thermal stratification qualitatively and reynolds was found. The result shown that Richardson number does not affect the thermal stratification SalwaBouadila, SafaSkouri, Sami Kooli, MeriemLazaar, AbdelhamidFarhat (2013) performed an experimental on solar air heater cum packed bed byusing PCM spherical capsules. The result showed that during discharging phase the useful heat remain uniform in solar air heater. The environment conditions such as flucutuation in sun ray does not affect the useful heat. The net effcincy of daily energy of SolarAir Heater with Latent Storage Collector (SAHLSC) varies from 32% to 45 % in closed and open mode respectively.

Nsofor et.al. (2001) done an experimental study and gives the correlations for Nusselt number and also the heat transfer coefficient for forced convection gas. Ozturk and Bascetincelik (2003) investigated experimentally the solar energy storage in a green house. They also concluded that fluids are not widely accepted and used for high temperature heat storage as compared to the solid materials which are economically sound also. Singh et al., (2006) reported while developing the correlations the effects of bed porosity and particle shape should also be taken into consideration. The correlations have been proposed for Nusselt number and friction factor as functions of Reynolds number and Void fraction. They have used these correlations to obtained the results with earlier studies satisfactory and reported the validity of these correlations precisely.

Maithani et al., (2013) analyzed the solar energy storage system using large size bed element and it has been found that the effective efficiency was a strong function of geometrical parameters of the storage bed. Optimum set of these parameters was a function of operating conditions. The optimum sets have been determined for different values of design condition, which can be used by the designer to obtain minimum possible friction losses in the storage system. CONCLUSION

Nallusamy et al., (2007) analyzed the latent and sensible heat storage systems with water as a medium of heat transferring fluid. During the heat transfer, the mass flow rate has very little effect on charging rate and heat transfer rate was directly proportional to inlet temperature of fluid. The heat and mass flow rate was also examined and concluded its important effect on the heat extraction and transfer rate. It was recommended to use dual storage system instead of conventional sensible heat storage system to achieve better performance

The extensive literature survey of packed bed heat storage system is conducted under present paper and it is concluded that the packed beds have been widely used for thermal storage system after investigating the system both analytically and experimentally. There have been various analytical studies done on the different effects of different parameters on the performance of packed bed system. On the basis of the cost effectiveness and also its optimization there is not much literature available on the topic. Numerous investigators have used apparently numerous materials in the experimental work and given various different correlations for various heat transfer factors and friction factor. Fan power is easily reduced by

Taole and Mawire (2011) concluded six different parameters namely temperature distribution along

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Chandigarh University Journal of Undergraduate Research and Innovation transfer process within rock beds”, Solar Energy, Vol29, No.6 (451 -462), 1982. 11. Adnan M. Waked, “Solar energy storage in rocks”, Solar & Wind technology Vol.3, No.1 (27-31), 1986. 12. K.G.T.Hollands&H.F.Sullivan, “Pressure drop across rock bedthermal storage systems”, Solar Energy, Vol.33, No.2 (221 -225), 1984. 13. A.S.A.Ammar& A.A. Ghoneim, “Optimization of a sensible heatstorage unit packed with spheres of a local market”, Renewable Energy, Vol.1, No.1 (91 -95), 1991. 14. K.Sagara&N.Nakahara, “Thermal performance and pressuredrop of rock beds with large storage materials”, Solar Energy, Vol.47, No.3 (157-163), 1991. 15. Mahmoud S. Audi, “Experimental study of a solar space heatingmodel using jordian rocks for storage”, Energy Convers.Mgmt.J. Vol.33, No.9 (833 -842), 1992. 16. M.M.El-Kassaby&A.A.Ghoneim, “Comparison of measured andpredicted performance of different heat storage systems”, Renewable Energy, Vol.3, No.8 (849-856), 1993. 17. C.Choudhury, P.M.Chauhan&H.P.Garg, “Economic design of arock bed storage device for storing solar thermal energy”, Solar Energy Vol.55, No.1 (29-37), 1995. 18. M.A.Al-Nimr, M.K.AbuQudais&M.D.Mashaqi, “Dynamicbehavior of a packed bed energy storage system”, Energy Convers.Mgmt.Vol.37, No.1 (23-30), 1996. 19. Ali A.jalalzadeh-Azar, W.Glenn Steele & George A.Adebiyi, “Performance comparison of high temperature packed bedoperation with pcm and sensible heat pellets”, International Journal of Energy Research, Vol.21 (1039-1052), 1997. 20. Ibrahim Dincer, Sadik Dost &Xianguo Li, “Performance analysisof sensible heat storage systems for thermal applications”, International Journal of Energy Research.Vol.21 (1257-1171), 1997. 21. Hassan E.Fath, “Technical assessment of solar thermal energystorage technologies”, Renewable Energy, Vol.14, Nos.1 -4 (35-40), 1998. 22. Hassan E.Fath, “Technical assessment of solar thermal energystorage technologies”, Renewable Energy, Vol.14, Nos.1 -4 (35-40), 1998. 23. K.A.R Ismail &R.Stuginsky, “A parametric study on possiblefixed bed models for

using large storage materials, but there are only very much few studies on the usage of large sized storage materials. Overall, it is concluded that materials other than rocks and pebbles have been studied in a few studies only. The important factor is the usage of solid phase physical property for the storage of different materials. The performance of system is significantly influenced by the shape and the size of the different materials which are used. The heat transfer rate and pressure drop characteristics of the packed beds system should be frequently or certainly improved by considering void fraction or the volume of the storage material filled in the packed bed system. REFERENCES 1. Harmeet Singh, “A review on packed bed solar energy storage systems” , Renewable and Sustainable Energy Reviews 14 (2010) 1059–1069. 2. T.E.W.Schumann, “Heat transfer: a liquid flowing through aporous prism”, Heat Transfer (405-416), 1929. 3. C.C. Furnas, “Heat transfer from a gas stream to a bed of brokensolids”, Industrial and Engineering Chemistry J. (721 -731), 1930. 4. Allan P. Colburn, “Heat transfer and pressure drop in emptybaffled, and packed tubes”, Industrial Engineering Chemistry J. Vol.23, No.8 (910-913), 1931. 5. Donald E. Beasley & John A. Clark, “Transient response of apacked bed thermal energy storage”, Int.J.Heat Mass transfer Vol.27, No.9 (1659-1669), 1984. 6. M.Riaz, “Transient analysis of packed –bed thermal storagesystems”, Solar Energy Vol.21 (123-128), 1978. 7. Charles Wyman, James Castle & Frank Kreith, “A review ofcollector and energy storage technology for intermediatetemperature applications”, Solar Energy Vol.24 (517-540), 1979. 8. N.Standish&J.B.Drinkwater, “The effect of particle shape onflooding rates in packed columns”, Chemical Engineering Science J. Vol.25 (19191621), 1970. 9. Pitam Chandra &D.H.Willits, “Pressure drop and heat transfercharacteristics of air rock bed thermal storage systems”, Solar Energy Vol.26, No.6 (547553), 1981. 10. J.PascalCoutier&E.A.Faber, “Two applications of a numericalapproach of heat

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Chandigarh University Journal of Undergraduate Research and Innovation pcm and sensible heat storage”, AppliedThermal Engineering, Vol.19, No.7 (757-788), 1999. 24. E.C.Nsofer& George A.Adebiyi, “Measurements of the gasparticle convective heat transfer coefficient in a packed bed forhigh temperature energy storage”, Experimental Thermal and Fluid Science24 (1 -9), 2001. 25. H.H.Ozturk& A. Bascetincelik, “Energy and exergy efficiency ofa packed bed heat storage unit for greenhouse heating”, Biosystems Engineering, Vol.86, No.2 (231 -245), 2003. 26. D.M.Crandall&E.F.Thacher, “Segmented thermal storage”, Solar Energy 77 (435-440), 2004. 27. Ranjit Singh, R.P.Saini&J.S.Saini, “Nusselt number and frictionfactor correlations for packed bed solar energy storage systemhaving large sized elements of different shapes”, Solar Energy 80 (760-771) 2006. 28. N.Nallusamy, S.Sampath&R.Velraj, “Experimental investigationon a combined sensible and latent heat storage system integratedwith

constant/varying (solar) heat source”, Renewable Energy 32 (1206-1227) 2007. 29. Mawire, A., and Taole, S. H.,” A comparison of experimentalthermal stratification parameters for an oil/pebble-bed thermalenergy storage (TES) system during charging”, Applied Energy 2011; Vol 88: p-p 4766-4778. 30. S.M.Hasnain, “Review on sustainable thermal energy storagetechnologies, part 1: heat storage materials and techniques” 31. Salwa BOUADILA, Safa SKOURI, Sami KOOLI, Meriem LAZAAR, Abdelhamid FARHAT (2013) “Experimental investigation of a new solar air heater with packed-bed latent storage energy”. 32. Rajesh Maithani, A.K. Patil, J.S. Saini (2013) “Investigaton of Effect of Stratification on theThermal Performance of Packed Bed SolarAir Heater”.

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