Liquid immersion cooling of small electronic devices

Abstract

The primary purpose of this investigation was to examine liquid immersion techniques for cooling minute heat sources. The study demonstrated that nucleate boiling is an effective means of cooling larger heat sources. However, for heat sources with surface areas less than 0·01 sq. cm, nucleate boiling was found to offer very little improvement in convective heat transfer over free convection with the same liquid. In addition, nucleate boiling may introduce mechanical stresses, contamination and physical design problems. For these reasons, two alternatives to boiling (forced convection and bubble induced mixing) were also investigated which reduced (or bypassed) some of these problems. In the forced convection study, boundary layer analysis showed the convective heat transfer coefficient would increase significantly as the heat source size decreased. This was verified experimentally with two different liquids. The experiments found the convection coefficient increased by a factor of 15 when the source size was decreased from 2·00 to 0·01 sq. cm. A similar increase was noted in the free convection and bubble induced mixing experiments. In addition, with small sources both bubble induced mixing and forced convection gave significantly larger heat transfer coefficients than were practical with boiling.