Visualization Study of Steam Condensation in Rectangular Channel of Multichannel Cylinder Dryer

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Yan Yan ◽  
Dong Jixian ◽  
Tang Wei ◽  
Feng Shiyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Regime ◽  
Mass Flux ◽  
Rectangular Channel ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Condensing Heat Transfer

The phenomenon of steam condensation occurring on one surface in a rectangular horizontal channel was experimentally studied. The experiment was conducted using a visualization method with a steam quality of 0.1–0.9 and mass flux of 20–50 kg/m2 s. Four flow patterns (annular, wave, slug, and plug) were observed, and the effects of quality and mass flux on the condensing heat transfer were analyzed. The mass flux and steam quality primarily affect the condensing heat transfer coefficient in the shear-dominated flow regime. The condensing heat transfer coefficients are nearly constant only in a certain range of steam quality. This result is disparate from what has been reported in previous literatures. It was also observed that the condensing heat transfer coefficient rises with an increase in the quality. Two flow regime maps were employed to predict the flow regimes observed in this study. The result reveals that the Tandon flow regime map agrees quite well with the experimental results.

An Analytical Model to Predict Condensation of R-410A in a Horizontal Rectangular Channel

2000 ◽  
Vol 122 (3) ◽  
pp. 613-620 ◽  
Author(s):  
Z. Guo ◽  
N. K. Anand
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Analytical Model ◽  
Rectangular Channel ◽  
Weighted Average ◽  
Condensation Heat Transfer ◽  
Mean Deviation ◽  
Transfer Coefficients ◽  
Condensation Heat Transfer Coefficient

An analytical model to predict condensation heat transfer coefficient in a horizontal rectangular channel was developed. The total local condensation heat transfer coefficient was represented as the weighted average of heat transfer coefficients for each wall. The analytical predictions compared well with the experimental data on the condensation of R-410A in a rectangular channel. The mean deviation was 6.75 percent. [S0022-1481(00)00503-X]

Experimental Investigation of Condensation Heat Transfer and Adiabatic Pressure Drop Characteristics Inside a Microfin and Smooth Tube

2017 ◽  
Vol 25 (03) ◽  
pp. 1750027 ◽  
Author(s):  
M. Mostaqur Rahman ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Frictional Pressure Drop

Experiments on condensation heat transfer and adiabatic pressure drop characteristics of R134a were performed inside smooth and microfin horizontal tubes. The tests were conducted in the mass flux range of 50[Formula: see text]kg/m2s to 200[Formula: see text]kg/m2s, vapor quality range of 0 to 1 and saturation temperature range of 20[Formula: see text]C to 35[Formula: see text]C. The effects of mass velocity, vapor quality, saturation temperature, and microfin on the condensation heat transfer and frictional pressure drop were analyzed. It was discovered that the local heat transfer coefficients and frictional pressure drop increases with increasing mass flux and vapor quality and decreasing with increasing saturation temperature. Higher heat transfer coefficient and frictional pressure drop in microfin tube were observed. The present experimental data were compared with the existing well-known condensation heat transfer and frictional pressure drop models available in the open literature. The condensation heat transfer coefficient and frictional pressure drop of R134a in horizontal microfin tube was predicted within an acceptable range by the existing correlation.

Condensing Heat Transfer Coefficients for R134a at Different Saturation Temperatures in Inclined Tubes

2013 ◽  
Author(s):  
Adekunle O. Adelaja ◽  
Jaco Dirker ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Inclination Angle ◽  
Saturation Temperature ◽  
Flow Distribution ◽  
Transfer Coefficients ◽  
Mass Fluxes ◽  
Inclination Angles ◽  
Condensing Heat Transfer

This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm. Experiments were conducted for inclination angles ranging from −90° (vertical downward) to +90° (vertical upward) for mass fluxes between 100 kg/m2s and 400 kg/m2s and vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30 °C and 50 °C. The results show that saturation temperature and inclination angles strongly influence the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally leads to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100 kg/m2s and 200 kg/m2s for the range of vapour qualities considered. Within the region of influence of inclination there is an optimum angle which is between 15° and −30° (downward flow). The inclination effect corresponds to the predominance of the effect of gravity on the flow distribution.

Condensation in Smooth Horizontal Tubes

1998 ◽  
Vol 120 (1) ◽  
pp. 193-213 ◽  
Author(s):  
M. K. Dobson ◽  
J. C. Chato
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Temperature Difference ◽  
Mass Flux ◽  
Flow Regimes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Transfer Behavior ◽  
Condensing Heat Transfer

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.

Heat Transfer of Impacting Water Mist on High Temperature Metal Surfaces

2003 ◽  
Vol 125 (1) ◽  
pp. 70-74 ◽  
Author(s):  
N. Sozbir ◽  
Y. W. Chang ◽  
S. C. Yao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Water Mist ◽  
Transfer Coefficients ◽  
Air Velocity ◽  
Liquid Mass ◽  
Air Jet ◽  
Mass Fluxes

Experimental studies were conducted to reveal the heat transfer mechanism of impacting water mist on high temperature metal surfaces. Local heat transfer coefficients were measured in the film-boiling regime at various air velocities and liquid mass fluxes. The test conditions of water mist cover the variations of air velocity from 0 to 50.3 m/s, liquid mass flux from 0 to 7.67 kg/m2s, and surface temperature of stainless steel between 525°C and 500°C. Radial heat transfer distributions were measured at different liquid mass fluxes. The tests revealed that the radial variation of heat transfer coefficients of water mist has a similar trend to the air jet cooling. At the stagnation point, heat transfer coefficient increases with both the air velocity and the liquid mass flux. The convective air heat transfer is consistent with the published correlation in the literature. The heat transfer contribution due to the presence of water increases almost linearly with the liquid mass flux. The total heat transfer coefficient can be established as two separable effects, which is the summation of the heat transfer coefficient of air and of liquid mass flux, respectively. This study shows that with a small amount of water added in the impacting air jet, the heat transfer is dramatically increased. The Leidenfrost temperature under water mist cooling was also measured. The Leidenfrost temperature increased with both the air velocity and the liquid mass flux.

Evaporative Heat Transfer and Pressure Drop of CO2 in a Microchannel Tube

2005 ◽  
Author(s):  
Siyoung Jeong ◽  
Eunsang Cho ◽  
Hark-koo Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Dry Out ◽  
The Heat Transfer Coefficient

Evaporation heat transfer and pressure drop characteristics of carbon dioxide were investigated in a multi-channel micro tube. The aluminum tube has 3 square channels with a hydraulic diameter of 2mm, a wall thickness of 1.5mm, and a length of 5m. The tube was heated directly by electric current. Experiments were conducted at heat fluxes ranging 4–16 kW/m2, mass fluxes from 150 to 750 kg/m2s, evaporative temperature from 0 to 10°C, and qualities from 0 to superheated state. The heat transfer coefficient measured was in the range of 6–15kW/m2K, and the pressure drop was 3–23kPa/m. For the qualities lower than 0.5, the heat transfer coefficient was found to increase with the quality, which is assumed to be the effect of convective boiling. For the qualities higher than 0.6, sudden drop in heat transfer coefficients was sometimes observed due to local dry-out. It was found that dry-out occurred at lower quality if mass flux was smaller. The average heat transfer coefficient was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of heat flux was the greatest. At given experimental conditions the pressure drop increased almost linearly with increasing quality. The total pressure drop was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of mass flux was the greatest. From the experimental results simple correlations for heat transfer coefficients and pressure drop were developed.

Two Phase Pressure Drop and Boiling Heat Transfer in Micro Pin Fin Channel

2016 ◽  
Author(s):  
Ki Moon Jung ◽  
Hee Joon Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pin Fin ◽  
Boiling Heat Transfer Coefficient

In this paper, boiling experiments were conducted to study two-phase pressure drop and the heat transfer coefficient in a staggered array micro pin fin channel of degassed water at a mass flux range of 9.3 to 46.6 kg/m2s and a heat flux of 0.5 to 0.9 W/cm2. Copper was used for the pin fin array microchannel heat sink, which was 31 mm in width and 82 mm in length. Micro pin fins, of 400 μm in diameter and 700 μm in height, were manufactured using a micro milling machine on the channel block. The distance between two pin fin surfaces is 300 μm. A thin film heater, which supplies a maximum constant heat flux of 1.55 W/cm2, was attached underneath the heat sink. From the experimental results, at a vapor quality of up to 0.04, the boiling heat transfer coefficient decreased as the quality increased. Results show that the heat transfer coefficient is dependent on the mass flux. The data also showed that the pressure drop increased with increasing mass flux. The data obtained in this study were compared to the existing correlations of boiling pressure drop and heat transfer coefficients. Results showed that the correlation with boiling pressure drop of Qu and Siu-Ho[22] yielded a prediction of 21.3% average error Additionally, as a result of comparison with the four existing correlations of boiling heat transfer coefficient, all correlations had a lower prediction for the heat transfer coefficients obtained in this study. Through visualization, it was found that the bubbles generated between the fins began to grow and moved downstream. We observed a stationary vapor pocket in which bubbles did not flow.

Boiling Heat Transfer of Carbon Dioxide in Horizontal Tubes

2007 ◽  
Author(s):  
Eiji Hihara ◽  
Chaobin Dang
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

In this study, boiling heat transfer coefficients of carbon dioxide in horizontally located smooth tubes were experimentally investigated. The inner diameter of heat transfer tubes was 1, 2, 4, and 6 mm. Experiments were conducted at evaporating temperature of 5 and 15 °C, heat fluxes from 4.5 to 36 kW/m2, and mass fluxes from 360 to 1440 kg/m2s. The heat transfer coefficients in the pre-dryout region and post-dryout region were investigated, as well as the dryout quality. Due to the small viscosity and surface tension of CO2, the dryout occurs at a small quality from 0.4 to 0.7. The inception quality decreases with the increase of mass flux, and is affected by the heat flux and tube diameter; the effects of heat flux on the heat transfer coefficient are much significant in the pre-dryout region, which is related with the activation of nucleate boiling. On the contrary, the effects of mass flux are relatively low due to the low two-phase density ratio near the critical point. In addition, this tendency becomes more significant when the small tube is tested; In the post-dryout region, mass velocity is the dominating factor on heat transfer coefficient. At small mass flux, the heat transfer coefficient decreases with the increase of quality, while at large mass flux such as 1440kg/m2s, the heat transfer coefficient turns to increasing with the quality. By increasing the evaporating temperature, the pre-dryout heat transfer coefficient increases, while the dryout inception quality and post-dryout heat transfer coefficient are not affected greatly by the evaporating temperature.

Two-Phase Refrigerant Mixture (R-407C) Flow in Smooth Meso-Scale Heat Exchangers

2001 ◽  
Author(s):  
Yasir M. Shariff ◽  
T. S. Ravigururajan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Mixture Flow ◽  
Refrigerant Mixture ◽  
Saturated Boiling

Abstract The paper presents results from an experimental study on refrigerant mixture flow (R-407C) in which the heat transfer coefficient was measured across a range of heat and mass fluxes. Flow characteristics in smooth horizontal mesochannels were measured for two different conditions, 1) subcooled and 2) saturated boiling with diameters of 1.59, 2.78, and 3.97 mm and a length of 50.8 mm in refrigerant mixture (R-407C). Experiments were performed at heat fluxes of 2 and 11 kW/m2 for the subcooled boiling and 15 and 29 kW/m2 for the saturated boiling. The mass flux was varied from 0.45 to 1.55 kg/min and the refrigerant was subcooled to 8°C. The saturated boiling experiments were conducted for ΔTsat = 0 to 27°C. The heat transfer coefficients were found to be dependent on channel size, heat flux, and mass flux variations. For smaller channel diameters, the heat transfer rate significantly increased as compared to larger channel diameters. The results showed an increase of 100% in heat transfer coefficient when compared to traditional and micro-channel boiling characteristics.

Stagnation Film Cooling and Heat Transfer, Including Its Effect Within the Hole Pattern

1988 ◽  
Vol 110 (1) ◽  
pp. 66-72 ◽  
Author(s):  
W. J. Mick ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Heat Load ◽  
Flux Ratio ◽  
Leading Edge ◽  
Surface Heat ◽  
Spanwise Direction ◽  
Transfer Coefficients

Detailed film effectiveness and surface heat transfer measurements were obtained for secondary air injection through rows of holes into the stagnation region of an incident mainstream flow. Tests were performed using a blunt body with a circular leading edge and a flat afterbody. Rows of holes were located at ±15 deg and +44 deg from stagnation. The holes in each row were spaced four hole diameters apart and were angled 30 deg to the surface in the spanwise direction. Measurements were taken for three cooling-to-incident flow mass flux ratios both in the leading edge region within the hole pattern and downstream to a distance of about 85 hole diameters. The results indicate that large spanwise variations in both film effectiveness and heat transfer coefficient exist, and that the highest values of each do not in general correspond. Near the holes, film effectiveness values as high as 0.7–0.8 were found, while heat transfer coefficients with injection were as much as three times those without. Far downstream the film effectiveness decayed to values near 0.1, while the heat transfer coefficient remained about 10 percent above that without injection. Nevertheless, it is shown that for typical turbine temperatures, leading edge injection reduces the surface heat load everywhere for all but the highest mass flux ratio. The exception produces an increase in heat load within the injection region.

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