An experimental optimization study on a tube-in-shell latent heat storage (original) (raw)

2007, International Journal of Energy Research

Thermal energy storage (TES) using phase change materials (PCMs) has recently received considerable attention in the literature, due to its high storage capacity and isothermal behaviour during the storage (melting or charging) and removal (discharging or solidification). In this study, a novel modification on a tube-in-shell-type storage geometry is suggested. In the proposed geometry, the outer surface of the shell is inclined and it is the objective of this study to determine the optimum range for the inclination angle of the shell surface. Paraffin with a melting temperature of 58.068C, which is supplied by the Merck Company, is used as the PCM. The PCM is stored in the vertical annular space between an inner tube through which the heat transfer fluid (HTF), hot water, is flowing and a concentrically placed outer shell. At first, the thermophysical properties of this paraffin are determined through the differential scanning calorimeter (DSC) analysis. Temporal behaviour of the PCM undergoing a non-isothermal solid-liquid phase change during its melting or charging by the HTF are determined for different values of the inlet temperature and the mass flow rate of the HTF. The new geometry is shown to respond well with the melting characteristics of the PCM and to enhance heat transfer inside the PCM for a specific range of the shell inclination angle. storage (LHTES) employing phase change material (PCM) has been widely noticed as an effective way due to its advantages of high energy storage density (i.e. low volume/energy ratio) and its isothermal operating characteristics (i.e. charging/discharging heat at a nearly constant temperature) during solidification and melting processes, which is desirable for efficient operation of thermal systems. In a latent heat storage system, energy is stored during melting and recovered during solidification of a PCM. The use of the latent heat of a PCM as a thermal energy storage medium has gained considerable attention recently by finding applications in conservation of energy and natural resources, recovery and use of waste industrial energy, space craft, refrigeration and air conditioning systems, solar energy systems, heating and cooling of buildings, etc. However, practical difficulties usually arise in applying the latent heat method due to the low thermal conductivity, density change, stability of properties under extended cycling, and sometimes phase segregation and subcooling of the PCMs. During the last 20 years, PCM for storing energy have developed rapidly. Their thermal and physical properties such as long-term stability and durability have been improved a lot.