Pool Boiling Heat Transfer of R 1 34a On Horizontal Tube

An experimental data base has been established for pool boiling of pure R12 and R134a from single tubes drawing plain and enhanced surfaces. Based on these measurements the following conclusions may be made.1- All enhanced tubes perform better than plain one at all conditions, exhibiting higher heat transfer coefficients. The enhancement ratio ranges from (1.1 to 2.8), for radially finned tube (RF), and (3 to 4.4) for longitudinally finned tube (L.F). Meanwhile it becomes more significant for the screen matrix tube and reaches to about5 times. This finding is of great use for flooded type evaporators. 2- The trend of enhancement can be explained from the considerationof various mechanisms of bubble formation and bubble dynamics~4j,i ... as well as nucleation sites density.3- For all tested tubes at a given saturation temperature, the pool boiling heat transfer coefficients of R 134a were higher than those for R12 as a result of improved thermo-physical properties of R134a. This enhancement decreases, when the screen matrix is tested due to the dominant effect of surface condition over physical properties.4- A correlation for plain and enhanced surfaces of the present boiling data were developed. This correlation satisfactorily expresses the influences of the operating conditions on the boiling coefficient. The correlation can be used to predict the pool boiling heat transfer coefficient with a reasonable accuracy.