In-tube condensation heat transfer of CO2 at low temperatures in a horizontal smooth tube

This paper presents the experimental investigation of CO2 condensation in a horizontal smooth tube at saturation temperatures between 0 and −15 °C with mass fluxes between 50 and 200 kg m−2 s−1 and for various vapour qualities. One tube-in-tube counter flow heat exchanger was designed together with an open-loop CO2 cycle to make up an experimental rig that condenses CO2 at these conditions. The inner test tube, with internal diameter of 6.52 mm, is cooled using Glycol Water flowing in the outer tube. Experimental trends show that the heat transfer coefficient decreases with increasing saturation temperatures. Decrease in heat transfer coefficients is also observed for lower mass fluxes and lower vapour qualities in two-phase. Based on the experimental data collected, a new empirical correlation was developed to improve CO2 heat transfer coefficient prediction. The new correlation agreed well with experimental and data from the literature, with an average deviation of −4.4%.