本研究針對風扇及散熱模組，以實驗方法觀察風扇之出、入口以及散熱模組內部的流場特徵。標的風扇為離心式風扇與軸流式風扇兩種;散熱模組是風扇與鰭片式散熱器的組合。使用雷射煙霧流動可視化技術，觀察風扇在出、入口及散熱模組鰭片間通道的流場特徵行為，使用質點影像測速儀(PIV)量測風扇出、入口及散熱模組內部鰭片之間的速度場。分析實驗的結果有許多新的發現，離心扇入口處的氣流呈現不均勻的進氣分佈，主要的進氣發生在靠近離心扇喉部區域的進氣口。離心扇的出口氣流可以區分為兩種氣流特徵，靠近離心扇喉部區域的出口氣流明顯地向外偏折，而遠離喉部區域的出口氣流呈現無偏折的順向流動，靠近喉部的風扇出口速度較遠離喉部的風扇出口速度小。在離心扇與散熱片組成的散熱模組中，靠近離心扇喉部的出口氣流通過鰭片間的流道之流場呈現波動的流場行為，然而，遠離離心扇喉部的出口氣流通過鰭片間的流道之的流場沒有產生波動的流場行為。受到離心扇出口速度分佈的影響，散熱模組的出口靠近離心扇喉部的速度明顯地比散遠離離心扇喉部的速度小，因此可能使得散熱模組之熱傳效能呈現不均勻的分佈。藉由分析有靜葉片及無靜葉片之軸流扇的出口流場，軸流扇出口安裝靜葉片能夠縮短軸流扇輪轂後方之迴流區域的尺寸。

The flow characteristics of the fans and thermal modules were experimentally investigated. Centrifugal and axial flow fans were selected in this work. The thermal modules were assemblies of fans and heatsinks. The laser-assisted smoke flow visualization technique was used to understand flow patterns of the inlets and exits of the fans and thermal modules. The flow patterns in-between the neighboring fins were also identified. The particle image velocimetry (PIV) was employed to measure the velocity field of the regions observed by flow visualization method. Some new findings were obtained from analyses of the experimental results. The inlet area of the centrifugal fan presented non-uniform inlet velocity distribution. At the exit of the centrifugal fan, two flow patterns were found. Near the throat of scroll, the exit flows were deflected outward significantly. Far away from the throat, the exit flows went forward without deflection. The exit velocities in the region near the throat were smaller than those in the region away from the throat. The flow field within the gap between neighboring fins of the thermal module presented wavy flow patterns in the region near the throat of scroll. While in the region away from the throat, no wave motions were observed. At the exit of the thermal module, the velocities in region away from the throat are significantly larger than those near the throat. Therefore, the heat dissipation efficiency of the thermal module may be non-uniformly distributed. By analyzing the exit flows of the axial flow fans with and without static blades, it is obtained that the static blades reduced the size of recirculation region appearing downstream the hub of axial fans.

[1] Eck, B., Fans: Design and Operation of Centrifugal, Axial-Flow and Cross-Flow Fans (translated and edited by R.S Azad, D.R. Scott), Pergamon Press, Oxford, 1973.
[2] Osborne, W. C., Fans, 2nd edition, Pergamon Press, Oxford, 1977.
[3] Lakshminarayana, B., Fluid Dynamics and Heat Transfer of Turbomachinery, John Wiley & Sons, New York, 1996.
[4] Bleier, F. P., Fan Handbook: Selection, Application, and Design, McGraw-Hill, New York, 1998.
[5] Chon, Y., Kim, K. I., and Kim, K., “A knowledge-based system for centrifugal fan blade design,”Engineering Application Artificial Intelligence, Vol. 6, No. 5, 1993, pp. 425-435.
[6] Tsai, B. J. and Wu, C. L., “Investigation of a miniature centrifugal fan,” Applied Thermal Engineering, Vol. 27, No. 1, 2007, pp. 229-239.
[7] Tsai, B. J. and Wu C. L., “Performance of a half-height, innovative cooling fan,” Journal of the Chinese Institute of Engineers, Vol. 31, No. 6, 2008, pp. 913-923.
[8] Walsh, P., Egan, V., Grimes, R., and Walsh, E., “Profile scaling of miniature centrifugal fans,” Heat Transfer Engineering, Vol. 30, No. 1-2, 2009, pp. 130-137.
[9] Li, H., “Cooling of a permanent magnet electric motor with a centrifugal impeller,” International Journal of Heat and Mass Transfer, Vol. 53, No. 4, 2010, pp. 797-810.
[10] Zhang, M. J., Pomfret, M. J., and Wong, C. M., “Three-dimensional viscous flow simulation in a backswept centrifugal impeller at the design point,” Computers and Fluids, Vol. 25, No. 5, 1996, pp. 497-507.
[11] Raj, D. and Swim, W. B., “Measurements of the mean flow velocity and velocity fluctuations at the exit of an FC centrifugal fan rotor,” ASME Journal of Engineering for Power, Vol. 103, No. 2, 1981, pp. 393-399.
[12] Younsi, M., Bakir, F., Kouidri, S., and Rey, R., “Influence of impeller geometry on the unsteady flow in a centrifugal fan: numerical and experimental analyses,” International Journal of Rotation Machinery, Vol. 2007, 2007, pp. 1-10.
[13] Younsi, M., Bakir, F., Kouidri, S., and Rey, R., “Numerical and experimental study of unsteady flow in a centrifugal fan, ”Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power And Energy, Vol. 221, No. 7, 2007, pp. 1025-1036.
[14] Mizuno, T. and Kikuchi, K., “Characteristics of axial flow fan with diagonal flow hub,” SAE Transactions, Vol. 99, No. 6, 1990, pp. 49-55.
[15] Shimada, K., Kimura, K., and Watanabe, H., “A study of radiator cooling fan with labyrinth seal,” JSAE Review, Vol. 24, No. 4, 2003, pp. 431-439.
[16] Estevadeordal, J., Gogineni, S., Copenhaver, W., Bloch, G., and Brendel, M., “Flow field in a low-speed axial fan: a DPIV investigation,” Experimental Thermal and Fluid Science, Vol. 23, No. 1-2, 2000, pp. 11-21.
[17] Lee, S. J., Choi, J., and Yoon, J. H., “Phase-averaged velocity field measurements of flow around an isolated axial-fan model,” Journal of Fluids Engineering (ASME Transactions), Vol.125, No. 6, 2003, pp. 1067-1072.
[18] Yoon, J. H. and Lee, S. J., “Stereoscopic PIV measurements of flow behind an isolated low-speed axial-fan,” Experimental Thermal and Fluid Science, Vol. 28, No. 8, 2004, pp. 791-802.
[19] Grimes, R. and Davies, M., “Air flow and heat transfer in fan cooled electronic systems,” Journal of Electronic Packaging, Transactions of the ASME, Vol. 126, No. 1, 2004, pp. 124-134.
[20] Knight, R. W., Goodling, J. S., and Hall, D. J., “Optimal thermal design of forced convection hear sinks-analytical,” Journal of Electronic Packaging, Vol. 113, No. 3, 1991, pp. 313-321.
[21] Knight, R. W., Goodling, J. S., and Gross, B. E., “Optimal thermal design of air cooling forced convection finned heat sinks-experimental verification,” IEEE Transaction on Components, Hybrids, and Manufacturing Technology, Vol. 15, No. 5, 1992, pp. 754-760.
[22] Bejan, A. and Sciubba, E., “The optimal spacing of parallel plates cooled by forced convection,” International Journal of Heat and Mass Transfer, Vol. 35, No. 12, 1992, pp. 3259-3264.
[23] Bejan, A. and Morrga, A. M., “Optimal arrays of pin fins and plate fins in laminar forced convection,” Journal of Heat Transfer, Vol. 115, No. 1, 1993, pp. 75-81.
[24] Jubran, B. A., Hamdan, M. A., and Abdualh, R. M., “Enhanced heat transfer, missing pin, and optimization for cylindrical pin fin arrays,” Journal of Heat Transfer, Vol. 115, No. 3, 1993, pp. 576-583.
[25] Kodo, Y., Marsushima, H., and Komatsu, T., “Optimization of pin-fin heat sink for impingement cooling of electronic packages,” Journal of Electronic Packaging, Vol. 122, 2000, pp. 240-246.
[26] Jonsson, H. and Moshfegh, B., “Modeling of thermal and hydraulic performance of plate fin, strip fin, and pin fin heat sink-influence of flow bypass,” The Institute of Electrical and Electronics Engineers, Vol. 24, No. 2, 2001, pp. 142-149.
[27] Sathyamurthy, P. and Runstadler, P. W., “Numerical and experimental evaluation of planar and staggered heat sinks,” Thermomechanical Phenomena in Electronic Systems Proceedings of The Intersociety Conference, 1996, pp. 132-139.
[28] Sikka, K. K., Torrance, K. E., Scholler, C. U., and Salanova, P. I., “Heat sinks with fluted and wavy plate fins in natural and low-velocity forced convection,” IEEE Transactions on Components and Packaging Technologies, Vol. 25, No. 2, 2002, pp. 283-292.
[29] Seri, L., “Optimum design and selection of heat sink,” IEEE Transactions on Components, Packaging, and Manufacturing Technology Part A, Vol. 18, No. 4, 1995, PP. 812-817.
[30] Iyengar, M. and Bar-Cohen, A., “Design for manufacturability of SISE parallel plate forced convection heat sinks,” Thermomechanical Phenomena in Electronic Systems Proceedings of the Intersociety Conference, Vol. 1, 2000, pp. 141-148.
[31] Thurlow, E., Prather, E., and Mansingh, V., “Fan swirl effects on cooling heat sinks and electronic packages,” Annual IEEE Semiconductor Thermal Measurement and Management Symposium, 2000, pp. 91-98.
[32] Loh, C. K., Nelson, D., and Chou, D. J., “Thermal characterization of fan-heat sink systems in miniature axial fan and micro blower airflow,” Annual IEEE Semiconductor Thermal Measurement and Management Symposium, 2001, pp. 111-116.
[33] Flagan, R. C. and Seinfeld J. H., Fundamentals of Air Pollution Engineering, Prentice Hall, Englewood Cliffs, New Jersey, 1998, pp. 295-307.