دانلود رایگان مقاله انگلیسی تحلیل عددی صفحه پره ای متراکم مبدل حرارتی برای کاربرد های هوافضایی - امرالد 2017

1. INTRODUCTION

Depending on the application, various types of augmented heat transfer surfaces such as wavy fins, offset strip fins, louvered fins, plain and perforated fins are used in aerospace applications. The surface geometries of wavy and OSF fins are described by the fin height (h), transverse spacing (s) and thickness (t). Interrupted flow length of the offset strip fin is described by offset strip/fin length (l), and that of the wavy fin, by the pitch of the wave (L). Thermo-hydraulic design of a compact heat exchanger is strongly dependent upon the performance of heat transfer surfaces (in terms of Colburn factor j and Fanning friction factor f vs. Reynolds number Re characteristics). We focus here on offset strip fins, wavy fins, plain and perforated fins. The orientation of inlet and outlet headers plays a major role in performance especially in aerospace applications, where the orientation of headers and nozzles are not straight and uniform due to space limitations. The accurate prediction of the thermal performance of a compact heat exchanger in the design stage is highly desirable for aerospace applications.

4. CONCLUSION

This paper presents both Finite Element Method and Computational Fluid Dynamic Analysis of Compact Heat Exchangers for Aerospace applications. Using FEM the Flow Non-uniformity, Temperature Non-uniformity and Longitudinal Heat Conduction effects are analysed. The combined effects of FN, TN and LHC are also estimated and compared with individual effects. The thermal performance deterioration of cross flow compact heat exchanger due to the combined effects LHC and FN is not always negligible, especially when the fluid capacity rate ratio of both fluids is equal to 1.0 and when the longitudinal heat conduction parameter(λ) is greater than 0.005.

Using CFD, the various types of fins such as Offset Strip fins, Wavy fins, Rectangular fins, Triangular fins, Triangular and Rectangular perforated fins, which are widely used in aerospace industry, are analysed. The expressions provided for the heat transfer coefficient in terms of Colburn j factor and friction factor f allows the computation for all values of Reynolds number, including the laminar and turbulent regions for CHE design ranges. In addition, the data of these correlations are compared with other numerical data by analyzing open literature thoroughly. These correlations are well formed in the laminar and fully turbulent regions, since they can be considered as the standard correlations.

The correlations for the friction factor f and Colburn factor j have found to be good by comparing with other references. The above FEM results and CFD correlations can be used by heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications.