NUCLEATE POOL BOILING HEAT-TRANSFER COEFFICIENTS OF DISTILLED WATER (H2O) AND R-134A OIL MIXTURES FROM RIB-ROUGHENED SURFACES/

Measurements of pool-boiling heat transfer coefficients in distilled w ater and R-134a/oil mixtures with up to 10 percent (by weight) miscibl e EMKARATE RL refrigeration lubricant oil are extensively studied for a smooth tube and four rib-roughened tubes (rib pitch 39.4 mm, rib hei ght 4 mm, rib width 15 mm, number of rib element 8, rib angle 30 deg-9 0 deg). Boiling data of pure refrigerants and oil mixtures, as well as the influences of heat flux level on heat transfer coefficient, are p resented and discussed. A correlation is developed for predicting that heat transfer coefficient for both pure refrigerants and refrigerant- oil mixtures. Moreover, boiling visualizations were made to broaden ou r fundamental understanding of the pool boiling heat transfer mechanis m for rib roughened surfaces with pure refrigerants and refrigerant-oi l mixtures.