Numerical Investigation of Forced Convective Heat Transfer and Performance Evaluation Criterion of Al2O3Water Nanofluid Flow inside an Axisymmetric Microchannel Al2O3water nanofluid conjugate heat transfer inside a microchannel is studied numerically. The fluid flow is laminar and a constant heat flux is applied to the axisymmetric microchannelxe2x80x99s outer wall, and the two ends of the microchannelxe2x80x99s wall are considered adiabatic. The problem is inherently threedimensional, however, in order to reduce the computational cost of the solution, it is rational to consider only a half portion of the axisymmetric microchannel and the domain is revolved through its axis. Hence. the problem is reduced to a twodimensional domain, leading to less computational grid. At the centerline (r  0), as the flow is axisymmetric, there is no radial gradient (xe2x88x82uxe2x88x82r  0, v  0, xe2x88x82Txe2x88x82r  0). The effects of four Reynolds numbers of 500, 1000, 1500, and 2000; particle volume fractions of 0% (pure water), 2%, 4%, and 6%; and nanoparticles diameters in the range of 10 nm, 30 nm, 50 nm, and 70 nm on forced convective heat transfer as well as performance evaluation criterion are studied. The parameter of performance evaluation criterion provides valuable information related to heat transfer augmentation together with pressure losses and pumping power needed in a system. One goal of the study is to address the expense of increased pressure loss for the increment of the heat transfer coefficient. Furthermore, it is shown that, despite the macroscale problem, in microchannels, the viscous dissipation effect cannot be ignored and is like an energy source in the fluid, affecting temperature distribution as well as the heat transfer coefficient. In fact, it is explained that, in the microscale, an increase in inlet velocity leads to more viscous dissipation rates and, as the friction between the wall and fluid is considerable, the temperature of the wall grows more intensely compared with the bulk temperature of the fluid. Consequently, in microchannels, the thermal behavior of the fluid would be totally different from that of the macroscale.

Characterization of Liquid Cooled Cold Plates for a Multi Chip Module (MCM) and their Impact on Data Center Chiller Operation Miniaturization of microelectronic components comes at a price of high heat flux density. By adopting liquid cooling, the rising demand of high heat flux devices can be met while the reliability of the microelectronic devices can also be improved to a greater extent. Liquid cooled cold plates are largely replacing air based heat sinks for electronics in data center applications, thanks to its large heat carrying capacity. A bench level study was carried out to characterize the thermohydraulic performance of microchannel cold plates which uses warm DeIonized (DI) water for cooling Multi Chip Modules (MCM). A laboratory built mock package housing mock chips and a heat spreader was employed while assessing the thermal performance of three different cold plate designs at varying coolant flow rate and temperature. The case temperature measured at the heat spreader for varying flow rates and input power were essential in identifying the convective resistance corresponding to the cold plates. The flow performance was evaluated by the measuring the pressure drop across cold plate module at varying flow rates. Cold plate with the enhanced microchannel design yielded better results compared to a traditional parallel microchannel design. The experimental results were validated using a numerical model which is further optimized for improved geometric designs. Finally, an estimation of chiller operating cost was obtained for a 100% air cooled facility and compared their performance to that of a 60% warm water cooled facility.