Determination of the Thermal Performance Limits for Single Phase Liquid Cooling Using an Improved Effectiveness-NTU Cold Plate Model

Abstract

Cold plates are at the heart of pumped liquid cooling systems. In this paper, we report on combined experimental, analytical, and computational efforts to characterize and model the thermal performance of advanced cold plates in order to establish their performance limits. A novel effectiveness-NTU formulation is introduced that models the fin array as a secondary “pseudo-fluid” such that accurate crossflow effectiveness models can be utilized to model the cold plates using well-known formulations. Experimental measurements and conjugate CFD simulations were made on cold plates with fin and channel features of order 100 um with water-propylene glycol (PG) mixtures as coolants. We show that for a fixed fin geometry, the best thermal performance, regardless of the pressure drop, is achieved when the flow rate is high enough to approach the low NTU convective limit which occurs for NTU approaching zero. For the model cold plate evaluated in this study, the lowest thermal resistance achieved at a flow rate of 4 LPM was 0.01 C/W, and the convective limit was 0.005 C/W. However, for a fixed pressure drop, the optimal cold plate should be designed to meet its TDP at the highest possible effectiveness in which the lower limit of thermal resistance is the advective limit achieved for NTU > 7. For the tested cold plate the advective limit for the thermal resistance is 0.003 C/W, but this limit can only be achieved if it is practically feasible to increase the surface area and heat transfer coefficient to maximize NTU for a targeted TDP.