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Boiling Heat Transfer in a Horizontal Small-Diameter Tube
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1993
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Heat Transfer ProcessFluid PropertiesNucleation MechanismEngineeringThermal HydraulicsHeat Transfer EnhancementMass FluxTransport PhenomenaMass TransferThermodynamicsHeat TransferHeat PipeThermal EngineeringConvective Heat TransferThermo-fluid SystemsBoilingRefrigeration
Small-diameter tubes exhibit high heat fluxes, low mass fluxes, and a dominant slug flow pattern, leading to high boiling numbers. Local heat transfer coefficients were measured across a range of heat flux, mass flux, and quality, and used to assess ten correlations, revealing that high boiling numbers and slug flow cause nucleation-dominated heat transfer. Correlations accounting for nucleation, notably Lazarek and Black (1982) and a simplified Stephan–Abdelsalam (1980) form, matched the data within 13 % mean deviation, demonstrating applicability to compact heat exchangers.
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 coefficients are measured for a range of heat flux (8.8–90.75 kW/m2), mass flux (50–300 kg/m2s), and equilibrium mass quality (0–0.9). The measured coefficients are used to evaluate 10 different heat transfer correlations, 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, based on a flow pattern map developed from adiabatic experiments with air-water mixtures, it has been shown that small-diameter channels produce 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 result, the two-phase correlations that predicted this dominance also predicted the data the best when they properly modeled the physical parameters. The correlation of Lazarek and Black (1982) predicted the data 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 than 13 percent. Results are applicable to boiling in compact heat exchangers.