04. Boiling and Multi-Phase Flow

As cooling devices for electronic devices are expected to become smaller and smaller to support high-density mounting, the dimensions of the flow path and envelope volume tend to be strongly limited. In addition, the cooling devices are expected to be able to handle the heat generated by the higher performance of electronic devices. The heat generation density of power semiconductors implemented as inverters in electric vehicles is expected to reach 1000 W/cm2. The high heat flux heat generation had to be intensively controlled by a smaller cooling device. Forced convection boiling is one possible solution. However, the bubbles generated by the forced convection boiling may impede the flow of the refrigerant, creating a bottleneck for heat transfer. In a previous report, it was pointed out that the pulsating flow seen in biological blood flow can be used to promote heat transfer in forced convection in a single-phase flow by efficiently removing flow stagnating in a detached region. This study investigates a heat transfer enhancement technique in which the release of vapor bubbles generated around a heating element is enhanced by the pressure fluctuation caused by the pulsating flow. In this paper, heat transfer experiments of forced convection boiling with pulsating flow around a heating element with high heat flux were conducted to evaluate the possibility of this phenomenon. The test section consists of an 8 mm diameter cylindrical rod heater inserted into a 2.5 mm high, 10 mm wide channel. Experimental results showed that the pulsating flow did not improve the heat transfer performance, but it was found to raise the dryout point. Pulsating flow is considered to have an advantage in refrigerant transport capacity in that it sends refrigerant deeper into the flow against flow obstruction.

Prof.

Yasushi Koito

Corresponding author