Theoretical Modeling of Vapor Condensation in the Presence of Noncondensable Gas on a Horizontal Tube

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Junhui Lu ◽  
Haishan Cao ◽  
JunMing Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Mass Flux ◽  
Horizontal Tube ◽  
Vapor Condensation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Mass Fluxes

Abstract Double-boundary layer theory was adopted to investigate the distributions of the liquid film, gas film, heat transfer coefficient, and condensate mass fluxes around a horizontal tube for vapor condensation with noncondensable gases like steam–air and steam–CO2 mixtures under free convection. The investigation considered the effects of the noncondensable gas concentration, surface subcooling temperature, and pressure. The thicknesses of the liquid and gas films increase gradually along the wall from top to bottom, whereas the local heat transfer coefficient and the condensate mass flux decrease. The film thicknesses do not change significantly around the upper part of the tube but increase sharply around the lower part. The liquid film thicknesses, gas film thicknesses, condensate mass fluxes, and heat transfer coefficients of steam–air systems are compared with those of steam–CO2 systems. The condensate mass flux in the steam–air system is smaller than that of steam–CO2 system under the condition of the same surface subcooling and gas mass fraction because air has more moles of molecules in the mixture than CO2 and the steam more easily diffuses through CO2 than through air. The predicted average condensation heat transfer coefficients agree well with the available experimental data.

Diffusion Layer Theory for Turbulent Vapor Condensation With Noncondensable Gases

1993 ◽  
Vol 115 (4) ◽  
pp. 998-1003 ◽  
Author(s):  
P. F. Peterson ◽  
V. E. Schrock ◽  
T. Kageyama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Transfer ◽  
Vapor Condensation ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Noncondensable Gases ◽  
Vertical Tubes

In turbulent condensation with noncondensable gas, a thin noncondensable layer accumulates and generates a diffusional resistance to condensation and sensible heat transfer. By expressing the driving potential for mass transfer as a difference in saturation temperatures and using appropriate thermodynamic relationships, here an effective “condensation” thermal conductivity is derived. With this formulation, experimental results for vertical tubes and plates demonstrate that condensation obeys the heat and mass transfer analogy, when condensation and sensible heat transfer are considered simultaneously. The sum of the condensation and sensible heat transfer coefficients becomes infinite at small gas concentrations, and approaches the sensible heat transfer coefficient at large concentrations. The “condensation” thermal conductivity is easily applied to engineering analysis, and the theory further demonstrates that condensation on large vertical surfaces is independent of the surface height.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

scholarly journals Combined Visualization and Heat Transfer Measurements for Steam Flow Condensation in Hydrophilic and Hydrophobic Mini-Gaps

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Xi Chen ◽  
Melanie M. Derby
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Mass Flux ◽  
Absolute Error ◽  
Open Loop ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Flow Condensation

Condensation enhancement was investigated for flow condensation in mini-channels. Simultaneous flow visualization and heat transfer experiments were conducted in 0.952-mm diameter mini-gaps. An open loop steam apparatus was constructed for a mass flux range of 50–100 kg/m2s and steam quality range of 0.2–0.8, and validated with single-phase experiments. Filmwise condensation was observed in the hydrophilic mini-gap; pressure drop and heat transfer coefficients were compared to the (Kim and Mudawar, 2013, “Universal Approach to Predicting Heat Transfer Coefficient for Condensing Mini/Micro-Channel Flow,” Int. J. Heat Mass Transfer, 56(1–2), pp. 238–250) correlation and prediction was very good; the mean absolute error (MAE) was 20.2%. Dropwise condensation was observed in the hydrophobic mini-gap, and periodic cycles of droplet nucleation, coalescence, and departure were found at all mass fluxes. Snapshots of six typical sweeping cycles were presented, including integrated flow visualization quantitative and qualitative results combined with heat transfer coefficients. With a fixed average steam quality (x¯ = 0.42), increasing mass flux from 50 to 75 to 100 kg/m2s consequently reduced average sweeping periods from 28 to 23 to 17 ms and reduced droplet departure diameters from 13.7 to 12.9 to 10.3 μm, respectively. For these cases, condensation heat transfer coefficients increased from 154,700 to 176,500 to 194,800 W/m2 K at mass fluxes of 50, 75, and 100 kg/m2 s, respectively. Increased mass fluxes and steam quality reduced sweeping periods and droplet departure diameters, thereby reducing liquid thickness and increasing heat transfer coefficients.

Low Mass Quality Flow Boiling in Microtubes at High Mass Fluxes

2011 ◽  
Vol 3 (4) ◽  
Author(s):  
Mehmed Rafet Özdemir ◽  
Alihan Kaya ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Wall Superheat

In this article, an experimental study on boiling heat transfer and fluid flow in microtubes at high mass fluxes is presented. De-ionized water flow was investigated over a broad range of mass flux (1000 kg/m2s–7500 kg/m2s) in microtubes with inner diameters of  ∼ 250 μm and ∼685 μm. The reason for using two different capillary diameters was to investigate the size effect on flow boiling. De-ionized water was used as working fluid, and the test section was heated by Joule heating. Heat transfer coefficients and qualities were deduced from local temperature measurements. It was found that high heat removal rates could be achieved at high flow rates under subcooled boiling conditions. It was also observed that heat transfer coefficients increased with mass flux, whereas they decreased with local quality and heat flux. Moreover, experimental heat flux data were compared with partial boiling correlations and fully developed boiling correlations. It was observed that at low wall superheat values, there was only a small inconsistency between the experimental data and the conventional partial boiling prediction method of Bergles, while the subcooled and low quality fully developed boiling heat transfer correlation of Kandlikar could fairly predict experimental results at high wall superheat values.

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.

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.

A Study on Gas–Liquid Film Thicknesses and Heat Transfer Characteristics of Vapor–Gas Condensation Outside a Horizontal Tube

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Huijun Li ◽  
Wenping Peng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Gas Condensation ◽  
Noncondensable Gas

Noncondensable gases deteriorate heat transfer in the condensation process. It is therefore necessary to study vapor–gas condensation heat transfer process and analyze main factors influencing the process. Based on the double-film theory and the Prandtl boundary layer theory, this investigation developed a mathematical model of gas–liquid film thicknesses and local heat transfer coefficient for studying laminar film condensation in the presence of noncondensable gas over a horizontal tube. Induced velocity in the gas film, gas–liquid interfacial shear stress, and pressure gradient were considered in the study. Importantly, gas–liquid film separations were analyzed in depth in this paper. It obtained the distributions of gas–liquid film thicknesses, local heat transfer coefficient, condensate mass flux, and gas–liquid interfacial temperature along the tube surface, and analyzed the influences of bulk velocity, total pressure, bulk mass concentration of noncondensable gas and wall temperature on them, providing a theoretical guidance for understanding and enhancing vapor–gas condensation heat transfer. Gas film thickness and gas–liquid film separations have certain effects on vapor–gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data from related literatures.

Experimental Investigation on Condensation in Corrugated Low Finned Tubes in Presence of Noncondensable Gas

2017 ◽  
Author(s):  
Bin Ren ◽  
Xiaoying Tang ◽  
Hongliang Lu ◽  
Dongliang Fu ◽  
Pan Song ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Structural Parameters ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Inlet Conditions ◽  
The Heat Transfer Coefficient

The phenomenon of condensation with noncondensable gas widely exists in many industrial processes. In this paper, the effect of noncondensable gas on condensation heat transfer inside corrugated low finned tubes is investigated experimentally. Air is mixed into steam playing the role of noncondensable gas. The effects of gas mixture inlet conditions and condensation tubes structural parameters are investigated. The results show that the influence mechanism inside corrugated low finned tubes is similar with that inside smooth tubes. The heat transfer coefficient decreases as noncondensable gas fraction increases. However, the decreasing rate is gradually reduced. Increasing inlet mass flux could enhance the heat transfer coefficient especially at small heat transfer rate. And the heat transfer coefficient decreases with the increase of inlet pressure. The heat transfer coefficients inside smaller pitches tubes are higher than that inside larger pitches tubes, and the declining rate is also slightly faster. When the noncondensable gas fraction is large enough, the difference of heat transfer coefficients between different enhanced tubes can be ignored. Tube with the largest protrusion height has the highest heat transfer coefficient. And the gap of heat transfer coefficients between different protrusion heights is larger than that between different pitches. This shows that the protrusion heights have greater influence on condensation compared with pitches.

A Parametric Study of Boiling Heat Transfer in a Horizontal Tube Bundle

1988 ◽  
Vol 110 (4a) ◽  
pp. 976-981 ◽  
Author(s):  
M. K. Jensen ◽  
J.-T. Hsu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Tube Bundle ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Boiling heat transfer outside of a section of a uniformly heated horizontal tube bundle in an upward crossflow was investigated using R-113 as the working fluid. The inline tube bundle had five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heat transfer coefficients obtained from the 14 instrumented tubes are reported for a range of fluid and flow conditions; slightly subcooled liquid inlet conditions were used. At most heat fluxes there was no significant variation in the local heat transfer coefficients throughout the tube bundle. However, at low heat fluxes and mass velocities, the heat transfer coefficient increased at positions higher in the tube bundle. As pressure and mass velocity increased so did the heat transfer coefficients. For the local heat transfer coefficient, a Chen-type correlation is compared to the data; the data tend to be overpredicted by about 20 percent. Reasons for the overprediction are suggested.

Sign in / Sign up

Export Citation Format

Share Document