Experimental investigation of flow and forced convection heat transfer, in fully filled rectangular duct using porous media

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.An experimental study was performed to investigate the heat transfer characteristics of the convection flow through a rectangular air duct with aspect ratio of 10 (a/b=10) which is filled with metallic porous materials. All four walls of the duct are subjected to a constant and uniform heat flux. The Reynolds number based on the hydraulic diameter has been kept between 500-2000 in order to ensure the laminar flow through the duct. The effect of different parameters such as variable porosity and density of porous layers have been investigated. For different porous layers configuration, heat flux at the walls, wall temperatures and air mass flow rate has been measured and the Nusselt number has been calculated. The results are compared with the clear flow case where no porous material was used. It can be concluded that higher heat transfer rates can be achieved in porous media flow case at the expense of a reasonable pressure drop. Based on the experimental data new empirical correlations for both Nusselt number and friction factor have also been developed for such air duct, which gives a good agreement between predicted values and experimental values of Nusselt number and friction factor.dc201

An exact solution for fully developed temperature distribution in laminar steady forced convection inside circular tubes with uniform wall temperature

In this paper the fully developed temperature distribution in laminar steady forced convection inside circular tubes with uniform wall temperature has been obtained using an exact analytical procedure. Up to now, the procedure for obtaining the temperature profile was a trial and error method. Kakac, Shah, and Aung [1], have reported an unpublished paper that proposed the solution in the form of a power series (cited in [1]). Any of the above processes seems quite sufficient to find the Nusselt number. However, a strictly exact analytical procedure does not exist. The aim of the present paper is to fill this gap in the literature. A numerical solution is also reported here. To achieve this goal a finite difference backward scheme with the truncation error of O(0.001) is utilized. It is observed that the results agree perfectly with those found by analytical solution. The agreement between the results of these two methods - numerical and analytical - left no suspicion that our analytical solution is the correct answer of the problem published for the first time

HT2008-56478 HEAT TRANSFER ENHANCEMENT IN TRIANGULAR FIN

ABSTRACT Fins are widely utilized in many industrial applications for example, fins are used in air cooled finned tube heat exchangers like car radiators, heat rejection devices, refrigeration systems and in condensing central heat exchangers. In this paper, heat transfer inside the fin system composed of a primary rectangular fin with a number of rectangular fins (secondary fins), which are attached on its surface, is modeled and analyzed numerically. The length of the secondary fins decreases linearly from the base of the primary fin to its tip. This modified triangular fin is a kind of improved tree fin networks. The effectiveness of the modified triangular fin is compared with the effectiveness of triangular fin which is calculated analytically. The results show that adding secondary fins increases the effectiveness of triangular fin significantly. Also, it is found that increasing the number of secondary fins in a constant length of primary fin will increase the effectiveness. In addition, by comparing the results it can be concluded that by shortening the length of the primary fin in modified triangular fin, the effectiveness will increase significantly to the contrary of the triangular fin, so smaller heat exchangers can be built by using the modified triangular fin. It is found that in a constant length of primary fin, there is an optimum thickness of secondary fins which maximize the effectiveness of the fin. INTRODUCTION The principle goal in improving the performance of existing thermal systems or in the design of new ones is to enhance heat transfer between hot or cold surfaces and the transport fluid. As such, several methods were proposed in the literature to achieve this task. These methods can be classifie

Evaluation of the heat transfer performance of helical coils of non-circular tubes

10.1631/jzus.A1000296Journal of Zhejiang University: Science A12163-7