Characterization of an integrated micro heat pipe

The characterization of a micro heat pipe system, integrated with a local heater, temperature and capacitive microsensors is presented. Two liquid charging schemes based on a single hole, requiring vacuum environment, and a pair of holes, utilizing capillary forces are compared. Taking advantage of the great disparity between the dielectric constants of liquids and gases, capacitance sensors are used for void fraction measurements. Since it is difficult to control the phase content of a liquid-gas mixture in a micro heat pipe, a calibration technique based on a traveling water-air interface due to evaporation is introduced. The integrated sensor capacitance for pure water is found to depend on measurement frequency, temperature and ion concentration, exhibiting trends that are different from previous reports. The measured temperature and void fraction distribution along the heat pipes are consistent with the two-phase flow patterns recorded during the microsystem operation.