Effect of roughness geometry on characteristics of phase change material storage unit for night coolness storage in summer season

Abstract

This paper presents a theoretical analysis of thermal storage unit using phase change material as storage medium. Storage unit consists of parallel rectangular channels for the air flow which are separated by phase change storage material. The purpose of storage unit is to absorb the night coolness and to provide cooled air at comfort temperature during day time in summer season. MATLAB simulation tool has been used to compute the air temperature variation with location as well as time, charging, and discharging time of storage unit. Phase change material used for analysis is selected in such a way that it's melting point lies between comfort temperature and minimum night ambient temperatures. The air flow rate needed for charging of phase change material is approximately four times greater than the flow rate required during day time to achieve comfort temperature for approximately eight hours, due to limited summer night time (only eight hours). The length of storage unit for which number transfer of units value is greater than or equal to five will give the exit air temperature equal to phase change material temperature for the case of latent heat utilization. It is found that artificial roughness on the duct surface effectively reduces the length of storage unit in the cost of some extra pressure drop across the duct.