Bubble pump in a closed-loop system for electronic cooling

This study experimentally and theoretically investigates bubble pump performance in a closed-loop system for electronic cooling. The system consists of a vertical flat evaporator acting as a bubble pump, a condenser, a rising tube, a falling tube and a reservoir, and is completely filled with working fluid. As the bubble pump absorbs heat, the differences in the working fluid density between the rising and falling tubes induce flow motion. The effects of the input heating power, the pump inlet temperature and the boiling surfaces are determined experimentally. There are three heat-transfer regions inside the pump, including natural convection, subcooled boiling and saturated boiling. A theoretical pressure drop model and a thermal resistance network are constructed to describe the performance of the bubble pump. The results indicate that the bubble pump performs better at saturated boiling conditions. When the pump inlet temperature is the saturated temperature, the maximum flow rate is 200 ml/min at 30 W and the maximum driving pressure of the pump is 962 Pa at 80 W. The results also show that the sudden contraction between the pump and the rising tube, inducing a pressure drop, will reduce the system flow rate. In addition, the results demonstrate that the fins on the boiling surface can effectively diminish the center temperature of the basic plate of the pump and of pump resistance.