Pin fins

For extended surfaces, which include fins mounted perpendicularly to the tubes or spiral-wound fins, pin fins, plate fins, and so on, friction data for the specific surface involved should be used. For details, see Kays and London (Compact Heat Exchangers, 2d ed., McGraw-HiU, New York, 1964). If specific data are unavailable, the correlation by Gunter and Shaw (Trans. ASME, 67, 643-660 [1945]) may be used as an approximation. 

For extended surfaces, which include fins mounted perpendicularly to the tubes or spiral-wound fins, pin fins, plate fins, and so on, friction data for the specific surface involved should be used. For... 

At this point we should remark that the installation of fins on a heat-transfer surface will not necessarily increase the heat-transfer rate. If the value of h, the convection coefficient, is large, as it is with high-velocity fluids or boiling liquids, the fin may produce a reduction in heat transfer because the conduction resistance then represents a larger impediment to the heat flow than the convection resistance. To illustrate the point, consider a stainless-steel pin fin which has k = 16 W/m °C, L = 10 cm, d = I cm and which is exposed to... 

The ralio of the perimeter to the cross-sectional area of the fm plA should be as high as possible. This criterion is satisfied by thin plate fins and slender pin fins. 

C Two pin fins are identical, except that tbe diameter of one of them is twice the diameter of the other. For which fin is the (a) fin effectiveness and (b) fin efficiency higher Explain. 

A hot surface at 100°C is to be cooled by attaching 3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m °C) to it, with a center-lo-cenler distance of 0.6 cm. The temperature of the surrounding medium is 30°C, and the heat transfer coefficient on the surfaces is 35 V7m °C. Determine the rate of heat tran.sfer from the surface for a 1-m X l-m section of the plate. Also determine the overall efiecliveuess of the fins. 

Aluminum square pin fins k = 237 W/ni C) of 3-cm-long, 2 mm x 2 mm cross-section with a total number of 150 are attached to an 8-cm-long, 6-cm-wide surface, the fin efficiency is 65 percent, the overall fin effectiveness for the surface is... 

Consider steady one-dimensional heat conduction in a pin fin of constant diajneter D with constant thermal conductivity. The fm is losing heal by conveclion to the ambient air at T with a heat transfer coefficient of A. The nodal network of the fm consists of nodes 0 (at Ihe base), 1 (in the middle), and 2 (at the fin tip) with a uniform nodal spacing of Ax. Using the energy balance approach, obtain the finite difference formulation of (his problem to determine T, and T2 for Ihe case of specified temperature at the fin base and negligible heat transfer at the fin tip. All temperatures are in C. 

The unsteady forward-difference heal conduction for a coiistaiil area. A, pin fin willi perimeter, p, exposed to air wliose temperature is Tq witli a convection heat transfer coefficient of It is... 

In this section we limited our consideration to tube banks witli base surfaces (no fins). Tube banks with finned surfaces are also commonly used in practice, especially when the fluid is a gas, and heat transfer and pressure drop correlations can be found in the literature for tube banks with pin fins, plate fins, strip fins, etc. 

F. M. Sparrow and S. B, Vemuri. Natural Conveclion/Radiation Heat Transfer from Highly Populated Pin Fin Arrays. Journal of Heat Transfer 107 (1985), pp. 190-197. 

The orifice plate, 0.5 mm thick, had 24 holes (140 pm in diameter), distributed on a square array pattern with 2 mm spacing. All the tests were conducted keeping the jet velocity approximately constant at 4.5 m/s. Aluminum pin fins, 20 mm long and 3.175 mm in diameter, were installed on the outside of the container in a 45 staggered pattern with both pitches equal to 10.16 mm. The fin tips are inserted into holes drilled into four aluminum plates, which are welded at the corners and form an external shroud. A small DC fan is mounted at the bottom that pushes ambient air over the fins. 

Rainey, K.N. and You, S.M., 2000, "Pool Boiling Heat Transfer from Plain and Mieroporous, Square Pin Finned Surfaces in Saturated FC-72," ASME Journal of Heat Transfer, Vol. 122, pp. 509-516. 

Honda, H., Takamastu, and Wei, J.J., 2002, Enhanced Boiling of FC-72 on Silieon Chips with Micro-Pin-Fins and Submicron-Scale Roughness , J. Heat Transfer, Vol. 124, pp.383-390... 

Circular pin fins have been tested by Chandran and Watson [147], Their average coefficients (total area basis) were as much as 200 percent above the smooth-tube values. Square pins have been proposed by Webb and Gee [148] a 60 percent reduction of fin material as compared to integral-fin tubing is predicted using a gravity drainage model. Notaro [149] described a three-dimensional surface whereby small metal particles are bonded randomly to the surface. The upper portions of the particles promote effective thin-film condensation, and the condensate is drained along the uncoated portion of the tube. 

Only up to 10% of heat can be removed with the cathode airflow since the water balance must be maintained. To remove the waste heat from the system additional heat sinks are needed. It was established that heat can be transferred very efficiently at the stack sides. Commercially available heat sinks were mounted at the sides using electrically isolating thermal interface materials. To add as little extra weight and volume as possible to the system, high performance pin fin coolers were used. The heat sinks are made of pure aluminum with a thermal conductivity of above 220 W m" by means of impact extrusion. 

Table 8-4. Maximum stack temperature with natural confection pin fin coolers at left and ride sides of the stack...

Figure 8-14. Investigated micro fuel cells and pin fin heat sinks...

Table 8-5. Numerical results of forced air pin fin cooling according to Figure 8-15...

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