Heat Transfer Coefficient and Pressure Drop Gas Cooling Measurements for CO2/Oil Mixture in a Micro Channel Tube

An experimental study was conducted to measure the heat transfer characteristics and pressure drop of supercritical Carbon Dioxide (CO2) in gas cooling conditions while flowing through a horizontal micro channel. Five experiments were conducted at operating conditions that included an inlet temperature of 70°, inlet pressures of 8 to 10 MPa, a mass flux of 400 kg/m2s, heat fluxes of 10 and 15 kW/m2, and oil concentration ratios of 6.58 to 10.72 wt.% with ND-8, polyalkylene glycol (PAG) oil. This data revealed trends that CO2 flowing through a micro channel has a reduced heat transfer coefficient and an increased pressure drop with an OCR over 6 wt.% in comparison to the predicted values. The measured heat transfer coefficient for the CO2 was 70% smaller than the predicted value using the Gnielinski correlation. The measured pressure drop for the CO2 was 150% larger than the predicted value using the Darcy-Weisbach correlation