  Heat and mass transfer inside the porous wick of a capillary evaporator is
studied using a mixed pore-network model. The impact of the thermal
conductivity of the wick on the overheating limit (defined as the difference
between the maximum temperature at the top of the metallic casing and the
saturated temperature), breakthrough (which occurs when the vapor reaches the
wick inlet) and the parasitic heat flux lost by conduction at the entrance of
the wick (which decreases the efficiency of the evaporator) is investigated.
The study suggests a bilayer wick as a possible better design to optimize the
performance of the evaporator. With this design, the inlet layer is of low
thermal conductivity with small pore size so as to reduce the parasitic heat
flux. The inlet layer also plays a role of capillary lock limiting the risk of
breakthrough. The second layer, right under the metallic casing, is more
conductive with a high thermal conductivity and larger pores so as to limit the
risk of overheating. It is shown that this design increases the range of heat
loads which can be applied to the evaporator.
