EXPERIMENTAL AND THEORETICAL ANALYSIS OF LATENT HEAT ENERGY STORAGE SYSTEM WITH & WITHOUT EXTENDED SURFACES

Abstract

The Latent heat energy storage system is an important way of storing the energy. It provides a high energy storage density and has the capacity to store heat as latent heat of fusion at constant temperature corresponding to the phase transition temperature of the Phase Changing Material, i.e. the storage material. In this system, the storage takes place at no or small temperature swing. System has smaller size and low weight per unit of storage capacity. Latent heat storage system has high energy storage density. Hence with a small storage volume large amount of energy can be stored. The storage comprises of two stages viz. melting (charging) and solidification (discharging). Charging includes the energy storage and discharging is the energy extraction. PCM has lower thermal conductivitty hence it require heat transfer enhancement. Various methods to improve the thermal conductivity are providing extended surfaces, dispersing high conductive material and with encapsulation. Vertical fins had given better results hence are employed in the present work In the present work, the charging and discharging processes are analyzed with and without fin configuration. Shell and tube arrangement has been used for that with Heat Transfer Fluid at the tube side and Phase Change Material at the shell side.. The experiments are performed to analyze the effect. A two dimensional model is developed to study the system. Natural convection is not considered in this modeling. The thermophysical properties ã1e consideredas they are -varying with time. A FORTRAN code is developed for the model. From the analysis of the system, it is found that with increase in the mass flow rate of Heat transfer fluid, storage material takes less time to charge completely. Same effect can be seen with increase in the temperature of heat transfer fluid. It is seen that the Phase changing material, which is away from the Heat transfer fluid, exhibits more resistance to the heat flux because of its low thermal conductivity. This is the reason that away from the tube, Phase changing material takes more time to change its phase completely. iii To improve the performance of the system, four vertical, axially arranged fins made of copper are employed in it. Form the experiments performed it can be drawn that the phase change process takes less time and completes in a smaller duration of time. The time taken by storage material to reach complete phase change in radial is drastically reduced. The temperature profile in the fins is approximately linear. A numerical model has been developed for this case also. This model consider three dimensional heat transfer but without numerical heat convection. The model is validated with the experimental results. iv