Numerical Simulation of a Microencapsulated Phase Change Material Slurry Flowing in a Helical Coil Heat Exchanger

Heat transfer analysis of microencapsulated phase change material (MCPM) slurry flowing through a helical coil heat exchanger was carried out numerically. MPCM slurry at different mass fractions with known thermal and physical properties was chosen as heat transfer fluid (HTF). MPCM slurries can carry significantly higher thermal load when the PCM undergoes phase change within a specified temperature range. However, little is known as to how MPCM behave in helical coil heat exchangers. Helical coil heat exchangers are being used widely in many industrial applications including air conditioning systems due to their compactness and high thermal effectiveness. Enhancing the heat transfer rate of coil heat exchanger by using MPCM slurry without altering the existing parameters of coil heat exchangers such as shell diameter should lead to energy savings due to reductions in HTF pumping energy demands at identical heat loads. The ultimate goal of this study is to show a significant enhancement in heat transfer when MPCM slurry is pumped through helical coil heat exchangers. Unlike traditional HTF used in helical coil heat exchangers, the proposed MPCM slurry could alter the flow structure and the internal convection by inducing and enhancing the formation of secondary flows, as a result of phase change in the microencapsulated phase change material. Specifically, a three dimensional numerical study was undertaken to understand the effects of the helical coil heat exchanger geometry and the HTF flow characteristics on heat transfer enhancement. Baseline numerical simulations were conducted using water as HTF in order to compare with MPCM slurry numerical results. The numerical model was solved based on the finite volume method. The temperature-dependent properties of MPCM slurry and boundary conditions were considered. The promising results of this numerical study demonstrate the importance of formulated HTF and the geometry of the heat exchanger on the heat transfer enhancement and energy savings.