Optimal microscale water cooled heat sinks for targeted alleviation of hotspot in microprocessors

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Hotspots in microprocessors arise due to non-uniform utilization of the underlying integrated circuits during chip operation. Conventional liquid cooling using microchannels leads to undercooling of the hotspot areas and overcooling of the background area of the chip resulting in excessive temperature gradients across the chip. These in turn adversely affect the chip performance and reliability. This problem becomes even more acute in multi-core processors where most of the processing power is concentrated in specific regions of the chip called as cores. We present a 1-dimensional model for quick design of a microchannel heat sink for targeted, single-phase liquid cooling of hotspots in microprocessors. The method utilizes simplifying assumptions and analytical equations to arrive at the first estimate of a microchannel heat sink design that distributes the cooling capacity of the heat sink by adapting the coolant flow and microchannel size distributions to the microprocessor power map. This distributed cooling in turn minimizes the chip temperature gradient. The method is formulated to generate a heat sink design for an arbitrary chip power map and hence can be readily utilized for different chip architectures. It involves optimization of microchannel widths for various zones of the chip power map under the operational constraints of maximum pressure drop limit for the heat sink. Additionally, it ensures that the coolant flows uninterrupted through its entire travel length consisting of microchannels of varying widths. The resulting first design estimate significantly reduces the computational effort involved in any subsequent CFD analysis required to fine tune the design for more complex flow situations arising, for example, in manifold microchannel heat sinks

Flow characteristics and heat transfer performance in a Y-Fractal mini/microchannel heat sink

This article presents a combined experimental and computational study to investigate the flow and heat transfer in a Y-fractal microchannel. Experimental apparatus was newly built to investigate the effect of three different control factors, i.e., fluid flow rate, inlet temperature and heat flux, on the heat transfer characteristics of the microchannel. A standard k-Ɛ turbulence computational fluid dynamics (CFD) model was developed, validated and further employed to simulate the flow and heat transfer microchannel. A comparison between simulated results and the obtained experimental data was presented and discussed. Results showed that good agreement was achieved between the current simulated results and experimental data. Furthermore, an improved new design was suggested to further increase the heat transfer performance and create uniformity of temperature distribution.Peer reviewe

Liquid cooling of non-uniform heat flux of chip circuit by submicrochannels

Sumbmicrochannels have been placed on the hotspots in a non-uniform heat generated chip circuit to increase the liquid/solid interaction area and then to enhance the heat dissipation. Main microchannels width is 185µm, which is twice the width of the submicrochannels and also includes the wall thickness of 35µm, and wall height is 500µm. The chip dimension is 10mm×10mm and the hotspot is 4mm×10m. Different positions of the hotspot have been investigated e.g. upstream, middle and downstream. Uniform heat flux is 100W/cm2 while for the hot spot is 150 W/cm2. Single channel simulation reveals that the downstream hotspot gives a lower temperature of the chip circuit surface; however the upstream hotspot has more uniform temperature distribution. A special design of manifold was adopted to ensure an equal mass distribution through the microchannels

Numerical investigation of aspect ratio effect on thermal parameters in laminar nanofluid flow in microchannel heat sink

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In this paper, laminar nanofluid flow of ethylene glycol-based of 4% volume fraction CuO(II) in a silicon rectangular microchannel heat sink with constant hydraulic diameter and different aspect ratios, with a constant heat flux, has been treated numerically. The effect of changing aspect ratios on the pressure loss and thermal parameters of the microchannel, such as Nusselt number(Nu), heat transfer coefficient(h) and non-dimensional temperature in fluid phase and solid(wall) phase have been investigated, using the finite volume method. In addition, the maximum and minimum values of thermal parameters and pressure loss have been calculated and the optimum aspect ratio for the performance of such systems has been evaluated

Simulation of copper-water nanofluid in a microchannel in slip flow regime using the lattice Boltzmann method with heat flux boundary condition

Laminar forced convection heat transfer of water–Cu nanofluids in a microchannel is studied using the double population Thermal Lattice Boltzmann method (TLBM). The entering flow is at a lower temperature compared to the microchannel walls. The middle section of the microchannel is heated with a constant and uniform heat flux, simulated by means of the counter slip thermal energy boundary condition. Simulations are performed for nanoparticle volume fractions equal to 0.00%, 0.02% and 0.04% and slip coefficient equal to 0.001, 0.01 and 0.1. Reynolds number is equal to 1, 10 and 50.The model predictions are found to be in good agreement with earlier studies. Streamlines, isotherms, longitudinal variations of Nusselt number and slip velocity as well as velocity and temperature profiles for different cross sections are presented. The results indicate that LBM can be used to simulate forced convection for the nanofluid micro flows. They show that the microchannel performs better heat transfers at higher values of the Reynolds number. For all values of the Reynolds considered in this study, the average Nusselt number increases slightly as the solid volume fraction increases and the slip coefficient increases. The rate of this increase is more significant at higher values of the Reynolds number