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Condensation, a process in which the phase changes from vapor to liquid, plays a crucial role in various industrial systems. So far, several techniques have been proposed to improve the characteris...

Industrial heat pumps have been developed to recycle surplus heat from various industrial processes for steam generation. A condenser in an industrial heat pump needs to meet the high condensation temperature. Alternative refrigerants are also needed for condensers. The objective of this study was to compare condensation heat transfer characteristics of R1234ze(E), an alternative refrigerant at high reduced pressure, and R134a, a conventional refrigerant. A test section of copper tube with a diameter of 1/2 inch and a length of 4 m was used. The test section was installed inside a PVC tube which was cooled with brine. Experimental conditions were: reduced pressure from 0.5 to 0.7 and mass flux of 500–600 kgm-2s-1. Condensation heat transfer coefficients of R1234ze(E) and R134a decreased with an increase in reduced pressure. Effects of mass flux on refrigerants decreased with an increase in reduced pressure. A Travis model showed the best performance for estimating condensation heat transfer coefficients of R1234ze(E) and R134a under high reduced pressure conditions.

This paper is concerned with the investigation of the effect of the nature of the surface of the condenste film on heat transfer during laminar film condensation. An idealized rippled nature of the film surface is proposed. Local heat transfer coefficients are calculated for film condensation on a vertical plate in laminar case. Calculations are performed numerically. For the proposed rippled nature of the film surface, the average heat transfer coefficients are up to 20% higher than that obtained for smooth surface.

The condensation heat transfer coefficient and the pressure drop were investigated experimentally and numerically in a microtube condenser using R134a. The microtube condenser comprises of trapezoi...

In the present study, nano-micro-structured surfaces have been systematically designed and manufactured in order to generate controlled dropwise condensation mode for enhanced heat transfer during phase-change from vapor to liquid. The conceptualization of micro-structures was conducted by using thermal modelling of an individ-ual droplet pinned at a single micro-hexagonal cavity. By varying droplet radius, resulting contact angles and geo-metric dimensions of micro-structure, threshold values have been determined for the later manufacturing process. According to the calculations for instance at contact angles of 150°, a subcooling of 1 K and a maximum droplet radius of 100 µm, the edge length and the depth of the micro-structures should be kept below 50 µm and 25 µm, respectively. Ensuring these parameters, a roughly 100 % larger heat transfer coefficient would result compared to that predicted by the classical Nusselt theory for filmwise condensation. Taking into account the mathematical analysis, laser ablation technique was adopted on 7075 aluminum samples to emboss hexagonal structures with respect to the predicted dimensions. After this step, the samples were electrochemically etched in order to achieve contact angles of more than 150° to ensure superhydrophobic solid-liquid interaction at the surface. Measurements with a high-precision microscope show that most of the structure dimensions and geometric shape were precisely manufactured. The Tensiometer results disclosed that the surface topography at all samples exhibit contact angles larger than 150° for a sessile droplet with a radius of 100 µm pinned on an individual micro-hexagon.

Aiming at studying the condensate flow phenomenon and air-steam–mixture condensation heat transfer underneath a containment vessel surface, a test bench was constructed. The plate dimension was 1.5...

It is a coupling solution for optimizing the materials with good thermal conductivity and anti-corrosive modified coating of flue-gas condensation heat exchangers. The paper experimentally studied ...

In this work, the condensation heat transfer and pressure drop characteristics of plate heat exchangers were simulated, and the 3-D temperature, pressure, and velocity fields were obtained. From the flow field, we can see that the velocity of vapor is higher than that of condensate. From the pressure field, we can see that the pressure shows a downward trend along the flow direction, and there is, the more pressure drop in the first half of the plate. From the temperature field, we can see that the temperature gradient increases with the increase of velocity and pressure gradient. Meanwhile, the effect of vapor mass-flow, dryness and super-heat on condensation heat transfer coefficients and pressure drops were investigated. The results show that the pressure drop and heat transfer coefficient both increase with the increase of dryness, degree of superheat and mass-flow. In addition, the correlation equations developed to predict the condensation heat transfer and friction factor perfectly agree with the experimental results.

The present paper presents a review of condensation heat transfer across smooth and enhanced horizontal surfaces due to its significance in refrigeration, air conditioning and heat pump applications. The emphasizes is on the recent understanding of experimental as well as the semi-empirical correlations to investigate the heat transfer phenomena during condensation associated with enhanced geometries. An effort has been made to submit free-convection condensation effects outside of single tubes and the tube bundle with the influence of tube geometries, condensate retention and gravity on film condensation; however, comparison of forced convection is also presented. Alternative of conventional refrigerants in condensation process by low-global warming potential (GWP) refrigerants is addressed as well due to increase in atmospheric burden affected by hydro-fluoro-carbons (HFCs). Although many researchers have reviewed the condensation impact across enhanced surfaces, a few of them revised its behavior across pin-fin tubes. The effects of geometry, surface wettability, and operating conditions on the location, amount and form of condensate film are discussed. Various theoretical models prediction with the new experimental data across pin-fin tubes is also revealed. This review is distributed into two main sections: the first section focuses on condensation across enhanced tubes, sub dividing the study into integral-fin and pin-fin tubes based on theoretical and experimental investigations. It covers the geometrical effects concerning three dimensional (3D) surfaces, fin density, fin spacing and fin thickness. The later part of the paper concentrates on condensation behavior across the tube bundle incorporating the effects of fin density and refrigerant mixtures highlighting both theoretical and experimental knowledge. Recent research shows an agreement between theoretical and experimental models in the defined area; though, a considerable amount of work on semi-empirical correlation formulation is visible in the literature. The strength of this paper is the latest findings on condensation against different geometrical parameters of extended surfaces specifically across pin- fin tubes and the tube bundle. Finally, theoretical enhancement factors along with many heat transfer correlations are presented and recommendations are suggested for the future work.

Condensation heat transfer of R1234yf inside smooth and microfin tube with 2.5 mm outer diameter are studied experimentally. The experiments are carried out at a saturation temperature of 20°C and 30°C, mass velocity ranging from 50 to 200 kg m−2s−1 and vapor quality ranging from 0-1. The effects of mass velocity, vapor quality, and saturation temperature on condensation heat transfer coefficient are analyzed with R1234yf and R134a. Condensation heat transfer correlation for smooth tube is developed considering present experimental data and other researchers’ data. Correlation is developed using experimental data for 2.5 mm to 10 mm outer diameter tubes and refrigerants are R134a, R1234yf, R123 and R1234ze (E) by including other researchers’ data. Newly developed correlation is successfully predicted experimental data and other sources data within mean deviation of 15 %. Experimental data are also compared with previous correlations proposed for smooth and microfin tube.

Enhancement in heat-transfer performance via dropwise condensation on superhydrophobic surfaces is much greater than that realized via generic condensation on a regular surface. However, if the supersaturation level during condensation increases above a specific value, water may seep to greater depths between structures. This may lead to attached condensation, which reduces condensation heat-transfer efficiency below that of ordinary surfaces. Therefore, it is critical to avoid the occurrence of supersaturation when superhydrophobic surfaces are employed in condenser design. The proposed study presents a simple method for regulating supersaturation on the laboratory scale. Experiments concerning droplet behavior on a superhydrophobic plate were performed to investigate droplet detachment and attachment in accordance with the surface and droplet temperatures. Results obtained have been represented as a ″droplet-behavior map″, which clearly depicts boundaries dividing the detachment and attachment regions. The supersaturation threshold obtained from the said map has been compared against results obtained from condensation heat-transfer experiments performed in an actual condenser environment. As observed, the two results demonstrate excellent agreement. Although superhydrophobicity of surfaces remains unchanged at room temperature, changes may occur in the extent of the supersaturation section, which improves condensation heat-transfer performance, depending on the surface-structure complexity. Therefore, droplet-behavior mapping has been used in this study to determine the available supersaturation section in accordance with the variation in surface roughness. Results confirm that the available supersaturation region increases with increasing surface roughness and structural complexity. Therefore, prior to applying superhydrophobicity to condensers, droplet-behavior mapping must be performed to avoid operation under the supersaturation conditions, which causes attached condensation.

The condensation heat transfer characteristics of a new environmental refrigerant mixture R1234ze (E)/R152a (mass ratio 40:60, named NCUR01) in a horizontal micro-fin tube with an outer diameter of...

Indirect evaporative cooling is a rapidly developing air-handling technology and has great application potentials for energy recovery in hot and humid regions. The condensation in dry channels of an indirect evaporative cooler (IEC) occurs when the dew point temperature of outdoor air is high. However, the dynamic heat transfer performance of an IEC during the process of condensation evolution was rarely discussed. This paper aims to experimentally investigate the dynamic behaviour of primary air condensation and its effects on the convective and total heat transfer rate of an IEC. A transparent cover plate is placed outside an aluminium heat exchanger plate to visualize the evolution process of droplets retained on the surface. The droplets' falling frequency was recorded and the accumulated condensate mass was correlated based on an analytical method taking into account the contact angle and droplet volume. Results showed that the dynamic dehumidification performance can pose great influences on the convective heat transfer in IEC. The gradually diminished dropwise regions and increase of filmwise regions deteriorate the wet-bulb effectiveness of IEC by 14.8%. The convective heat flux keeps decreasing with the accumulation of condensate retention until a dynamic equilibrium is achieved between the retained and falling droplets.

Self-propelled jumping of condensate droplets (dew) enables their easy and efficient removal from surfaces and is essential for enhancing the condensation heat transfer coefficient and for delaying the frost growth rate on supercooled surfaces. Here, we report the droplet-jumping phenomenon using nanoporous vertically aligned carbon nanotube (VA-CNT) microstructures grown on smooth silicon substrates and coated with poly-(1

In industrial fields, heat source over 130°C are widely needed, and for this development of industrial high-temperature heat pump systems has been promoted. For the heat release process in such the heat pump systems, it is considered to use of a plate heat exchanger (PHE) in which a high pressure working refrigerant flows. In this study, to examine the effect of chevron angle on heat transfer of refrigerants flowing in chevron PHEs at supercritical pressure and high subcritical pressure, experiments were conducted using a chevron PHE with a chevron angle 75°. The measured heat transfer coefficient was compared with the data of three chevron PHEs with respective chevron angles 30°, 47.5° and 65° obtained previously. The effect of chevron angle on heat transfer at 65° and more was smaller than that at less than 65°, and the heat transfer coefficient in 75° PHE was almost the same with that in 65° PHE, considering difference in hydraulic diameter between the PHEs. Furthermore, the value of heat transfer coefficient achieved in 65° or 75° PHE was estimated to be almost maximum between 0° to 90°. On the other hand, the friction factor of 75° PHE was markedly larger than that of 65° PHE.

Condensation proceeds as dropwise or filmwise depending on the wettability of the condensing surface. These two modes of condensation have disparate heat transfer coefficients, with dropwise often exceeding filmwise. This work reports a surface with switchable superhydrophilic to hydrophobic wetting behavior that can exhibit both modes of condensation. Relative to the highly wetting state, which yields filmwise condensation, the nonwetting state exhibits dropwise condensation and twice the heat transfer coefficient. Relevance to thermal management is additionally discussed.

Basic structures of liquid-vapor separation cooling plates (LSCPs) and a liquid-vapor separation plate condenser (LVSPC) are innovatively designed. Strengthening heat transfer principle of the LSCPs is demonstrated by theoretical analysis. The average condensation heat transfer coefficients (ACHTCs) of the LSCPs are calculated and compared with conventional cooling plate (CCP). Results show that for a laminar flow, the ACHTCs of 2-parts liquid-vapor separation cooling plate and 3-parts liquid-vapor separation cooling plate are respectively 19% and 32% higher than the ACHTCs of the CCP in the same conditions. The ACHTC ratio of N-parts liquid-vapor separation cooling plates (NLSCP) to CCP is $\sqrt[4]{N}$in the same conditions. For a turbulent flow, results show the smaller the height of condensation area, the greater the ACHTCs of cooling plate. In the LVSPC study, operation conditions include the refrigerant R134a mass flux ranging from 22 to 32 kg/(m2.s) and inlet vapor quality from 0.5 to 1 for the saturated temperature of 40∘C. Calculation results showed that the ACHTCs of the LVSPC are 6–24% higher than the ACHTCs of the given common plate condenser (CPC), and similar to the CPC, the ACHTCs of the LVSPC increases with the increase of mass flux and vapor quality.

Recently, lubricant-impregnated surfaces (LIS) have emerged as a promising condenser surface by facilitating the removal of condensates from the surface. However, LIS has the critical limitation in that lubricant oil is depleted along with the removal of condensates. Such oil depletion is significantly aggravated under high condensation heat transfer. Here we propose a brushed LIS (BLIS) that can allow the application of LIS under high condensation heat transfer indefinitely by overcoming the previous oil depletion limit. In BLIS, a brush replenishes the depleted oil via physical contact with the rotational tube, while oil is continuously supplied to the brush by capillarity. In addition, BLIS helps enhance heat transfer performance with additional route to droplet removal by brush sweeping. By applying BLIS, we maintain the stable dropwise condensation mode for > 48 hours under high supersaturation levels along with up to 61% heat transfer enhancement compared to hydrophobic surfaces.

One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.

An experimental investigation on condensation heat transfer of R290 with inside diameter of 6.3 mm in horizontal micro-fin tube was presented. Effects of each case on the condensation heat transfer...

Boiling and condensation, a kind of convective heat transfer characterized by high heat fluxes, are widely encountered in many engineering applications. Fluids are the main heat carriers in heat transfer applications, and hence performance of a thermal system is remarkably linked with the working fluid's thermophysical properties. In thermal systems, nanofluids have been embarked upon to use as a working fluid because of their improved specifications. Pool boiling and condensation heat transfer characteristics of a new kind nanofluid consisting of hexagonal boron nitride nanoparticles and dichloromethane base fluid were investigated experimentally. Experiments were performed with dichloromethane and hexagonal boron nitride/dichloromethane nanofluid solutions to specify nanoparticles' effect on thermal performance. Nanofluid solutions were prepared at varying volumetric concentrations ranging from 0.5% to 1.5% to analyze the impacts of nanoparticle concentration rate. Experiments were conducted under varying input powers ranging from 50 W to 350 W. Boiling curves, the changes in pressure versus heat flux, heat transfer coefficients both in boiling and condensation processes were determined. Viscosity was also measured for each working fluid. It was figured out that nanoparticle addition to the base fluid dramatically affected thermal characteristics. Some enhancements of 27.6% and 17.65% for boiling and condensation processes have been achieved.

In order to study the condensation heat transfer characteristics of non-azeotropic hydrocarbon mixtures in helically coiled tubes for large-scale spiral-wound heat exchangers, a simplified physical model of three-section helical tubes was proposed. Reasonable governing equations and boundary conditions were set up, and the grid independence was verified. Then, the condensation heat transfer characteristics of mixture refrigerants were analyzed. In addition, considering the effect of mass transfer resistance of non-azeotropic mixtures on heat transfer during condensation, a method combining numerical simulation with the Bell and Ghaly correction method was proposed to calculate the condensation heat transfer coefficient of mixtures. By comparing with the experimental results, the accuracy of the calculation model is verified, which provides theoretical support for the design of large-scale spiral-wound heat exchangers.

During condensation process, the formation of condensate film is main resistance to retard heat transfer. This liquid condensate on horizontal pin-fin tube is known as condensate retention that generally blocks the lower part of tube and act as an insulation resulting in the form of resistance to heat transfer. Various, tube geometries experimentally tested with different pin-fin longitudinal and circumferential thickness and spacing, pin-fin height, internal and external tube diameters under the effect of vapour velocity are selected for model development. As it is extremely important to estimate the extent of condensate retention on such pin-fin tubes in order to make more effective horizontal pin-fin tubes in terms of heat transfer. The development of semi empirical correlations for condensate retention on pin-fin tubes as a function of vapour velocity (forced convection condensation) is proposed in this paper. Various geometric parameters and fluids are considered for model development. Accurate data are used for the model development. The proposed model which is based upon the dimensional analysis successfully predicts available data to within 5%. Relative standard deviation was about 2.44, 2.30 and 1.73 for water, ethylene glycol and refrigerant respectively. The development of such a semi empirical model is the first important step required for the development of full-scale heat transfer model of condensation heat transfer on horizontal pin-fin tubes during forced convection.

This study aims to provide an experimental investigation and comparison of the condensation heat transfer characteristics in a plate–fin heat exchanger (PFHE). The heat flux, mass flux, and saturation pressure were adjusted as experimental parameters to verify the effects on the condensation heat transfer. In addition, condensation heat transfer correlation of two-stream PFHEs was provided based on the experimental data for utilization as a design reference for the heat exchanger. The turbulence is the most influential in heat transfer. One of the ways to foster turbulence is to increase shear stress. The higher flow velocity results in the higher shear stress. That was why increasing mass flux or the flow with higher vapor quality showed the higher heat transfer coefficient (HTC). Refrigerant properties such as viscosity and specific volume of vapor changed according to the saturation pressure. It is expected they affect the degree of turbulence too in similar manners. The mass flux was more influential than the heat flux and saturation pressure. Thus, the equivalent mass flux of the refrigerant is dominant in the derived correlation model. The average difference between experimental and calculated HTC from correlations was about 6.5%. Multi-stream PFHE comprises an additional heat transfer surface, which implies a more active droplet formation. The average pressure drop in the multi-stream is 15% larger than that of the two-stream.

An experimental investigation of shell-side flow condensation was performed on three-dimensional surface enhanced tubes, including a herringbone micro-fin tube and a newly developed 1-EHT tube. An equivalent plain tube was also tested for performance comparison. All the test tubes had similar geometry parameters, i.e., inner diameter 11.43 mm and outer diameter 12.7 mm. The outer shell diameter was 24.5 mm with a wall thickness of 0.6 mm. Tests were conducted using R410A as the working fluid at a dew point of 45 °C. The mass flux range of 10–55 kg/(m2 · s) with an inlet quality of 0.8 and an outlet quality of 0.1. Experimental results showed that the plain tube exhibited a better condensation heat transfer performance. Moreover, the mass flux had a significant influence on the heat transfer coefficient for shell-side condensation. A new prediction model based on the Cavallini’s equation was developed to predict the condensing coefficient where the mean absolute error is less than 4%.

In general, the dropwise condensation supported by superhydrophobic surfaces results in enhanced heat transfer relative to condensation on normal surfaces. However, in supersaturated environments that exceed a certain supersaturation threshold, moisture penetrates the surface structures and results in attached condensation, which reduces the condensation heat transfer efficiency. Therefore, when designing superhydrophobic surfaces for condensers, the surface structure must be resistant to attached condensation in supersaturated conditions. The gap size and complexity of the micro/nanoscale surface structure are the main factors that can be controlled to maintain water repellency in supersaturated environments. In this study, the condensation heat exchange performance was characterized for three different superhydrophobic titanium surface structures via droplet behavior (DB) mapping to evaluate their suitability for power plant condensers. In addition, it was demonstrated that increasing the surface structure complexity increases the versatility of the titanium surfaces by extending the window for improved heat exchange performance. This study demonstrates the usefulness of DB mapping for evaluating the performance of superhydrophobic surfaces regarding their applicability for industrial condenser systems.

The main objective of this work is to develop a numerical model to analyze heat transfer and condensation of a rising spherical bubble. The model included the bubble shrinkage during condensation, which can be utilized to analyze the bubble’s total energy loss, raising velocity, and condensation rate of a single bubble compared to multiple bubbles with the same total thermal energy. The equations of motion, heat, and mass transfer were developed. The model results were verified with the bubble condensation experiment data in the literature, in which they exhibited a good agreement. For the validation, the model results were compared with bubble condensation experiment data in the literature, which showed a good agreement with the experimental results. The dynamic term of the model is developed using the force balance on a gravity-driven bubble, including hydrodynamic drag force and gravity/buoyancy force, which acting with and against the bubble’s motion direction. For the thermal part of the model, a condensation correlation has been adapted to represent the Nusselt number as a function of Reynolds number (Re), Jakob number (Ja), and Prandtl number (Pr). A MATLAB code is developed in order to calculate the instantaneous velocity, the radius, and the mass loss of the vapor bubble in each time step. Moreover, the fundamental behavior for a single bubble and multiple bubbles was investigated in various initial conditions under the same total thermal energy. The effects of the initial bubble radius and the temperature difference between the liquid and vapor phases were analyzed for both scenarios in order to examine the condensation rate. It was found that the thermal behavior of the condensing bubble can be improved by forcing the bubble to collapse into sub bubbles, which will increase the total interfacial area and the rising velocity. Farther, due to generated sub bubbles, the resultant velocity increased the turbulency and the heat transfer rate accordingly. This study can lead to improve the heat transfer rate and allow for more intensive research to enhance the condensation rate.

In this paper, condensation on plates with different rough-surface geometries has been experimentally investigated, and compared with smooth plates. The surface roughness on all plates was produced through laser marking with similar operational parameters of the device, and the roughened area on each plate was measured. The generated roughness on the plates was then examined through SEM images. Then, the values of heat flux and heat transfer coefficient were measured at different temperatures, according to the differences in the geometry of roughness generated on each plate, and compared. Investigation of the SEM images showed that the roughness created on the plates was in the form of cavities, with the mean diameter and depth of 50 and 5 µm, respectively. The cavities were identical all through the roughened zones, despite the different geometries of the roughened surfaces on the plates. The obtained results revealed that the geometry and area of roughened zones on the plate were effective parameters in the measured values of heat transfer coefficient and heat flux, meaning that their combined effects might lead to an increase in heat flux and heat transfer coefficient values.

Experiments on the two-phase flow condensation heat transfer of R410A, R22, R32, and R290 (propane) inside a multiport minichannel tube are investigated in this study. The experiments are conducted...

Metal foams have great potential for improving the condensation heat transfer characteristics of shell-and-tube heat exchangers in FLNG plants, and the drainage characteristics in metal foam under sloshing conditions should be promoted through modifying the surface wettability. For revealing the liquid drainage mechanism of metal foam with different surface wettability, the influence of surface wettability on liquid drainage characteristics under sloshing conditions was experimentally investigated in the present study. The tested samples include the hydrophilic, uncoated and hydrophobic metal foams; the experimental conditions include foam pore density of 5–40 PPI (pores per inch), the sloshing frequency of 0–1 Hz and the angle from 0° to 25°. The experimental results show that, the decreasing wettability of metal foam promotes the liquid drainage characteristics, and the promotion effect is more significant for the metal foam with larger PPI. The liquid retention mass in metal foam with various surface wettability decreases maximally by 30% under the rolling motions, while it only decreases by 5% under the swaying and heaving motions. The wettability impact factors of the hydrophilic and hydrophobic metal foams under the sloshing conditions are within 0.96–1.33 and 0.26–0.97, respectively. A correlation for predicting the liquid retention mass in metal foam with various wettability under the sloshing conditions is developed within a deviation of 25%.

A new type of three-dimensional pin–fin plate with elliptical cross-section was proposed. Condensation heat transfer of FC-72 in a narrow rectangular channel with the proposed pin fins was experimentally studied in normal gravity and microgravity. The effects of pin geometry, thermal conductivity, mass flow rate and gravity on condensation heat transfer were investigated. The visualization experiment under microgravity was carried out and the condensate behaviour was observed by high CCD camera. The results showed that all the elliptical pin-fin plates exhibited substantially better performance than the flat plate. The influence of pin geometry and thermal conductivity on condensation heat transfer coefficient was great. The smaller pin size and higher thermal conductivity were favourable for condensation enhancement. The average condensation heat transfer coefficient increased with the increase of mass flow rate. In microgravity, obvious fluctuations and climbs occurred in gas-liquid interface. However, the condensate behaviour on the condensing surface was unconspicuous. For unsteady state, the vapor-side temperature difference increased evidently in microgravity. Microgravity had a certain effect on temperature evolution of the condensing base. Short-term microgravity degraded the condensation heat transfer coefficient in quasi-steady state or unsteady state, but had little effect on pulsating state.

Steam condensation on the containment vessel is a significant cooling strategy to cope with the design basis accidents in the third-generation reactors with passive safety features. Aiming to evaluate the heat removal capacity of steam condensation, a number of condensation experiments have been conducted on a horizontal plate with the same surface condition as CAP1400 containment vessel. The effects of surface sub-cooling, air concentration, bulk pressure and different steam injecting models on condensation heat transfer have been experimentally investigated. In the experiments, the condensation heat transfer coefficients (within the range of 77–1297 W/m2 K) on the downward-facing plate are successfully obtained under the conditions of bulk pressure ranging from 0.154 to 0.607 MPa, air molar fraction ranging from 1.1% to 82.9% and surface sub-cooling ranging from 12.6 to 49.3 °C. In addition, an empirical correlation for heat transfer prediction has been developed based on the experimental data in this work. Besides, the experimental data have also been compared with four existing empirical correlations proposed by Uchida, Tagami, Dehbi and Liu, respectively. The comparing results show that most of condensation heat transfer coefficient data on the test plate could be overestimated by these four correlations.

Coalescence-induced droplet jumping behavior of superhydrophobic surfaces has attracted increasing attention for condensation heat transfer, antifrosting, self-cleaning, and electrostatic energy harvesting applications. The potential of applying such functionalized behavior for atmospheric corrosion protection, however, is unknown. Herein, we experimentally demonstrate, for the first time, the feasibility of applying coalescence-induced droplet jumping behavior of a superhydrophobic surface for atmospheric corrosion protection. Based on the rational fabrication of two kinds of superhydrophobic surfaces that are advantageous and not advantageous for coalescence-induced droplet jumping behavior, we reveal a novel atmospheric corrosion protection mechanism by studying the correlations of the surface structure, droplet jumping behavior, and atmospheric corrosion resistance of the two surfaces. Our results demonstrate that the superhydrophobic surface with coalescence-induced droplet jumping behavior presents a better atmospheric corrosion resistance than the superhydrophobic surface without coalescence-induced droplet jumping behavior. This is because coalescence-induced droplet jumping behavior of the superhydrophobic surface offers a possible mechanism to switch the droplets from a partial wetting state to the mobile Cassie state, and this switch is critical for facilitating the recovery of the air film trapped in the microstructure of a surface. In particular, the recovered air film enhances the atmospheric corrosion resistance of a superhydrophobic surface due to its barrier-like character. The insights gained from this work not only open a new avenue for designing first-rank anticorrosion materials but also offer new opportunities for understanding the physics of jumping droplets in other promising applications.

Steam condensation tests were conducted on titanium corrugated tubes at the pressure of 5 kPa and 10 kPa, which are the operating pressures of a power plant condenser. Seven 22.2 mm O.D titanium corrugated tubes had 6.4 mm ≤ p ≤ 22.1 mm and 0.2 mm ≤ e ≤ 0.6 mm. The condensation heat transfer coefficient increased as the corrugation pitch or the corrugation depth decreased. The tube having p = 6.4 mm and e = 0.2 mm yielded the highest heat transfer coefficient with the enhancement from 57 % to 75 %. Comparison with Mehta and Raja Rao [17] correlation revealed that the data are predicted within ±15 %.

This study experimentally investigated the condensation heat transfer and pressure drop characteristics of R1234ze(E) inside horizontal small-diameter (4.0-mm) microfin tubes with three different t...

We have generated precise values for several key energies that are relevant to Cu-graphene or Cu-graphite systems. Such systems may find technological applications that range from graphene synthesis, to condensation heat transfer, to electrical contacts to graphene, to composites. Using density functional theory, we have calculated surface energies of the three low-index faces of bulk Cu. We find that these surface energies, calculated with the PBEsol functional, are significantly higher than with the more common PBE functional and agree more closely with experiment. We have also calculated the surface energies of graphene and graphite, the exfoliation energy between graphene and graphite, and the adhesion energies between graphene or graphite and a Cu(111) slab. The adhesion energy between a carbon layer and Cu(111) is close to the exfoliation energy and cleavage energy of graphite, the four sets of values spanning a range of only 0.394–0.456 J/m2. Our results are consistent with the earlier experimental observation of three-dimensional growth of Cu on top of graphite. The energies are also used to perform a continuum Winterbottom analysis and also discrete (atomistic) variants of this analysis to predict the equilibrium shapes of Cu particles supported on graphite.

A numerical study of condensation heat transfer in curved square and triangle microchannels with various curvatures is conducted. The model is based on the volume of fluid approach and user-defined...

Low-permeability interlayer is common in reservoir, which can hinder the steam chamber expansion and the gravity drainage in SAGD. It is crucial to find an economical and practicable method to promote the steam chamber to break through the interlayer. In this work, four condensation heat transfer experiments were conducted to investigate the effect of flue gas on steam condensation heat transfer. On this basis, 2D visualization tests, including a SAGD experiment and two flue gas assisted SAGD experiments, were carried out to see if the steam chamber can break through the interlayer under the effect of flue gas. Results show with the increase of gas proportion in the steam-flue gas mixture, the condensation heat transfer coefficient decreased and the condensation pattern was transformed from drop condensation to film condensation gradually. This indicates that flue gas can inhibit the condensation heat transfer, which has great influence on the heat transfer and steam chamber growth in SAGD. Visualization tests show the interlayer could block the steam chamber development. After the interlayer was heated sufficiently, flue gas could penetrate the interlayer and promote steam chamber to break through the interlayer because of its inhibiting effect on condensation heat transfer. Besides, the horizontal sweep efficiency was improved significantly under the synergistic effects of steam, gas, and interlayer. The gas addition can reduce the adverse impact of interlayer on SAGD performance, which provides a potential method to improve SAGD development in the reservoir with interlayer.