Effect of the wick characteristics on the thermal behaviour of a LHP capillary evaporator

The present work aims at investigating the effect of the characteristics of porous wicks integrated in a flat disk-shaped LHP evaporator on their thermal performance and operating limits. Several wicks were manufactured by sintering of copper powder following a design of experiment, and characterised in terms of permeability, porosity, pore radius and thickness. A specific test bench was designed, consisting of a LHP evaporator uncoupled from the condenser. Water and pentane were used as the working fluids. The theoretical capillary and boiling limits of the wicks in the test bench were studied and compared to the experimental data. It was observed that a high permeable wick (K > 10−13 m2) is likely to reach the boiling limit before the capillary limit because the fluid easily percolates through it. The heat transfer coefficient between the evaporator wall and the evaporating fluid is significantly higher with pentane than with water. It reaches a maximum value of 2340 W m−2. K−1 with water and 5310 W m−2. K−1 with pentane, but no clear tendency could be highlighted concerning the effect of the wick characteristics on this parameter. The maximum dissipated heat transfer rate before the wick dry-out varies in a smaller range with pentane than with water. The highest measured values are equal to 88 kW m−2 with water and 56 kW m−2 with pentane.