A comparative numerical study about the impact of rectangular and T shaped fins on melting of PCM in a rectangular enclosure

Abstract

A comparative numerical study is performed on the melting of RT42 phase change material (PCM) in a rectangular enclosure using two basic fin geometries: a regular fin and a flanged fin (T-shape) having a constant fin area. Five cases of each fin type, representing ten double fin arrangements, based on an upper (Lu) and lower fin (Ld) length ratio were examined. Hence, for cases I(I’), II(II’), III(III’), IV(IV’), and V(V’), theLu/Ld ratio is 1, 1.5, 4, 0.67, and 0.25, respectively. Furthermore, two more cases (VI and VII) with a single flanged fin at the upper and lower position were considered with flanged (Lf) to web (Lu, d) ratio of 0.136. Five performance indicators were employed: total melting time (tm), total stored energy (Et), average Nusselt number (Nu¯), mean power (Pm), and cost per mean power (Cpw) to evaluate the effect of fin geometry on the heat transfer mechanism governing the melting of PCM. An enthalpy-porosity model governed the phase change process. The mathematical models were simulated and verified against the reference theoretical results in ANSYS 2020 R2, CFD software. Mesh and time independent studies were also performed, and a time step of 0.1 s and 26,026 quad cell elements were recommended for a balanced computational accuracy and cost. The result shows that for the double fin arrangement cases, a decrease in the tm was observed as the Lu/Ld ratio was decreased. Case V, with the regular fin of Lu/Ld ratio 0.25, has the maximum melting rate and completely melts the PCM in 3696 s. However, the single flanged fin at the lower position (case VII) melts the PCM entirely in 2940 s, which is 41.2 % and 20.45 % faster than case I and V, respectively. Each case stores approximately the same amount of energy over time. However, for case VII, a high latent and sensible heat absorption rate was observed, followed by cases V and V’. Also, the Pm for case VII is 163 W, 71.32 %, and 25.66 % higher than case I and V, respectively. For the cost analysis, Cpw is employed, a ratio of the system’s total cost ($ 43.2) to the Pm. The Cpw for case VII is 0.27 $/W, 40 %, and 18.2 % less than case I (0.45 $/W) and V (0.33 $/W). The above result indicates that the double fin geometry can be replaced with a single flanged fin system for a high melting rate and low Cpw. Hence, a further study is required based on flanged to web ratio (Lf/Ld) and the positioning of the single flanged fin. A minimum tm (2806 s) and Cpw (0.252 $/W) were obtained for the Lf/Ld ratio of 0.25, placed 15 mm above the bottom of the container.