Experimental investigation of steady-state, transient and cyclic ice–water phase change in a rectangular plate-fin enclosure for cold thermal energy storage

Ice-based cold thermal energy storage systems require reliable experimental data relating to interface evolution, stored-ice fraction and thermal response under steady, transient and cyclic operating conditions. This paper experimentally investigates ice–water phase change in a horizontal rectangular plate-fin enclosure designed to represent a module of a cold thermal storage system. The enclosure consisted of an aluminium rectangular duct with the left and right walls acting as cold and hot walls, and the upper and lower walls functioning as continuous plate fins. Calibrated Type-E thermocouples were used to measure wall and fin temperatures, while the ice–water interface was recorded using optical imaging and image processing to estimate the ice fraction. Eight steady state cases, specifically two single-step transient excursions, two cyclic operating cases and repeatability runs were considered. For the steady-state tests, the cold-wall temperature increased from −6.18 °C to −2.40 °C with the input from nominal heater increasing from 85 to 190 W. The ice fraction reduced from 43.13% to 4.53%. During the transient tests, increasing the heater input from 85 W to 130 W resulted in melting-dominant behaviour, while 130 W to 85 W led to freezing-dominant behaviour. Four cycles each lasting 7200 s generated repeatable charging and discharging during cyclic operation, with a reduction in the ice fraction during high power half-cycles and an increase during low power half cycles. The results indicated that the morphology did not develop as a planar one-dimensional front, but determined by the interaction of heat conduction through the ice, conduction along the fins normal to the flow direction, natural convection in the liquid-water phase and density inversion of water near 4 °C. Concerning the design and validation of cold thermal energy storage systems, the work provides a benchmark for steady-state, transient, cyclic and repeatability experimental data from a rectangular plate-fin ice–water enclosure.