Film Condensation in Microchannels: Effect of Tube Inclination

Wang, Huasheng; Rose, John

doi:10.1115/icnmm2006-96049

Cited by 10 publications

(9 citation statements)

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“…First, the correlation was developed primarily for refrigerants, but water has a higher surface tension value. Surface tension may cause condensate to gather in sharp mini-channel corners, thereby thinning the liquid film around the perimeter and increasing heat transfer, although this liquid film thinning is dependent on the fluid and geometry [62][63][64][65]. Second, the mini-gap had a large aspect ratio (20:1), and the flow was developing in the test section.…”

Section: Condensation Heat Transfer and Flow Visualization In A Hydromentioning

confidence: 99%

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

Chu

Derby

2016

Journal of Heat Transfer

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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/m 2 s and steam quality range of 0.2-0.8, and validated with single-phase experiments. Filmwise condensation was observed in the hydrophilic minigap; 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 ¼ 0.42), increasing mass flux from 50 to 75 to 100 kg/m 2 s 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 lm, respectively. For these cases, condensation heat transfer coefficients increased from 154,700 to 176,500 to 194,800 W/m 2 K at mass fluxes of 50, 75, and 100 kg/m 2 s, respectively. Increased mass fluxes and steam quality reduced sweeping periods and droplet departure diameters, thereby reducing liquid thickness and increasing heat transfer coefficients.

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Section: Condensation Heat Transfer and Flow Visualization In A Hydromentioning

confidence: 99%

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

Chu

Derby

2016

Journal of Heat Transfer

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“…been developed by Wang et al [6] and described in detail by Wang and Rose [7] (see also [8][9][10][11][12][13][14][15] temperature which is less than that of the vapour so that condensation commences at the inlet. Fig.…”

Section: Condensation In Micro Channelsmentioning

confidence: 99%

“…It is now established that this is negligible except for very high condensation rates which may occur when the condensate resistance is small as in the cases of condensation of liquid metals, for the smallest drops in dropwise condensation and in other cases where condensate films are very thin. In these circumstances the temperature drop at the condensate surface may be estimated by (11) f = (1+ ,d)2 + 2(dLJ/dqJ)2 -(1+,d) d 2,dldqJ2 (12) { (1+,d)2+(dLJ/dqJ)2}3/2 b.=t5IR (13) A=JlpgR 2 (14) B = Jlkb.T 1R 3 pb.pghr g (15) and ;: = R + t5 . When this pressure gradient is included in an otherwise Nusselt treatment, the differential equation for the condensate film thickness becomes It is readily seen that when gravity dominates over surface tension, i.e.…”

Section: Introductionmentioning

confidence: 99%

Surface tension-affected laminar film condensation problems

Wang

Rose

2007

J Mech Sci Technol

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Following Nusselt [1] there were few developments in the theory of laminar film condensation until the advent of digital computers in the 1950s. Approximations used by Nusselt, namely neglect of inertia, convection and surface shear stress (for the free convection case) were then found to give very accurate results for the normal practical range of vapour-to-surface temperature difference. Subsequent developments treated the gas phase and dealt with superheated vapour, condensation in the presence of a non-condensing gas and condensation of mixtures. The temperature discontinuity at the vapour-liquid interface has been studied experimentally and theoretically since the 19 th century and more recently in the 1960s by experiments using liquid metals.In the present paper the focus is on the condensate film and, in particular, the role played by surface tension which is important for condensation on finned surfaces and in microchannels, owing to abrupt changes in curvature of the condensing surface. The way in which surface tension affects condensation heat transfer and difficulties which arise are first illustrated by reference to condensation on a smooth horizontal tube, where the effect of surface tension on heat transfer is minimal. Practically more relevant cases of condensation in microchannels and on finned surfaces and are then discussed and recent results presented.

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“…Wang and Rose [6] modified a model for condensation in inclined rectangular microchannels. In their research, the influence of inclination angle variation on the condensate film thickness around the channel inside the perimeter and the mean heat transfer coefficient along the channel length was addressed for square channels 0.5, 1.0, and 3.0 mm in size.…”

Section: Introductionmentioning

confidence: 99%

Theoretical modeling and numerical solution of stratified condensation in inclined tubes

Saffari

Naziri

2010

J Mech Sci Technol

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The heat transfer phenomenon occurring during stratified condensation inside an inclined tube is investigated theoretically and numerically. Differential equations governing the kinematic, dynamic, and thermal aspects for vapor condensation inside inclined tubes, which are derived from a thin film flow modeling, are solved simultaneously. These solutions are achieved by applying an explicit finite difference numerical method to predict the condensation heat transfer coefficient variations along the tangential and axial coordinates. The inclination angle is found to have a significant effect on condensation heat transfer coefficient inside inclined tubes. In addition, in accordance with the given physical and thermal condition of working fluids, there is a specific optimum inclination angle. In this study, the 30°-50° range from the horizontal position is found to be the range of the optimum inclination angle for achieving the maximum condensation heat transfer coefficient, with R134a, R141b, and R11 as the working fluids. The results of the present study are compared with experimental data, and a good agreement is observed between them.

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Film Condensation in Microchannels: Effect of Tube Inclination

Cited by 10 publications

References 0 publications

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

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

Surface tension-affected laminar film condensation problems

Theoretical modeling and numerical solution of stratified condensation in inclined tubes

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