Heat Exchanger Performance in Latent Heat Thermal Energy Storage

An experimental study was made of the heat transfer in a component of a low temperature thermal energy storage system using latent heat of fusion of a phase change material (PCM). Measurements were made of the temperature rise of water flowing in a channel adjacent to a container filled with a freezing PCM, Gulfwax 33. In addition, temperature measurements within the PCM provided the location of the liquid/solid interface as a function of time. A simple analytical prediction is compared with the data to provide a verification of the qualitative observations. Certain multidimensional effects which occur during the freezing (discharge) mode of operation are identified especially the enhancement of freezing rates when the PCM container sidewalls (those not in contact with the heat exhange fluid) are conducting and are closely spaced. One limitation to storage systems of this type is the resistance to heat transfer of the solid phase, requiring a significant temperature drop for acceptable discharge rates. The additional “heat path” provided by the conducting container walls is shown to significantly reduce this resistance. Some observations concerning the implications for design of actual storage components are also provided.