Effect of eccentricity on the thermo-hydraulic performance in an annular microchannel

Abstract

The cost of implementation is the hurdle of the proliferation of microchannels in applications where space is not the prime consideration. A cost-effective way of implementing the microchannel by using the readily-available machining methods has been demonstrated. An annular microscale gap is formed by placing a solid cylinder concentrically into another hollow cylinder, in which both geometries are machined using commonly found Computer Numerical Control (CNC) methods. However, the effect of eccentricity of the annular gap on the thermal and hydrodynamic performance has yet to be studied. Although there are existing studies on the effect of eccentricity on annular channels, the applicability on a micro-sized channel is yet to be concluded. Therefore, this work studies numerically the effect of eccentricity on the heat transfer and hydrodynamic performance in a micro-sized channel of 300 microns in average gap size. The study is conducted from 1 to 7 L/min with a constant heat flux of 53.0 W/cm2, at an interval of 1 L/min. Eccentricity ratio of 0, 0.25, 0.50 and 0.75 are investigated with a constant radius ratio of 0.97 for a microchannel of 30 mm length. The channels with eccentricity ratio of 0.25 and 0.50 show negligible difference in thermal performance as compared to a concentric channel. The channel with an eccentricity ration of 0.75 shows a maximum 19.0 % difference in thermal performance as compared to a concentric one at lower flow rates. The pressure drop across the microchannel increases with eccentricity ratio. However, the maximum difference is below 5 and 10 percent for eccentricity ratio of 0.25 and 0.50 respectively. Microchannel with an eccentricity ration of 0.75 has a lower pressure drop as compared to a concentric channel at lower flow rates and increases with flow rate. In overall, channels with eccentricity ratio 0.25 and 0.50 show insignificant difference as compared to the concentric channel in terms of the thermal-hydraulic performance. This study is essential as a reference for the acceptable machining tolerance for the CNC processes to avoid redundant high cost and long machining hours and yet achieving a reasonably good thermal-hydraulic performance.