Reduction of boiling thermal hysteresis in immersed electronics cooling on micro-configured graphite-metal conposite surfaces

摘要

It is known that hysteresis is an important and unique dynamic characteristics in two-phase systems in motion with or without rotation. In pool boiling which generates vapor phase, the system is set in motion due to a pumping action near the heating surface caused by the departure of bubbles whose space is replaced by the surrounding liquid body. However, its dynamic behavior at the same surface superheat differs when the boiling heat flux undergoes an increasing trend and when it undertakes a decreasing trend. The discrepancy in a boiling curve is generally recognized as boiling hysteresis which is especially evident in boiling of a highly wetting liquid. The present work investigates (i) difference in the start-up/restart cycles between the micro-configured graphite fiber-metal composite surface and pure metal surface, and (ii) mechanism for reduction of boiling thermal hysteresis on the composite surfaces. The graphite fiber surfaces possess two distinguished properties that are suitable to avoid retardation of bubble nucleation in highly wetting electronics cooling liquids. One is their ill-wetted character for most liquids and the other is their high thermal conductivity.