Showing papers by "Ralph L. Webb published in 1997"
TL;DR: In this article, heat transfer and friction characteristics for single-phase flow in single-grooved and cross-grained micro-fin tubes were analyzed for forced convection condensation and evaporation.
91 citations
TL;DR: In this paper, a model is developed for predicting the boiling coefficient of nucleate pool on plain surfaces, as a function of bubble dynamics characteristics (nucleation site density, bubble departure diameter and bubble frequency).
83 citations
TL;DR: In this paper, a multiple regression technique was used to predict the air-side heat transfer coefficient and friction factor as a function of flow conditions and geometric variables of the heat exchanger.
Abstract: This paper deals with heat exchangers having plate fins of herringbone wave configuration. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of flow conditions and geometric variables of the heat exchanger. Correlations are provided for both staggered and in-line arrays of circular tubes. A multiple regression technique was used to correlate 41 wavy fin geometries by Beecher and Fagan (1987), Wang et al. (1995) and Beecher (1968). For the staggered layout, 92% of the heat transfer data are correlated within {+-}10%, and 91% of the friction data are correlated within {+-}15%.
71 citations
TL;DR: In this paper, a semi-empirical model is proposed to predict the condensation coefficient inside small hydraulic diameter extruded aluminum tubes having micro-grooves, and the model accounts for the effects of vapor shear and surface tension forces.
Abstract: A semiempirical model is proposed to predict the condensation coefficient inside small hydraulic diameter extruded aluminum tubes having microgrooves. The model accounts for the effects of vapor shear and surface tension forces. Surface tension force is effective in enhancing the condensation coefficient as long as the fin tips are not flooded by condensate. This enhancement increases as mass velocity is reduced. At high mass velocity the flow is vapor shear controlled and the surface tension contribution is very small. The surface tension effect is strongly affected by the fin geometry. A smaller fin tip radius provides a higher surface tension drainage force. A large cross sectional area in the interfin region will allow the surface tension enhancement to occur at lower vapor quality. Separate models are developed for the surface tension and vapor shear controlled regimes and the models are combined in the form of an asymptotic equation. The vapor shear model is based on use of an equivalent mass velocity and the heat-momentum transfer analogy. The surface tension model is analytically based. The model is validated by predicting the authors' data for two tube geometries using R-12 and R-134a, and the model predicts 95 percent of the condensation data within ±16 percent.
65 citations