A numerical and experimental study of three-dimensional natural convection in a discretely heated cavity

Theodore J Heindel, Purdue University

Abstract

Numerical and experimental studies, with and without surface augmentation, were performed for a 3 x 3 array of discrete heat sources. This geometry was addressed to quantify heat transfer edge effects in multi-chip electronic packages. Numerical models were developed to simulate two- and three-dimensional nonconjugate and conjugate laminar natural convection. Experimental facilities were designed and constructed to perform heat transfer measurements and flow visualization of natural convection from flush-mounted and finned discrete heat sources in a cavity. The three-dimensional numerical model captured edge effects which could not be predicted by the two-dimensional model and should be employed for accurate heat transfer predictions when $\rm A\sb{htr}\sbsp{\sim}{<}3.0.$ Experimental data, corrected for conjugate heat losses, were in excellent agreement with three-dimensional predictions. The data were also well correlated for each heater row. Two-dimensional conjugate heat transfer models can be used to predict general heat transfer trends from discrete heat sources as well as from the substrate in which they are mounted. If the substrate/fluid thermal conductivity ratio is relatively high ($\rm R\sb{s}\sbsp{\sim}{>}4.7),$ three-dimensional conjugate calculations should be utilized to obtain accurate thermal spreading predictions. Overall, thermal resistances were recorded between $\rm40\ cm\sp{2\circ}C/W\ and\ 110\ cm\sp{2\circ}C/W$ for a 3 x 3 array of flush-mounted heat sources immersed in FC-77. Modeling dense parallel plate fin arrays as a porous medium was shown to be a good first-order approximation, with numerical predictions being in fair agreement with experimental data. Discrete heat sources with attached parallel plate fin arrays increased heat transfer over flush-mounted heat sources by as much as 24 and 15 times when the cavity was oriented vertically and horizontally, respectively. Furthermore, orienting the cavity horizontally produced uniform heat transfer from the discrete heat source array. Thermal resistances on the order of $\rm2\ cm\sp{2\circ}C/W$ can be expected with the dense parallel plate fin arrays used in this study, while using FC-77 as the coolant and maintaining the maximum temperature difference below $70\sp\circ$C.

Degree

Ph.D.

Advisors

Ramadhyani, Purdue University.

Subject Area

Mechanical engineering

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