Condensation in horizontal tubes, part 2: new heat transfer model based on flow regimes

Condensation in Horizontal Tubes, Part 1: Two-Phase Flow Pattern Map

This paper proposes a new method to determine the condensation heat transfer coefficient of fluids flowing into horizontal smooth tubes with internal diameters D > 3 mm. The method has been drawn up as simply as possible and is ready to use in heat exchanger modeling and design applications. It is also suitable to work very well with old and new fluids used in the refrigeration, air conditioning, and heat pump industries. Particular attention is given to accuracy: it has been tested over a wide updated experimental database and comes from many different independent researchers with reduced experimental uncertainties. In order to obtain an easy structure, only two equations are employed, related respectively to & Delta; T-independent and to & Delta; T-dependent fluid flows. All the parameters that influence the condensation heat transfer have been included. A comparison has been conducted against HCFCs, HFCs, HCs, carbon dioxide, ammonia, and water data. Zeotropic mixtures with two and three components are...

Condensation in Horizontal Smooth Tubes: A New Heat Transfer Model for Heat Exchanger Design

This paper reports experimental heat transfer coefficients and pressure drops measured during condensation inside a smooth tube when operating with pure HFC refrigerants (R134a, R125, R236ea, R32) and the nearly azeotropic HFC refrigerant blend R410A. Data taken when condensing HCFC-22 are also reported for reference. The experimental runs are carried out at a saturation temperature ranging between 30 and 50°C, and mass velocities varying from 100 to 750 kg/(m2 s), over the vapour quality range 0.15–0.85. The effects of vapour quality, mass velocity, saturation temperature and temperature difference between saturation and tube wall on the heat transfer coefficient are investigated by analysing the experimental data. A predictive study of the condensation flow patterns occurring during the tests is also presented. Finally comparisons with predictions from the model by Kosky and Staub (Kosky PG, Staub FW. Local condensing heat transfer coefficients in the annular flow regime. AIChE J 1971;17:1037) are reported for all the data sets.

Experimental investigation on condensation heat transfer and pressure drop of new HFC refrigerants (R134a, R125, R32, R410A, R236ea) in a horizontal smooth tube

Providing a comprehensive introduction to the fundamentals and applications of flow and heat transfer in conventional and miniature systems, this fully enhanced and updated edition covers all the topics essential for graduate courses on two-phase flow, boiling, and condensation. Beginning with a concise review of single-phase flow fundamentals and interfacial phenomena, detailed and clear discussion is provided on a range of topics, including two-phase hydrodynamics and flow regimes, mathematical modeling of gas-liquid two-phase flows, pool and flow boiling, flow and boiling in mini and microchannels, external and internal-flow condensation with and without noncondensables, condensation in small flow passages, and two-phase choked flow. Numerous solved examples and end-of-chapter problems that include many common design problems likely to be encountered by students, make this an essential text for graduate students. With up-to-date detail on the most recent research trends and practical applications, it is also an ideal reference for professionals and researchers in mechanical, nuclear, and chemical engineering.

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Two-phase flow, boiling and condensation in conventional and miniature systems

An experimental study of heat transfer and flow regimes during condensation of refrigerants in horizontal tubes was conducted. Measurements were made in smooth, round tubes with diameters ranging from 3.14 mm to 7.04 mm. The refrigerants tested were R-12, R-22, R-134a, and near-azeotropic blends of R-32/R-125 in 50 percent/50 percent and 60 percent/40 percent compositions. The study focused primarily on measurement and prediction of condensing heat transfer coefficients and the relationship between heat transfer coefficients and two-phase flow regimes. Flow regimes were observed visually at the inlet and outlet of the test condenser as the heat transfer data were collected. Stratified, wavy, wavy annular, annular, annular mist, and slug flows were observed. True mist flow without a stable wall film was not observed during condensation tests. The experimental results were compared with existing flow regime maps and some corrections are suggested. The heat transfer behavior was controlled by the prevailing flow regime. For the purpose of analyzing condensing heat transfer behavior, the various flow regimes were divided into two broad categories of gravity-dominated and shear-dominated flows. In the gravity dominated flow regime, the dominant heat transfer mode was laminar film condensation in the top of the tube. This regime was characterized by heat transfer coefficients that depended on the wall-to-refrigerant temperature difference but were nearly independent of mass flux. In the shear-dominated flow regime, forced-convective condensation was the dominant heat transfer mechanism. This regime was characterized by heat transfer coefficients that were independent of temperature difference but very dependent on mass flux and quality. Heat transfer correlations that were developed for each of these flow regimes successfully predicted data from the present study and from several other sources.

M. K. Dobson

Papers

Condensation in Smooth Horizontal Tubes