Heat transfer and pressure drop during evaporation and condensation of R22 inside 9.52-mm OD microfin tubes of different geometries

Saturated flow boiling and convective condensation experiments for oil-free Refrigerant-22 have been carried out with a microfin tube with a new cross-section profile, as well as with two traditional microfin tubes and with a smooth one. All tubes have the same outer diameter. Data are for mass fluxes ranging from about 90 to 400 kg/m(2).s. In boiling tests, the nominal saturation temperature is 5 degrees C, with inlet quality varying from 0.2- to 0.6 and the quality variation along the test section ranging from 0.1 to 0.5. In condensation, results are for saturation temperature equal to 35 degrees C, with inlet and outlet qualities of 0.8 and 0.2, respectively. The new microfin tube shows the best thermal performances among the microfin tubes tested, especially in evaporation. For this case, the enhancement factor comes up to 4. Experimental results for microfin tubes are compared with predictions of a correlation scheme recently proposed; these predictions correlate well only with data for the microfin tube with a geometry much similar to one accounted by the scheme.