Microchannel Cooling in Computing Platforms: Performance Needs and Challenges in Implementation

2004 ◽  
Author(s):  
Himanshu Pokharna ◽  
Kuroda Masahiro ◽  
Eric DiStefano ◽  
Rajiv Mongia ◽  
Jim Barry ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Cooling System ◽  
Heat Sinks ◽  
System Level ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Fluid Resistance ◽  
Microchannel Heat Sinks ◽  
Computing Platforms

Remote cooling is the established cooling scheme in notebook computers, and increasingly, other computing sectors like desktops and servers are evaluating this approach as an option for cooling future platforms. While remote cooling facilitates a larger heat exchanger than the space directly over the processor would allow, it introduces an additional thermal resistance, in particular, θp-f (plate to fluid resistance) — the resistance in getting the heat from the cold plate to the fluid. For any remote cooling system, this resistance needs to be carefully evaluated and minimized. Pumped fluid loops incorporating microchannel heat exchangers are a viable option to achieve low plate-to-fluid resistances. In this paper we will identify a reasonable target for θp-f and subsequently describe two similar but fundamentally different thermal systems to accomplish this target performance: single-phase and two-phase pumped loops. Although two phase flows are traditionally thought of as the way to accomplish the highest heat transfer coefficients and thus the lowest resistances, with microchannel heat sinks the contrast is not so acute. We will present results from our experimental work on single- and two-phase heat transfer from microchannel heat sinks and demonstrate a transition where single-phase performance matches that of two-phase operation. This will be followed by the analysis methods used to predict the heat transfer and the pressure drop data. Moreover, we will discuss system level issues and other hurdles that need to be overcome in commercialization of microchannel technology for cooling computer systems.

Modeling and Numerical Simulations of Vapor-Liquid Flow and Heat Transfer Within Microchannel Heat Sinks

2012 ◽  
Author(s):  
Chengyun Xin ◽  
Jianhua Wang ◽  
Jianheng Xie ◽  
Yuee Song
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Solid Wall ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Flowing Fluid ◽  
Liquid Coolant ◽  
Microchannel Heat Sinks

Microchannel heat sinks have demonstrated the ability to dissipate large amounts of heat flux. This ability can be strongly enhanced by phase change of a liquid coolant. This paper numerically simulates the processes of liquid coolant flow, heat absorption and phase change within a microchannel, which is heated at one side by given heat fluxes. The two-phase flow model widely used in the investigations on heat and mass transfer within porous media is firstly introduced into microchannnel heat sinks by this paper. Experiential equations of the heat transfer coefficients in single phase and boiling region within microchannels are employed to calculate the convective heat exchange between solid wall and flowing fluid by an iterative process. The numerical results of pressure and temperature distributions obtained at different conditions are exhibited and analyzed. The results indicated that the trends predicted by this approach agree well with the previous references. Therefore the modeling is validated in some sense. At the same time, two phenomena, countercurrent flow in two-phase region and special pressure variations near the transition point, are exhibited.

Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase Flow ◽  
Annular Channel ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Narrow Annuli ◽  
Narrow Gaps

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.

Bubble Injection to Enhance Heat Transfer in Microchannel Heat Sinks

2009 ◽  
Author(s):  
Amy Rachel Betz ◽  
Daniel Attinger
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Single Phase ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Segmented Flow ◽  
Liquid Cooling ◽  
Microchannel Heat Sinks ◽  
Convective Resistance ◽  
Parallel Microchannels

Liquid cooling is an efficient way to remove heat fluxes with magnitude of 1 to 10,000 W/cm2. One limitation of current single-phase microchannel heat sinks is the relatively low Nusselt number, because of laminar flow. In this work, we experimentally investigate how to enhance the Nusselt number in the laminar regime with the periodic injection of non-condensable bubbles in a water-filled array of microchannels in a segmented flow pattern. We designed a polycarbonate heat sink consisting of an array of parallel microchannels with a low ratio of heat to convective resistance, to facilitate the measurement of the Nusselt Number. Our heat transfer and pressure drop measurements are in good agreement with existing correlations, and show that the Nusselt number of a segmented flow is increased by more than a hundred percent over single-phase flow provided the mass velocity is within a given range.

Cryogenic Single-Phase Heat Transfer in a Microscale Pin Fin Heat Sink

2013 ◽  
Author(s):  
Eric D. Truong ◽  
Erfan Rasouli ◽  
Vinod Narayanan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Sinks ◽  
Variable Cross ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients

A combined experimental and computational fluid dynamics study of single-phase liquid nitrogen flow through a microscale pin-fin heat sink is presented. Such cryogenic heat sinks find use in applications such as high performance computing and spacecraft thermal management. A circular pin fin heat sink in diameter 5 cm and 250 micrometers in depth was studied herein. Unique features of the heat sink included its variable cross sectional area in the flow direction, variable pin diameters, as well as a circumferential distribution of fluid into the pin fin region. The stainless steel heat sink was fabricated using chemical etching and diffusion bonding. Experimental results indicate that the heat transfer coefficients were relatively unchanged around 2600 W/m2-K for flow rates ranging from 2–4 g/s while the pressure drop increased monotonically with the flow rate. None of the existing correlations in literature on cross flow over a tube bank or micro pin fin heat sinks were able to predict the experimental pressure drop and heat transfer characteristics. However, three dimensional simulations performed using ANSYS Fluent showed reasonable (∼7 percent difference) agreement in the average heat transfer coefficients between experiments and CFD simulations.

Microchannel Size Effects on Two-Phase Local Heat Transfer and Pressure Drop in Silicon Microchannel Heat Sinks With a Dielectric Fluid

2007 ◽  
Author(s):  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
The Heat Transfer Coefficient

Two-phase heat transfer in microchannels can support very high heat fluxes for use in high-performance electronics-cooling applications. However, the effects of microchannel cross-sectional dimensions on the heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer in microchannel heat sinks. The effect of channel size on the heat transfer coefficient and pressure drop is studied for mass fluxes ranging from 250 to 1600 kg/m2s. The test sections consist of parallel microchannels with nominal widths of 100, 250, 400, 700, and 1000 μm, all with a depth of 400 μm, cut into 12.7 mm × 12.7 mm silicon substrates. Twenty-five microheaters embedded in the substrate allow local control of the imposed heat flux, while twenty-five temperature microsensors integrated into the back of the substrates enable local measurements of temperature. The dielectric fluid Fluorinert FC-77 is used as the working fluid. The results of this study serve to quantify the effectiveness of microchannel heat transport while simultaneously assessing the pressure drop trade-offs.

Heat Transfer Enhancement in Microchannels Incorporating Slanted Grooves

2008 ◽  
Author(s):  
Poh-Seng Lee ◽  
Chiang-Juay Teo
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fluid Temperature ◽  
Additional Energy ◽  
Pressure Drops ◽  
Microchannel Heat Sinks ◽  
Significant Temperature

The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques. Microchannel heat sinks have the potential to satisfy these requirements. However, significant temperature variations across the chip persist for conventional single-pass parallel flow microchannel heat sinks since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. To accommodate higher heat fluxes, enhanced microchannel designs are needed. The present work presents an idea to enhance the single-phase convective heat transfer in microchannels. The proposed technique is passive, and does not require additional energy to be expended to enhance the heat transfer. The idea incorporates the generation of a spanwise or secondary flow to enhance mixing and hence decrease fluid temperature gradients across the microchannel. Slanted grooves can be created on the microchannel wall to induce the flow to twist and rotate thus introducing an additional component to the otherwise laminar flow in the microchannel. Numerical results are presented to demonstrate the effectiveness of such an enhanced microchannel heat sink. The heat transfer was found to increase by up to 12% without incurring substantial additional pressure drops.

Simulation of Two-Phase Flow and Heat Transfer in Mini- and Micro-Channels for Concentrating Photovoltaics Cooling

2011 ◽  
Author(s):  
Devin Pellicone ◽  
Alfonso Ortega ◽  
Marcelo del Valle ◽  
Steven Schon
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Single Phase ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Micro Scale ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Micro Channels

Advances in concentrating photovoltaics technology have generated a need for more effective thermal management techniques. Research in photovoltaics has shown that there is a more than 50% decrease in PV cell efficiency when operating temperatures approach 60°C. It is estimated that a waste heat load in excess of 500 W/cm2 will need to be dissipated at a solar concentration of 10,000 suns. Mini- and micro-scale heat exchangers provide the means for large heat transfer coefficients with single phase flow due to the inverse proportionality of Nusselt number with respect to the hydraulic diameter. For very high heat flux situations, single phase forced convection in micro-channels may not be sufficient and hence convective flow boiling in small scale heat exchangers has gained wider scrutiny due to the much higher achievable heat transfer coefficients due to latent heat of vaporization and convective boiling. The purpose of this investigation is to explore a practical and accurate modeling approach for simulating multiphase flow and heat transfer in mini- and micro-channel heat exchangers. The work is specifically aimed at providing a modeling tool to assist in the design of a mini/micro-scale stacked heat exchanger to operate in the boiling regime. The flow side energy and momentum equations have been implemented using a one-dimensional homogeneous approach, with local heat transfer coefficients and friction factors supplied by literature correlations. The channel flow solver has been implemented in MATLAB™ and embedded within the COMSOL™ FEM solver which is used to model the solid side conduction problem. The COMSOL environment allows for parameterization of design variables leading to a fully customizable model of a two-phase heat exchanger.

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