1 Copyright © 2004 by ASME MICROCHANNEL EXPERIMENTAL STRUCTURE FOR MEASURING TEMPERATURE FIELDS DURING CONVECTIVE BOILING Theresa A. Kramer, Roger D. Flynn, David W. Fogg, Evelyn N. Wang, Carlos H. Hidrovo, and Kenneth E. Goodson Department of Mechanical Engineering Stanford University Stanford, California 94305 Ravi S. Prasher, David S. Chau, and Sridhar Narasimhan Intel Corporation ATD Chandler, Arizona 85226 ABSTRACT This work designs and fabricates a microchannel structure for measurement of wall temperature fields in two-phase flow. The microchannel with hydraulic diameter of 100 micrometers is etched into a suspended beam of silicon with three independently heated regions and integrated doped silicon resistors sensitive to channel temperature. Doped silicon resistors are also sensitive to strain in the silicon caused by pressure transients in the channel, so sensors are designed with two different orientations and thus two different piezoresistive coefficients to allow decoupling of pressure and temperature effects. Use of a 400 micrometer wide suspended beam reduces side-wall conduction compared to a bulk sample and provides better opportunities to measure the influence of flow regimes on heat transfer coefficients in future work. Use of the central heater reduces fluid preheating in the inlet plenum. The measured temperature distributions at flowrates up to 0.25 ml/min with heat fluxes into the silicon beam up to 78 W/cm 2 show initial capabilities of the structure. KEYWORDS Microchannel, two-phase convection, heat exchanger INTRODUCTION Two-phase flow of water in microchannels has attracted attention as a means of removing heat from microprocessors in computers [1]. To understand convective boiling in microchannels, single and multiple channel structures have been developed using conventional machining [2], [3] and silicon micromachining [4] – [9]. Silicon micromachining allows integration of heaters and sensors onto the test structure. Peng and Wang [2] observed an absence of partial nucleate boiling in 600 μm by 700 μm rectangular microchannels machined into a stainless steel plate with thermocouples on the backside. The same results were observed by Peng et al. [3] in V-shaped microchannels with hydraulic diameters of 200 μm to 600 μm. Jiang et al. [4] reported phase change in V-shaped microchannels with hydraulic diameters of 40 μm and 80 μm using a localized heating element with distributed polysilicon temperature sensors, and Lee et al. [5] observed phase change in parallel rectangular channels with a 24 μm hydraulic diameter. Hetsroni et al. [6] used infrared imaging to determine steady- state temperature distributions in two-phase flow through parallel triangular microchannels with 103 μm to 129 μm hydraulic diameter under uniform and non-uniform heating. Peles et al. [7] studied steady flow regimes using parallel triangular microchannels with hydraulic diameters of 50 μm to 200 μm. Zhang et al. [8], [9] microfabricated suspended single channel test structures to reduce axial conduction in the silicon, using integrated aluminum heaters to achieve uniform heating and doped silicon sensors for distributed temperature measurements. Zhang et al. [9] then measured pressure transients at 30 - 40 Hz associated with bubble formation using the doped silicon sensors. They were not able to fully decouple pressure and temperature effects on a single sensor, and the heated beam led to fluid preheating in the inlet with a 2 mm separation between the heater and reservoir. The present work develops, fabricates, and characterizes single microchannel structures that allow decoupled Proceedings of IMECE04 2004 ASME International Mechanical Engineering Congress and Exposition November 13-20, 2004, Anaheim, California USA IMECE2004-61936 Downloaded 08 Aug 2012 to 18.111.60.113. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm