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The thermal charging performance of paraffin wax combined with compressed expanded natural graphite foam was studied for different graphite bulk densities. Constant heat fluxes between 0.39 W/cm² and 1.55 W/cm² were applied, as well as a constant boundary temperature of 60 °C. Thermal charging experiments indicate that, in the design of thermal batteries, thermal conductivity of the composite alone is an insufficient metric to determine the influence of the graphite foam on the thermal energy storage. By dividing the latent heat of the composite by the time to end of melt for each applied boundary condition, the energy storage performancemore » was calculated to show the effects of composite thermal conductivity, graphite bulk density, and latent heat capacity. For the experimental volume, the addition of graphite beyond a graphite bulk density of 100 kg/m³ showed limited benefit on the energy storage performance due to the decrease in latent heat storage capacity. These experimental results are used to validate a numerical model to predict the time to melt and for future use in the design of heat exchangers with graphite-foam based phase change material composites. As a result, size scale effects are explored parametrically with the validated model.« less

Residential refrigerator designs have improved significantly over the recent years to achieve the required federal minimum energy standard and match with consumer expectations. Designers have been able to use innovative design features and components; however, evaporator designs have lagged in performance improvement due to the need to properly manage frost and maximize the freezer interior volume. Rotating Heat Exchangers (RHX) provide an innovative solution that addresses both of these concerns. The rotation of the fins results in continuous disruption to the boundary layer, hence reducing the overall thermal resistance. Thus, for the same capacity, the heat transfer area can bemore » greatly reduced. Furthermore, the rotation inhibits frost growth on the fins and reduces the time and frequency of defrosting. In this paper, we present an experimental evaluation of the RHX in a benchtop refrigerant loop system showing results for different operating configurations. Cooling capacity, cooling COP, and overall energy consumption are investigated. High-speed imaging is also used to capture frost growth patterns over time on the RHX fins in the presence and absence of rotation. The results show that the rotating heat exchanger evaporator is capable of meeting the 100 W capacity requirement of residential refrigerators, while offering the potential of significant reduction in defrost energy consumption.« less