SINOPSIS

The present paper reports results from an experimental investigation involving the Convective Boiling of refrigerant R-134a in smooth brass tubes of internal diameters varying from 6.2 mm to 17.4 mm. An electrically heated test section 1.5 m long has been used in the investigation which covered both adiabatic and heating tests. Tests have been carried out under the following operational conditions: saturation temperature: 5°C; specific heat flux: 5 and 10 kW/m^;2 mass velocity: from 25 kg/s.m^;2 to 500 kg/s.m^;2; quality: from 5% to 90%. Flow patterns have been mapped out from pictures taken through a sight glass at the test section exit. Three flow regimes seem to be dominant under convective boiling conditions: intermittent, stratified and annular. The effect of the operational conditions on the flow regime has been investigated along with that of the tube diameter. Thus, whereas intermittent flow seems to be associated to low quality and high mass flow rates, annular flow occurs under high qualities and mass flow rates. It has been found out that the diameter has a significant effect over the flow regime, affecting specially the stratified and annular regimes. Maps from the literature are confronted with results from the reported visual observations, and a critical analysis is made of the observed differences and similarities.