Experimental study on flow boiling of pure CO2 and CO2-oil mixtures inside horizontal smooth and micro-fin copper tubes.

In this paper, experiments on the flow boiling of pure CO2 and CO2-PAG oil mixtures are carried out using a 2.064 m long double-pipe counter-flow heat exchanger, in which the refrigerant CO2 flows inside the inner tube and the heat source water flows counter-currently in the outer annulus. A smooth copper tube and a micro-fin copper tube are used as the inner tube. The pressure drop and heat transfer characteristics of CO2 are measured in the ranges of the pressure of 3 to 5 MPa, the mass velocity of 360 to 650 kg/m2.s and the oil concentration of 0.04 to 7 wt%.