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Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The experimental investigation on condensation heat transfer coefficients of R1234yf and R32 inside small diameter microfin tube. • A new general correlation of condensation heat transfer coefficients inside microfin tubes has been developed. • The new correlation could broadly be applied to horizontal microfin tubes with inner diameters between 2.5 and 8.8 mm. • The proposed correlation can be applied to a wide range of mass velocities and many kinds of refrigerants. This study investigated the condensation heat transfer characteristics of the pure refrigerants R1234yf and R32 in a microfin tube with a small diameter of 3.5 mm outside diameter and 3.18 mm inner mean diameter. Experiments were carried out at mass velocities between 50 and 200 kg m -2 s-1, saturation temperatures of 20 and 30 °C, and vapor quality between 0 and 1. The effects of vapor quality, mass velocity, saturation temperature, and refrigerant properties on condensation heat transfer characteristics were investigated. A new correlation is also developed to predict condensation heat transfer coefficients that can be applied to horizontal microfin tubes with inner diameters between 2.5 and 8.9 mm. The new correlation is validated with the database containing 1240 experimental data points from 10 independent research groups. The comparison results show that the three existing correlations overestimate the heat transfer coefficient data with mean deviation greater than 30.0 %. Meanwhile, the new correlation predicted the present experimental data and other researchers' data with mean deviation of 19.8 %. [ABSTRACT FROM AUTHOR]

This study investigates the impact of surface roughness on the condensation Heat Transfer Coefficient (HTC) of R123yf refrigerant in a uniquely designed test rig with pre-condenser and post-condenser for quality regulation. In mining industries, the mining equipment consumes more amount to power for the Air Conditioning system. To reduce the power consumption of copper metal inside the surface morphology needs to be changed. Experiments were conducted in a 750 mm long, 8.4 mm internal diameter copper tube, with regard to mass flux varying from 150 kg.m-2.s-1 to 300 kg.m-2.s-1, refrigerant quality varying from 0.3 to 0.8, and saturated temperature from 35°C to 45°C. The impact of varying surface roughness (1.5 µm, 2.5µm, 3.4 µm, and 6.7 µm) on HTC was examined. The plane tube condensation experimental results agreed with M M Shah's heat transfer coefficient correlations, with a 20% absolute mean deviation. It was observed that increasing surface roughness enhanced the HTC. The optimal surface roughness was determined to be 3.4 µm, as it resulted in a significant increase in HTC (26.25%) with a moderate rise in power consumption (15.40%). Higher surface roughness led to a drastic increase in power consumption, making it less desirable for practical applications. Through a systematic analysis of the experimental data, this study identifies the critical trade-off between surface roughness and power consumption, providing guidance for the design of energy-efficient condensation heat transfer systems using R123yf refrigerant. By pinpointing an optimal surface roughness for copper tubes used in refrigeration, this study offers a pragmatic solution for enhancing the efficiency of air conditioning systems in mining equipment, a sector notorious for high energy expenditures. The findings indicate a direct application in mining operations where equipment cooling demands contribute significantly to energy consumption. Implementing the recommended surface modifications can lead to substantial energy savings, thereby reducing operational costs and improving the sustainability of mining activities. Furthermore, the adaptation of R123yf refrigerant systems with optimized surface roughness could serve as a model for energy conservation measures across various facets of the mining industry.. [ABSTRACT FROM AUTHOR]

This paper proposed the application of two types of wavy structures for spiral wound heat exchanger, and conducted numerical simulations on the condensation flow of a hydrocarbon mixture with methane, ethane, and propane in them. The effects of saturation pressure and mass velocity are also studied. It was found that both types of helical wavy pipes produce higher condensation heat transfer coefficients and frictional pressure drop than those in helical smooth one, and both of them increase with the rise in mass velocity and the decrease of saturation pressure. The influence of saturation pressure on heat transfer and pressure drop is greater than that of mass velocity. Meanwhile, the comprehensive performance of the two types of helical wavy pipes is analyzed using entropy generation. It can be found that the horizontal wavy pipe has a better overall performance than vertical wavy one with a lower irreversible loss. Finally, prediction models for the condensation heat transfer coefficients and frictional pressure drops are established using RBF neural networks, with 95 % of the predicted results having a relative deviation within 10 %.

Phase change materials, such as paraffin waxes, have recently been introduced in surface science. Paraffin-based slippery liquid-infused porous surfaces (P-SLIPSs) provide switchable wettability and various adhesion states. Herein, P-SLIPSs were fabricated on copper plates. To study condensation heat transfer, two condensation rigs were fabricated and optimized via a comparison between the experimental and theoretical heat transfer coefficients, finding a good agreement in the short cold-finger-assisted rig. The condensation mode on P-SLIPSs is dropwise mode. Consequently, the condensation heat transfer coefficients on P-SLIPSs were found to be higher compared with that of pristine copper plates.

In this study, three condensation models of the CUPID code, i.e., the resolved boundary layer approach (RBLA), heat and mass transfer analogy (HMTA) model, and an empirical correlation, were tested and validated against the COPAIN and CAU tests. An improvement on HMTA model was also made to use well-known heat transfer correlations and to take geometrical effect into consideration. The RBLA was a best option for simulating the COPAIN test, having mean relative error (MRE) about 0.072, followed by the modified HMTA model (MRE about 0.18). On the other hand, benchmark against CAU test (under natural convection and occurred on a slender tube) indicated that the modified HMTA model had better accuracy (MRE about 0.149) than the RBLA (MRE about 0.314). The HMTA model with wall function and the empirical correlation underestimated significantly, having MRE about 0.787 and 0.55 respectively. When using the HMTA model, consideration of geometrical effect such as tube curvature was essential; ignoring such effect leads to significant underestimation. The HMTA and the empirical correlation required significantly less computational resources than the RBLA model. Considering that the HMTA model was reasonable accurate, it may be preferable for large-scale simulations of containment.

In this study, two types of wave-structured pipes for heat exchangers that are easy to process are proposed, and the condensation pressure drop and heat transfer performances for hydrocarbon refrigerant upward flow in wave helical pipes are investigated. A numerical method based on the inhomogeneous two-fluid model is introduced and validated by experimental data in literature. The effect of wave parameters (wave height and wave length) on heat transfer, pressure drop and flow patterns are studied. At lower vapor quality conditions, it is found that as wave height increases, frictional pressure drop and heat transfer coefficient exhibit a trend of initially increasing, followed by decreasing, and then increasing again. However, under higher vapor quality conditions, frictional pressure drop and heat transfer coefficient continue to increase. Besides, both the frictional pressure drop and heat transfer coefficient increase with the decrease of wave length. The averaged enhancement on frictional pressure drop for vertical wave pipes and horizontal wave pipes are respectively 1.279–5.148 and 1.238–5.808 times, while the average augmentation in heat transfer coefficient is 1.243–3.006 and 1.316–3.579 times, respectively. The comprehensive thermal performance of wave pipes was assessed using the performance evaluation criterion. The range of averaged performance evaluation criteria (under different vapor qualities) in vertical wave pipes and horizontal wave pipes are respectively 1.150–1.737 and 1.230–2.026. The horizontal wave pipe when the wave height is 5 mm and wave length is 5.24 mm shows the best overall thermal performance, with an averaged performance evaluation criterion of 2.026. The two types of wave-structured pipes proposed in this paper can increase the pipe length of the spiral-wound heat exchanger at the same volume, while also improving the performance of the spiral-wound heat exchanger. The outcomes of the study can offer some assistance in creating simple but effective spiral wound heat exchangers.

This study analyzed the RT8HC melting in a spherical vessel employing air as a heat transfer fluid. The phase change process was followed both visually and by thermal measurements. Photographs and thermographs allow the following phases' evolution and melting mechanisms. We observed that the melting process was not symmetric around the vertical axis; implications of non-symmetric conditions on the melting mechanisms and heat transfer are discussed and analyzed. This work also includes the effects of outer water vapor condensation on heat transfer in the analyses. We proposed a mathematical model to quantify the heat flux that only requires humidity and temperature measurements and considers both heat convection and condensation effects. Results show that condensation significantly affects heat transfer during the initial stage of the melting process. Beside, these effects extend beyond the condensation time due to the liquid film draining from the spherical vessel surface. Regarding thermography, this technique may be a valuable tool for analyzing and following melting processes inside vessels; however, the presence of liquid film over the sphere affects the temperature measurements obtained from the thermograph analysis. This investigation provides relevant information about using phase change materials in cold thermal energy storage applications, latent thermal loads, and humidity control, which are essential aspects of air-conditioning system designs. [ABSTRACT FROM AUTHOR]

An experimental study was performed that compared tube side condensation heat transfer characteristics of enhanced tubes (hydrophobic surface tubes (HYD), herringbone micro fin tube (HB), and a composite hydrophobic/herringbone (micro fin) tube (HYD/HB)) to the performance of a smooth tube (ST). The condensation heat transfer coefficient (HTC) was calculated from data that were recorded for smooth and enhanced tubes that had an outer diameter (OD) of 12.7 mm. Data were collected (as a function of mass flow rate) using a couple of refrigerants (R410A and R32), for saturated temperatures of 35 °C and 45 °C, with vapor qualities that ranged from 0.8 to 0.2. Several previously reported smooth tube HTC models were used to calculate values that could be compared to experimentally obtained HTC values. The correlation model that demonstrated the best accuracy (for the conditions considered) was then modified for use with the enhanced tubes from this study. Results from the modified correlation show differences with experimental values that ranged from −10% to +17%; the new modified correlation demonstrates high prediction accuracy. An accurate correlation allows the evaluation of enhanced heat transfer tubes for use in high-efficiency heat exchanger systems. The development of this new model is significant in the study of enhanced heat transfer. [ABSTRACT FROM AUTHOR]

• The condensation of NH 3 /H 2 O with mass concentrations of 80%−96% is measured. • High concentration NH 3 /H 2 O shows the same flow pattern characteristics as pure NH 3. • The heat transfer coefficients decrease with lower mass concentrations. • The sensitivity of frictional pressure drop indicates separated flow. • The investigated parameters are mass concentration, vapor quality, mass flux, etc. High concentration NH 3 /H 2 O is suitable for Kalina cycles used for the recovery of low grade heat. Plate heat exchangers (PHEs) are compact and reduce the charge of working fluid. This paper investigates the condensation of NH 3 /H 2 O with NH 3 mass concentrations of 80%-96%. The vapor and liquid concentrations are close to equilibrium state, which are different from normal absorbers. The apparent heat transfer coefficients (HTCs) and frictional pressure drop are presented, covering the mass fluxes of 32–86 kgm−2s−1, the averaged vapor qualities of 0.08–0.65 and the saturated pressure of 610 to 780 kPa. Larger mass fluxes noticeably increase the apparent HTCs and frictional pressure drop. At the mass concentrations of 96%, 91% and 88%, higher vapor qualities increase the apparent HTCs for large mass fluxes. The apparent HTCs decrease slightly with vapor qualities for 80% mass concentration. The experimental results are compared with those of pure NH 3. The flow patterns of high concentration NH 3 /H 2 O are considered as full film flow and partial film flow, which are the same as for NH 3. The mass transfer resistance deteriorates the heat transfer especially for partial film flow, which happens at small liquid mass fluxes. The mass transfer resistance has negligible influences on frictional pressure drop. [ABSTRACT FROM AUTHOR]

Spiral wound tube heat exchanger (SWHE) was confirmed as the core equipment of natural gas liquefaction (LNG). However, there was rare experimental research on large-scale SWHE for LNG, and the theory of heat transfer is not perfect. To investigate the tube-side flow and heat transfer characteristics in spiral tubes, an experimental system was proposed. To ensure the accuracy of the experimental data, the heat transfer coefficients of liquid propane under different conditions were measured, and the data acquired through the experiment were compared with two classical heat transfer correlation (Dittus–Boelter and Geielinski) under the identical working conditions. The applicability of the existing correlation was analyzed using the experimental data, and a novel heat transfer correlation was developed. As indicated by the results, the deviation between the experimental system and the classical correlation under the identical working condition was lower than ±10%. Furthermore, the error comparison between the novel correlation prediction value and the experimental data was less than ±15%. [ABSTRACT FROM AUTHOR]

In order to successfully study the condensation and separation of a steam–CO2 mixture, a boundary layer model was applied to the mixture condensation of steam and CO2 on horizontal and vertical plates. The modified condensation boundary layer model of steam and CO2, given the CO2 solubility in the condensate, was established, numerically solved, and verified with existing experimental data. Different condensation data of steam–air and steam–CO2 mixtures were compared, and the effect of CO2 solubility on the mixed gas condensation was analyzed under multiple pressure conditions (1 atm–10 MPa). The simulation data show that the presence of CO2 will deteriorate the condensation heat transfer, just like air. Given that CO2 is slightly soluble, some CO2 can pass through the gas–liquid interface to enter the condensate film and reduce the accumulated CO2 on the gas–liquid interface, which improves the condensation. However, the solubility of CO2 is only significant under high-pressure conditions, inducing its effects on condensation. A comparison of the condensation coefficients of the steam–CO2 mixture shows the lower impact of CO2 condensation on the horizontal plate compared to that on the vertical plate. For most conditions, the steam–CO2 mixture gas condensation heat transfer coefficient on the vertical plate surface is still larger than that on the horizontal plate surface, and the improvement in the condensation heat transfer coefficient caused by low CO2 solubility (2 or 10%) at 10 MPa on the vertical plate is also larger than that of the horizontal plate. [ABSTRACT FROM AUTHOR]

Due to the recent interest in renewable energy and waste heat for power generation, organic Rankine cycle (ORC) has drawn considerable attention. By applying a dual-pressure evaporation strategy, the exergy loss in the evaporators can be reduced significantly, resulting in an enhanced system performance. In this study, detailed modelling analyses have been conducted to evaluate the effect of zeotropic working fluids on the performance of two dual-pressure ORC (DPORC) arrangements, namely, DPORC-P (parallel) and DPORC-S (in-series), where the working fluid pair R245fa and R152a has been selected to form a representative zeotropic mixture. It has been found that as a zeotropic mixture is used, both systems show improved cycle net power outputs. Interestingly, the highest power outputs occur at mass fractions that result in matching temperature profiles between the hot and cold fluids in the condenser. At a heat source temperature of 120 °C, a DPORC-S always has a greater net power output regardless of the mass fraction of the zeotropic mixture; as heat source temperature reduces, the difference of power output between the two systems tends to drop: for a heat source temperature of 90 °C, a DPORC-P has a better performance as the mixture mass fraction is between 0.4 and 0.9. The influence of zeotropic fluids to the heat transfer of the condenser has also been investigated and it indicates that a significantly larger heat transfer area is required for a zeotropic fluid; based on a fixed heat transfer area, the performance enhancement of a zeotropic system is only seen as the condenser heat transfer area is considerably large.

In order to study the heat transfer of R410A in extreme environments, the properties of several stainless steel and copper-enhanced tubes were evaluated using R410A as the working fluid, and the results were compared with those of smooth tubes. Tubes evaluated include: smooth, herringbone (EHT-HB) and helix (EHT-HX) microgroove, herringbone/dimple (EHT-HB/D); herringbone/hydrophobic (EHT-HB/HY); and composite enhancement 1EHT (three-dimensional). Experimental conditions include a saturation temperature of 318.15K with a saturation pressure of 2733.5 kPa; a mass velocity in the range between 50 and 400 kg/(m2·s); and an inlet quality controlled at 0.8 and an outlet quality of 0.2. Results indicate that the EHT-HB/D tube produces the best overall condensation heat transfer characteristics (high heat transfer performance and low frictional pressure drop). Using the performance factor (PF) to compare tubes for the range of conditions considered, the PF of the EHT-HB tube is greater than one, the PF of the EHT-HB/HY tube is slightly greater than one, and the PF of the EHT-HX tube is less than one. In general, as the mass flow rate increases, PF initially decreases and then increases. Previously reported smooth tube performance models that have been modified (for use with the EHT-HB/D tube) can predict the performance for 100% of the data points to within ±20%. Furthermore, it was determined that the thermal conductivity of the tube (when comparing stainless steel and copper) will have some effect on the tube-side thermal hydraulic performance. For smooth tubes, the heat transfer coefficients (HTC) of copper and stainless steel tubes are similar (with copper tube values being slightly higher). For enhanced tubes, performance trends are different; the HTC of the copper tube is larger than the SS tube. [ABSTRACT FROM AUTHOR]

Slippery liquid-infused porous surface (SLIPS) realized on commercial materials provides various functionalities, such as corrosion resistance, condensation heat transfer, anti-fouling, de/anti-icing, and self-cleaning. In particular, perfluorinated lubricants infused in fluorocarbon-coated porous structures have showed exceptional performances with durability; however, they caused several issues in safety, due to their difficulty in degradation and bio-accumulation. Here, we introduce a new approach to create the multifunctional lubricant-impregnated surface with edible oils and fatty acid, which are also safe to human body and degradable in nature. The edible oil-impregnated anodized nanoporous stainless steel surface shows a significantly low contact angle hysteresis and sliding angle, which is similar with general surface of fluorocarbon lubricant-infused systems. The edible oil impregnated in the hydrophobic nanoporous oxide surface also inhibits the direct contact of external aqueous solution to a solid surface structure. Due to such de-wetting property caused by a lubricating effect of edible oils, the edible oil-impregnated stainless steel surface shows enhanced corrosion resistance, anti-biofouling and condensation heat transfer with reduced ice adhesion. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of condensation heat transfer by gradient heatmetry. The experiments were carried out during the condensation of saturated steam at atmospheric pressure on the cooled surface of a horizontal pipe. The distributions of the local heat flux, surface temperature, and heat transfer coefficient along the circumference of the horizontal pipe were experimentally determined. The surface average condensation heat flux on the horizontal pipe was about 141.06 kW/m 2 . The proposed method allows us to determine the area of condensate accumulation on the pipe (in the range of azimuth angle φ = 150...180 ∘ ) in which the heat flux decreases by 34% of the average value. The heat flux per unit area relative uncertainty was about 5.2%. The surface-averaged heat transfer coefficient during condensation on the horizontal pipe was about 5.5 kW/(m 2 × K), and relative uncertainty was about 9.4%. [ABSTRACT FROM AUTHOR]

To clarify the influencing mechanisms of the experimental condition and the tube structure on the pressure drop of heat transfer fluid, the two-phase flow condensation pressure drop of R134a inside the microfin tube was experimentally studied at high mass flux, which is different from other conventional researches. The experimental result shows the pressure drop is proportional to mass flux and fin helical angle, and is inversely proportional to condensation temperature and coolant Reynolds number. Moreover, the experimental data of pressure drop was compared with the predicted value of some existing correlations for the microfin tube. It can be found that the correlations of Cavallini et al. Han et al. and Haraguchi et al. show a good prediction effect with mean relative deviation (MRD) of 13.89, 16.08 and −2.19%, respectively. The correlations of Pierre/0.053, Kedzierski et al. and Choi et al. all underestimate most of the experimental data of the pressure drop inside the tube, and their prediction deviations are >10%. That is, the application effect of the separated flow model is better than that of the homogeneous flow model. Finally, the Kedzierski et al. correlation was improved to realize a high-precision prediction of the fluid flow mechanism inside the tube. Because the prediction deviation of the improved correlation between the experimental value and the predicted value was greatly reduced, its prediction deviation is <10% for R134a and R410A; therefore, it can be said the improved correlation has a good predictive result for the pressure drop. [ABSTRACT FROM AUTHOR]

A condensation heat transfer model is essential to accurately predict the performance of the passive containment cooling system (PCCS) during an accident in an advanced light water reactor. However, most of existing models tend to predict condensation heat transfer very well for a specific range of thermal-hydraulic conditions. In this study, a new correlation for condensation heat transfer coefficient (HTC) is presented using machine learning technique. To secure sufficient training data, a large number of pseudo data were produced by using ten existing condensation models. Then, a neural network model was developed, consisting of a fully connected layer and a convolutional neural network (CNN) algorithm, DenseNet. Based on the hold-out cross-validation, the neural network was trained and validated against the pseudo data. Thereafter, it was evaluated using the experimental data, which were not used for training. The machine learning model predicted better results than the existing models. It was also confirmed through a parametric study that the machine learning model presents continuous and physical HTCs for various thermal-hydraulic conditions. By reflecting the effects of individual variables obtained from the parametric analysis, a new correlation was proposed. It yielded better results for almost all experimental conditions than the ten existing models.

In order to improve the condensation heat transfer efficiency of tungsten--copper alloy by changing its hydrophilicity, a copper nanowire array was fabricated on the surface of tungsten--copper alloy by electroplating with porous anodic aluminum oxide (AAO) as a template, and then a superhydrophobic nanostructured surface was formed by modification with octadecanethiol. In this way, the condensation state on tungsten--copper alloy surface was transited from filmwise to dropwise. The results showed that the electroplated copper nanowire array was highly uniform, and no droplets stuck on the superhydrophobic surface obtained by further modification under atmospheric condition. In a steam of 40 °C, the superhydrophobic surface featured a heat flux density of 89.14 kW/cm2 and a heat transfer coefficient of 44.28 kW/(m²⋅K) at a subcooling degree of 2 K, and its heat transfer efficiency was twice of that of the smooth tungsten--copper alloy surface. The superhydrophobic surface kept a dropwise condensation mode even when the subcooling degree was increased to 15 K. [ABSTRACT FROM AUTHOR]

• Developed a mechanistic model for dropwise condensation heat transfer on a vertical surface. • Predicted the effect of droplet/rivulet parameters quantitatively. • Improved prediction of length effects on dropwise condensation heat transfer. Rivulet flows can form and thereby affect heat transfer during dropwise condensation on long vertical surfaces. Under noncondensable gas conditions, including in heat exchangers in small modular reactors, droplet/rivulet heat transfer becomes more complicated. A new dropwise condensation heat transfer model is proposed herein to incorporate vertical length effects in the presence of noncondensable gas. Heat transfer through rivulets and the sweeping effects of rivulet flows were modeled to obtain heat flux through node-based calculations. Droplet/rivulet parameters, which are crucial for calculating heat transfer in the model (departure droplet radius, rivulet velocity, and sweeping period), were compared to experimental results. The model's prediction of heat flux is in good agreement with the experimental data and exhibits better accuracy than existing models, with an error range of -40 % for 76 % of the data. [ABSTRACT FROM AUTHOR]

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 the condensation heat transfer between the wet air and 3-D finned-tube heat exchanger surface in three different ways, i.e. non-coating, Ni-Cu-P organic pure-coating, and Ni-Cu-P chemical organic composite coating. Impacts of mass flow rate, moisture content, temperature of exhaust flue gas, and cooling water on the condensation heat transfer performance were investigated. The results showed that the heat transfer coefficient of the heat exchanger surface with a pure-coating layer achieves 3.1–7.4% higher compared to that with the composite coating. The pure-coating surface is inferior to the non-coating surface. The heat transfer coefficient of the copper-based heat exchanger achieves 30.1–47% higher compared to the steel-based surface. The condensate pH of modified surfaces heat exchangers is ranged from 3.08–7.17. Furthermore, the nondimensional correlations governing the flue-gas convection condensation heat transfer for different coating surfaces were established and validated with the experimental data. The validation indicates that the theoretical results are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The spiral wound heat exchanger (SWHE) has been recognized as the first choice for large-scale liquefied natural gas plants, in which the condensation characteristic in the spiral tube plays an essential role in the SWHE. In this study, a numerical model is built in accordance with the SWHE parameter and then verified. The condensation characteristics of methane/ ethane/ propane (mole fraction: 0.4/ 0.3/ 0.3) mixed hydrocarbon mediums in spiral tube are studied. And, the effects arising from mass flux, saturation pressure, and vapor quality on void fraction, heat transfer coefficient and friction pressure drop are explored. A conclusion of this study is drawn, showing that the void fraction increases by 56.14% with the increase in the vapor quality from 0.1 to 0.9; the void fraction increases by 12.67% with the mass flux increasing from 200 kg•(m2•s)−1 to 600 kg•(m2•s)−1. Moreover, the heat transfer coefficient increases monotonously with the increase of the vapor quality when the mass flux is 200 kg•(m2•s)−1; at 400 and 600 kg•(m2•s)−1, the heat transfer coefficient and the friction pressure drop increase first and then tend to be smooth or decrease slightly at high vapor quality. This study provides a reference for the design, development, and application of the large-scale SWHE. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A numerical study was carried out to analyze the condensation phenomena in a vertical channel between two flat plates. To solve the three-dimensional governing equations including conservation of the mass, momentum, and energy, the Volume of Fluid model was adopted. For the phase change phenomena, the Lee model was used. The tuning for the model parameter was performed using existing experimental data. To obtain the heat transfer coefficients under desired conditions, a model based on machine learning using artificial neural network was developed, which shows good accuracy and the future possibility of using the model for the tuning and validation of the phase-change model. A super-hydrophilic (10°), hydrophilic (58°), and hydrophobic surface (130°) were considered together with the variation of the gap spacing and the inlet velocity. The different condensation behavior according to the various surfaces wettability conditions was clearly identified. The formation of a liquid bridge in the channel for the dropwise condensation was observed, and its effects on the thermal and pressure drop performance were assessed. Details on the its performance were summarized quantitatively. It is expected that the present result and numerical method could provide useful information for the fin-type heat exchanger design.

An experimental study was performed that compared tube side condensation heat transfer characteristics of enhanced tubes (hydrophobic surface tubes (HYD), herringbone micro fin tube (HB), and a composite hydrophobic/herringbone (micro fin) tube (HYD/HB)) to the performance of a smooth tube (ST). The condensation heat transfer coefficient (HTC) was calculated from data that were recorded for smooth and enhanced tubes that had an outer diameter (OD) of 12.7 mm. Data were collected (as a function of mass flow rate) using a couple of refrigerants (R410A and R32), for saturated temperatures of 35 °C and 45 °C, with vapor qualities that ranged from 0.8 to 0.2. Several previously reported smooth tube HTC models were used to calculate values that could be compared to experimentally obtained HTC values. The correlation model that demonstrated the best accuracy (for the conditions considered) was then modified for use with the enhanced tubes from this study. Results from the modified correlation show differences with experimental values that ranged from −10% to +17%; the new modified correlation demonstrates high prediction accuracy. An accurate correlation allows the evaluation of enhanced heat transfer tubes for use in high-efficiency heat exchanger systems. The development of this new model is significant in the study of enhanced heat transfer.

Spiral wound tube heat exchanger (SWHE) was confirmed as the core equipment of natural gas liquefaction (LNG). However, there was rare experimental research on large-scale SWHE for LNG, and the theory of heat transfer is not perfect. To investigate the tube-side flow and heat transfer characteristics in spiral tubes, an experimental system was proposed. To ensure the accuracy of the experimental data, the heat transfer coefficients of liquid propane under different conditions were measured, and the data acquired through the experiment were compared with two classical heat transfer correlation (Dittus–Boelter and Geielinski) under the identical working conditions. The applicability of the existing correlation was analyzed using the experimental data, and a novel heat transfer correlation was developed. As indicated by the results, the deviation between the experimental system and the classical correlation under the identical working condition was lower than ±10%. Furthermore, the error comparison between the novel correlation prediction value and the experimental data was less than ±15%.

In order to successfully study the condensation and separation of a steam–CO2 mixture, a boundary layer model was applied to the mixture condensation of steam and CO2 on horizontal and vertical plates. The modified condensation boundary layer model of steam and CO2, given the CO2 solubility in the condensate, was established, numerically solved, and verified with existing experimental data. Different condensation data of steam–air and steam–CO2 mixtures were compared, and the effect of CO2 solubility on the mixed gas condensation was analyzed under multiple pressure conditions (1 atm–10 MPa). The simulation data show that the presence of CO2 will deteriorate the condensation heat transfer, just like air. Given that CO2 is slightly soluble, some CO2 can pass through the gas–liquid interface to enter the condensate film and reduce the accumulated CO2 on the gas–liquid interface, which improves the condensation. However, the solubility of CO2 is only significant under high-pressure conditions, inducing its effects on condensation. A comparison of the condensation coefficients of the steam–CO2 mixture shows the lower impact of CO2 condensation on the horizontal plate compared to that on the vertical plate. For most conditions, the steam–CO2 mixture gas condensation heat transfer coefficient on the vertical plate surface is still larger than that on the horizontal plate surface, and the improvement in the condensation heat transfer coefficient caused by low CO2 solubility (2 or 10%) at 10 MPa on the vertical plate is also larger than that of the horizontal plate.

The use of transport membrane condenser (TMC) technology to recover heat and mass from the flue gas has been increasing recently. The heat and mass transfer from the TMC tube bundle have been studied experimentally and numerically, and several numerical models have been proposed. Although many heat transfer and pressure drop correlations are available for single-phase flows over tube bundles of solid walls, to the best of our knowledge, there is a lack of heat and mass transfer and pressure drop correlations for the porous membrane tubes with condensing flue gas that cover a wide range of parameters. In this study, the heat transfer, mass transfer, and pressure drop imposed by the crossflow ceramic nanoporous tubes in TMC have been studied numerically within wide ranges of tube diameters (4.57-7.62 mm), number of rows (2-24 rows), and Reynolds number (170-8900), under flue gas condensation. The turbulent flow of the flue gas mixture was modeled by the shear stress transport SST k-ω turbulence model. A hybrid/mixed condensation model written in user defined functions was employed to calculate the water vapor condensation rate. Numerical results with condensing flue gas are compared to available correlations for single-phase Nusselt number and pressure drops in the literature. It was found that except for selected conditions, the single-phase correlations noticeably differed from the TMC numerical results. Empirical TMC correlations for heat transfer and pressure drops with respect to condensation rate, number of rows, and the nanoporous membrane geometrical properties were derived thereby. The derived correlations for TMC show a good agreement with numerical data for all investigated parameters and can predict the 96% of the convective Nusselt number, overall Nusselt number, and friction factor inside the TMC within ±10%, ±10%, and ±15%, respectively. The effects of key parameters on the heat transfer, mass transfer, and pressure drops are illustrated and discussed in detail. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Refrigeration is the property of Journal of Refrigeration Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The intermediate fluid vaporizer (IFV), different from other liquefied natural gas (LNG) vaporizers, has many advantages and has shown a great potential for future applications. In this present paper, studies of IFV and its heat transfer characteristics in the LNG vaporization unit E2 are systematically reviewed. The research methods involved include theoretical analysis, experimental investigation, numerical simulation, and process simulation. First, relevant studies on the overall calculation and system design of IFV are summarized, including the structural innovation design, the thermal calculation model, and the selection of different intermediate fluids. Moreover, studies on the fluid flow and heat transfer behaviors of the supercritical LNG inside the tubes and the condensation heat transfer of the intermediate fluid outside the tubes are summarized. In the thermal calculations of the IFV, the selections of the existing heat transfer correlations about the intermediate fluids are inconsistent in different studies, and there lacks the accuracy evaluation of those correlations or comparison with experimental data. Furthermore, corresponding experiments or numerical simulations on the cryogenic condensation heat transfer outside the tubes in the IFV need to be further improved, compared to those in the refrigeration and air-conditioning temperature range. Therefore, suggestions for further studies of IFV are provided as well. [ABSTRACT FROM AUTHOR]

A methanol–steam reformer (MSR) can safely provide hydrogen-rich fuel for a fuel cell system. Since the operating temperature of an MSR is relatively low, convective heat transfer is typically used to provide thermal energy to the endothermic reactions in the MSR. In this study, the use of phase change heat transfer to provide thermal energy to the endothermic reactions was investigated, which enhanced the temperature uniformity longitudinally along the MSR. ANSYS Fluent® software was used to investigate the performance of the reforming reactions. A comparative analysis using sensible heat and latent heat as the heat supply sources was performed. Using latent heat as a heat source achieved a lesser temperature drop than sensible heat that was under 5.29 K in the outer pipe. Moreover, a sensitivity analysis of methanol–steam-reforming reactions that use phase change heat transfer in terms of the carbon ratio, gas hourly velocity (for the inner and outer pipes of the MSR), inlet temperature (inner and outer pipes), reactor length, and operating pressure (inner pipe) was performed. When the phase change energy of water vapor is used, the wall temperature of the MSR is conveniently controlled and is uniformly distributed along the channel (standard deviation: 0.81 K). Accordingly, the methanol conversion rate of an MSR that uses phase change energy is ~4% higher than that of an MSR that employs convective heat transfer. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• n -butane is investigated as refrigerant with low global warming potential. • single tube and tube bundle experiments for smooth and finned condensation tubes. • variation of fin density and fin height for copper and cooper/nickel tubes. • analytical prediction model is tested for a large variation of finned tubes. The present study examines the condensation heat transfer coefficient α cond of n -butane on the outside of different horizontal tubes and in corresponding tube bundles. Experiments were conducted with a smooth tube, finned tubes with various fin densities, fin heights and tube materials, and a high-performance condensation tube (HPT) at vapor temperatures of (40 and 78) °C and varying heat flux densities q̇. The influence of inundation on α cond was systematically investigated by varying the mass flow of liquid condensate at q̇ of (20 and 60) kW· m −2. Differences between the experimental results from this work and previous ones for propane on the same condensation tubes could be explained with the help of the thermophysical properties and, thus, the retention angle of the condensate in the channels between the fins and the condensate layer thickness. For single copper tubes, α cond increased with increasing fin densities from (19 to 48) fins per inch and was between 9 and 17 times larger than for the smooth tube. This enhancement factor even reached a value of about 24 for the HPT. These increases can be attributed in part to the increased surface area, but the strongest effect appears to be related to surface tension-driven drainage of the condensate. In addition to the experimental investigations, α cond of the finned condensation tubes was predicted using an analytical model for the condensation heat transfer on finned tubes. Here, excellent agreement with an average deviation from the experimental results of 6.6 % could be found. Studies of the inundation effect have shown that the expected decrease in α cond due to the additional condensate impinging on the tubes inside bundles and increasing the film thickness often holds, but is partially counteracted by other effects and depends on the tube geometry. [ABSTRACT FROM AUTHOR]

• propane is investigated as refrigerant with low global warming potential. • new experimental setup for determining the condensation heat transfer is presented. • single tube and tube bundle experiments for smooth and finned condensation tubes. • variation of fin density and fin height for copper and cooper/nickel tubes. • analytical prediction model is tested for a large variation of finned tubes. The condensation heat transfer of propane on the outside of single horizontal tubes and in tube bundles was investigated by determining the condensation heat transfer coefficient α cond in a newly designed experimental setup. To study the influence of different surface structures and tube materials, experiments were conducted with a smooth tube, finned tubes with various fin densities and heights, and a high-performance condensation tube at vapor temperatures of 30 and 40 °C and varying heat flux densities. In addition, the influence of inundation on α cond was systematically investigated by varying the mass flow of liquid condensate at heat flux densities of 20 and 60 kW·m−2. The experimental setup was successfully validated using smooth tubes by a comparison of the resulting α cond with literature data and Nußelt's film theory. For the single copper tubes with fin densities from 19 to 48 fins per inch, α cond increased and was by factors of 9 to 21 larger than for the smooth tube at the same heat flux density. Investigations of the inundation effect have shown that the additional condensate can lead to an increasing condensate film thickness, which decreases α cond due to its increased thermal resistance, and/or can lead to turbulences in the condensate film, which increases α cond. The interplay of the two effects depends highly on the surface geometry. An increasing fin height always enhanced α cond , whereas a lower thermal conductivity of the tube material leads to a smaller α cond. [Display omitted] [ABSTRACT FROM AUTHOR]

• Verified rivulet behavior during dropwise condensation on vertical surface • Identified effects of surface length and rivulet flow on heat transfer • Related rivulet-covered area and dropwise condensation heat transfer Due to its superior heat transfer performance, dropwise condensation has been studied for industrial applications. This paper experimentally reports the effects of vertical length on dropwise condnsation in the presence of noncondensable gas. The formation of rivulet flows, which reduce heat transfer due to droplet coalescence, was observed. Compared to the upper side, rivulet flows on the lower side of the condensing surface were faster and more frequent. Lower heat flux was also measured on the lower side, indicating a correlation between heat transfer and rivulet flow parameters during dropwise condensation on the vertical surface. These findings represent the first study of the effects of rivulet flows on dropwise condensation heat transfer, and they can be applied to evaluate condensation heat transfer on long vertical surfaces, such as those found in small modular reactor containment systems as well as large containment building with passive containment cooling systems. [ABSTRACT FROM AUTHOR]

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors. • Wall wettability can change the immiscible condensates flow behavior and thus affect condensation heat transfer. • The smaller the condensate droplets departure diameter on the wall, the greater the condensation heat transfer performance. • The condensation heat transfer coefficient on the super-hydrophobic wall surface was the highest. [ABSTRACT FROM AUTHOR]

• A new individual-based model is developed to simulate dropwise condensation (DWC). • The hybrid MATLAB® and C parallel code allows simulation up to 1.1 × 107 drops. • Numerical results are compared against DWC experimental data. • The effect of sliding droplets on a vertical surface (height-to-width ratio equal to 25) is studied. • Computed heat flux and droplet population are compared against available models. Computational modeling is essential for understanding dropwise condensation (DWC) mechanisms, droplet life-cycle, and predicting heat transfer. However, the multiscale nature of DWC increases the computational cost, thus making the study of the droplet distribution more difficult. Population-based models available in the literature rely on empirical or statistical methods for determining the drop-size distribution. Differently, in the present study, a new individual-based model developed in hybrid MATLAB® and C codes and based on parallel computing is developed to simulate the whole dropwise condensation process, addressing the growth of each droplet, without making any assumption on the droplet population and considering a number of drops never reached in previous similar studies. The proposed model's computational efficiency is significantly improved when considering more than 1 million drops in the computational domain. To optimize the calculation time, the effects of time step, computational domain size, and simulation duration on the overall heat flux and drop-size distribution are discussed. The numerical results are compared against predictions from population-based models available in the literature. The proposed model is also used to study the droplet population and the instantaneous heat flux during DWC at different positions along a vertical condensing surface (upper, middle and lower areas). As a final step, a preliminary comparison is carried out between the present model and experimental data acquired during dropwise condensation on a nearly hydrophobic vertical surface. Considering a nucleation size density of 5 × 1012 m−2 (11 × 106 drops in the computational domain), the simulation is able to predict the experimental heat flux and the large drop-size distribution. [ABSTRACT FROM AUTHOR]

• Post-test calculation of COSMEA tests utilizing sophisticated measurement systems. • Detailed analysis of simulation results for different condensation models. • Recommendations for improvements of ATHLET heat transfer package. • Implemented model improvements show much better agreement with experimental data. • Best results are obtained by using the Thome condensation model. Based on a series of COSMEA experiments conducted in the scope of the PANAS project, the paper presents results of post-test simulations performed with a standard version of ATHLET as well as with an improved version of the code. After an overview on the research topics, the paper discusses the heat transfer phenomena in an emergency condenser pipe, the corresponding physical models implemented in ATHLET and the input deck developed to simulate the COSMEA tests. First results of the simulations with version 3.3 of ATHLET showed a significant underestimation of the heat transfer, an overestimation of the condensate outlet temperature and, depending on the experimental conditions, an underestimation or overestimation of the condensation rate. An in-depth analysis of the results helps to identify possible reasons for the deviations. The second set of simulations with an improved version of the code shows much better agreement with the experimental data. The corresponding part of the paper describes the modifications to the source code in the convection and condensation heat transfer models, the physical reasons behind these modifications and the improvements obtained with the updated models. In comparing three condensation models against experimental outcomes, including the Dobson-Chato, KONWAR, and Thome models, the Thome model demonstrated the highest degree of congruence with experimental data. Additionally, the study revealed that heat transfer correlations tailored for the rough flow regime are essential to elucidate the heat transfer phenomena on the secondary side of the COSMEA test section, leading to their subsequent integration into the ATHLET code. [ABSTRACT FROM AUTHOR]

• A detailed examination of flow morphology and heat transfer during steam condensation in a single inclined condenser tube was performed for pressures up to 65 bar and steam qualities at inlet down to 2.8 %. • Test experiments were carried out at five pressure stages up to 65 bar and for different inlet steam qualities. • The flow patterns were investigated using two advanced measurement techniques namely X-ray computed tomography and X-ray radiography. • The wall heat flux distribution and integral condensation rate were measured. • The interrelation between flow morphologies and wall heat flux were investigated. We report on an experimental study of high-pressure (up to 65 bar) steam condensation heat transfer in a slightly inclined tube at the thermal–hydraulic test facility COSMEA. The study is part of an extended experimental program on this topic and focused this time on heat transfer and two-phase flow at low inlet steam qualities (down to 2.8 %). We determined condensation rates respectively total heat transfer, wall heat flux distribution and flow morphology using X-ray imaging and local temperature measurements. [ABSTRACT FROM AUTHOR]

In order to study the heat transfer of R410A in extreme environments, the properties of several stainless steel and copper-enhanced tubes were evaluated using R410A as the working fluid, and the results were compared with those of smooth tubes. Tubes evaluated include: smooth, herringbone (EHT-HB) and helix (EHT-HX) microgroove, herringbone/dimple (EHT-HB/D); herringbone/hydrophobic (EHT-HB/HY); and composite enhancement 1EHT (three-dimensional). Experimental conditions include a saturation temperature of 318.15K with a saturation pressure of 2733.5 kPa; a mass velocity in the range between 50 and 400 kg/(m2·s); and an inlet quality controlled at 0.8 and an outlet quality of 0.2. Results indicate that the EHT-HB/D tube produces the best overall condensation heat transfer characteristics (high heat transfer performance and low frictional pressure drop). Using the performance factor (PF) to compare tubes for the range of conditions considered, the PF of the EHT-HB tube is greater than one, the PF of the EHT-HB/HY tube is slightly greater than one, and the PF of the EHT-HX tube is less than one. In general, as the mass flow rate increases, PF initially decreases and then increases. Previously reported smooth tube performance models that have been modified (for use with the EHT-HB/D tube) can predict the performance for 100% of the data points to within ±20%. Furthermore, it was determined that the thermal conductivity of the tube (when comparing stainless steel and copper) will have some effect on the tube-side thermal hydraulic performance. For smooth tubes, the heat transfer coefficients (HTC) of copper and stainless steel tubes are similar (with copper tube values being slightly higher). For enhanced tubes, performance trends are different; the HTC of the copper tube is larger than the SS tube.

Slippery liquid-infused porous surface (SLIPS) realized on commercial materials provides various functionalities, such as corrosion resistance, condensation heat transfer, anti-fouling, de/anti-icing, and self-cleaning. In particular, perfluorinated lubricants infused in fluorocarbon-coated porous structures have showed exceptional performances with durability; however, they caused several issues in safety, due to their difficulty in degradation and bio-accumulation. Here, we introduce a new approach to create the multifunctional lubricant-impregnated surface with edible oils and fatty acid, which are also safe to human body and degradable in nature. The edible oil-impregnated anodized nanoporous stainless steel surface shows a significantly low contact angle hysteresis and sliding angle, which is similar with general surface of fluorocarbon lubricant-infused systems. The edible oil impregnated in the hydrophobic nanoporous oxide surface also inhibits the direct contact of external aqueous solution to a solid surface structure. Due to such de-wetting property caused by a lubricating effect of edible oils, the edible oil-impregnated stainless steel surface shows enhanced corrosion resistance, anti-biofouling and condensation heat transfer with reduced ice adhesion.

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 9.52 mm were experimentally investigated. Experiments were conducted at saturation temperatures of 30°C, 35°C and 40°C, heat flux ranged from 3 to 8 kW·m−2, mass flux ranged from 25 to 75 kg·m−2·s−1, and vapor quality up to 1.0. Flow patterns of NCUR01 were estimated based on flow pattern maps. The effects of saturation temperature, heat flux, mass flux, and vapor quality on heat transfer coefficients and friction pressure drops were analyzed. The results demonstrate that the flow patterns of NCUR01 during condensation are predominantly stratified and stratified-wavy. The condensation heat transfer coefficients and friction pressure drops increase with mass flux and mean vapor quality, while decrease with saturation temperature. Heat flux has a positive correlation with heat transfer coefficients, but has little effect on friction pressure drops. In addition, experimental data were compared with predicted values of correlations in the literature, and the correlations with high accuracy were selected. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 N4$\sqrt[4]{N}$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.

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 paper presents an experimental investigation of condensation heat transfer by gradient heatmetry. The experiments were carried out during the condensation of saturated steam at atmospheric pressure on the cooled surface of a horizontal pipe. The distributions of the local heat flux, surface temperature, and heat transfer coefficient along the circumference of the horizontal pipe were experimentally determined. The surface average condensation heat flux on the horizontal pipe was about 141.06 kW/m2. The proposed method allows us to determine the area of condensate accumulation on the pipe (in the range of azimuth angle φ = 150…180∘) in which the heat flux decreases by 34% of the average value. The heat flux per unit area relative uncertainty was about 5.2%. The surface-averaged heat transfer coefficient during condensation on the horizontal pipe was about 5.5 kW/(m2×K), and relative uncertainty was about 9.4%.