Charge and Discharge Characteristics of a Direct Contact Latent Thermal Energy Storage Unit Using Form-Stable High-Density Polyethylene

For solar thermal energy utilization in relatively low temperatures, a lab-scale direct contact, latent thermal energy storage unit using a form-stable high-density polyethylene (HDPE) was developed. The phase change material (PCM), the form-stable HDPE, does not fluidize nor adhere even after melting, and this particular property permits a direct contact heat transfer between the PCM and a heat transfer fluid (HTF). The storage column in the present study consists of a bundle of vertically arranged thin HDPE rods, where HTF flows in the axial direction and contacts with the HDPE surface directly. A series of experiments were performed for both charge and discharge modes under conditions of different flow rates, initial temperatures in the column, and HTF inlet temperatures. A numerical simulation was also made to study further detailed performance of the storage unit. The charge and discharge characteristics of the storage unit are discussed.