A Synthesis of the Total Process of Dropwise Condensation Using the Method of Computer Simulation

Tanasawa, Ichiro; Tachibana, Fujio

doi:10.1615/ihtc4.1280

Cited by 10 publications

(9 citation statements)

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“…N is the drop-size distribution in drops/m 2 /m and described in further detail in the Methods section of this text. Other theoretical models agree well with the Le Fevre and Rose model. − The power law expression in Le Fevre and Rose’s model has been experimentally validated for distributions in the range r > 5 × 10 –5 m, but drop-size distributions for smaller drop sizes have not been reported due to the difficulty of imaging these drops. ,,, Further, in reports that do include drop size measurements in the range 5 × 10 –5 m < r < 5 × 10 –4 m, the distribution function resolution is coarse.…”

Section: Introductionmentioning

confidence: 58%

“…The present work reports a computational approach to obtain the steady state drop-size distribution and associated time-averaged heat transfer rates for dropwise condensation over a range of contact angles from 90 to 180°. Condensation is simulated in a Lagrangian approach, similar in form to previous computational approaches, allowing for coalescence at naturally occurring drop sizes. ,− Unlike previous computational simulations, the present work considers how the departure of drops both by jumping and gravity-induced sweeping influences the steady state drop-size distribution and associated time-averaged heat transfer rates. The present work spans also a larger range of physical conditions than previous studies.…”

Section: Introductionmentioning

confidence: 99%

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Simulation of Drop-Size Distribution During Dropwise and Jumping Drop Condensation on a Vertical Surface: Implications for Heat Transfer Modeling

et al. 2019

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Accurate models for condensation heat transfer are necessary to improve condenser design. Drop-size distribution is an important aspect of heat transfer modeling that is difficult to measure for small drop sizes. The present work uses a numerical simulation of condensation which incorporates the possibility of coalescence and coalescenceinduced jumping over a range of drop sizes. Results of the simulation are compared with previous theoretical models and the impact of the assumptions used in those models is explored. In particular, previous drop-size distribution models may predict heat transfer rates less accurately for high contact angles and for coalescence-induced jumping since coalescence occurs over a range of drop sizes and does not always result in departure. The influence of various input parameters (nucleation site distribution approach, nucleation site density, contact angle, maximum drop size, heat transfer modeling to individual drops, and minimum jumping size) on the drop-size distribution and overall heat transfer rate is explored. Assignment of the nucleation site spatial distribution and heat transfer model affect both the drop-size distribution and predicted overall heat transfer rate. Results from the simulation suggest that, when the contact angle is large (as on superhydrophobic surfaces) and no coalescence-induced jumping occurs, the heat transfer may not be as sensitive to the maximum drop-size as previously supposed. Furthermore, this work suggests that when coalescenceinduced jumping occurs, reducing the maximum drop size may not always increase heat transfer since drops similar in size to those removed by coalescence-induced jumping can contribute significantly to the overall heat transfer rate.

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Section: Introductionmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Simulation of Drop-Size Distribution During Dropwise and Jumping Drop Condensation on a Vertical Surface: Implications for Heat Transfer Modeling

et al. 2019

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“…Since the seventies, researchers have tried to obtain the distribution of drop size from such numerical simulations. For instance, Tanasawa and Tachibana, 5 modeling the growth and coalescence of drops on a surface, showed that up to 400 000 coalescences are necessary to form a 1 mm radius drop. Unfortunately, their simulations used a low nucleation site density (10 4 cm −2 ), which is several orders of magnitude less than the one classically considered by other authors.…”

Section: ■ Introductionmentioning

confidence: 99%

About the Role of Falling Droplets’ Sweeping in Surface Renewal during Dropwise Condensation

2020

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To determine the heat transfer coefficient during dropwise condensation, two models are necessary: a heat transfer model through a single drop and a model of drop-size distribution.To model the distribution of the drop size, most studies dissociate the drop population into two distinct parts. A semiempirical model is then used to evaluate the drop-size distribution of "large" drops (i.e., typically greater than few micrometers), while the drop-size distribution of "small" drops is modeled using a statistical approach based on population balance. Currently, no accurate data are available to validate this latter distribution. In the present study, the statistical approach is compared to an individual-based numerical approach. This numerical approach takes into account the entire lifecycle of a drop: nucleation, growth, coalescence, and disappearance by sweeping of moving drops (jumping droplets are not considered in this paper). The drop-size distributions of large drops obtained thanks to this model are very similar to those obtained from the classical law in all configurations studied. Nevertheless, the distributions of "small" drops are notably different between the two types of modeling. In the configurations considered in the present study, an analysis of the main hypotheses used in the statistical approach (in particular, the assumption of a constant removal characteristic time τ irrespective of the range of drop size) revealed that the main mechanism for surface renewal is not the sweeping of the surface by moving drops. From these results, a modification of the statistical model is proposed and discussed.

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“…Graham and Griffith [11] investigated the distribution of larger size droplets and obtained their distribution function, however, for the droplets less than 10 microns, the distributions had to be inferred from the heat transfer measurements because of the limitation of the experimental instruments. In order to deal with the effect of numerous coalescences between droplets on the droplet size distribution, Gose et al [12], Tanasawa and Tachibana [13] and Glicksman and Hunt [14] attempted to simulate the entire process of dropwise condensation, namely growth, coalescence and re-nucleation of droplets, by using a computer. Wu and Maa [15] deduced the droplet size distribution of the droplets less than the critical radius and growing up mainly through the direct condensation of steam based on the population balance theory, and for the larger droplets, the droplet size distribution function proposed by Le Fevre and Rose [10] was still used.…”

Section: Introductionmentioning

confidence: 99%

Molecular clustering physical model of steam condensation and the experimental study on the initial droplet size distribution

Song

Lan

et al. 2009

International Journal of Thermal Sciences

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A Synthesis of the Total Process of Dropwise Condensation Using the Method of Computer Simulation

Cited by 10 publications

References 0 publications

Simulation of Drop-Size Distribution During Dropwise and Jumping Drop Condensation on a Vertical Surface: Implications for Heat Transfer Modeling

Simulation of Drop-Size Distribution During Dropwise and Jumping Drop Condensation on a Vertical Surface: Implications for Heat Transfer Modeling

About the Role of Falling Droplets’ Sweeping in Surface Renewal during Dropwise Condensation

Molecular clustering physical model of steam condensation and the experimental study on the initial droplet size distribution

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