Thermal Characteristics of Phase Change Material Solidification Behavior in Annulus

ABSTRACT Saving energy or converting it to different forms requires a continuous technique to improve the thermal performance of the applications. The present investigation analyzed the thermal performance and temperature distribution of the phase change material (PCM) discharging process both numerically and experimentally within an annulus of concentric tubes. The inlet temperature of the heat‐transfer fluid (HTF) in the inner tube of the annulus was maintained to be lower than the solidification points of the PCM (paraffin wax). The four domains (tubes, PCM, and HTF) have been simulated as a 3D transient model for the coupled system. Under various flow rates (0.0134, 0.032, 0.0713, and 0.0952 kg/s), the inlet and outlet temperatures are measured for the PCM and HTF. They found that computational predictions well predicted the acquired experimental data. The experimental results showed that there is an inverse proportional relationship between the amount of mass flow rate and the time required for the solidification of the PCM. The optimum times (155, 128, 66, and 55 min) are reached to obtain hot water above 37°C for domestic use compared with the previously mentioned mass flow rates during the discharge process. The computational model presents a new solution that lies in the establishment of two initial conditions (I.C.). The first initial condition (I.C.‐1) is based on the melting temperatures at the measurement points in the PCM system, with the rest of the domains being based on the inlet HTF temperature. The second initial condition (I.C.‐2) is based on the stability of all domains at the PCM melting temperature. The numerical results showed the highest difference of 2.5°C between the two I.C. solutions in the first minute. After comparing the experimental and numerical solutions, the highest average percentage error rate value did not exceed 16%, with complete consistency in the thermal behavior.