Thermal performance and capillary limit of a ceramic wick applied to LHP and CPL

The performance of a ceramic wick working as a capillary evaporator of a Loop Heat Pipe (LHP) and a Capillary Pumped Loop (CPL) is analyzed. The LHP and the CPL have a capillary evaporator with 10 mm of inner diameter and 25 mm of length. The LHP compensation chamber has the same diameter as the evaporator and a length of 50 mm. The ceramic wick was sintered from alumina and mullite powders, achieving 50% of porosity, 1–3 μm pore size distribution and permeability of 35 × 10−15 m2, and then machined to properly fit the evaporators. The performance tests were carried out using deionized water as the working fluid for power inputs of up to 30 W. The thermal performance, capillary limit and area-specific thermal resistance of these systems were analyzed with the support of basic heat transfer and fluid flow lumped models. The lowest area-specific thermal resistance values of 31.7 °C/W/cm2 for CPL and 25.0 °C/W/cm2 for LHP were reached when dissipating 3.18 W/cm2, while the highest values of 52.8 °C/W/cm2 for CPL and 38.8 °C/W/cm2 for LHP were reached while dissipating 0.53 W/cm2 and 1.06 W/cm2, respectively. The analysis shows that the systems operate well at their capillary limit and their performance is equivalent to similar devices operating with acetone and ammonia reported in the literature.