In this study, experiments on the flow boiling of nearly pure CO<sub>2</sub> and CO<sub>2</sub>-PAG oil mixture are carried out using a 2.064 m long double-pipe counter-flow heat exchanger, in which the refrigerant 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. In case of nearly pure CO<sup>2</sup>, the present experimental results of heat transfer coefficient in smooth tube with rough surface agree well with the predicted results using Yu et al. correlation , in which the surface roughness effect is taken into account. It is also confirmed that the values of heat transfer coefficient for both smooth and micro-fin tubes are almost analogous, while the values of pressure drop for micro-fin tube are slightly higher than those of smooth tube. By comparing the experimental results between nearly pure CO<sup>2</sup> and CO<sup>2</sup>-oil mixture, it is confirmed that the oil concentration effects on heat transfer coefficient and pressure drop in micro-fin tube have different characteristics from those of smooth tube.
|Translated title of the contribution||Experimental Study on Flow Boiling of CO_2 and CO_2-PAG Oil Mixture in Smooth and Micro-fin Tubes|
|Number of pages||9|
|Publication status||Published - Dec 31 2005|