Analysis Of The Influence Of Operating Conditions And Geometric Parameters On Thermal Characteristics Of Low Temperature N-octadecane Latent Heat Storage

This work presents a numerical study of the thermal characteristics of low temperature n-octadecane latent heat storage unit (LHSU) in a shell-and-tube configuration. Phase change material (PCM) is filled in the shell space. The heat transfer fluid (HTF) flow through the tube and transfer the heat to PCM. First, a mathematical model is developed based on the enthalpy formulation and solved through the governing equations for different parameters. Second, the effects of Stefan and Reynolds number on the unsteady temperatures evolution of PCM as well as the unsteady total energy stored evolution are studied. Third, some operating conditions and geometric parameters are then undertaken to assess the effects of HTF inlet temperature, HTF inlet velocity and inner tube radius on melting time. The results show that charging process has three periods for the change of temperature regarding to time in PCM: rapidly changing period, no changing period and slowly changing period. The total energy stored gradually increases from minimum value which define the beginning of the charging process to maximum value defined the end of the process. The effects of Stefan number on the total energy stored show that heat storage capacity is large for high Stefan number. The Reynolds number has little influences on the amount of total energy stored, except the time needed for completing charging process. The results show also that within the studied parameters, the HTF inlet temperature has the largest effect on LHSU rate. With HTF inlet temperature increasing from 302.7 K to 325.7 K, the melting time reduces 92 %. The second influential factor is the HTF inlet velocity. When inlet velocity increases from 0.01 m/s to 0.6 m/s, the melting time reduces 32 %. Tube radius has the lowest effect. With inner tube radius increasing from 6.35 mm to 50 mm, the melting time augments 49 %. Results show that these operating conditions and geometric parameters must be chosen carefully in order to optimize the thermal performance of the LHSU.