Air-Cooled Loop Thermosyphon Cooling System for High Heat Load CPUs—Part I: Design and Performance Simulation
Jackson B. Marcinichen, Guilherme S. R. B. Armas, Gautier Rouaze, John R. Thome, L. Winston Zhang
Abstract
This article proposes and evaluates the thermal-hydraulic performance of a compact, lightweight, and high heat-transfer capacity cooling system for central processing unit (CPU) temperature control. The cooling loop, defined as a closed loop thermosyphon (LTS), has a passive flow driven mainly by the buoyancy in the riser. It is a self-modulated system, i.e., without heat flow ceases but it increases with increasing heat load. The LTS is a partially passive system since energy is still required to drive the fan blowing air through its condenser. The main advantage relative to conventional forced air-cooled heat spreaders is its ability to transfer much higher levels of heat while consuming less fan power. The innovative patented LTS system has two thermosyphon loops working in parallel, composed of a multimicrochannel evaporator, a multiport tube louvered fin condenser, two risers, and one downcomer. The simulations show that it is able to cool 600 W from a 50 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 50 mm CPU footprint without dryout or surpassing the critical heat flux. It was specifically simulated for a CPU of 2U server, considering a height of only 66 mm and width of 214 mm. Thus, two of these units can be installed side-by-side in a 2U server, which means a total cooling capacity of 1200 W per server. Several simulations are presented showing the high thermal-hydraulic performance of the LTS and a case study showing the reduction of fan energy consumption when comparing the proposed LTS with an actual air-cooled heat spreader system. The LTS was prototyped, experimentally tested, and its simulations successfully validated in Part II of this study.