Thermal modeling of a rotary heat pump: effects of key parameters on performance

This study presents a transient thermal analysis of a rotary electrocaloric (EC) heat pump in which fluids circulate through channels bounded by electrocaloric material. The transient conjugate heat transfer problem is solved using both a finite-element model and a reduced-order analytical model. The reduced-order model predicts the cooling capacity with an average deviation of 8.08% from the finite-element solution while requiring significantly lower computational effort. Under the baseline operating conditions, the heat pump delivers a cooling capacity of 23.33 W, a coefficient of performance (COP) that includes electrical and mechanical power requirements of 22.827 and a relative Carnot efficiency of 7.79%. The analysis reveals the existence of a reverse heat pumping zone at the beginning of each heating and cooling stage, caused by the displacement of fluid transported from the previous stage, which reduces the net cooling capacity. Parametric calculations show that this reverse heat pumping effect becomes more pronounced at lower rotational speeds, lower fluid velocities, longer channel lengths, and larger temperature differences between the hot and cold reservoirs, ultimately limiting the operating range of the device. A conceptual tandem configuration employing alternating fluid inlets and inter-stage recirculation is proposed as a potential approach for increasing the achievable temperature span of a four-stage rotary electrocaloric heat pump to 4.8349∘C and the relative Carnot efficiency to 38.16%.