Measurement of Entropy Generation in Microscale Thermal-Fluid Systems

A new nonintrusive and whole field method for the measurement of entropy generation in microscale thermal-fluid devices is presented. The rate of entropy generation is a measure of the thermodynamic losses or irreversibilities associated with viscous effects and heat transfer in thermal-fluid systems. This method provides the entropy generation distribution in the device, thus enabling the designers to find and modify the areas producing high energy losses characterized by large entropy production rates. The entropy generation map is obtained by postprocessing the velocity and temperature distribution data, measured by micro particle image velocimetry and laser induced fluorescence methods, respectively. The velocity and temperature measurements lead to the frictional and thermal terms of entropy generation. One main application of this method is optimizing the efficiency of microchannel heatsinks, used in cooling of electronic devices. The minimum amount of entropy generation determines the optimum design parameters of heatsinks, leading to highest heat removal rates and at the same time, the lowest pressure drop across the heatsink. To show the capability of this technique, the entropy generation field in the transition region between a $100μm$ wide and a $200μm$ wide rectangular microchannel is measured. This method is used to measure thermal and frictional entropy generation rates in three different flow area transition geometries. The results can be used to determine which geometry has the highest thermal and hydraulic efficiencies.