No abstract

Remote cooling is the established cooling scheme in notebook computers, and increasingly, other computing sectors like desktops and servers are evaluating this approach as an option for cooling future platforms. While remote cooling facilitates a larger heat exchanger than the space directly over the processor would allow, it introduces an additional thermal resistance, in particular, θp-f (plate to fluid resistance) — the resistance in getting the heat from the cold plate to the fluid. For any remote cooling system, this resistance needs to be carefully evaluated and minimized. Pumped fluid loops incorporating microchannel heat exchangers are a viable option to achieve low plate-to-fluid resistances. In this paper we will identify a reasonable target for θp-f and subsequently describe two similar but fundamentally different thermal systems to accomplish this target performance: single-phase and two-phase pumped loops. Although two phase flows are traditionally thought of as the way to accomplish the highest heat transfer coefficients and thus the lowest resistances, with microchannel heat sinks the contrast is not so acute. We will present results from our experimental work on single- and two-phase heat transfer from microchannel heat sinks and demonstrate a transition where single-phase performance matches that of two-phase operation. This will be followed by the analysis methods used to predict the heat transfer and the pressure drop data. Moreover, we will discuss system level issues and other hurdles that need to be overcome in commercialization of microchannel technology for cooling computer systems.

No abstract

Notebooks represent an increasing percentage of PC client market with growth surpassing that of desktop computers. Heat pipe has been an integral part of notebook computer system cooling and will remain so for the foreseeable future. Heat pipe allows for efficient transport of heat from the CPU and other high power components to a location where there is more room for accommodating motherboard cutout for a fan and a heat exchanger. The thermal resistance along this path must be minimized to enable maximum cooling. This paper first briefly describes the contributing resistance in a heat pipe and ways to measure them for a notebook thermal solution. Since there are several parameters that can affect the performance of the heat pipes, we use an experimental procedure utilizing DOE (Design of Experiments) to first understand the sensitivities of these design, manufacturing and usage parameters on performance and then to arrive at an optimum level of these parameters to minimize various resistances in a heat pipe. We show that for various different wick technologies, it is possible to optimize the heat pipes to achieve an evaporator performance of the level of 0.1 C-cm2/W. Furthermore, we show some simple design rules to minimize the condenser resistance and also results of a design study to optimize the design of heat pipe block at the CPU end to minimize the evaporator resistance. We want to encourage the heat pipe vendor community to use these methods to optimize their products for performance as well as process enhancements to produce higher performing parts, at lower cost.