Author(s)

Lian-Tuu Yeh ¹

Affiliation(s)

¹ Ph D & PE, ASME Fellow, Dallas, Texas

Corresponding Author

Lian-Tuu Yeh

ABSTRACT

It would save a lot of time and efforts if individual heat sinks are thermally optimized prior to using the CFD tools for system analysis and design. The practical example of such process which employs an existing correlation for optimization of finned heat sinks is presented. Several CFD simulations are first performed to compare with the results from the correlations.  The good agreement of the U-channel heat transfer coefficient between the correlation and CFD results further validates the accuracy of the correlation.
The main focus of the present work is to perform a detailed CFD analysis on the heat sink with the fin optimal spacing of 0.439”. The flow field ultimately determines the heat transfer from the heat sink. Therefore, an effort is made to provide the insight view of the detailed flow fields which has never been done before. The velocity is relatively uniform when the air first enters the finned heat sink from the bottom side (low end). However, due to the entrant flow entering spacing between the fin tips at the face of the heat sink, the velocity of the air flow increases along the length of the heat sink when the air flows upwards. The CFD results indicate that the heat loss per zone decreases along the heat sink length (height). The total natural convection heat loss of this heat sink is 96.61 watts. The heat transfer coefficient of the entire heat sink is 0.7 Btu/hr-ft2 while the heat transfer coefficient from the U-channels alone is 0.61 Btu/hr-ft2.
The results indicate that system with the cover in contact with fins perform better thermally than that of the case without the cover. It is also found that there is no effect of the cover/shroud on the heat loss or entrant flow rate as long as the distance between the cover and the heat sink fin tips is greater than 4.36” with the fin height of 2.0”. Based on the limited data in this work, one may conclude that there is no effect of the cover on the heat transfer of a finned heat sink if the distance between the heat sink and the cover is greater than 2.5 times of the fin height.

KEYWORDS

Thermal Optimizations, CFD Analysis, Finned Heat Sinks, Natural Convection

CITE THIS PAPER

[1] Starner, K.E., and McManus, H. N, “An Experimental Investigation of Free Convection Heat Transfer from Rectangular Fin Arrays”, J Heat Transfer 85, 1963
[2] Welling, J.R. and Wooldridge, C. R., “Free Convection Heat Transfer Coefficients from Rectangular Vertical Fins”, J Heat Transfer 87, 1965
[3] Izume, K, and Nakamura, H, “Heat Transfer by Convection on Heated surface with Parallel Fins”, Jap. Soc. Mech. Eng., 34, 1969
[4] Van De Pol, D. W., and Tierney, J.K., “Free Convection Nusselt Number for Vertical U-Shaped Channels”, Journal of Heat Transfer, 95, 1973
[5] Yeh, L.T., “Natural Convection from Finned Heat Sinks with/without Cover/Shroud”, 19th International Symposium on Transport Phenomena, Reykjavik, Iceland, August 17th – 21st, 2008
[6] Yeh, L.T., and Chu, R. C., Thermal Management of Microelectronic Equipment”, 2nd Edition, ASME Press, 2016

REFERENCES

[1] Starner, K.E., and McManus, H. N, “An Experimental Investigation of Free Convection Heat Transfer from Rectangular Fin Arrays”, J Heat Transfer 85, 1963
[2] Welling, J.R. and Wooldridge, C. R., “Free Convection Heat Transfer Coefficients from Rectangular Vertical Fins”, J Heat Transfer 87, 1965
[3] Izume, K, and Nakamura, H, “Heat Transfer by Convection on Heated surface with Parallel Fins”, Jap. Soc. Mech. Eng., 34, 1969
[4] Van De Pol, D. W., and Tierney, J.K., “Free Convection Nusselt Number for Vertical U-Shaped Channels”, Journal of Heat Transfer, 95, 1973
[5] Yeh, L.T., “Natural Convection from Finned Heat Sinks with/without Cover/Shroud”, 19th International Symposium on Transport Phenomena, Reykjavik, Iceland, August 17th – 21st, 2008
[6] Yeh, L.T., and Chu, R. C., Thermal Management of Microelectronic Equipment”, 2nd Edition, ASME Press, 2016

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