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 (sCO(2)) in the vicinity of its critical point for thermal management applications. In the present study, sCO(2) 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 mu m (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 sCO(2) 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 degrees C) 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.