Evaporation de nouveaux réfrigérants sur des tubes à surface améliorée.

The substitution of old refrigerants in refrigeration systems, heat pumps and organic Rankine cycles for heat recovery, request a good knowledge of heat transfer properties of substitute fluids. The test measurmements in LENI test facility (concentric tubes with water flowing in a counter-current flow) with new refrigerants like HFC134a, HCFC 123, R-404A, R-402A, have established a new data band with new refrigerants, a comparison with old refrigerants like CFC11, CFC12 CFC/HCFC502 and with existent correlations. Correlations were programmed to calculate and compare heat transfer coefficient during the tests. To develop a new correlation based on flow regimes, a high speed Sony video tape camera is used to observe and identify flow patterns. Important images are captured, digitalized, stored for later analysis and sended to a color plotter. Several flow pattern maps were programmed and compared to flow regimes observed on the test rig. Local flow boiling heat transfer coefficients were measured for HFC 134a and HCFC 123 evaporating inside a microfin tube test data was investigated. The presence of oil in the evaporator have an effect on heat transfer coefficient. Local flow boiling heat transfer coefficients were measured for refrigerant HFC 134a-oil ester (Mobil EAL Arctic 68). A new thermodynamic approach for modeling mixtures of refrigerants and lubricating oils is developed. A very high accuracy, staight vibrating tube type of density flowmeter is used to measure oil concentrations of flowing HFC134a-oil mixtures