BOILING HEAT-TRANSFER IN A HORIZONTAL SMALL-DIAMETER TUBE

Results of a study on boiling heat transfer of refrigerant R-113 in a small-diameter (2.92 mm) tube are reported. Local heat transfer coeffi cients are measured for a range of heat flux (8.8-90.75 kW/m2), mass f lux (50-300 kg/m2s), and equilibrium mass quality (0-0.9). The measure d coefficients are used to evaluate 10 different heat transfer correla tions, some of which have been developed specifically for refrigerants . High heat fluxes and low mass fluxes are inherent in small channels, and this combination results in high boiling numbers. In addition, ba sed on a flow pattern map developed from adiabatic experiments with ai r-water mixtures, it has been shown that small-diameter channels produ ce a slug flow pattern over a large range of parameters when compared with larger-diameter channels. The effects of high boiling number and slug flow pattern lead to domination by a nucleation mechanism. As a r esult, the two-phase correlations that predicted this dominance also p redicted the data the best when they properly modeled the physical par ameters. The correlation of Lazarek and Black (1982) predicted the dat a very well. It is also shown that a simple form, suggested by Stephan and Abdelsalam (1980) for nucleate pool boiling, correlates the data equally well; both correlations are within a mean deviation of less th an 13 percent. Results are applicable to boiling in compact heat excha ngers.