Abstract
The ability to use supercritical fluids as a heat transfer medium has benefits near the critical point as the specific heat and thermal conductivity approach infinity. However, because of these large thermodynamic property variations estimates for the heat transfer coefficients and wall temperatures can be difficult. With large changes in thermodynamic properties, threedimensional simulations have been used for heat transfer predictions, which can be time-consuming and computationally expensive. To reduce computational expenses, a comparison is made between 2D-axisymmetric and 3D horizontal round tubes using STAR CCM+ 2206. 2D and 3D cases are investigated at various inlet temperatures, mass fluxes, heat-flux to mass-flux ratios, pipe diameters, and pressures to investigate the impact on axisymmetric simulation approximations. A comparison between 3D and 2D-axisymmetric simulations for the circumferentially averaged heat transfer coefficients, Richardson number, and expected pressure drop is made. Across all cases, the maximum percent difference in heat transfer coefficient was 9.4% for an inlet temperature of 295 K, mass flux of 400 kg · m−2 · s−1, operating pressure of 7.5 MPa, applied heat flux of 32 kW · m−2, through a 6 mm pipe. At an inlet temperature of 295 K, a mass flux of 200 kg · m−2 · s−1, an operating pressure of 8 MPa and an applied heat flux of 12 kW · m−2 through a 2 mm pipe, the maximum percent difference in Richardson number was 40.87%. With an inlet temperature of 307 K, mass flux of 600 kg · m−2 · s−1, an operating pressure of 8 MPa, and applied heat flux of 36 kW · m−2, through a 12 mm pipe, the maximum percent difference in pressure drop was 16.87%. The utilization of 2D-axisymmetric domains for supercritical fluids can reduce computational expenses while producing similar results to their 3D counterparts within 40% depending on parameter.
