Modeling of a Thermosiphon to Recharge Phase Change Material Based Thermal Battery for a Portable Air Conditioning Device

Abstract

Closed loop two phase thermosiphons have a broad range of applications due to their simplicity, reliability, low cost and the ability to dissipate high heat fluxes from minimal temperature differences. The present study focuses on one thermosiphon operation which solidifies a phase change material (PCM) based thermal battery for a portable air conditioner called Roving Comforter (RoCo). RoCo uses vapor compression cycle (VCC) to deliver cooling and stores the heat released from the condenser into a com-pact phase change material (PCM) based thermal battery. Before its next cooling operation, the PCM needs to be re-solidified. This is achieved by the thermosiphon, which operates within the same refrigerant circuitry with the help of a pair of valves. The molten PCM which acts as heat source affects the dynamics of the thermosiphon which in turn affects the solidification process. Thus the dynamics of both the PCM and thermosiphon are coupled. For ac-curate transient modeling of this process, the PCM model considers the solidification over a temperature range, vari-able effects of conduction and natural convection during the phase change and variable amounts of heat release at different temperatures within the temperature range of phase change. The paper discusses component modeling for this transient operation of thermosiphon and its valida-tion with experimental data.