A device and technique to measure the heat transfer limit of a planar heat pipe wick

Abstract

Heat pipes are increasingly being utilized in applications for cooling electronics such as micro-processors. Heat pipes afford a very high heat transfer rate with only a small temperature difference between the heat source and heat sink. However, heat pipes have several operating limits, known as heat transfer limits, that can cause a severe reduction in the heat transfer rate and lead to catastrophic failure of the micro-processor. Two of these limits, known and the capillary limit and boiling limit are primarily a function of the heat pipe wick. In the present work, we developed a test apparatus and technique to determine the heat transfer limit of a planar heat pipe wick. The advantage of this apparatus and technique is a quantifiable measurement of the wick’s heat transfer limit without being confounded by other operating limit mechanisms such as the viscous or sonic limits. The apparatus and technique also yields the wick’s effective thermal conductivity. The apparatus is compatible with many of the low temperature heat pipe working fluids such as water or methanol, can be operated in any orientation with respect to the gravity vector, accounts for parasitic heat losses, provides for flow visualization studies, and is adaptable to a wide range of wick thicknesses.