A fractal dropwise condensation heat transfer model including the effects of contact angle and drop size distribution

2015 ◽  
Vol 83 ◽  
pp. 259-272 ◽  
Author(s):  
Baojin Qi ◽  
Jinjia Wei ◽  
Li Zhang ◽  
Hong Xu
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Size Distribution ◽  
Drop Size ◽  
Heat Transfer Model ◽  
Drop Size Distribution ◽  
Condensation Heat Transfer ◽  
Transfer Model ◽  
Dropwise Condensation

Submicron Superhydrophobic Surface Treatment Suitable for High Performance Condensers: A Modeling

2009 ◽  
Author(s):  
Sunwoo Kim ◽  
Kwang J. Kim ◽  
John M. Kennedy ◽  
Jiong Liu ◽  
Ganesh Skandan
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Theoretical Model ◽  
Size Distribution ◽  
Drop Size ◽  
Drop Size Distribution ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Superhydrophobic Coating ◽  
Single Droplet

The effect of the drop-contact angle on dropwise condensation heat transfer of saturated steam on a single horizontal copper tube with the superhydrophobic coating was investigated theoretically. The theoretical model is established by combining heat transfer through a single droplet with a well-known drop size distribution theory. The analysis of single droplet heat transfer incorporates resistances due to vapor-liquid interface, drop curvature, conduction through the drop, and conduction through the superhydrophobic coating layer. Each resistance is expressed as a function of the contact angle. The total resistance for a drop with a fixed radius increases as the contact angle increases. A population balance model is used to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from the empirical equation proposed by Le Fevre and Rose (1966). The results indicate that the contact angle has a strong correlation with the maximum drop radius, which plays a pivotal role in determining drop size distribution. A high contact angle leads to a significant reduction in the radius of the largest drop that is about to fall down due to gravity and sweep away drops in its path. Thus, there are more areas on the condensing surface for small drops, allowing for greater heat transfer. Also, it is shown that surface wettability affects the performance of dropwise condensation heat transfer and our theoretical model successfully predicts this phenomenon.

Dropwise Condensation Modeling Suitable for Superhydrophobic Surfaces

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Sunwoo Kim ◽  
Kwang J. Kim
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Size Distribution ◽  
Drop Size ◽  
Contact Angles ◽  
Drop Size Distribution ◽  
Balance Model ◽  
Dropwise Condensation ◽  
Interfacial Resistance ◽  
Single Droplet

A mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic (contact angle greater than 150 deg) features. The model is established by synthesizing the heat transfer through a single droplet with the drop size distribution. The single droplet heat transfer is analyzed as a combination of the vapor-liquid interfacial resistance, the resistance due to the conduction through the drop itself, the resistance from the coating layer, and the resistance due to the curvature of the drop. A population balance model is adapted to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from a well-known empirical equation. The evidence obtained suggests that both the single droplet heat transfer and drop distribution are significantly affected by the contact angle. More specifically, the model results indicate that a high drop-contact angle leads to enhancing condensation heat transfer. Intense hydrophobicity, which produces high contact angles, causes a reduction in the size of drops on the verge of falling due to gravity, thus allowing space for more small drops. The simulation results are compared with experimental data, which were previously reported.

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

2011 ◽  
Vol 199-200 ◽  
pp. 1604-1608
Author(s):  
Yun Fu Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Fractal Model ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
Small Contact Angle ◽  
Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

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%.

scholarly journals ASSESSMENT OF CONDENSATION HEAT TRANSFER MODEL TO EVALUATE PERFORMANCE OF THE PASSIVE AUXILIARY FEEDWATER SYSTEM

2013 ◽  
Vol 45 (6) ◽  
pp. 759-766 ◽  
Author(s):  
YUN-JE CHO ◽  
SEOK KIM ◽  
BYOUNG-UHN BAE ◽  
YUSUN PARK ◽  
KYOUNG-HO KANG ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Transfer Model

scholarly journals A Review of Research on Dropwise Condensation Heat Transfer

2021 ◽  
Vol 11 (4) ◽  
pp. 1553
Author(s):  
Xuechao Hu ◽  
Qiujie Yi ◽  
Xiangqiang Kong ◽  
Jianwei Wang
Keyword(s):  
Heat Transfer ◽  
Theoretical Models ◽  
High Heat ◽  
Condensation Heat Transfer ◽  
Formation Mechanisms ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
High Heat Transfer ◽  
Nucleation Sites ◽  
Enhancing Heat Transfer

Dropwise condensation is considered to be an effective method of enhancing heat transfer due to its high heat transfer performance. However, because the effect of dropwise condensation is affected by many complex factors, there is no systematic review summarized on the law of dropwise condensation heat transfer by scholars. In this paper, the main methods and problems of promoting dropwise condensation were reviewed based on the dropwise condensation mechanism and theoretical model. The three different hypotheses about the mechanism of dropwise condensation and the heat transfer model of dropwise condensation based on the hypothesis of nucleation sites were summarized. The methods for promoting dropwise condensation and the problems that influence dropwise condensation heat transfer are introduced in this paper. The research showed that many researchers focused on how the surface fabricated forms dropwise condensation rather than whether it enhances heat transfer. In this paper, we point out that the droplet shedding rate is the key to enhancing dropwise condensation heat transfer. Much more research on droplet formation mechanisms and theoretical models of different surfaces is supposed to be carried out in the future.

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