Experimental study on the friction coefficient of supercritical carbon dioxide in pipes

This paper has attained friction coefficients of supercritical carbon dioxide (SC-CO2) with various pressures and temperatures in pipes through experiments, of which the temperature range is 30-150 °C, the pressure range is 3.5-40 MPa, the Reynolds number range is 200-2.0 × 106, and relative roughness of pipeline is 0.005, 0.015 and 0.025, respectively. Temperature and pressure affect viscosity and density of SC-CO2, then affect the Reynolds number Re and make friction coefficients of CO2 change abruptly near the critical point, but Re can reflect variations of viscosity and density comprehensively, therefore, function λ = f (Re) can still be used to determine the friction coefficient of SC-CO2. The experimental relationship between the friction coefficient of SC-CO2 and Re corresponds with the functional relation λ = 64/Re in the laminar flow region, for which the absolute average error is 2.39%. In the transition region, compared 5 relations of friction coefficient with the experimental data, it is found that the absolute average error of Churchill's equation is smaller, but when the Reynolds number is larger than 2800, the absolute average error is up to 10.35%. Proposed calculation model of friction coefficient in the transition region is regressed and its absolute average error is 2.81%. In the turbulent region, compared 15 relations of friction coefficient with the experimental data, it is found that Colebrook-White equation as a representative fits in better. The error in the low Reynolds region (3400 < Re < 11,000) is relatively bigger, but the absolute average error is within 10%. A modified calculation model of friction coefficient, with the absolute average error 1.94%, is proposed based on the experiment data.