Condensation Heat Transfer Characteristics Research Articles

Experimental Analysis of the Condensation Flow and Heat Transfer characteristic in a spiral tube under Ocean Swell conditions

The floating liquefied natural gas platform is a key enabling technology for the development of marine natural gas resources. It’s core component, the spiral wound heat exchanger, is frequently subjected to offshore sloshing conditions, which present a significant challenge for the technology. To clarify the condensation flow and heat transfer characteristics in the spiral tube under offshore shaking conditions, an experimental system with a sloshing platform was constructed. The impact of sloshing mode (sway and roll), displacement (sway: 250∼1500mm or roll: 3∼15°), and period (10∼16s) on the heat transfer coefficient (h) and frictional pressure drop (ΔPfric) were analyzed under different operational parameters (mass flux, vapor quality and pressure). Additionally, the comprehensive sloshing factor (CSF) was used to evaluate the overall effect of shaking on condensation process. The results show that the sway and roll motions positively impact the h and ΔPfric. The impact decreases with the increases in mass flux and vapor quality and is negatively correlated with operating pressure. In sway motion, the CSF ranges from 1.39% to 11.82%, with an average of 5.15%. In roll motion, the CSF ranges from 1.15% to 5.13%, with an average of 2.57%.

Identification of flow patterns in an opaque condenser tube by distributed fiber Bragg gratings

Two-phase loops with phase change heat transfer are pivotal for cooling electronics under high heat flux and for thermal control in spacecraft. Numerous studies aim to clarify the mechanisms behind these loops to enhance cooling capacity and stability, which are closely tied to flow patterns. However, conventional flow pattern identification methods, requiring transparent tubes for direct observation, are impractical for simultaneous heat transfer measurement, especially during condensation. This paper introduces a novel approach for identifying flow patterns within an opaque, vertical condensation tube using embedded distributed fiber Bragg gratings (DFBGs) for R134a. The method involves a “fingerprint” derived from temperature profile derivatives and additional criteria based on temperature variation characteristics. These include the relative deviation from saturation temperature, the relative spatial temperature gradients, and the relative amplitude of temperature fluctuations. Validation against high-speed camera images confirms the method’s efficacy. It enables the determination of flow pattern lengths, the endpoint of condensation, and the construction of a flow regime map. Additionally, it allows for the measurement of vapor velocity in slug flow, facilitating the calculation of slip ratio and void fraction, which correlates reasonably with the Zuber-Findlay model, with systematic positive deviations up to 30%. This method also paves the way for simultaneous measurement of in-tube condensation heat transfer characteristics for various flow patterns.

Numerical study on the fluid flow and condensation heat transfer characteristics of two-phase NaCl-H2O fluids on the external swept spiral coil in a hydrothermal vent

The substantial thermal energy of two-phase NaCl-H2O hydrothermal fluids makes them a significant target for utilizing deep-sea energy. A fundamental understanding of the thermal performance of two-phase NaCl-H2O hydrothermal fluids during condensation is crucial for heat energy harnessing. It aims to obtain the flow and condensation heat transfer characteristics of two-phase NaCl-H2O fluids during the heat transfer process outside a spiral coil structure in this paper. The properties of the NaCl-H2O binary systems were adopted instead of pure water, and the salt transport equation was considered to reflect the impact of salinity change on heat transfer, making the simulation more representative of natural venting fluids. The results indicated a significant tangential velocity when the fluids externally swept the spiral coil. Secondly, the heat transfer area can be divided into the “normal region” and the “island region,” of which convection and condensation contribute to the heat transfer mechanisms. The “island region” formation was attributed to both vapor condensation and the spoiler effect caused by the spiral structure. Moreover, the heat flux increased with decreasing salinity in the “island region,” and a weak interaction was observed between heat flux and salinity in the “normal region.” Finally, the spiral structure's heat transfer performance was superior to the straight structure's. This investigation may provide a basis for designing and optimizing the heat transfer equipment for deep-sea hydrothermal extraction.

Numerical simulation on the condensation heat transfer and flow characteristics outside smooth and enhanced tubes

Most of the current studies only conducts two-dimensional simulations of condensation heat transfer and flow outside enhanced tubes, which cannot accurately reflect the flow and heat transfer characteristics of liquid film outside enhanced tubes. In order to provide theoretical support for the design optimization of enhanced tubes, this study adopts the VOF multiphase model and Lee condensation model to simulate the condensation heat transfer(HTC) of refrigerants outside smooth and enhanced tubes. The instantaneous film flow characteristics of the liquid film outside the horizontal smooth and enhanced tubes are analyzed, and the thickness of the liquid film and the relationship with the condensation heat transfer coefficient of the smooth and enhanced tubes under different working conditions are calculated. The refrigerants are compared under the same working conditions, and the results are shown: The simulation results are in good agreement with the experimental data and the Nusselt analytical solution, and the error is all within 15%; the distribution of liquid film is highly sensitive to the magnitude of local condensation heat transfer coefficients, and the condensation HTC outside the enhanced tube is approximately six times of that of smooth tube. Combining the distribution of the liquid film and the thermophysical properties of the refrigerants, it was determined that R410A has the highest HTC, while R1234yf has the lowest HTC.

Experimental study on heat transfer characteristics of steam condensation in the presence of air and CO2 outside a vertical tube

Under severe accident conditions, in addition to steam and air, there are also other non-condensable gases inside the containment, such as CO2 produced by the molten corium concrete interaction (MCCI). Due to the significantly higher molecular weight and density of CO2 compared to steam and air, CO2 will have a significantly different impact on the steam condensation process compared to air. However, few scholars have paid attention to the impact of CO2 on the condensation process, and there is no empirical correlation applicable to this condition. Therefore, this article investigates the effect of different CO2 concentrations on the steam condensation heat transfer coefficient (CHTC) in the range of system pressure from 0.2 to 1.3 MPa and subcooling from 30 to 130 °C through experimental methods. Meanwhile, based on relevant experimental data, a new correlation suitable for calculating the steam CHTC in the presence of CO2 and air was fitted. The results indicate that under low steam concentration conditions, the addition of CO2 will reduce CHTC, while under high steam concentration conditions, CO2 will increase CHTC. The increase in system pressure will strengthen the condensation promotion effect of CO2 and weaken its inhibitory effect on condensation. In addition, by comparing experimental data under different component conditions, it was found that the new empirical correlation has high computational accuracy, and the calculation results of this correlation can contain more than 90 % of the data within a 15 % error range.

Numerical investigation of heat and mass transfer characteristics of steam condensation containing non-condensable gas in vertical corrugated tube

A numerical simulation of steam condensation containing non-condensable gas is conducted in this paper to analyze the heat and mass transfer characteristics in vertical corrugated tube. The species transport model, Euler liquid film model and diffusion-balance model with Dehbi factor to correct the diffusion effect are applied to simulate the mass and energy transfer processes. The effects of different corrugated tube structural parameters and inlet steam parameters on steam condensation rate, liquid film distribution and heat transfer are simulated. The results show that vortex and accumulated non-condensable gas in the corrugated region significantly influence condensation heat transfer, which are closely related to corrugation height (H=0–5 mm) and corrugation length (L=13, 16, 19, 22, and 25 mm) of the corrugations, as well as inlet velocity (Vin = 5, 7, 9, 11, 13, and 15 m·s−1) and inlet steam content (Ws = 0.6, 0.7, 0.8, 0.9, 0.99, and 1). The total heat transfer coefficient varies linearly with inlet velocity when inlet velocity increase from 5 m·s−1 to 15 m·s−1, which increase 89.6–108.1 %; total heat transfer coefficient increases almost exponentially when inlet steam content increase from 0.6 to 1, which increase 389–460 %; and the best corrugated tubes are those with corrugation height of 0.075 times diameter of tube and corrugation length of 0.325 times diameter of tube.

Condensation characteristics of flows in newly developed three-dimensional enhanced heat transfer tubes

Condensation heat transfer characteristics were studied experimentally in order to evaluate the heat transfer performance of horizontal copper heat transfer tubes (smooth and enhanced). Using R410A and R32 as refrigerants, condensation heat transfer experiments were carried out for a saturation temperature of 45 °C; inlet vapor quality of the tube was 0.8 and outlet quality was 0.2; refrigerant mass flow rate range was in the range from 68 to 371 kg/(m2·s). Single-phase heat balance verification found that the heat loss is less than 6 %, with the deviation between single-phase experimental results and various correlations being less than 15 %. The condensation heat transfer coefficient increases with an increase in mass flow; as the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient (HTC) increases. Experimental results determined that the performance factor ratio (enhanced tube/smooth tube) of the three-dimensional surfaces investigated here are greater than 1. Tubeside heat transfer enhancement factor (EF) of the HB/D tube is the highest (max 1.76); its performance is closely related to increasing fluid turbulence and improving drainage. Performance factor (PF) of the HB/D tube (max 1.38) is the highest for most of the flowrates. All this indicates excellent thermal performance. Flow model-based analysis was performed in order to develop a correlation for the condensation heat transfer coefficient and the pressure drop for the enhanced surface tubes. Both prediction models accurately predicted all data points within a limited margin of error.

Numerical investigation on flow condensation in zigzag channel of printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) has a great potential for the application in various compact energy systems. However, the there is no existing heat transfer and pressure drop correlations on condensation in PCHE zigzag semicircular channel. In this study, the flow and heat transfer characteristics of condensation in the PCHE zigzag semicircular channel were analyzed numerically. The flow patterns of annular flow, annular wavy flow and plug flow were observed in the channel, and the flow pattern transition line correlations were developed. As the mass flux increases, the transition vapor quality from annular flow to intermittent flow decreases gradually. Both the condensation pressure drop and the heat transfer coefficient reach their peaks as the vapor quality is around 0.78, and the pressure drop decreases with the increase of saturation temperature. The heat transfer coefficient decreases as the saturation temperature increases when the vapor quality is less than 0.6, while it increases slightly as the saturation temperature increases when the vapor quality is greater than 0.6. New correlations for condensation pressure drop and heat transfer in PCHE zigzag semicircular channel are developed. The average errors of the developed condensation pressure drop and heat transfer correlations are 11.0 % and 7.9 %, respectively.

Comparisons of two-phase condensation and single-phase heat transfer and frictional pressure drop characteristics and energy-saving performance analysis of R-32 and R-410A in plate heat exchanger

In this study, the heat transfer and frictional pressure drop characteristics of R-32 and R-410A in a plate heat exchanger are experimentally evaluated. The study comprises two-phase condensation, single-phase vapor, and liquid cooling experiments of R-32 and R-410A, as well as an independent single-phase water heat transfer experiment. The effects of heat flux, mass flux, condensing pressure, mean vapor quality, and refrigerant Reynolds number on heat transfer and pressure drop are assessed for comparisons of R32 and R410A. The results demonstrate that the heat transfer performance and frictional pressure drop increase with rising mass flux and mean vapor quality and decrease with declining condensing pressure in the two-phase condensation experiments. Furthermore, increasing the heat flux enhances the heat transfer performance while having negligible impact on the frictional pressure drop. In the single-phase cooling experiments, both heat transfer performance and frictional pressure drop rise with increasing refrigerant flow rate. Based on the experimental results, Nusselt number and friction factor correlations for two- and single-phase flows of R-32 and R-410A are developed and compared with the correlations from other studies. Finally, energy-saving performance is evaluated and compared between the refrigerants.

Research on the R513A condensation heat transfer characteristics in horizontal microfin tubes

R513A has been proposed as alternative to R134a due to its lower GWP. So, it is necessary to investigate the condensation heat transfer characteristics and pressure drop of R513A in the horizontal tubes. The 12.70-mm-OD and 9.52-mm-OD tubes were selected for condensation tests. It was found that the R134a condensation heat transfer coefficient in the 12.70-mm-OD microfin tube was similar to the R513A condensation heat transfer coefficient, and the deviation was about −3% ∼ +9%; R513A yielded 4.44% ∼ 16.01% lower pressure drop than R134a. The R513A heat transfer coefficient of the microfin tube was about 1.42–1.74 times of that of the smooth tube, and the pressure drop was 39.11% ∼ 76.63% than that in the smooth tube. Additionally, the condensation heat transfer coefficient and pressure drop of the 9.52-mm-OD test tube were 23.88% ∼ 41.62% and 40.79% ∼ 71.86% higher than those of the 12.70-mm-OD tube, respectively. The micro-fin structure inside the microfin tube resulted in efficient heat transfer, but also increased the fluid flow power consumption. Moreover, as the tube diameter decreased, the effects of sheer stress and surface tension increased. Furthermore, experimental data were also compared with previous correlations proposed for microfin tubes. More experiments are still required to develop more applicable theoretical correlations in future.

Experimental research on condensation flow and heat transfer characteristics of immiscible binary mixed vapors on different wettability wall surfaces

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.

Numerical study of condensation heat transfer characteristics of R134a/R290 and R134a/R1270 refrigerant blends as alternatives to replace R404A

R404A needs to be replaced due to its higher GWP in the context of green development. In this study, M1 (R134a/R290, 55/45) and M2 (R134a/R1270, 43/57) were proposed to replace R404A refrigerant. The thermodynamic properties were compared. The heat transfer and pressure drop characteristics of condensation for R404A, M1 and M2 inside horizontal microtube (D = 1 mm) at saturation temperature of 40℃ were investigated numerically. The results showed that the COP of M1 and M2 were higher than that of R404A, while the GWP of M1 and M2 is 81.83 % and 85.79 % lower than that of R404A, respectively. The heat transfer coefficients and pressure gradients increase with increasing mass flux and vapor quality, the heat transfer coefficient of M1 and M2 were on 50 ∼ 55 % and 78 ∼ 80 % higher than that of R404A. However, the pressure gradients of M1 and M2 were on 95 ∼ 110 % and 105 ∼ 115 % larger than that of R404A. The liquid film thicknesses of M1 and M2 were smaller than that of R404A. M1 and M2 could be used as low GWP alternatives to R404A with regard to thermodynamic performance and heat transfer properties. The results of the study have important guiding value for the replacement of R404A.

Experimental study of the effect of different heat transfer plates on the heat transfer characteristics of flue gas condensation

Experimental study of the effect of different heat transfer plates on the heat transfer characteristics of flue gas condensation

Flow condensation heat transfer correlation development of R32-oil mixture inside a micro-fin tube

The air-conditioners employ R32 as refrigerant because it has low GWP. The heat transfer performance of R32 in the heat exchangers would be influenced by the lubricating oil cycled with R32. In order to obtain the quantitative effect of oil on the flow condensation heat transfer characteristics, flow condensation heat transfer correlation of R32-oil mixture is needed. In this study, an experimental rig for testing the flow condensation heat transfer coefficients of R32-oil mixture is established. The test conditions covering the actual working conditions of air-conditioners are designed, including the condensation temperature ranging from 40 to 50 °C, mass flux ranging from 100 to 400 kg m − 2 s − 1, vapor quality ranging from 0.1 to 0.9 and oil concentration ranging from 0 % to 5 %. The results show that the flow condensation heat transfer coefficients decrease with the increasing of oil concentration because of the high viscosity of the oil. A new condensation heat transfer correlation is developed based on the enhanced structure of the micro-fin tube and physical properties of the working fluid, and it agrees with 82 % of the experimental results within a deviation of ± 20 %.

Two-phase flow condensation heat transfer characteristics of R-134a inside three-dimensional cylindrical micropillar enhanced tube

This paper presents an experimental investigation for evaluation of heat transfer coefficient, frictional pressure drops and flow regimes with their transitions during the condensation of R-134a inside a smooth, two microfins (MF1 and MF2) and a newly developed micropillar (MP) tubes. The experiments are carried out for a range of mass flux at an average saturation temperature of 35°C. Micropillar tube has produced the maximum heat transfer coefficient, while the microfin (MF1) tube resulted the highest frictional pressure gradient compared to other tubes. The experimental observations of microfin and micropillar tubes are plotted on the mass flux versus vapor quality flow map and Taitel and Duckler flow map to discuss the transitions within different flow patterns achieved. Visual inspection of the flow regimes with varying mass flux and vapor quality showed stratified-wavy, intermittent, and annular flow regimes. The occurrence of annular flow is found to be more in MF1 and MP tube. A performance evaluation factor (PEF) is defined to evaluate the thermal-hydraulic performance of the tubes. Using the same, it has been observed that the newly developed MP tube has a PEF value greater than unity which suggest augmentation of heat transfer coefficient at the expense of lesser pressure drop penalty.

Numerical evaluations on enhanced steam–air condensation outside S-type tubes under natural convection conditions

Steam-air condensation is extensively utilized in various industrial fields. In pursuit of better efficiency in applications, this study promoted a novel structure of heat transfer enhancing tube named S-type tube. It combines the superior heat transfer performance of short tubes and inclined tubes, demonstrating a high potential for enhanced condensate heat transfer. To evaluate the heat transfer property and obtain the optimized S-type tube structure, three-dimensional CFD methods were used, coupled with the liquid film model in STAR-CCM + software. The effcts of wall sub-cooling, pressure, air mass fraction and downward forced velocity, bend radius, horizontal section length on the steam–air condensation heat transfer characteristics outside S-type tubes were investigated. It was identified that S-type tubes can enhance the steam–air condensation heat transfer capability, and the enhanced heat transfer ability increases with the increase of pressure and the decrease of air mass fraction, and remains basically unchanged with changes in sub-cooling. The condensation heat transfer coefficients outside S-type tubes are 0.9 ∼ 1.71 times that of vertical tube range 0.2 MPa to 0.8 MPa. The main mechanisms affecting the condensation heat transfer are summarized: the scouring effect between tube segments to enhance heat transfer and the air layer pileup effect to inhibit heat transfer. The heat transfer enhancement capacity for the S-type tube is determined by the relative magnitude between the scouring effect and the pileup effect. Both effects increase as bend radius decreases; therefore, selecting an appropriate bend radius is crucial.

Experimental study and general correlation for condensation heat transfer coefficient inside microfin tubes

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 %.

Experimental Study on Condensation Heat Transfer Performance of Hydrophilic/Hydrophobic Microstructured

In order to study the condensation and heat transfer characteristics of similar microstructure surfaces, two similar microstructure surfaces, cylindrical and circular, were fabricated by femtosecond laser technology on a 0.5 mm silicon wafer. The cylindrical surface is superhydrophobic when the contact angle is more than 150°, and the circular surface is hydrophilic when the contact angle is less than 90°. The difference in condensation heat transfer characteristics between superhydrophobic and hydrophilic microstructures was analyzed, and a visual condensation experimental platform was built. Experimental research showed that: At the same flow rate, the heat transfer coefficient of the superhydrophobic surface and the hydrophilic surface decreases significantly with the increase of the surface subcooling degree, but the heat transfer coefficient of the cylindrical surface is still much larger than that of the circular surface. In addition, the heat transfer performance of the hydrophobic microstructure surface is better than that of the hydrophilic surface at medium and high-speed cooling water flow rates. Although the surface microstructures are similar in shape, the heat transfer performance of cylindrical microstructures is much better than that of circular microstructures under the same conditions, and the heat flux of cylindrical microstructures is 2.2 times that of circular microstructures.

Analysis of influence of inlet vapor quality on heat transfer and flow pattern in mini-channels during flow condensation process

Micro/mini-channel heat sinks are extensively utilized in heat dissipation systems that involve high heat flux components. These heat sinks are preferred due to their compact size and excellent heat transfer efficiency. The selection of a refrigerant condensation system for the heat dissipation system under vapor conditions is crucial. In order to investigate the heat transfer characteristics of flow condensation in a mini-channel, a visual experiment system was used with a hydraulic diameter of 2 mm and a volume flowrate of 30 mL/min, 60 mL/min, 90 mL/min, 120 mL/min respectively. The study focused on the effect of inlet vapor quality on the flow pattern and heat transfer characteristics of flow condensation in the mini-channel. The results indicate that the flow pattern in flow condensation process can be classified into annular flow, transition flow, slug flow and bubble flow in sequence along the flow direction. As the inlet vapor quality (xin) increases, the dominance of annular flow gradually increases, making it difficult to capture the bubble flow with high volume flowrate and high inlet vapor quality. This phenomenon is observed under experimental conditions when: 1) xin is equal to or greater than 0.75 at a volume flowrate of 60 mL/min, 2) xin is equal to or greater than 0.55 at a volume flowrate of 90 mL/min, and 3) xin is equal to or greater than 0.25 at a volume flowrate of 120 mL/min. The increase in inlet vapor quality is beneficial to the improvement of condensation heat transfer coefficient. In this experiment, it was observed that the local heat transfer coefficient was decreased by up to 83.7 % when comparing the lowest vapor quality to the highest at the same volume flowrate, emphasizing the significance of inlet vapor quality in the flow condensation during the heat transfer process.

The Effect of Heat Exchanger Tube Structure on the Condensation Heat Transfer of R1234ze(E)/R152a Inside Smooth Tubes

Abstract In this paper, the flow condensation heat transfer characteristics of the environmentally friendly nearly-azeotropic refrigerant R1234ze(E)/R152a (mass ratio of 40:60) in smooth tubes with varying structures were numerically investigated. Under the operating conditions of mass flux of 400 kg/m2/s, heat flux of 12 kW/m2, and saturation temperature of 308.15 K, this study investigated the influence of circular tube inner diameter, elliptical tube aspect ratio, and installation orientation on condensation heat transfer, while the influence on pressure drop has not been taken into account in the present study. The results indicate that the condensation heat transfer coefficient in the tube increases as the inner diameter of the circular tube decreases. The condensation heat transfer coefficient increases by 1.086 times when the circular tube inner diameter is reduced from 10.7 mm to 5 mm. Under identical operating conditions, the condensation heat transfer coefficient of the mixed refrigerant in elliptical tubes increases with an increase in the aspect ratio. The average condensation heat transfer coefficient increases by 18.21% as the aspect ratio of the elliptical tube increases from 1 to 2. Compared to a vertical elliptical tube, a horizontal elliptical tube is more favorable for condensation heat transfer within the tube.