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Channel diameter is one of the most important parameters of a heat exchanger especially for a highly viscous fluid-flow. Narrow channel heat exchangers are believed to have better energy efficiency due to elevated heat transfer characteristics. Heat transfer and Fluid-flow behaviors of Automatic Transmission Fluid (ATF) have been experimentally investigated in a closed loop integrated thermal wind tunnel test facility using wavy finned Minichannel Heat Exchanger (MICHX). The experiment was conducted by varying the ATF Reynolds number from 3 to 30. The flow friction factors in minichannel were evaluated. For a fully developed laminar flow the friction factors were evaluated considering fluid viscosity effects due to temperature variation. The flow correlated with a Poiseuille equation while friction factors were analyzed considering constant property ratio. However, it showed different correlation when considered variable property ratio.

Mini and micro-scale channels have drawn researchers' attention in the past three decades. The use of these tiny channels in a heat exchanger is considered as one of the pioneered works on the narrow channels as minichannels provide high heat transfer rates per unit volume. Motor oil, known as engine oil, is one of the vital fluids in automotive applications. Its cooling process is confronted by its thermo-physical properties, especially viscosity, which makes this process difficult. In current investigations, experimental endeavors have been performed using a closed loop thermal wind tunnel to verify the aptness of cooling the motor oil through a cross-flow minichannel heat exchanger. The prototype heat exchanger consists of 3 circuits; each circuit has five slabs which are connected to each other by four serpentines. There are 68 channels of 1 mm circular diameter drilled through each slab. The minichannel heat exchanger comprises of wavy fins arranged parallel to the flow of air.

Narrow-channel Heat Exchangers have received diversified research and application interests due to the miniaturized geometry, elevated heat transfer characteristics, and better energy efficiency. Automatic Transmission Fluid (ATF) cooling is one of the most important challenges in recent automotive industries due to the quick response to thermo-physical properties with temperature variations. Although a wide range of investigation on characterization of heat transfer and fluid-flow in Minichannel Heat Exchanger (MICHX) for various fluids is available, literatures examining ATF heat transfer and Fluidflow behaviors in the MICHX are scarce. In the current study, attempts have been made to justify the suitability of MICHX application in cooling of ATF. Experimental investigations have been conducted in a well-equipped closed loop integrated thermal wind tunnel test facility using wavy finned-MCHX as a test specimen.