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  See discussions, stats, and author profiles for this publication at: Thermal Energy Storage System using Phase Change Materials – Constant HeatSource Conference Paper  · January 2010 CITATION 1 READS 228 5 authors , including: Some of the authors of this publication are also working on these related projects: Nano fluids, IC engines.Refrigeration and air-condition   View projectAnalysis of Design Parameters of Radiator   View projectR. Meenakshi ReddyG.Pulla Reddy Engineering College 35   PUBLICATIONS   61   CITATIONS   SEE PROFILE Nallusamy NallusamySri Sivasubramaniya Nadar College of Engineering 52   PUBLICATIONS   475   CITATIONS   SEE PROFILE Dr. T. HariPrasadSree Vidyanikethan Engineering College 43   PUBLICATIONS   148   CITATIONS   SEE PROFILE K. Hema Chandra ReddyJawaharlal Nehru Technological University, Anantapur 95   PUBLICATIONS   1,251   CITATIONS   SEE PROFILE All content following this page was uploaded by Dr. T. HariPrasad on 17 May 2014. The user has requested enhancement of the downloaded file.  Proceedings International Conference on Advances in Mechanical Engineering ICAME-2010 January 4-6, 2010 Editor Dr. R. Venkata Rao Department of Mechanical Engineering S. V. National Institute of Technology Surat-395007, Gujarat, India  Proc. of the 3 rd  International Conference on Advances in Mechanical Engineering, January 4-6, 2010 S.V. National Institute of Technology, Surat – 395 007, Gujarat, India 70 Thermal Energy Storage System using Phase Change Materials – Constant Heat Source R.Meenakshi Reddy 1* , N.Nallusamy 2 , T.Hari Prasad 1 , B.Anjaneya Prasad 3 , K. Hemachandra Reddy 4   1 Sri Venkateswara college of Engineering & Tech., Chittoor – 517 127 A.P. India, 2 Sri Venkateswara college of Engineering, Sriperumbudur-602 105, India. 3 JNTU College of Engineering, Hyderabad – 500 024, India. 4 JNTU College of Engineering, Pulivendula-516 390, A.P. India. *Corresponding author ( The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in small volume. The present experimental investigation on the thermal energy storage (TES) system is developed using paraffin and stearic acid as PCM. In the present system constant heat source is used as heat source to store the thermal energy in the form of sensible heat and latent heat. In the TES system paraffin and stearic acid are stored in the form of spherical capsules of 38 mm diameter (commercially available size and low cost). Investigation results related to the charging time and recovery of stored energy are presented. 1. Introduction Thermal Energy Storage (LHTES) system using Phase Change Materials (PCMs) as a storage medium offers advantages such as high heat storage capacity, small unit size and isothermal behavior during charging and discharging when compared to the sensible heat storage system (SHS).However, latent heat thermal energy storage systems are not in commercial use due to poor heat transfer rates during heat storage and recovery process. The efforts are going on to overcome this problem. Cho and Choi [1] investigated the thermal characteristics of paraffin in a spherical capsule during freezing and melting processes. Experiments were performed with paraffin. Nallusamy N. et al.[2] studied effective utilization of solar energy for water heating applications using combined sensible heat and latent heat storage system.Fouda et al.[3] studied the characteristics of Glauber’s salt as the PCM in the solar storage system. The effect of several variables was observed over many complete cycles of the unit, including variable HTF flow rate, inlet temperature, wall thickness, etc. Mehling et al.[4] presented experimental and numerical simulation results of energy storage density of solar hot water system using different cylindrical PCM modules. Results showed that adding PCM modules at the top of the water tank would give the system of higher storage density and compensate heat loss in the top layer. Thermal performance of LHTES systems integrated with solar heating systems was also investigated by Ghoneim et al. [5], The objective of the present work is to predict the suitable PCM among paraffin and stearic acid for sensible and latent heat thermal energy storage unit integrated with constant heat source. Parametric studies are carried out to examine the effects of the PCM and HTF flow rates on the performance of the storage unit for varying inlet fluid temperatures. The experiments were carried out for both energy storage and recovery periods using water as heat transfer fluid (HTF). 2. Experimental Investigation  A schematic diagram of the experimental setup is shown in figure 1. This consists of an insulated cylindrical TES tank, which contains PCM encapsulated spherical capsules, constant heat source, flow meter with an accuracy of 0.5 lph and a circulation pump (500lit/hr). The stainless steel tank has capacity of 51 liters (360 mm diameter and 504 mm height) to supply hot water for a family of 5 to 6 persons. There are two plenum chambers on the top and the bottom of the tank and a flow distributor is provided on the top of the tank to make uniform flow of HTF. The storage tank is insulated with glass wool of 50 mm thick. The  Proc. of the 3 rd  International Conference on Advances in Mechanical Engineering, January 4-6, 2010 S.V. National Institute of Technology, Surat – 395 007, Gujarat, India 71 outer diameter of spherical capsule is 38mm and it is made of high-density polyethylene (HDPE) with wall thickness of 1.00 mm. The total number of capsules in storage tank in case of paraffin and stearic acid are 870 and 836 which store the 10,000 KJ of heat. The spherical capsules are uniformly packed in layers and each layer is supported by wire mesh. The paraffin is used as PCM that has a melting temperature of 61 ± 1 0 C and latent heat of fusion of 213 KJ/Kg. Water is used as both SHS material and HTF. Stearic acid is used as another PCM that has a melting temperature of 57 ± 1 0 C and latent heat of fusion of 198 KJ/Kg. The TES tank is divided into four segments i.e. at x/L =0.25, 0.5, 0.75 and 1.0 (L is length of the TES tank, mm; x is the axial distance from the top of the TES tank, mm; x/L is the dimension less axial distance from the top of the TES tank) along its axial direction and the RTDs with an accuracy of ±0.3 0 C are placed at the inlet, outlet and four segments of the TES tank to measure the temperatures of HTF. Another four numbers of RTDs are inserted into the PCM capsules and they are placed at four segments of the TES tank to measure the temperatures of PCM. The position and number of RTDs are also designated in fig.1. The RTDs are connected to a temperature indicator, which provides instantaneous digital outputs. Figure 1. Schematic of Experimental Figure 2. Photograph of TES tank with Set-Up constant heat source For the experiment with constant heat source, an insulated tank of 70 liters capacity is used (shown in fig.2) as the constant temperature water bath is fitted with three electric heaters of varying capacities of 1kW, 2kW and 3kW with thermostat control to maintain the constant temperature in the bath. The photographic view of experimental set-up integrated with constant temperature bath is shown in figure 2. The key experimental parameters are different PCMs, HTF inlet temperature and its flow rate. Several experiments are conducted with different flow rates of HTF. During the charging process the HTF is circulated through the TES tank continuously. The HTF exchanges its energy to PCM capsules and at the beginning of the charging process, the temperature of the PCM inside the packed bed capsules is 32 0 C, which is lower than the melting temperature. Initially the energy is stored inside the capsule as sensible heat until the PCM reaches its melting temperature. As the charging process proceeds, energy storage is achieved by melting the PCM at a constant temperature. As the charging process proceeds, energy storage is achieved by melting the PCM at a constant temperature. Finally, the PCM becomes superheated. The energy is then stored as sensible heat in liquid PCM. Temperature of the PCM and HTF at different locations of the TES tank as shown in Fig.1 are recorded at an interval of 3 minutes. The charging process is continued until the PCM temperature reaches the value of 70 0 C. 3. Results and Discussion 3.1 Charging Process The charging experiments are conducted for the combination of various parameters of mass flow rates, different PCMs and HTF inlet temperatures.  


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