Novel concept of magnetocaloric heat pipe and its micro-unit regeneration cycle.

Magnetocaloric Refrigeration (MR) presents a viable alternative to the Vapor Compression Cycle (VCC). The Active Magnetic Regenerator (AMR) has thus far been hindered by challenges related to low operational frequencies and inadequate heat transfer coefficients. The Micro-Unit Regeneration (MUR) cycle demonstrates nearly flawless performance within the caloric thermodynamic cycle, but its fully solid-state prototype suffers from extremely low thermal conductivity, rendering it impractical for real-world applications. This paper introduces a novel concept of Magnetocaloric Heat Pipe (MCHP). It integrates Magnetocaloric Effect (MCE) with phase change heat transfer to enhance heat transfer efficiency between Magnetocaloric Materials (MCMs). A MCHP-MUR cycle for magnetic heat pump is developed, a small temperature difference between micro-unit of MCMs drives the evaporation-condensation phase change heat regeneration. Additionally, a thermal resistance model of the MCHP unit and multi-stage MUR cycle are constructed for performance evaluation at 1.5 T magnetic intensity. Experimental results indicate that the heat transfer process, characterized by a small temperature difference of 4.0 K, can be completed and reach equilibrium within 0.5 s, which is a 99 % reduction in equilibrium time compared to solid-state heat conduction. A system temperature span of 3.2 K was attained in basic two-stage MCHP-MUR cycle. In numerical simulations, a dual 16-stage MCHP-MUR cycle demonstrated a maximum no-load temperature span of 25.3 K and a peak heating capacity of 3.5 W g^-1 at zero temperature span. The paper also offers recommendations and discussions that may inform the design and optimization of the innovative MCHP-MUR cycle.