Experimental Investigation of Heat Transfer Characteristics of Pseudocritical Carbon Dioxide in a Circular Horizontal Tube

Forced convection heat transfer of supercritical carbon dioxide in circular horizontal tube, d = 8.7 mm, at relatively high Reynolds number (2×104 < Re < 105) is investigated. Experiments are carried out at two mass flow rates of 0.011 and 0.014 kg/s, for fluid inlet temperatures from 20 to 70°C, system pressures from 75 to 90 bar and constant heat flux of 20 kW/m2. Averaged heat transfer coefficients at several locations are obtained to investigate the influence of the fluid bulk temperature and pressure, respectively, on the forced convection heat transfer in the tube. The, the experimental results are then compared with a widely used empirical correlation. The results indicate that the effect of buoyancy on the heat transfer coefficient cannot be ignored in the near-critical and pseudocritical regions of fluid in this flow geometry. This dependency is believed to be due to the extreme dependence of fluid properties to temperature and pressure in this region.© 2012 ASME