如何計(jì)算散熱器的散熱功率參考word

1、 如何計(jì)算散熱器的散熱功率Calculation CornerEstimating Parallel Plate-Fin Heat Sink Thermal ResistanceRobert E. Simons, Associate Editor, IBM CorporationAs noted previously in this column, the trend of increasing electronic module power is making it more and more difficult to cool electronic packages with air. A

2、s a result there are an increasing number of applications that require the use of forced convection air-cooled heat sinks to control module temperature. An example of a widely used type of heat sink is the parallel plate configuration shown in Figure 1. Figure 1. Parallel plate fin heat sink configu

3、ration.       In order to select the appropriate heat sink, the thermal designer must first determine the maximum allowable heat sink thermal resistance. To do this it is necessary to know the maximum allowable module case temperature, Tcase, the module power dissipation, Pm

4、od, and the thermal resistance at the module-to-heat sink interface, Rint. The maximum allowable temperature at the heat sink attachment surface, Tbase, is given by推薦精選The maximum allowable heat sink resistance, Rmax, is then given bywhere Tair-in, is the temperature of the cooling air at the inlet

5、to the  heat sink passages. At this point many thermal engineers will start looking at heat sink vendor catalogs (or more likely today start searching vendors on the internet) to find a heat sink that will fit in the allowable space and provide a heat sink thermal resistance, Rhs, less than Rma

6、x at some specified flow rate. In some cases, it may be useful to do a sizing to estimate Rhs for various plate-fin heat sink designs to determine if a feasible design configuration is possible. The remainder of this article will provide the basic equations to do this. The thermal resistance of the

7、heat sink is given bywhere h is the convective heat transfer coefficient, Abase is the exposed base surface area between fins, Nfin is the number of fins, fin is the fin efficiency, and Afin is the surface area per fin taking into account both sides of the fin.       To proc

8、eed further it is necessary to establish the maximum allowable heat sink volume in terms of width, W, height, H, and length in the flow direction, L. It is also necessary to specify a fin thickness, tfin. Using these parameters the gap, b, between the fins may be determined fromThe exposed base surf

9、ace area may then be determined from推薦精選and the heat transfer area per fin fromAt this point it is necessary to specify the air flow rate either in terms of the average velocity, V, between the fins or a volumetric flow rate, G. If a volumetric flow rate is used, the corresponding air velocity betwe

10、en the fins isTo determine the heat transfer coefficient acting upon the fins, an equation developed by Teertstra et al. 1 relating Nusselt number, Nu, to Reynolds number, Re, and Pr number, Pr, may be employed. This equation isThe Prandtl number iswhere is the dynamic viscosity of air, cp the speci

11、fic heat of air at constant pressure, and k is the thermal conductivity of air. The Reynolds number used in (8) is a modified channel Reynolds number defined as where is the density of air. Equation (8) is based upon a composite model spanning the developing to fully developed laminar flow regimes a

12、nd was validated by the authors 1 by comparing with numerical simulations over a broad range of the modified channel Reynolds number (0.26 < Re推薦精選b < 175) and with some experimental data as well. Using the Nusselt number obtained in (8) the heat transfer coefficient is given by Note: Kfi

13、n should be K. 20051017where kfin is the thermal conductivity of the heat sink material. The efficiency of the fins may be calculated usingwhere  m is given byUsing these equations it is possible to estimate heat sink thermal performance in terms of the thermal resistance from the temperature a

14、t the base of the fins to the temperature of the air entering the fin passages. It may be noted that the relationship for Nusselt number (8) includes the effect of the temperature rise in the air as it flows through the fin passages. To obtain the total thermal resistance, Rtot, to the base of the h

15、eat sink it is necessary to add in the thermal conduction resistance across the base of the heat sink. For uniform heat flow into the base Rtot is given byFor purposes of illustration these equations were used to estimate heat sink thermal resistance for a 50 x 50 mm aluminum heat sink. The effect o

16、f increasing the fin height and the number of fins is shown in Figure 2 for a constant air velocity and in Figure 3 for a constant volumetric flow rate. In both cases it may be seen that there are limits to how much heat sink thermal resistance may be reduced by either increasing fin length or addin

17、g more fins. Of course to determine how a heat sink will actually perform in a specific application it is necessary to determine the air velocity or volumetric flow rate that can be delivered through the heat sink. To do this it is necessary to estimate the heat sink pressure drop characteristics an

18、d match them to the fan or blower to be used. This is a topic for consideration in a future article.推薦精選Figure 2. Effect of fin height and number of fins on heat sink thermal resistance at an air velocity of 2.5 m/s (492 fpm). Figure 3. Effect of fin height and number of fins on heat sink thermal re

19、sistance at a volumetric air flow rate of 0.0024 m3/s (5 CFM).     推薦精選References1.      Teertstra, P., Yovanovich, M.M., and Culham, J.R., "Analytical Forced Convection Modeling of Plate Fin Heat Sinks," Proceedings of 15th IEEE Semi-Therm Symp

20、osium, pp. 34-41, 1999.如何計(jì)算散熱器的散熱功率 計(jì)算角 估計(jì)平行板翅式散熱器的熱阻 羅伯特E西蒙斯，副主編，IBM公司 正如以前在本專欄中，增加電力電子模塊的趨勢(shì)正在使越來越多的困難與空氣冷卻電子封裝。結(jié)果有一個(gè)應(yīng)用程序，需要強(qiáng)制對(duì)流風(fēng)冷散熱器來控制模塊的溫度越來越多。的一個(gè)廣泛使用的散熱器類型的例子是平行板的配置如圖1所示。 圖1。平行板翅式散熱器的配置。 為了選擇合適的散熱器，熱設(shè)計(jì)者必須首先確定最大允許散熱器熱阻。要做到這一點(diǎn)，要知道最大允許模塊外殼溫度，TCASE，模塊的功耗，PMOD，并在模塊到散熱片接口，RINT熱阻。最大的散熱片附著在表面，TBASE，允許

21、溫度由下式給出 允許的最大散熱片電阻，R最大，然后給出 在新臺(tái)的，是冷卻空氣入口溫度對(duì)散熱器的通道。在這一點(diǎn)上許多熱工程師將開始在散熱器供應(yīng)商目錄（或更可能今天開始在互聯(lián)網(wǎng)上搜索供應(yīng)商）希望找到一個(gè)散熱器，將適合在允許的空間，并提供一個(gè)散熱器熱阻，RHS，小于R最大在某些特定的流量。在某些情況下，它可能是有用的做大小來估計(jì)各種板翅式散熱器設(shè)計(jì)RHS，以確定是否一個(gè)可行的設(shè)計(jì)配置是可能的。本文的其余部分將提供基本方程來做到這一點(diǎn)。該散熱器的熱阻由下式給出 其中h是對(duì)流換熱系數(shù)，侮是裸露的基地面積鰭片之間，Nfin是數(shù)量的鰭，鰭鰭效率，AFIN是每鰭表面積考慮到雙方的鰭。 要繼續(xù)進(jìn)一步就必須建立在寬度，W，高度H，并在流動(dòng)方向上所允許的最大長度散熱器體積，L.還必須指定一個(gè)翅片厚度，tfin。使用這些參數(shù)的差距，B之間的鰭，可確定從 基面的暴露面積，然后確定可能從 和每翅片換熱面積從 推薦精選此時(shí)有必要指定的平均速度，V之間的鰭或體積流量，G.，條款空氣流速或者如果體積流量使用，相應(yīng)的鰭之間的空氣流速是 要確定傳熱系數(shù)后，鰭，由Teertstra等人開發(fā)一個(gè)公式行事。 1與努塞爾數(shù)，