Effect of Mini/Micro/Nanostructures on Filmwise Condensation of Low-Surface-Tension Fluids

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Ablimit Aili ◽  
QiaoYu Ge ◽  
TieJun Zhang
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Condensation Heat Transfer ◽  
Structured Surfaces ◽  
Nanostructured Surfaces ◽  
Hydrophobic Coating ◽  
Pin Fins ◽  
Solid Friction ◽  
Solid Liquid ◽  
The Impact

Micro/nanostructured surfaces have been widely explored to enhance condensation heat transfer over the past decades. When there is no flooding, micro/nanostructures can enable dropwise condensation by reducing solid-droplet adhesion. However, micro/nanostructures have mixed effects on filmwise condensation because the structures can simultaneously thin the condensate film and increase the fluid–solid friction. Although oil infusion of structured surfaces has recently been shown to render filmwise condensation dropwise in many cases, challenges remain in the case of extremely low-surface-tension fluids. This work aims to provide a unified experimental platform and study the impact of mini/micro/nanostructures on condensation heat transfer of low-surface-tension fluids in a customized environmental chamber. We first investigate the effect of microstructures, hydrophobic coating, as well as oil infusion on the filmwise condensation of a low-surface-tension fluid, e.g., refrigerant, on microporous aluminum surfaces. And we show that for low-surface-tension condensates, microstructures, hydrophobic coating, or oil infusion do not play a considerable role in enhancing or deteriorating heat transfer. Next, we study how the addition of nanostructures affects the condensation performance of the refrigerant on copper mini-fin structures. It is found that nanostructures slightly deteriorate the condensation performance due to the dominance of solid–liquid friction, although the performance of these mini-fins with nanostructured surfaces is still better than that of the mini-pin-fins. These results provide guidelines of designing mini/micro/nanoscale surface structures for enhanced condensation applications.

Condensation of Low-Surface-Tension Fluids on Microstructured Surfaces at Low Temperature

2017 ◽  
Author(s):  
Abulimiti Aili ◽  
Qiaoyu Ge ◽  
TieJun Zhang
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Low Temperature ◽  
High Surface ◽  
Condensation Heat Transfer ◽  
Lubricant Oil ◽  
Microstructured Surfaces ◽  
Performance Deterioration ◽  
Coated Surface ◽  
Coated Surfaces

Filmwise condensation of a low surface tension fluid (i.e. refrigerant) on microstructured aluminum surfaces is studied to investigate the effect of the structures on condensation heat transfer at low temperature. The hypothesis is that the structures may cause thinning of the condensate film at micro-scales, thus resulting in an enhancement of condensation heat transfer. However, the structures may also decrease the mobility of the condensate near the surface due to increased friction, thus potentially leading to performance deterioration. The aim of this work is to investigate which of the two counteracting mechanisms dominate during filmwise condensation. Condensation experiments are carried out in a low-temperature vacuum chamber. Compared with the Nusselt model of condensation, the microstructured surfaces, either coated or uncoated, show similar performance, with potentially slight enhancement at low subcooling degree and slight deterioration at high subcooling degree. When the microstructured and silane-coated surface is infused with a non-volatile and very low-surface-tension lubricant oil, the lubricant is displaced by the condensate and there is almost no change in the condensation performance. Our results show that, unlike the case of dropwise condensation of high-surface tension fluids, microstructured and coated surfaces with/without infusing oil is not exciting to enhanced filmwise condensation of low-surface-tension fluids.

The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

2013 ◽  
Author(s):  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Thermal Contact ◽  
Heat Pumps ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Condensing Heat Transfer ◽  
The Impact ◽  
Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

A Computational Study of Thin Film Dynamics on Micro-Structured Surfaces

2016 ◽  
Author(s):  
Linyu Lin ◽  
Nam T. Dinh ◽  
Ram Sampath ◽  
Nadir Akinci
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Surface Tension ◽  
Contact Line ◽  
Boiling Heat Transfer ◽  
Smooth Surface ◽  
High Heat ◽  
Structured Surfaces ◽  
Structured Surface ◽  
Dry Patch

The present study is motivated by interest in understanding of physical mechanisms that govern the effect of material and micro-structural characteristics of heat surface on boiling heat transfer and burnout at high heat fluxes. The effect was reported and investigated experimentally and analytically over several past decades. Only recently, with the advent of nanotechnology including microscale manufacturing, it becomes possible to perform high heat-flux boiling experiments with control of surface conditions. Of particular importance for practice is the potential for significant enhancement of boiling heat transfer (BHT) and critical heat flux (CHF) in pool and flow boiling on heaters with specially manufactured and controlled micro-structured surfaces. This enhancement is very important to a very wide range of engineering applications, like heat exchanger and cooling system, where maximum flux is needed. Currently, there are many controlled experiments that investigate such effect and they lend themselves a subject for detailed computational analysis. The focus of this study is micro-hydrodynamics of the evaporating thin liquid film at the receding triple contact line, corresponding to formation of dry spot in the footprint of a growing bubble. Parametric investigations are performed to assess the hypotheses that micro-structured surfaces enhance resilience to burnout due to residual liquid in the dry patch after contact line receding. Towards the study objective, a particle-based (mesh-less) method of computational fluid dynamics called Smoothed Particle Hydrodynamics (SPH) is adopted. The SPH method is selected for its capability to handle fluid dynamics in complex geometries and free surface problems without mass loss (characteristic of alternative interface capturing schemes used in mesh-based methods). Both surface tension and surface adhesion (hydrophilicity) are implemented and tested. The solid (heater) surface and manufactured micro-structures are represented by solid-type particles. Heat transfer, phase change (evaporation) and vapor dynamics are not included in the present simulation. The bouncing drop case measures the contact time of water droplet with solid surface. This case is used for “mesh” sensitivity (particle size) study and calibration of boundary conditions and surface tension coefficient. Subsequently, case studies are formulated and performed for contact line dynamics on heater surfaces with the fabricated Micro Pillar Arrays surfaces (MPA) and smooth surface. Variable characteristics include surface tension and pillar density on structured surface (modified by changing distance between pillars). First of all, residual fluid are found in all simulations with structured surface, while fluid are drained for smooth cases. For structured surface, it’s found that after the contact line recedes, fluid with higher surface tension resides in the dry patch more than fluid with lower coefficient, and the relation tends to be non-linear. While for smooth surface, all fluid will be drained after certain time and the relations are non-monotonic; it’s also found that the amount of residual fluid increase as the distance between pillars decreases until a limit. The fluid then starts to decrease with pillars being set further apart. The increase starts from 30 μm and the limit is around 10 μm.

A Systematic Study of Pool Boiling Heat Transfer on Multiscale Structured Surfaces

2014 ◽  
Author(s):  
Russell P. Rioux ◽  
Eric C. Nolan ◽  
Calvin H. Li
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Multiple Scales ◽  
Pool Boiling ◽  
Theoretical Models ◽  
Sintering Process ◽  
Structured Surfaces ◽  
Pool Boiling Heat Transfer ◽  
Nanostructured Surfaces ◽  
Modified Surfaces

A study has been conducted to examine the effects of macroscale, microscale, and nanoscale surface modifications in water pool boiling heat transfer and to determine the effects of combining the multiple scales. Nanostructured surfaces were created by acid etching, while microscale and macroscale surfaces were manufactured through a sintering process. Six structures were studied as individual and/or collectively integrated surfaces: polished plain, flat nanostructured, flat porous, modulated porous, nanostructured flat porous, and nanostructured modulated porous. Boiling performance was measured in terms of critical heat flux (CHF) and heat transfer coefficient (HTC). Both HTC and CHF have been greatly improved on all modified surfaces compared to the polished baseline. The CHF and HTC of the hybrid multiscale modulated porous surface have achieved the most significant improvements of 350% and 200% over the polished plain surface, respectively. Nanoscale, microscale, and macroscale integrated surfaces have been proven to have the most significant improvements on HTC and CHF. Experimental results were compared to the predictions of a variety of theoretical models with an attempt to evaluate both microscale and nanoscale models. It was concluded that models for both microscale and nanoscale structured surfaces needed to be further developed to be able to have good quantitative predictions of CHFs on structured surfaces.

20315 Condensation Heat Transfer on Micro Structured Surfaces

2014 ◽  
Vol 2014.20 (0) ◽  
pp. _20315-1_-_20315-2_
Author(s):  
Tomohiro YABE ◽  
Hiromu OHNO ◽  
Hiroyasu OHTAKE ◽  
Koji HASEGAWA
Keyword(s):  
Heat Transfer ◽  
Condensation Heat Transfer ◽  
Structured Surfaces

Study on Condensation Heat Transfer on Micro Structured Surfaces (Effect on Condensation Heat Transfer of Metal Sputtering Surfaces)

2013 ◽  
Author(s):  
Kohei Yamazaki ◽  
Hiroyasu Ohtake ◽  
Koji Hasegawa
Keyword(s):  
Heat Transfer ◽  
Metal Film ◽  
Copper Surface ◽  
Thin Metal Film ◽  
Thin Metal ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Transfer Coefficients ◽  
Structured Surfaces ◽  
Heat Transfer Coefficients

The present study was intended to examine how the condensation heat transfer, especially the dropwise condensation, was affected by modifying the surface nature. In the present study, condensation heat transfer experiments for steam were performed by using mirror-finished copper surface and some very thin metal-film surfaces by using sputtering on mirror-finished copper block. That is, the effects on pattern of condensation heat transfer, i.e., dropwise or film-wise condensation, of metal-sputtered surfaces were examined experimentally and qualitatively. The present experimental results showed that the condensation on sputtered metal surfaces of Copper (Cu), Chromium (Cr) and Lead (Pb), became dropwise condensation. The heat transfer coefficients were ten times higher than the Nusselt equation. The condensation on sputtered metal surface of Titanium (Ti) became filmwise condensation. High contact angle was trended to be dropwise condensation on very thin metal-film surfaces by using sputtering.

An Exploration of Transport Within Microdroplet and Nanodroplet Clusters During Dropwise Condensation of Water on Nanostructured Surfaces

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Hector Mendoza ◽  
Sara Beaini ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Droplet Size ◽  
Experimental Studies ◽  
Dropwise Condensation ◽  
Maximum Heat ◽  
Nanostructured Surfaces ◽  
Maximum Heat Transfer ◽  
The Impact

Experimental studies of dropwise condensation have generally indicated that higher heat transfer coefficients correspond to smaller mean sizes for droplets growing through condensation on the surface. Recent investigations of dropwise condensation on nanostructured surfaces suggest that optimizing the design of such surfaces can push mean droplet sizes down to smaller values and significantly enhance heat transfer. This paper summarizes a theoretical exploration of the limits of heat transfer enhancement that can be achieved by pushing mean droplet size to progressively smaller sizes. A model analysis is developed that predicts transport near clusters of water droplets undergoing dropwise condensation. The model accounts for interfacial tension effects on thermodynamic equilibrium and noncontinuum transport effects, which become increasingly important as droplet size becomes progressively smaller. In this investigation, the variation of condensing heat transfer coefficient for droplet clusters of different sizes was explored for droplet diameters ranging from hundreds of microns to tens of nanometers. The model predictions indicate that the larger droplet transport trend of increasing heat transfer coefficient with decreasing mean droplet size breaks down as droplet size becomes smaller. The model further predicts that as drop size becomes smaller, a peak heat transfer coefficient is reached, beyond which the coefficient drops as the size continues to diminish. This maximum heat transfer coefficient results from the increasing importance of surface tension effects and noncontinuum effects as droplet size becomes smaller. The impact of these predictions on the interpretation of dropwise condensation heat transfer data, and the implications for design of nanostructured surfaces to enhance dropwise condensation are discussed in detail.

Cell Growth Morphology on Nano-Structured Surface Based on Wetting

2014 ◽  
Vol 1061-1062 ◽  
pp. 575-578
Author(s):  
Ge Qin ◽  
Hao Xue Li ◽  
Meng Die Ma ◽  
Juan Juan Li ◽  
Ya Fei Deng
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Cell Morphology ◽  
Nanostructured Surface ◽  
Growth Morphology ◽  
Nanostructured Surfaces ◽  
Microstructured Surface ◽  
Solid Liquid ◽  
The Impact ◽  
Growth Shape

This paper studied the growth morphology of the cells on the nanostructured surfaces of the bio-electrodes implanted in human patients. A transition model of the cells on those surfaces, which is the W model or C-B model, was deduced according to the effect of the microstructures on the wetting characteristics and the solid-liquid contact angle models of the microstructured surface. According to the contact angle formula of the model of the droplet on the solid surface, the formula was derived to describe the morphology of the ells on the nanostructured surface. The results of the experiments showed the impact of nanostructured to the morphology of the cells. The changes of the cell morphology on the smooth surface and the nanostructured surface showed that the cell morphology was affected by the nanostructures of solid surface, and the growth shape of cell was different when the sizes were different.

Study on Condensation Heat Transfer of Micro Structured Surfaces

2009 ◽  
Author(s):  
Hiroyasu Ohtake ◽  
Yasuo Koizumi ◽  
Soichiro Miyake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Film ◽  
Copper Surface ◽  
Heat Fluxes ◽  
Condensation Heat Transfer ◽  
Silicon Surfaces ◽  
Copper Surfaces ◽  
Structured Surfaces ◽  
Mems Technology

Condensation heat transfer experiments for steam were performed by using mirror-finished copper surfaces, mirror-finished silicon surfaces and silicon surfaces with micro grooves or micro pins on it. The micro-grooves and the micro-pins were created by the MEMS technology. The film- and also the drop-wise condensation were observed on the copper surface. The film-wise condensation heat flux was in good agreement with the values of the Nusselt equation. It was approximately one-tenth of the drop-wise condensation heat flux. The condensation on the mirror-finished silicon surface was the drop-wise condensation. The heat flux was approximately one-tenth of the drop-wise condensation heat flux on the copper surface. The condensation on the micro-grooved and the micro-pin silicon surfaces was film-wise. The condensation heat fluxes were approximately one-tenth of the copper surface film-wise condensation heat flux. When the contact angle was smaller than 70 degree, the condensation was film-wise and when larger than the value, drop-wise. It seemed that the hollow parts of the micro-grooved or the micro-pin surface were filled with condensate first after the condensation was initiated. It made the surface hydrophilic and the condensation film-wise.

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