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 t ubes and with a smooth one. All tubes have the same outer diameter. Da ta are for mass fluxes ranging from about 90 to 400 kg/m(2).s. In boil ing tests, the nominal saturation temperature is 5 degrees C, with inl et quality varying from 0.2- to 0.6 and the quality variation along th e test section ranging from 0.1 to 0.5. In condensation, results are f or saturation temperature equal to 35 degrees C, with inlet and outlet qualities of 0.8 and 0.2, respectively. The new microfin tube shows t he best thermal performances among the microfin tubes tested, especial ly in evaporation. For this case, the enhancement factor comes up to 4 . Experimental results for microfin tubes are compared with prediction s of a correlation scheme recently proposed; these predictions correla te well only with data for the microfin tube with a geometry much simi lar to one accounted by the scheme.