Filmwise Condensation Research Articles

Temperature distribution considering the film-wise condensation and its impact on multi-stage oil production during the co-injection of steam-CO2

The co-injection of steam and CO2 into oil sands reservoirs has proved to be one of the most efficient and environmentally friendly methods to produce bitumen. Nevertheless, the condensation mechanism of steam in the reservoir is film-wise condensation under the effect of CO2, which reduces the heat transfer efficiency of steam. To obtain accurate oil production during the co-injection of steam-CO2, it is critical to predict the temperature distribution considering the film-wise condensation and clear its impact on oil production. In this study, laboratory experiments with different injectors were conducted to clear the effect of film-wise condensation on temperature distribution in the formation. Then, a mathematical model considering film-wise condensation was established to predict the temperature distribution and oil production, compared with the measured experiment result and multi-stage oil production from field data. Finally, the effect of temperature distribution on multi-stage oil production was analyzed through different injection volumes. The results indicated that the impact of film-wise condensation inhibits the development of the steam zone(Ts) but explicitly expands the hot water zone(Ts ∼ Tr). Moreover, the different injection components affect film-wise condensation, and CO2 has a more pronounced effect, whereas steam has little impact on the hot water zone despite its significant effect on steam zone expansion by weakening the film-wise condensation. Furthermore, the oil production exhibits the multi-stage characteristic controlled by different heating zones(the steam zone and the hot water zone), such that the steam zone contributes to higher oil production in the rising stage, and a larger hot water zone induces a longer life of the rising stage and the stable stage.

Dropwise condensation performance of sprayable polymer/copper oxide composite coating

Even though dropwise condensation (DWC) has received significant attention for its potential to enhance heat transfer performance at a higher order than filmwise condensation (FWC), the scalability of durable DWC-promoting surfaces to sustain prolonged condensation remains challenging. The spray coating presents itself as a potential scalable method to deposit hydrophobic coating onto a metallic substrate. However, the conventional sprayable fluoropolymer exhibits poor adhesion to the substrate and thus requires a base coat before it can be deposited on a metallic substrate. To address this challenge, this study investigated dropwise condensation performance on a polytetrafluoroethylene/imide-based binder/copper oxide composite (PTFE/PI/CuO) coating that is deposited into a copper substrate using simple one-step spray coating and thermal annealing. The PTFE particles provide the necessary hydrophobic characteristics. At the same time, the polymer binder fills the pores between the particles, preventing droplet nucleation within the structure and minimizing the occurrence of flooding that can lead to undesirable droplet pinning. The PTFE/PI/CuO coating successfully promotes pinned-free dropwise condensation, leading to approximately two times higher heat transfer enhancement than filmwise condensation. Moreover, the formation of micro-scale hydrophilic CuO clusters at the top of the coating surface acts as nucleation sites that increase droplet growth rate and departure frequency without altering the droplet departure radius. As a result, PTFE/PI/CuO exhibits 1.4x times higher heat transfer over the PTFE/PI. Furthermore, a durability enhancement was obtained by adding sub-micron copper particles. While PTFE/PI coating failed after exposure to steam, no visible damage was observed from PTFE/PI/CuO, thus indicating enhanced durability. Moreover, the PTFE/PI/CuO composite also exhibited resistance against mechanical damage as its heat transfer performance remained similar even after being subjected to abrasion. Finally, the pull-off adhesion test revealed that PTFE/PI/CuO has higher adhesion strength than PTFE/PI, making it more suitable for dropwise condensation application.

Infrared Spectral Emissivity Dynamics of Surfaces Under Water Condensation

AbstractWater condensation on a surface strongly affects its effective emissivity, especially in the atmospheric window, a wavelength range essential for outdoor applications related to energetically passive cooling and heating. The evolution of emissivity of a silicon surface during dropwise and filmwise water deposition is studied. The evolution of the spectral radiative properties shows that the increase in effective emissivity due to the growth of a droplet pattern is steeper than for a growing water film of equivalent thickness. The change of surface emissivity takes place in the first moments of condensation where droplets as small as 10 µm drastically impact the reflectance of the pristine surface. The upper limit of effective emissivity is reached for a droplet radius or film thickness of 50 µm. During dropwise condensation, effective emissivity is weighted by the drop surface coverage and then remains within an asymptotic maximum value of 0.8, while in case of filmwise condensation, it is shown to reach 0.9 corresponding to water emissivity. Micrometer‐scale spatially‐resolved infrared spectral images enable to correlate the spatial variation of spectral properties to the droplet size and localization. Such findings are of interest to the implementation of moisture‐controlled emissivity tuning and radiative sky‐coolers for dew harvesting.

Desalination setup coated by silicone epoxy nanocomposite: A study on hydrophobic characteristics and condensation mechanisms

The formation of tortuous filmwise condensation in desalination setup alongside with reduction in thermal conductivity is a challenge accompanied by efficiency loss. This issue is directly influenced by hydrophobicity, which is a function of surface roughness, as well as surface chemistry. In this sense, the hydrophobicity of variant silicone epoxy based nanocomposites was evaluated to identify the optimum proportion composite for surface condensation of desalination setup. To this end, three types of fumed silica with distinct surface chemistry were utilized in a matrix at the weight percentage of 0.5, 1, 1.5, and 2. To investigate the hydrophobicity, roughness, and distribution of reinforcement, a series of characterization techniques, including contact angle, AFM, and FESEM were used. It was found that, in comparison to pure matrix, the nanocomposite modified with 5 wt % of hydrophobic additive and 0.5 wt % of hydrophilic fumed silica nanoparticles (SE/5B/0.5R200) has the highest contact angle (about 35%) and roughness (13 times), due to the migration of nanoparticle onto the surface. Also, coating the condensation surface of the desalination setup with optimum thickness, i.e. 60 × 10−6 m, resulted in the efficiency improvement by about 33 % compared to the uncoated setup, even after 168 hrs. Indeed, dropwise condensation, straight path movement of droplets, besides thermal conductivity adjust the efficiency.

Investigation of dropwise condensation of water through an efficient individual-based model

In recent years, researchers have directed their studies towards solutions aimed at enhancing heat exchangers effectiveness. In this context, dropwise condensation (DWC) has been identified among the most promising solutions to increase the condensation heat transfer coefficient (HTC). In fact, DWC provides heat transfer coefficients up to ten times higher than those achievable during filmwise condensation (FWC), resulting in both economic and energy benefits. The DWC phenomenon is usually modelled by combining the heat exchanged through a single droplet and the drop-size distribution. The latter can be divided into a distribution of large droplets N(r), determinable analytically by semi-empirical models, and a distribution of small droplets n(r), typically determined through statistical approaches called population-based models. Another possibility for the determination of the droplet-size density is to simulate the DWC process by an individual-based model (IBM). In this case, each drop is tracked throughout its entire life cycle (nucleation, growth, coalescence, sliding), and the drop-size distribution is obtained as a result. In this paper, a new IBM for the simulation of DWC of steam is proposed. The developed model allows for the simulation of more than 10 million droplets while keeping an acceptable simulation time thanks to the implementation of parallel computing. The predictions obtained from the model, in terms of drop-size distribution and condensation heat flux, are compared against both PBM results and experimental data.

Experimental investigation of condensation heat transfer on vertically inclined grooved aluminium surfaces

This study details the experimental investigation of surface condensation heat transfer on vertically inclined aluminium surfaces with simple modifications. A bespoke experimental apparatus was constructed to control the saturation conditions inside the condensation chamber where the test surface is located. The degree of subcooling of the test surface was precisely controlled by an external heat exchanger. The meter bar technique was used to evaluate the condensation heat flux. Using distilled water as the working fluid and a plane aluminium test surface as the baseline case, the experimental apparatus was validated by comparison of the determined heat transfer coefficient with Nusselt’s model of filmwise condensation on a vertical plane surface, where an excellent agreement was obtained. 7 different aluminium test surfaces were subsequently investigated, each one modified with grooves measuring 0.5mm by 0.5mm (height and width), with a consistent spacing of 0.5mm between them. Groove angles relative to the vertical axis of 0° (180°), 30°, 45°, 60°, 90°, 120°, and 150° were investigated, where grooves were symmetrically mirrored at the centre of each test surface. Results highlighted a significant influence of groove angle on the heat transfer coefficient, with the best-performing sample (150˚) producing a maximum enhancement of 45% and an average enhancement of 34% compared to the baseline test surface over the respective range of subcooling.

Patterned Quasi‐Liquid Surfaces for Condensation of Low Surface Tension Fluids

AbstractExtensive research concerns dropwise condensation of low surface tension fluids to promote energy efficiency and decarbonization in thermal energy systems. However, it is challenging as these fluids typically result in filmwise condensation. Drawing inspiration from the Namib desert beetle that enhances condensation through patterned wettability, conventional beetle‐inspired surfaces excel in water condensation but flood when condensing low surface tension fluids. In this work, a patterned quasi‐liquid surface is reported that achieves exceptional dropwise condensation of low surface tension fluids. The surface consists of alternating stripes with low surface energy, that is, a perfluoropolyether (PFPE) and fluorinated quasi‐liquid surface (FQLS), that shows ultralow contact angle hysteresis for ethanol and hexane. The PFPE stripes are slightly more slippery, acting as slippery bridges that accelerate droplet coalescence and removal. It is experimentally demonstrated that the striped PFPE‐FQLS pattern exhibits a heat transfer coefficient 85%, 330%, and 550% higher than that of PFPE, fluorinated silane, and filmwise condensation, respectively. This study reveals that a high contact angle is desired to sustain dropwise condensation, irrespective of contact angle hysteresis. These findings provide a new paradigm for promoting the dropwise condensation of low surface tension fluids and offer valuable insights into surface design for energy sustainability.

Numerical investigation of surface wettability effect on two-phase closed thermosyphon

A two-phase closed thermosyphon (TPCT) is promising for heat removal due to its simple structure and high performance in heat transfer. However, investigating the phase change process in TPCT through experiments with current technology is still challenging. To study the various surface wettability effects on TPCT, this is the first systematical volume of fluid (VOF) method-based numerical study. The wettability in terms of contact angles (5°, 40°, 120°, and 175°) is endowed on the surfaces of TPCT. The numerical results of heat transfer coefficients of the TPCT show good agreement compared with the correlations. The simulation results reveal that the hydrophilic evaporator and the hydrophobic condenser benefit heat transfer. Within the input power of 376.14 W, the hydrophilic evaporator can reduce the thermal resistance of the evaporator to 35.3 % and delays the vapor film formation. The hydrophobic condenser decreases the thermal resistance of the condenser at 3.64 % and prevents filmwise condensation. The surface wettability is critical to the temperature distribution along the evaporator, but the main temperature drop is located between the adiabatic section and the condenser. It is also noted that the thermal resistance of the condenser is dominant to the overall thermal resistance. This study provides a detailed physical insight into the surface wettability effect on TPCT and benefits the future design in thermal engineering applications.

Comparative wetting behavior of condensed and sessile drops on single micro-scale textured hydrophobic surfaces: Physical insights for condenser design

Dropwise condensation (DWC) has gained significant attention in industrial applications for enhancing heat transfer efficiency. The wetting behavior of condensed droplets on patterned surfaces is crucial in DWC but has yet to be systematically investigated. In this study, we search for single micro-scale textured surfaces that can form Cassie condensed droplets. A total of 153 square-pillar-array-patterned hydrophobic substrates with various solid fractions and roughness factors were fabricated. An inverted optical microscopy system was applied to observe the wetting behavior of bottom-up growing condensed droplets and top-down depositing sessile drops on all substrates directly. Condensed droplets may exhibit different temporary wetting states simultaneously until their diameter exceeds 177.6 μm. Cassie condensed droplets can form through frequent dewetting transition on substrates with pillar-height ranging between 3.31 and 6.56 μm and pillar-spacing not exceeding 5.0 μm. Sessile droplets on superhydrophobic surfaces with excessively high pillar-heights always exhibit the Cassie state. However, condensed droplets on such surfaces exhibit an irregularly shaped Wenzel state instead, leading to filmwise condensation. Cassie and Wenzel DWC substrates demonstrate 28.3 % degradation and 36.9 % enhancement in experimentally obtained heat flux compared to a Teflon-coated flat surface. Our findings provide a guideline for the condenser's textured surface design to improve DWC.

Experimental Heat Transfer Coefficients for Zeotropic Mixture Condensation of Hexamethyldisiloxane/Octamethyltrisiloxane and Ethanol/Hexamethyldisiloxane

AbstractLegal requirements for refrigerants necessitate a continuous development of these fluids, also focusing on mixtures. This article contributes three aspects to the ongoing research: (1) Experimental mean heat transfer coefficients were determined for the condensation of two novel zeotropic mixtures, hexamethyldisiloxane (MM)/octamethyltrisiloxane and ethanol/MM, gathered for filmwise condensation on a vertical tube. (2) Both mixtures were investigated with several compositions to provide a comprehensive understanding of the mixture effects. (3) The results were taken to develop a novel superposition approach to predict mixture condensation.

Investigation of the effects surface alteration via coatings on the condensation heat transfer and wettability

Background Heat exchangers are a critical component in organic Rankine cyclic (ORC) geothermal power plants as they represent more than 50% of the capital. In this study, the thermal performance of coatings devised for condensation heat exchangers have been studied. Methods For this purpose, a mock-up heat exchanger rig was designed and fabricated. The coatings used for the trials are of hydrophobic nature, in order to promote a change in the heat transfer mode from film-wise condensation to drop-wise condensation. The coatings for this study were developed by chemical vapour deposition and magnetron sputtering on aluminium substrates. The wettability and adhesion of the coatings was characterized before and after the tests. Statistical analysis was used to analyse the heat transfer related data. Results The results indicate that the silica based coating produced an improvement in the heat transfer performance indicators and the working fluid caused a deterioration of the wetting properties. However, even at the end of the tests, the coated samples performed better than the substrate material in terms of heat transfer performance. Conclusions The results of this research prove that shifting from film-wise condensation to drop-wise condensation is viable method to improve heat transfer efficacy. However, a one to one correlation could not be established with water contact angles measured in water or diiodomethane suggesting that wettability properties in ORC fluid could differ to established in these conventional fluids for contact angle measurements.

Study of filmwise condensation heat transfer enhancement by removal of condensate using wettability difference

Study of filmwise condensation heat transfer enhancement by removal of condensate using wettability difference

Metal Surface Engineering for Extreme Sustenance of Jumping Droplet Condensation.

Water vapor condensation on metallic surfaces is critical to a broad range of applications, ranging from power generation to the chemical and pharmaceutical industries. Enhancing simultaneously the heat transfer efficiency, scalability, and durability of a condenser surface remains a persistent challenge. Coalescence-induced condensing droplet jumping is a capillarity-driven mechanism of self-ejection of microscopic condensate droplets from a surface. This mechanism is highly desired due to the fact that it continuously frees up the surface for new condensate to form directly on the surface, enhancing heat transfer without requiring the presence of the gravitational field. However, this condensate ejection mechanism typically requires the fabrication of surface nanotextures coated by an ultrathin (<10 nm) conformal hydrophobic coating (hydrophobic self-assembled monolayers such as silanes), which results in poor durability. Here, we present a scalable approach for the fabrication of a hierarchically structured superhydrophobic surface on aluminum substrates, which is able to withstand adverse conditions characterized by condensation of superheated steam shear flow at pressure and temperature up to ≈1.42 bar and ≈111 °C, respectively, and velocities in the range ≈3-9 m/s. The synergetic function of micro- and nanotextures, combined with a chemically grafted, robust ultrathin (≈4.0 nm) poly-1H,1H,2H,2H-perfluorodecyl acrylate (pPFDA) coating, which is 1 order of magnitude thinner than the current state of the art, allows the sustenance of long-term coalescence-induced condensate jumping drop condensation for at least 72 h. This yields unprecedented, up to an order of magnitude higher heat transfer coefficients compared to filmwise condensation under the same conditions and significantly outperforms the current state of the art in terms of both durability and performance establishing a new milestone.

Durable, Ultrathin, and Antifouling Polymer Brush Coating for Efficient Condensation Heat Transfer.

Heat exchangers are made of metals because of their high heat conductivity and mechanical stability. Metal surfaces are inherently hydrophilic, leading to inefficient filmwise condensation. It is still a challenge to coat these metal surfaces with a durable, robust, and thin hydrophobic layer, which is required for efficient dropwise condensation. Here, we report the nonstructured and ultrathin (∼6 nm) polydimethylsiloxane (PDMS) brushes on copper that sustain high-performing dropwise condensation in high supersaturation. Due to the flexible hydrophobic siloxane polymer chains, the coating has low resistance to drop sliding and excellent chemical stability. The PDMS brushes can sustain dropwise condensation for up to ∼8 h during exposure to 111 °C saturated steam flowing at 3 m·s-1, with a 5-7 times higher heat transfer coefficient compared to filmwise condensation. The surface is self-cleaning and can reduce the level of bacterial attachment by 99%. This low-cost, facile, fluorine-free, and scalable method is suitable for a great variety of heat transfer applications.

Condensation enhancement experiment investigation of pure steam and steam-air mixture over the chrome-plated tube with different plating thickness

The condensation enhancement research of pure steam and steam with non-condensable gas is of great significance for reactor safety. In this study, to evaluate the influence of chrome-plated tubes on condensation enhancement, pure steam and steam with air condensation heat transfer experiments are conducted, and the plating thicknesses of 1 μm (tube #1) and 10 μm (tube #2) are considered. The results show that dropwise condensation (DWC) occurred in the part of tube #1 surface, while tube #2 surface is filmwise condensation (FWC). For the pure steam condition, the steam condensation heat transfer coefficient (HTC) of tube #2 is higher than that of tube #1, and both are greater than the theoretical analysis of Nusselt. Thus, the condensation enhancement effect of the chrome-plated tubes is remarkable. For the steam with air condition, a new condensation HTC expression is proposed, which is related to gas pressure, wall subcooling, and air mass fraction. Compared with the widely used experimental correlations and the experimental data of polishing tubes, it is found that the condensation enhancement performance is not significant. This is because the dominant thermal resistance affecting heat transfer is the air layer at the gas-liquid interface. Thus, enhancing the disturbance of the gas layer is the key to the condensation enhancement of steam with non-condensable gas.

Femtosecond laser induced porous surface on polymethyl methacrylate for filmwise condensation to improve solar still productivity

The decline in freshwater availability has spurred research into employing solar desalination technology. Recent research has concentrated on investigating the use of surface modification to improve the productivity of solar still for desalination. This paper presents the use of femtosecond laser texturing to induce a porous surface on the polymethyl methacrylate (PMMA) cover of a solar still for producing filmwise condensation. Vertical lines 2.5 mm wide were fabricated on the PMMA surface using ultrafast laser texturing, and experiments were conducted using the modified cover on a solar still at a constant basin water temperature. Results show that the static water contact angle measured on the cleaned laser textured surface is hydrophobic. However, the formation of the porous structure leads to a change in wetting state from Cassie-Baxter to Wenzel upon exposure to water vapour. This change in wetting state enables the formation of filmwise condensation under the continuous presence of water vapours. The solar still productivity improves by 15.4 % and 23.1 % using both cleaned and uncleaned laser textured surfaces respectively. The modified surface is stable upon repeated exposure to water vapour, thus proving to be an excellent surface modification method for enhancing PMMA covered solar still performance.

Hydrogel-based intelligent greenhouse films for simultaneous fogging prevention and indoor environmental monitoring

Fogging prevention and environmental monitoring in a greenhouse are usually accomplished by different components, as the former relies on persistent surface-wetting capability, while the latter requires conductivity or capacitance to vary with ambient conditions. Combining these seemingly unrelated functions presents a significant challenge. Here, we report an all-in-one hydrogel that integrates these exclusive functions, enabling it to simultaneously work as an anti-fogging coating and environmental monitor in greenhouses. The strategy involves constructing loosely crosslinked hydrophilic networks enriched with abundant free ions and a specific amount of glycerol. The transparent hydrogel, composed of long-chain polymers, exhibits excellent adhesion to the inner surface of the greenhouse film and significantly decreases its water contact angle by filmwise condensation, thereby reinforcing the anti-fogging properties of the film without sacrificing its transparency. Meanwhile, the presence of glycerol and free ions enables the gel to sustain a wide range of temperature and humidity while displaying environmentally sensitive conductivity, endowing the gel with the same function as conventional rigid environmental sensors. As a proof-of-concept demonstration, a wireless indoor environmental monitoring system in a homemade lean-to greenhouse is established by utilizing hydrogel as the sensing module, which also performs well in prohibiting fogging on the greenhouse film. We hope this work could provide some inspiration for the development of multifunctional intelligent greenhouse films.

Investigation of filmwise condensation and flow characteristics on inner curved heat transfer surface

Investigation of filmwise condensation and flow characteristics on inner curved heat transfer surface

Condensation mode transition and droplet jumping on microstructured surface

Condensation enhancement on the micropillar structured surfaces is studied using a three-dimensional lattice Boltzmann model, and the optimal micropillar configuration is assessed. The impacts brought by varying micropillar geometric parameters on heat transfer and droplet dynamics during dropwise-to-filmwise transition are explored. Increasing micropillar width and spacing or decreasing height accelerates nucleation and improves nucleation density in the dropwise condensation stage, while radial contraction of the liquid film is hindered and the heat transfer area is increased in the filmwise condensation stage. Compared with its plain competitor, the maximum number of the isolated droplets is increased by 525%, the nucleation time is advanced by 57.1% and the heat flux is increased by 187.4% on the optimal micropillar surface. The entire condensation process spanning over nucleation, coalescence and jumping of multiple condensate droplets on the micropillar surface is realized using the present three-dimensional lattice Boltzmann model for the first time. The effects of height and spacing of micropillar arrays on jumping height and velocity are analyzed. The results show that the micropillar height poses little effect on the jumping height and velocity when the micropillar spacing is 0.1. When the micropillar spacing is 0.15, the jumping height and velocity first increase but then decrease with the increase of the micropillar height. Finally, the condensation heat transfer mechanism under different subcooling on the hierarchical surface is analyzed in detail.

Scalable micro/nanostructured superhydrophobic surface modifications for enhanced energy efficiency and heat transfer performance in stainless steel and titanium

Condensation refers to the change of a substance from a gaseous phase to a liquid phase, an example of which is the condensation of water vapor in nature. Condensation is used in many industries, such as energy generation and seawater desalination. On a general surface, filmwise condensation is the main phenomenon in which gaseous water vapor is condensed in the form of a film. However, film condensation acts as a factor that reduces energy efficiency as the liquid film formed on the surface interferes with heat transfer. A phenomenon opposite to film condensation is dropwise condensation, which is immediately separated after condensation in the form of droplets, and thus a film is not formed, greatly improving heat transfer efficiency. Because of these advantages, many studies have been conducted, and most studies have induced dropwise condensation by modifying the surface to be superhydrophobic. However, in the case of a superhydrophobic surface, it takes a lot of time and money in the process, so there is a great difficulty in increasing the area. Among them, stainless steel and titanium, which are most materials for industrial heat exchangers, have high robustness, so there are few studies on improving the condensation performance after surface modification due to the difficulty of processing. For this reason, there is a large gap between the currently conducted studies and the actual industry. Our research team succeeded in modifying the surface of a stainless steel and titanium tube the size of an actual heat exchanger into superhydrophobicity with a simple process. We confirmed that the condensation performance was improved on the superhydrophobic surface through experiments under various conditions. By comparing the improvement in the heat transfer performance of stainless steel and titanium under several conditions, the main cause of the performance improvement was proved. This study is expected to play a major role in the eco-friendly future industry where energy efficiency is important by improving the heat transfer performance of stainless steel and titanium, which are mainly used throughout the industry.