The Effect of CPU Location in Total Immersion of Microelectronics

Authors: A. Almaneea, N. Kapur, J. L. Summers, H. M. Thompson

Abstract:

Meeting the growth in demand for digital services such as social media, telecommunications, and business and cloud services requires large scale data centres, which has led to an increase in their end use energy demand. Generally, over 30% of data centre power is consumed by the necessary cooling overhead. Thus energy can be reduced by improving the cooling efficiency. Air and liquid can both be used as cooling media for the data centre. Traditional data centre cooling systems use air, however liquid is recognised as a promising method that can handle the more densely packed data centres. Liquid cooling can be classified into three methods; rack heat exchanger, on-chip heat exchanger and full immersion of the microelectronics. This study quantifies the improvements of heat transfer specifically for the case of immersed microelectronics by varying the CPU and heat sink location. Immersion of the server is achieved by filling the gap between the microelectronics and a water jacket with a dielectric liquid which convects the heat from the CPU to the water jacket on the opposite side. Heat transfer is governed by two physical mechanisms, which is natural convection for the fixed enclosure filled with dielectric liquid and forced convection for the water that is pumped through the water jacket. The model in this study is validated with published numerical and experimental work and shows good agreement with previous work. The results show that the heat transfer performance and Nusselt number (Nu) is improved by 89% by placing the CPU and heat sink on the bottom of the microelectronics enclosure.

Keywords: CPU location, data centre cooling, heat sink in enclosures, Immersed microelectronics, turbulent natural convection in enclosures.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1100120

References:

[1] Shah, A., et al. Impact of rack-level compaction on the data center cooling ensemble. in Thermal and Thermomechanical Phenomena in Electronic Systems, 2008. ITHERM 2008. 11th Intersociety Conference on. 2008: IEEE.
[2] Anderson, D., F. Sparacio, and R.M. Tomasulo, The IBM System/360 model 91: Machine philosophy and instruction-handling. IBM Journal of Research and Development, 1967. 11(1): p. 8-24.
[3] deVahl Davis, G., Natural convection of air in a square cavity: a bench mark numerical solution. International Journal for Numerical Methods in Fluids, 1983. 3(3): p. 249-264.
[4] Tian, Y. and T. Karayiannis, Low turbulence natural convection in an air filled square cavity: part I: the thermal and fluid flow fields. International Journal of Heat and Mass Transfer, 2000. 43(6): p. 849-866.
[5] MacGregor, R., Free convection through vertical plane layers-moderate and high Prandtl number fluids. Trans. ASME, Journal of Heat Transfer, 1969. 91: p. 391-403.
[6] Phan-Thien, Y.L., Nhan, An optimum spacing problem for three chips mounted on a vertical substrate in an enclosure. Numerical Heat Transfer: Part A: Applications, 2000. 37(6): p. 613-630.
[7] Heindel, T., S. Ramadhyani, and F. Incropera, Conjugate natural convection from an array of protruding heat sources. Numerical Heat Transfer, Part A Applications, 1996. 29(1): p. 1-18.
[8] Keyhani, M., L. Chen, and D. Pitts, The aspect ratio effect on natural convection in an enclosure with protruding heat sources. Journal of Heat Transfer (Transactions of the ASME (American Society of Mechanical Engineers), Series C);(United States), 1991. 113(4).
[9] Wroblewski, D. and Y. Joshi, Liquid immersion cooling of a substrate-mounted protrusion in a three-dimensional enclosure: the effects of geometry and boundary conditions. Journal of heat transfer, 1994. 116(1): p. 112-119.
[10] Nada, S., Natural convection heat transfer in horizontal and vertical closed narrow enclosures with heated rectangular finned base plate. International Journal of Heat and Mass Transfer, 2007. 50(3): p. 667-679.
[11] Çengel, Y.A., R.H. Turner, and J.M. Cimbala, Fundamentals of thermal-fluid sciences 2008. p. 534.
[12] Holman, J., Heat transfer, 9th. 2002, McGraw-Hill. p. 335-337.
[13] Chi, Y.Q., Jonathan Summers, Peter Hopton, Keith Deakin, Alan Real, NikKapur and Harvey Thompson, Case Study of a Data Centre Using Enclosed, Immersed, Direct Liquid-Cooled Server, in Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM). 2014, IEEE.
[14] Zitzmann, T., et al. Simulation of steady-state natural convection using CFD. in Proc. of the 9th International IBPSA Conference Building Simulation 2005. 2005: Montréal: IBPSA.
[15] Rundle, C. and M. Lightstone. Validation of turbulent natural convection in a square cavity for application of CFD modelling to heat transfer and fluid flow in atria geometries. in 2nd Canadian Solar Buildings Conference, Calgary. 2007.
[16] Aounallah, M., et al., Numerical investigation of turbulent natural convection in an inclined square cavity with a hot wavy wall. International Journal of Heat and Mass Transfer, 2007. 50(9): p. 1683-1693.
[17] Wilcox, D.C., Turbulence modeling for CFD. Vol. 2. 1998: DCW industries La Canada, CA.