Heat exchangers having a bypass stream have wide ranging engineering applications such as heat sinks for electronics cooling. Due to their operating conditions, studies on the effect of the bypass region on the aero-thermal performance of heat exchangers have usually focused on the low-speed flow regime. Recently, however, the need for research on the high-speed bypass effect is increasing, especially in connection to aero-engine applications. The surface cooler, which is mounted on the fan casing of an aero-engine, uses a cold bypass stream to dissipate the heat from the oil system or the power generator devices of the engine. In this paper, a fundamental numerical study to evaluate the aero-thermal characteristics of a fin-type heat exchanger having a bypass duct under high-stream operating conditions has been conducted. A simplified bypass duct model has been used to formulate new performance correlations of the pressure drop and heat transfer coefficient by varying the bypass ratio and other important geometric parameters. The tested Mach number of the bypass stream was as high as 0.6. The obtained results are compared with previous low-speed correlations in both qualitative and quantitative terms. The newly summarized correlations could be useful for the preliminary design of heat exchangers for high-speed operating conditions in the early stage of the heat exchanger design. Comparison between the flow-network analysis results and the two-dimensional calculations showed the advantage of using the new correlations.
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.