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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.

Remote heat pipe based heat exchanger cooling systems are becoming increasingly popular in cooling of notebook computers. In such cooling systems, one or more heat pipes transfer the heat from the more populated area to a location with sufficient space allowing the use of a heat exchanger for removal of the heat from the system. In analsysis of such systems, the temperature drop in the condenser section of the heat pipe is assumed negligible due to the nature of the condensation process. However, in testing of various systems, non linear longitudinal temperature drops in the heat pipe in the range of 2 to 15 °C, for different processor power and heat exchanger airflow, have been measured. Such temperature drops could cause higher condenser thermal resistance and result in lower overall heat exchanger performance. In fact the application of the conventional method of estimating the thermal performance, which does not consider such a nonlinear temperature variations, results in inaccurate design of the cooling system and requires unnecessarily higher safety factors to compensate for this inaccuracy. To address the problem, this paper offers a new analytical approach for modeling the heat pipe based heat exchanger performance under various operating conditions. The method can be used with any arbitrary condenser temperature variations. The results of the model show significant increase in heat exchanger thermal resistance when considering a non linear condenser temperature drop. The experimental data also verifies the result of the model with sufficient accuracy and therefore validates the application of this model in estimating the performance of these systems.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Mobile Original Equipment Manufacturers (OEMs) place great emphasis on creating unique system designs to differentiate themselves in the mobile market. Intel Corporation's introduction of low-power, high-performance Intel® processors based on original 45 nm Intel Core™ microarchitecture, originally referred to by the codename Penryn, brings a new level of opportunity for differentiation into the mainstream segment without sacrificing performance. The Mobile Penryn family of processors offers mainstream performance at 25 watts (W) Thermal Design Power (TDP), 10 W less than previous generation processors. In this paper we discuss the fundamentals of system cooling capabilities in any given form factor and look at how power relates to the thinner, cooler, and quieter systems.

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