Experimental thermal–hydraulic evaluation of constructal microfluidic structures under fully constrained conditions

An experimental investigation was conducted to study the relative hydrodynamic and thermal performance of microfluidic, constructal-based, self-similar bifurcated flow channel arrangements with branching angles of 90°. The complexity of the microchannel arrangement was varied from zero to three bifurcation levels while the heat transfer area was held constant for all complexity levels. Constraining the area facilitates comparison of the thermal performance of test sections of different complexities. Each of the channel arrangements considered was incorporated into an independent, modular test section, which had overall dimensions of 10 mm by 10 mm. Using soft lithography and other standard microfabrication techniques, each test section was fabricated and assembled from a silicon heat transfer layer and two polydimethylsiloxane (PDMS) layers which were stacked and bonded to form a monolithic test section. For the testing, an experimental apparatus was designed that allowed for experiments to be run at fixed pressure drops. Experiments were performed for single fixed inlet fluid and heater temperatures and at various pressure drops. The results, which are reported in terms of mass flow rate, heat transfer rate, pumping power, and overall test section coefficient of performance (COP), indicate that complexity has a strong effect on both the pressure drop and heat transfer. When the pumping power required to produce a given heat transfer rate is taken into account, the results suggest that higher complexity arrangements can be beneficial under certain conditions, as theoretically shown in the literature. This conclusion is also confirmed by the trends observed in the COP.