Periodic Two-Phase heat transfer coefficient in an Electronic Cooling Mini Evaporator

In the case of indirect cooling, the metallic mass of the evaporator can play an important role in all periodic cooling devices. This paper presents two different methods of measuring an heat transfer coefficient changing over time. The first method determines the output power removed by the fluid by measuring the temperature close to the heat transfer surface and approximating the temperature distribution in the copper evaporator with a finite difference method, while the second method directly measures the two-dimensional temperature distribution in the evaporator. Both methods have shown good accordance if applied to a PTPT device with a periodic heat transfer coefficient. The PTPT device presents a maximum heat transfer coefficient of 11000 W/m2·K if the periodic liquid pool volume in the evaporator is higher than 64·10-6 m3, while it falls to 5000 W/m2·K if the periodic liquid pool volume in the evaporator is lower than 3.5·10-6 m3. This evaporator, with a mass of 0.155 kg, presents temperature oscillations lower than 6 K even in the case of a liquid pool volume of 3.5·10-6 m3.