Heat transfer in rectangular microchannels during volumetric heating of the substrate ☆ Shantanu S. Shevade, Muhammad M. Rahman ⁎ Department of Mechanical Engineering, University of South Florida, Tampa, Florida 33620, USA Available online 26 March 2007 Abstract Convective heat transfer in microchannels with rectangular and square cross sections are analyzed for volumetric heat generation in the substrate due to an imposed magnetic field. Gadolinium was used as the substrate material and water as the working fluid. Gadolinium is a magnetic material that exhibits high temperature rise during adiabatic magnetization around its transition temperature of 295 K. A thorough investigation for velocity and temperature distributions was performed by varying channel aspect ratio, Reynolds number, and heat generation rate in the substrate. With the increase in Reynolds number, the outlet temperature decreased and the average Nusselt number increased. © 2007 Elsevier Ltd. All rights reserved. Keywords: Microchannel; Magnetic heating/cooling; Volumetric heat generation 1. Introduction Liquid flow and heat transfer in microchannels are critical to the design and process control of various Micro- Electro-Mechanical-Systems (MEMS) and biomedical lab-on-a-chip devices. Experimental and theoretical studies in the literature have shown that a very high rate of heat transfer in microchannels is the key to the high heat flux thermal management technologies being developed. This paper presents a systematic analysis of fluid flow and heat transfer processes during the magnetic heating of the substrate material. Heat is generated in the substrate material when a magnetic field is imposed due to change in orientation of the molecules. As a result, the substrate temperature rises. Similarly, the temperature drops during demagnetization when the field is removed. It is proposed to use liquid flow through microchannels fabricated by precision machining of the substrate material for the thermal management of the substrate material during magnetization and demagnetization and use the recovered energy for useful heating or refrigeration. The purpose of this study is to explore the steady state heat transfer coefficient when the fluid is circulated through the substrate via microchannels. Pfund et al. [1] determined friction factors for high aspect ratio microchannels. Reynolds numbers were between 60 and 3450. Pressure drops were measured within the channel. Transitions to turbulence were observed with flow International Communications in Heat and Mass Transfer 34 (2007) 661 – 672 www.elsevier.com/locate/ichmt ☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: rahman@eng.usf.edu (M.M. Rahman). 0735-1933/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.icheatmasstransfer.2007.02.009