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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Energy Conversion and Management, Volume 44, Issue 11, July 2003, Pages 1787–1803
This paper presents the heat transfer and friction characteristics and performance analysis of convective heat transfer through a rectangular channel with square cross-section pin fins attached over a flat surface. The pin fins were arranged in a staggered manner. Various clearance ratios (C/H) and interfin distance ratios (Sx/D) were used. The performance analysis was made under a constant pumping power constraint. The experimental results showed that the use of square cross-section pin fins may lead to an advantage on the basis of heat transfer enhancement. For higher thermal performance, lower interfin distance ratio and clearance ratio and comparatively lower Reynolds numbers should be preferred for the staggered arrangement. The results of the staggered configurations were also compared with the results of the inline arrangement.
Extended surfaces (fins) are frequently used in heat exchanging devices for the purpose of increasing the heat transfer between a primary surface and the surrounding fluid. Various types of heat exchanger fins, ranging from relatively simple shapes, such as rectangular, cylindrical, annular, tapered or pin fins, to a combination of different geometry, have been used. These fins may protrude from either a rectangular or cylindrical base. One of the commonly used heat exchanger fins is the pin fin. A pin fin is a cylinder or other shaped element attached perpendicular to a wall, with the transfer fluid passing in crossflow over the element. There are various parameters that characterize the pin fins, such as shape, height, diameter, height to diameter ratio etc. In addition, the pin fins may be positioned in arrays that are either staggered or inline with respect to the flow direction. The heat transfer and friction characteristics of pin fin array systems have been the subject of extensive investigation because of its importance in a wide variety of engineering applications, such as compact heat exchangers and the cooling of advanced gas turbine blades and electronic devices. Pin fins having a pin height to diameter ratio, H/D, between 0.5 and 4 are accepted as short pin fins, whereas long pin fins have pin height to diameter ratio, H/D, greater than 4. The large height to diameter ratio is of particular interest in heat exchanger applications in which the attainment of very high heat transfer coefficients is of major concern. Arrays of pin fins with low/intermediate height to diameter ratio (from 0.5 to 4), short pin fins, are commonly used in many industrial applications, especially in the trailing edges of gas turbine blades, in some modern electronic systems and in the aerospace industry . There have been many investigations of the heat transfer and pressure drop of channels with pin fins, which are restricted to pin fins with circular cross-section , , , , , , , , , , ,  and . Sparrow and coworkers  and  were among the first to investigate the heat transfer performance of inline and staggered wall attached arrays of cylindrical fins. Metzger et al.  investigated the heat transfer characteristics of staggered arrays of cylindrical pin fins. Simoneau and Vanfossen  also studied the heat transfer from a staggered array of cylindrical pin fins. Matsumoto et al.  studied the end wall heat transfer in the presence of inline and staggered adiabatic circular pin fins. A review of staggered array pin fin heat transfer for turbine cooling applications was presented by Armstrong and Winstanley . While the studies regarding circular pin fin arrays are abundant, the research on pin fins with other cross-sections is relatively sparse. Grannis and Sparrow  and  investigated the heat transfer and pressure drop characteristics and numerically simulated the fluid flow through an array of diamond shaped pin fins. Tanda  performed an investigation of the heat transfer and pressure drop for a rectangular channel equipped with arrays of diamond shaped elements. Both inline and staggered fin arrays were considered in the thermal performance analysis under constant mass flow rate and constant pumping power constraints. The heat transfer performance of arrays of cubic and diamond shaped fins inside a rectangular channel was reported by Chyu et al. . Al-Jamal and Khashashneh  performed a study on convective heat transfer of staggered pin fin and triangular fin arrays. Goldstein et al.  conducted an investigation to determine the effect of fin shape on the mass transfer and pressure loss of a staggered short pin fin array in a rectangular duct. Şara et al.  investigated the heat transfer and friction characteristics of rectangular channels with inline square pin fins. The literature survey on the investigations of pin fin array systems indicates that these studies have examined the heat transfer and friction characteristics and various parameters, such as interfin spacing in both streamwise direction and spanwise direction, gap clearance ratio, height to diameter ratios etc. on the basis of maximum heat transfer rate per unit base area. It is well known that the pin fin arrays produce higher heat transfer than plain channels without fins. However, the increase in heat transfer is always accompanied by a substantial increase in pressure loss. Therefore, in most applications of pin fins, both the heat transfer and pressure loss characteristics must be considered. Although there are some pin fin investigations in which the performance analysis is made by using a performance evaluation criterion (PEC) , ,  and , in general, in these investigations, the heat transfer and friction characteristics have been obtained and the optimal parameters generally determined on the basis of maximum heat transfer rate or maximum heat transfer per unit base area  and . Therefore, it is necessary to perform a performance analysis by the PEC and to state performance in terms of at least four interrelated characteristics: heat transfer, fluid pumping power, size and shape. On the other hand, the pin fins with various cross-sections have different heat transfer and flow resistance characteristics, and it is by no means clear that circular pin fins are the best for heat transfer, friction and performance. Therefore, it is essential to investigate various pin fins with different cross-sections in order to enhance the heat transfer and decrease the flow resistance. It is the aim of this study to investigate the heat transfer, pressure and performance characteristics for the staggered square pin fins array attached on a flat surface in a rectangular duct and to compare with those for the inline arrangement.
نتیجه گیری انگلیسی
The enhancement of the heat transfer from a flat surface in a rectangular channel flow by the attachment of staggered square cross-sectional pin fins was investigated experimentally. The effects of the flow and geometrical parameters on the heat transfer and friction characteristics were determined, and the constant pumping power criterion was used to evaluate the performance of the staggered pin fin array systems. The conclusions are summarized as: (1) The average Nusselt number increased with decreasing clearance ratio and interfin distance ratio. (2) The friction factor increased with decreasing clearance ratio and interfin distance ratio. (3) Nu∗ increased with decreasing C/H, which means that longer pin fins have better performance. (4) Nu∗ increased with decreasing Sx/D, which means that higher number of pin fins have better performance. (5) At lower Reynolds numbers, the channel with pin fin arrays gives higher performance than those at higher Reynolds numbers. (6) The heat transfer enhancement factors, Nu∗, are higher than unity for all investigated conditions. This means that the use of pin fins leads to an advantage on the basis of heat transfer enhancement.