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We report the design and analysis of a novel compensation chamber for use in PHUMP, a multiple condenser loop heat pipe (LHP) capable of dissipating 1000 W. The LHP is designed for integration into a high performance air-cooled heat sink to address thermal management challenges in advanced electronic systems. The compensation chamber is integrated into the evaporator of the device and provides a region for volumetric expansion of the working fluid over a range of operating temperatures. Additionally, the compensation chamber serves to set the liquid side pressure of the device, preventing both flooding of the condensers and dry out of the evaporator. The compensation chamber design was achieved through a combination of computational simulation using COMSOL Multiphysics and models developed based on experimental work of previous designs. The compensation chamber was fabricated as part of the evaporator using Copper and Monel sintered wicks with various particle sizes to achieve the desired operating characteristics. Currently, the compensation chamber is being incorporated into a multiple condenser LHP for a high performance air-cooled heat sink. Copyright © 2013 by ASME., United States. Defense Advanced Research Projects Agency. Microsystems Technology Office. Microtechnologies for Air-Cooled Exchange Program (Grant Number W31P4Q-09-1-0007)

We present the characterization of a compact, high performance air-cooled heat sink with an integrated loop heat pipe. In this configuration, heat enters the heat sink at the evaporator base and is transferred within the heat pipe by the latent heat of vaporization of a working fluid. From the condensers, the heat is transferred to the ambient air by an integrated fan. Multiple condensers are used to increase the surface area available for air-cooling, and to ensure the equal and optimal operation of the individual condensers, an additional wick is incorporated into the condensers. We demonstrated with this design (10.2 cm × 10.2 cm × 9 cm), a total thermal resistance of less than 0.1 °C/W while dissipating a heat load of 500 W from a source at 75 °C. Furthermore, constant thermal resistance was observed in the upright as well as sideways orientations. This prototype is a proof-of-concept demonstration of a high performance and efficient air-cooled heat sink design that can be readily integrated for various electronics packaging and data center applications., United States. Defense Advanced Research Projects Agency. Microsystems Technology Office. Microtechnologies for Air-Cooled Exchangers (Grant Number W31P4Q-09-1-0007)

Thermal management of modern electronics is rapidly becoming a critical bottleneck of their computational performance. Air-cooled heat sinks offer ease and flexibility in installation and are currently the most widely used solution for cooling electronics. We report the characterization of a novel loop heat pipe (LHP) with a wick in the condenser, developed for the integration into an air-cooled heat sink. The evaporator and condenser are planar (102 mm × 102 mm footprint) and allow for potential integration of multiple, stacked condensers. The condenser wick is used to separate the liquid and vapor phases during condensation by capillary menisci and enables the use of multiple condensers with equal condensation behavior and performance. In this paper, the thermal–fluidic cycle is outlined, and the requirements to generate capillary pressure in the condenser are discussed. The LHP design to fulfill the requirements is then described, and the experimental characterization of a single-condenser version of the LHP is reported. The thermal performance was dependent on the fan speed and the volume of the working fluid; a thermal resistance of 0.177 °C/W was demonstrated at a heat load of 200 W, fan speed of 5000 rpm and fluid volume of 67 mL. When the LHP was filled with the working fluid to the proper volume, capillary pressure in the condenser was confirmed for all heat loads tested, with a maximum of 3.5 kPa at 200 W. When overfilled with the working fluid, the condenser was flooded with liquid, preventing the formation of capillary pressure and significantly increasing the LHP thermal resistance. This study provides the detailed thermal–fluidic considerations needed to generate capillary pressure in the condenser for controlling the condensation behavior and serves as the basis of developing multiple-condenser LHPs with low thermal resistance., United States. Defense Advanced Research Projects Agency (W31P4Q-09-1-0007)