Effectiveness-NTU correlation for a TES tank comprising a PCM encapsulated in a sphere with heat transfer enhancement

Abstract

This paper presents a numerical investigation of a thermal energy storage tank consisting of phase change material (PCM) encapsulated in a sphere, using the effectiveness-number of transfer unit (ε-NTU) method. An experimental validated simulation model was used to validate the ε-NTU model. Three configurations of PCM container were investigated; a plain sphere, a sphere with conducting pins, a copper-plated sphere with conducting pins. The results showed that the local effectiveness values were increased by an average of 65% for the employment of 32 embedded pins. The average effectiveness was further improved by almost 256% when using copper plated sphere. A good comparable results from the experimental and simulation work indicates that the ε-NTU method is applicable to the formulation of heat transfer in the PCM encapsulated sphere despite the change in geometry. Furthermore, the method of defining thermal resistance was found to be applicable to the modified configurations. The values of p factor (isothermal–parallel path ratio) for the PCM sphere with pinned sphere and copper plated sphere with conducting pins were found to be 0.73 and 0.198, respectively. The results suggested that the heat flow through the pinned sphere predominately followed a parallel path, while through the copper-plated sphere was predominately isothermal.