Investigation of Condensation Heat Transfer on a Tube With Wavy Fins

2019 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Condensation Heat Transfer ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Transfer Capability ◽  
Falling Film Evaporation ◽  
Insight Into ◽  
Good Agreement

Abstract In this work, heat transfer coefficient during condensation of a refrigerant on the outside surface of a copper tube with wavy fins was experimentally investigated. To fully characterize the condensation heat transfer, the experiments were conducted under two conditions: no refrigerant overfeed and subject to various degree inundation. The results under the condition of no overfeed are compared with the Beatty and Katz model. While the trend of degradation with increasing subcooling was in good agreement with the model (within 5%), the condensation heat transfer coefficients from the wavy fins were 11–15% higher. Based on the Nusselt model, the surface tension effect is not taken into account in the Beatty and Katz model, which plays an important role in condensation on a surface with fins. The photographs taken during the experiments showed that the condensate dripping columns have a pitch is in agreement with that proposed by Yung et al. [24] for falling film evaporation applications. The second part of the experiments under the various degree of inundation provides further insight into the heat transfer capability of the surface with wavy fins.

Experimental Studies on Heat Transfer Coefficients of Horizontal Tube Falling Film Evaporation With Seawater

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Shengqiang Shen ◽  
Xue Chen ◽  
Xingsen Mu ◽  
Changkun Jiang
Keyword(s):  
Heat Transfer ◽  
Horizontal Tube ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Evaporation Temperature ◽  
Spray Density ◽  
Falling Film Evaporation

The overall heat transfer process in a horizontal tube falling film evaporator is mainly influenced by the falling film evaporation outside horizontal tube due to the average heat transfer coefficient which is about 50% of that of the condensation inside tube. A series of experimental studies were conducted to investigate the heat transfer coefficients of the falling film evaporation outside the horizontal tube with parameters such as the spray density, the evaporation temperature, the salinity, and the tube spacing. Experiments were conducted by using Al-brass tubes with 19 mm outer diameter and 1600 mm length. The horizontal tubes are arranged vertically in the evaporator. The test tube is heated by an internal electric heater with uniform heat flux. Temperatures of the test tube surface and saturated vapor measured by thermocouples are used to calculate the heat transfer coefficients. The seawater with salinity of 1.5%, 3.0%, and 4.5% was used as experimental fluid. The spray density varied between 0.017 and 0.087 kg/(m s), and the evaporation temperature was controlled in the range of 50–70 °C. Results show that the average heat transfer coefficients of water under different salinities increase obviously with the spray density until a certain point. The average heat transfer coefficients of seawater decrease slightly with the evaporation temperature, decrease with the salinity, increase with the tube spacing, and are almost independent of the heat flux. In addition, the comparisons with 25.4 mm outer diameter tube and the circumferential distribution of local heat transfer coefficient are presented in this study.

A New Model for Predicting Falling Film Evaporation Heat Transfer Coefficients

2016 ◽  
Author(s):  
Apurva Baruah ◽  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Design ◽  
Falling Film ◽  
Transfer Coefficients ◽  
New Model ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Falling Film Evaporation

For falling film evaporation, the most important considerations from a thermal design standpoint are the onset of film dryout and the local heat transfer coefficients in partially and fully wet conditions. Previous methods developed for the prediction of (i) pool boiling heat transfer coefficient (HTCs), (ii) the onset of dryout, and (iii) falling film heat transfer coefficient consist of empirical, tube-specific constants which are quite difficult, if not impossible, to determine, and hence have limited utility. New methods to predict these parameters have been developed in the present study, which eliminate the special constants by incorporating dimensionless parameters that capture the effect of refrigerant properties and macro-level tube-geometry. The predictions of the new model have been found to be better than or comparable to those of the best available existing models.

Falling Film Evaporation of Water on Horizontal Configured Tube Bundles

2010 ◽  
Author(s):  
Wei Li ◽  
Xiaoyu Wu ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Inlet Temperature ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Film Evaporation ◽  
Tube Bundles ◽  
Falling Film Evaporation

This paper reports an experimental study on falling film evaporation of water on 6-row horizontal configured tube bundles in a vacuum. Three types of configured tubes, Turbo-CAB-19fpi and −26fpi, Korodense, including smooth tubes for reference, were tested in a range of film Reynolds number from about 10 to 110. Results show that as the falling film Reynolds number increases, falling film evaporation goes from tubes partial dryout regime to fully wet regime; the mean heat transfer coefficients reach peak values in the transition point. Turbo-CAB tubes have the best heat transfer enhancement of falling film evaporation in both regimes, but Korodense tubes’ overall performances are better when tubes are fully wet. The inlet temperature of heating water has hardly any effects on the heat transfer, but the evaporation pressure has controversial effects. A correlation with errors within 10% was also developed to predict the heat transfer enhancement capacity.

Falling Water Film Evaporation on Horizontal Finned Tube Arrays at Low Pressure

2011 ◽  
Author(s):  
Xiao-Yu Wu ◽  
Wei Li ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Experimental Studies ◽  
Water Film ◽  
Finned Tube ◽  
Heat Fluxes ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Film Evaporation ◽  
Falling Film Evaporation

Experimental studies have been done on falling film evaporation of water on four types of finned tubes arrays at the pressure of 1000 Pa. The Reynolds numbers are in the laminar range of about 10 to 110. Results show that the finned tubes that can distribute liquid longitudinally have the best performances in the partial dryout regime, and those with high fins could enhance heat transfer most in the fully wet regime. High heat fluxes will make more liquid evaporate, but also generate more dry patches on the tubes. Additionally, the inner enhancement of the tubes will also improve the overall heat transfer coefficients. And four heat transfer enhancement methods of falling film evaporation are summarized in the paper.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 557-563 ◽  
Author(s):  
Paul L. Sears ◽  
Libing Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Drag Reducing Additive ◽  
Good Agreement

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.

Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels

2006 ◽  
Vol 128 (10) ◽  
pp. 1050-1059 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Akhil Agarwal ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Low Flow ◽  
Transfer Model ◽  
Shear Stresses ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.

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