Phase Change Process inside Toroidal Tube Heat Exchanger with Internal Fins

Abstract

Inadequate melting of phase change material (PCM) in concentric tube and shell and tube heat exchangers appeal motivations for innovative latent heat thermal energy storage (LHTES) systems. In the current research, a novel application of toroidal tubes inside the LHTES system for charging of PCM is presented. The proposed heat exchanger geometry is numerically investigated with the help of enthalpy – porosity approach. Toroidal tubes are assumed to be filled with PCM (i.e., coconut oil) and fabricated inside cylinder accommodating the heat transfer fluid (HTF). To establish and accelerate homogenous melting, flat thin fins are attached inside the toroidal tubes, and transient simulations are performed. The system performance is investigated for variations of (i) fin numbers (Nf), (ii) fin length (L0), and (iii) fin orientations (Fo) in terms of (i) melt fraction (MF), (ii) average PCM temperature, (iii) energy stored by PCM, and (iv) Nusselt number (Nu). Simulation results indicate that fin orientation stands out as the dominant factor for heat transfer enhancement compared to fin numbers and fin length. In the toroidal tube LHTES system, it is found that even though fin numbers and fin length are identical, correctly oriented fins (i.e., case 8) can provide 50.52% more rate of energy storage than a system with random fin orientation (i.e., case 5). Moreover, the optimum fin orientation (i.e., case 8) can (i) save 65.28% time for 100% melting and (ii) provide 168% more rate of energy storage than a system without fins. Based on the melting progression pattern, the current study encourages the use of multiple PCMs having dissimilar melting point temperatures with fins.