Dynamic model of a supercritical carbon dioxide heat exchanger

A dynamic model of a heat exchanger for heating supercritical carbon dioxide under turbulent conditions is presented in this paper. The model takes into account the resistance to heat transfer in the gas as well as in the heating fluid (liquid water at ambient pressure) and across the stainless steel wall of the inner tube. Experimental data on convective heat transfer to supercritical carbon dioxide was measured in a vertical double-pipe stainless steel heat exchanger, in the pressure range 10–21 MPa, temperatures ranging from 313 to 343 K, and carbon dioxide mass flowrates from 3 to 12 kg/h. The corresponding Reynolds (Re) and Prandtl (Pr) numbers ranged from 5 × 103 to 3 × 104 and from 1.5 to 3, respectively. Based on the experimental data, a correlation was developed for the heat-transfer coefficient of supercritical carbon dioxide in the inner pipe as a function of Re and Pr. The dynamic model is able to predict the temperature of the outlet gas flow stream under steady-state conditions within ±2.3% of the experimental values, and the dynamic response of the heat exchanger to step disturbances in process variables.