Experimental investigation of supercritical carbon dioxide in horizontal micro pin arrays with non-uniform heat flux boundary conditions

This study is part of the preliminary experimental investigations designed to assess the feasibility of using supercritical carbon dioxide (sCO₂) in the vicinity of its critical point for thermal management applications. In the present study, sCO₂ was used as a working fluid in a diffusion bonded 316/316L stainless steel test section having staggered micro pin fin array flow passages of hydraulic diameter 679 µm (0.679 mm). The test section was subjected to a single wall non-uniform heat flux boundary condition and was operated in a horizontal orientation. The primary objective was to characterize the heat transfer performance of sCO₂ as it flows through the staggered pin fin array for experimental conditions that span its critical and pseudo-critical point. Data analysis methods employing 2-D and 3-D heat transfer models of the test section were used to calculate the average heat transfer coefficients for a given set of experimental conditions. Experiments were conducted by varying the inlet temperature (18 = T_in = 50 ^oC) and for fixed mass flux (300 kg m^-2 s^-1), heat flux (40 W cm^-2), and reduced pressure (1.1). Experimental data were also compared against the predictions of a correlation proposed for single phase flows in microchannel staggered diamond pin arrays. The correlation predicted the data within 4.3 % when the ratio, T_Bulk/T_PC exceeded 1. It was also found that the enhancement in the heat transfer, a result of employing staggered pin array flow geometry instead of microchannels, carries a commensurate penalty in pressure drop.