Condensation Characteristics Research Articles

Sensitivity analysis from the blade angle regulation of the forced draught fans in an air-cooled steam condenser

For enough cooling air flowing through the finned tube heat exchangers, the performance of the forced draught fans are always pivotal for the final characteristics of the air-cooled steam condenser (ACSC) as well as the power station. Hence, it is necessary to optimize the fan operation for a superior performance. In this paper, a previous numerical model is designated to execute the impact analysis from the blade angle regulation for forced draught fans with different positions on the performance of the air-cooled system at the prevailing wind angle of β=22.5°. The simulation results indicate the fan volumetric effectiveness, heat transfer rate and the related equilibrium back pressure are influenced significantly once the fan blade angle is regulated. Compared with the design case, it is found that a maximum elevation of net power, 17.76MW, is obtained for the fan array case when the wind speed is vm=2m·s−1. Furthermore, it is found that the windward and peripheral case almost have a same effect to raise the net power of the power plant.

Parametric Analysis of Condensation Heat Transfer Characteristics of AMTEC Wick Condenser

By using theoretical analysis method, effects of different parameters on condensation heat transfer characteristics of porous wick condenser of alkali metal thermal to electric converter (AMTEC) are discussed. The results show that, along the radius direction r of the condenser, the condensate film thickness δ(r) increases gradually, and the Nusselt number Nu(r) decreases. With increasing of the permeability K or decreasing of the effective thermal conductivity λe and the heat transfer temperature difference ΔT, the condensate film thickness δ(r) decreases significantly, and the Nusselt number Nu(r) increases. However, the BASE tube temperature TB and condensate film temperature TS have little impact on condensation heat transfer characteristics, which indicates that for AMTEC condenser, the latent heat releasing dominates the total heat transfer while the radiation heat transfer almost has no influence.

Rapid and continuous synthesis of methacrolein with high selectivity by condensation of propanal with formaldehyde in laboratory

AbstractAn experimental device with a micro‐tubular reactor for continuous reaction process was designed and constructed based on the reaction mechanisms and characteristics of condensation of propanal with formaldehyde, a short mean residence time (a few seconds) for the reactive mixture was acquired to increase selectivity to methacrolein (MAL) by reducing the side reactions. Diethylamine and acetic acid aqueous solution was used as catalysts for the reaction. The reactor temperature ranged between 100 and 210 °C. The reactor pressure was set at 4.5–6.0 MPa to make sure that the reaction can be carried out in liquid phase. The results indicated that the reaction rate was heavily influenced by the concentration of the catalysts and the feed preheating temperature. When the feed preheating temperature was about 132 °C, the mass concentration of diethylamine was about 6 %, the reaction pressure was 4.5–5.0 MPa, and the mean residence time varied from 4.5 to 5.5 s, high conversion of propanal (99.9 %) and high selectivity to MAL (98.7 %) were acquired. High catalytic activity and high selectivity were maintained after the catalysts had been recycled six times.

Self-trapping and tunneling of Bose-Einstein condensates in a cavity-mediated triple-well system

We have investigated tunneling characteristics of Bose-Einstein condensates (BECs) in a triple-well potential coupled to a high finesse optical cavity within a mean field approach. Due to the intrinsic atom-cavity field nonlinearity, several interesting phenomena arise which are the focuses of this work. In the dynamical process, an extensive numerical simulation of localization of the BECs for atoms initially trapped in one-, two-, and three-wells are performed for the symmetric and asymmetric cases in detail. It is shown that the the transition from the oscillation to the localization can be modified by the cavity-mediated potential, which will enlarge the regions of oscillation. With the increasing of the atomic interaction, the oscillation is blocked and the localization emerges. The condensates atoms can be trapped either in one-, two-, or in three wells eventually where they are initially uploaded for certain parameters. In particular, we find that the transition from the oscillation to the localization is accompanied with some irregular regime where tunneling dynamics is dominated by chaos for this cavity-mediated system.

Numerical simulation of R410A condensation in horizontal microfin tubes

ABSTRACTThe heat transfer characteristics of condensation for R410A inside horizontal microfin tubes with 0° and 18° helical angles were investigated numerically. The numerical data fit well with the experimental results and with the empirical correlations. The results indicate that local heat transfer coefficients increase with increasing mass flux, vapor quality, and helical angle. The heat transfer enhancement in the helical microfin tubes is more pronounced at higher mass flux and vapor quality. The centrifugal force induced by the microfin with a 18° helical angle tends to spread the liquid from the bottom to the top, leading to a nearly symmetrical liquid–vapor interface during condensation. Swirling flows in the liquid phase are observed in the tube with the 18° helical angle, but the liquid phase tends to flow to the bottom due to gravity in the tube with the 0° helical angle.

The effect of gravity on R410A condensing flow in horizontal circular tubes

ABSTRACTHeat transfer characteristics of R410A condensation in horizontal tubes with the inner diameter of 3.78 mm under normal and reduced gravity are investigated numerically. The results indicate that the heat transfer coefficients increase with increasing gravitational accelerations at a lower mass flux, whereas their differences under varying gravity are insignificant at a higher mass flux. The liquid film thickness decreases with increasing gravity at the top part of the tube, whereas the average liquid film thickness is nearly the same under different gravity accelerations at the same vapor quality and mass flux. The local heat transfer coefficients increase with increasing gravity at the top of the tube and decrease with increasing gravity at the bottom. The proportion of the thin liquid film region is important for the overall heat transfer coefficients for the condensing flow. A vortex with its core lying at the bottom of the tube is observed under normal gravity because of the combined effect of gravity and the mass sink at the liquid–vapor interface, whereas the stream traces point to the liquid–vapor interfaces under zero gravity. The mass transfer rate under zero gravity is much lower than that of normal gravity.

CFD modeling of condensation process of water vapor in supersonic flows

The condensation phenomenon of vapor plays an important role in various industries, such as the steam flow in turbines and refrigeration system. A mathematical model is developed to predict the spontaneous condensing phenomenon in the supersonic flows using the nucleation and droplet growth theories. The numerical approach is validated with the experimental data, which shows a good agreement between them. The condensation characteristics of water vapor in the Laval nozzle are described in detail. The results show that the condensation process is a rapid variation of the vapor-liquid phase change both in the space and in time. The spontaneous condensation of water vapor will not appear immediately when the steam reaches the saturation state. Instead, it occurs further downstream the nozzle throat, where the steam is in the state of supersaturation.

Interfacial characteristics of steam jet condensation in crossflow of water in a vertical pipe

An experimental study is performed to investigate the interfacial characteristics of steam jet condensation in crossflow of water in a vertical pipe. A high-speed camera is applied to capture the raw images of the condensing jet in the flow visualization test section. According to both the gray and gray-gradient profiles of the original images, an interfacial identification method is proposed to reveal the interfacial characteristics, including the jet plume shape, jet centerline trajectory and jet penetration length. Based on the expansion features of the two phase interface, the condensation regimes are classified into five categories, including double expansion-contraction, expansion-contraction, cylinder, contraction and hemisphere shapes. The steam mass flux, scaled by critical steam mass flux at ambient pressure, is found to be irrelevant to the transitional lines among the hemisphere, conical and expansion-contraction shapes in the condensation regime map. The jet momentum ratio as a dominant factor is introduced to correlate the jet centerline trajectory, and the predicted results are within ±20% of the experimental data. The dimensionless jet penetration length decreases with increase of ambient pressure, and is found to be in the range of 0.58–6.49 in present experiments. A correlation for prediction of the dimensionless jet penetration length is established, and the discrepancies between the predicted results and experiments are within ±15%.

복합 구조형 배수 배관재의 소음 및 결로 특성에 관한 연구

The present study investigates noise and condensation characteristics of polyvinyl chloride (PVC), which is widely used for drainage piping materials, complex double structure by comparing to those of PVC single structure piping materials. In addition, effects of insulation on drainage noise has been measured experimentally. As the results of the experiments, noise reduction effect of PVC complex double structure is superior to that of PVC single structure in terms of elbow and vertical piping materials which are employed for drainage pipes of toilet bowls and bathtub. The insulation barely have effect on the noise reduction in case of the PVC single structure since there is almost no changes in noise occurrence even though the insulation is applied on both elbow and vertical piping materials. Temperature differences between inside and outside of the pipes have been measures for the PVC single and complex double structures as well. In consequence, outside temperature of the PVC complex double structure is higher than that of the PVC single structure. The condensation occurrence time of the PVC complex double structure shows a distinct difference from that of the PVC single structure, thus, the PVC complex double structure has outstanding effect on preventing the condensation.

Condensate characteristics of bosons in a tilted optical lattice

In this work we study the properties of interacting bosons in a tilted triple well optical lattice potential. A tilted optical lattice is possible to create in an experiment with charged bosons in presence of an electric field. The ground state energy, occupation densities in each well and first order correlation function of occupation densities as a function of the tilt parameter for N = 90 bosons using recently developed Multiconfigurational time-dependent Hartree method for bosons (MCTDHB) are studied. The ground state energy falls off with the tilt parameter for a given value of the barrier height and interparticle interaction. Also the tilt parameter is observed to restrict the fragmentation of the occupation densities in each well and thus promote condensation. Further the correlation between the bosons in different wells enhances with the tilt parameter and at large values the bosons in the first and the third wells are correlated apart from the correlation among the bosons in the same well, while the occupancy in the middle one seems to be uncorrelated with the other two. Such correlation between different wells is not observed in absence of the tilt effect for the same barrier height of the potential and interparticle interaction strength.

Numerical study on heat transfer and pressure drop characteristics of R410A condensation in horizontal circular mini/micro‐tubes

AbstractHeat transfer and pressure drop characteristics of condensation for R410A inside horizontal circular tubes with inner diameters ranging from 0.25–4 mm were investigated numerically. The effects of mass flux, vapour quality, tube diameters, and gravity on heat transfer and pressure drop characteristics were discussed. Liquid‐vapour interfaces and stream‐traces were also presented to give a better understanding of these effects on the condensing flow. Numerical heat transfer coefficients and pressure gradients fitted well with the empirical correlations. The results indicate that local heat transfer coefficients and pressure drop increase with increasing mass flux, vapour quality, and with decreasing tube diameters. A thin liquid film is formed at the upper part of the tube in mini‐channels, while a symmetrical annular flow is observed in microchannels. A vortex with its core lying at the bottom of the tube is formed in the tubes with an inner diameter of 4 mm, while the stream‐traces start from the z‐axis and point to the liquid‐vapour interface when dh is 0.25 mm. The gravity effect on heat transfer is important in larger tubes at lower vapour quality, where stratified flow may occur.

Optimization of thermal and flow characteristics of R-404A vapor condensation inside corrugated tubes

In the present study the condensation pressure drop and heat transfer coefficient of R-404A flowing through the corrugated tubes are experimentally investigated. The test section is a horizontal 1m long double-pipe counter-flow heat exchanger where R-404A flows in the inner tube with internal diameters of 8.7mm and coolant water flows through the annulus. The pressure drop and heat transfer coefficient are obtained for the plain tube and nine corrugated tubes, mass velocities ranging from 187 to 561kg/m2s, vapor quality from 0.18 to 0.85 and average condensing temperature from 29.2 to 35.8°C. Investigation shows that using the corrugated tube increases the heat transfer coefficient and pressure drop up to 59% and 115% above the plain tube values, respectively. New empirical correlations are developed to predict the heat transfer coefficient and pressure drop inside the corrugated tubes. Finally, artificial neural network and multi-objective genetic algorithm are used for finding optimal operational conditions during the condensation of R-404A refrigerant inside the corrugated tubes.

Gas-side fouling, erosion and corrosion of heat exchanger for middle and low temperature flue gas waste heat recovery

With the ongoing emphasis on the efficient use of energy, much effort is put on the development and application of various heat recovery technologies. Heat exchangers play an important role in energy transfer and utilization and are widely used to recover waste energy from different kinds of heat sources in many fields such as energy and power engineering, petroleum and chemical engineering, air conditioning and refrigeration, aviation and aerospace, etc. In the heat exchangers for waste heat recovery, the gas-side fluid mediums usually are unclean and corrosive. The problems of fouling, erosion and corrosion of heat exchangers in the middle and low temperature flue gas-side caused by the high ash content, viscous and corrosive components are inevitable, and how to effectively solve the problems has been the subject of much research in recent years. In this paper, the researches of fouling, erosion and corrosion characteristics in middle and low temperature flue gas heat exchangers are reviewed. The causes and influence factors are discussed. Firstly, the fouling mechanisms of heat exchangers are introduced and the existing theoretical models, empirical models, and numerical methods of particle transport, impact and deposition are reviewed. The ash fouling characteristics of 6-row tube heat exchangers are presented and the effects of flue gas velocity, particle diameter, spanwise tube pitch, longitudinal tube pitch, tube shape and geometry conditions on fouling rate are discussed. Both decrease of the longitudinal tube spacing and increase of spanwise spacing can effectively reduce the deposition of particles. The geometry of elliptical tubes can fulfill this requirement for fouling reduction with smaller longitudinal spacing and larger spanswise pitch. The feasibility of using oval tube is explored for the fouling reduction. Compared with the circular tube arrangement, the deposition rate of the elliptical tube was decreased by 68.8%. Secondly, the existing erosion mechanisms, theories and methods are introduced. Different erosion models, including the model advantages and disadvantages are also summarized. The dynamics behaviour of the entrained solid particles in the flow and the deformation of the tube surface due to erosion are presented. The effects of particle diameter, particle mass flow rate and fluid Reynolds number are discussed. Among the three parameters, fluid Reynolds number has the most important effect on the erosion of tube surface. Erosion mainly occurs at the first part of the single tube surface. Thirdly, the existing mechanisms, theories and methods of corrosion characteristics of heat exchangers are introduced. Then a coupling numerical model, developed in author’s previous research, is discussed to predict the condensation characteristics of sulfuric acid vapor on heat exchanger surfaces. The corrosion risk can be reduced by decreasing the water vapor concentration and increasing the flue gas temperature. The effects of operating parameters and geometry conditions on the sulfuric acid condensation and corrosion characteristics are also discussed. A correlation of Sh number of sulfuric acid versus fin geometries for a 10-row tube bundle is provided. In order to reveal the anti-corrosion characteristics of different materials and the coupling mechanisms between the fouling and dewpoint corrosion, the online water-cooled test system and laboratory static sample test system on the corrosion characteristics of heat exchangers are introduced. Some dewpoint corrosion resistant steels are presented. The mechanism of dewpoint corrosion is revealed, the relationship between the thickness of corrosion layer and wall temperature is discussed and the coupling mechanisms between the fouling and dewpoint corrosion are also discussed. The corrosion products are composed of the ash and acid reaction products in the outer layer, iron sulfate in the middle layer, and iron oxide in the inner layer. The innermost layer is the main corrosion layer. Finally, the research needs and prospect of fouling, erosion and corrosion research are discussed. Hope to solve the problems of designing the anti-fouling, anti-erosion and anti-corrosion heat exchangers, and promote the development of efficient utilization technologies in middle and low temperature flue gas heat exchangers.

Condensation of refrigerants in a multiport tube with rectangular minichannels

This study investigated the condensation heat transfer and pressure drop characteristics of refrigerants R134a, R32, R1234ze(E), and R410A in a horizontal multiport tube with rectangular minichannels, in the mass velocity range of 100–400 kg m−2 s−1 and saturation temperature set at 40 and 60 °C. The effect of mass velocity, vapor quality, saturation temperature, refrigerant properties, and hydraulic diameter of rectangular channels on condensation characteristics is clarified. A new correlation is proposed for predicting the frictional pressure drop for condensation flow in minichannels. A heat transfer model for condensation heat transfer in rectangular minichannels is developed considering the flow patterns and effects of vapor shear stress and surface tension. Then, based on this model, a new heat transfer correlation is proposed. The proposed correlations successfully predict the experimental frictional pressure drop and heat transfer coefficients of the test refrigerants in horizontal rectangular minichannels.

Analysis of enhanced vapor desuperheating during condensation inside a plate heat exchanger

The presence of superheated vapor in condenser heat exchanger is common in many applications, as heat pump or organic Rankine cycle. Rarely taken into consideration in the literature of plate heat exchangers, the present article focuses on the influence of the superheated vapor on the condensation characteristics of an organic fluid (pentane) in a brazed plate heat exchanger (BPHE). A specific experimental approach has been developed for this objective. The tested BPHE prototype consists of 2 channels with chevron angle of 55°, and a hydraulic diameter equal to 4.4 mm. The effect of the pentane mass flux, 9–30 kg m−2 s−1, and the vapor superheat, 5–25 K, at a mean constant saturation temperature of 36.5 °C (1.029 bars), on the global and local thermo-hydraulic characteristics has been identified. An infrared (IR) metrology is used to distinguish the different fluid state distributions, which are representative of various heat transfers along the BPHE. The IR thermography shows a significant impact of the vapor superheat, on the fluid distribution at the channel inlet depending on the mass flux.Comparing the results with vapor superheat going from 5 to 25 K, we note: 1/an increase of the heat transfer coefficient reaching 70% for the lowest mass flux; 2/an increase of the pressure drop, whose rate (18%) is equivalent to the increase of the heat transfer coefficient for the larger mass fluxes. Superheated vapor is therefore very favorable to heat transfer for condensation in the gravity mode compared to the convective one. Based on experimental measurements and observations, various vapor desuperheating scenarios are tested. The analysis justifies that the suitable desuperheating scenario involves condensation from superheated vapor directly from the channel inlet with liquid vaporization from the condensate film.

Fabrication and condensation characteristics of metallic superhydrophobic surface with hierarchical micro-nano structures

Metallic superhydrophobic surfaces have various applications in aerospace, refrigeration and other engineering fields due to their excellent water repellent characteristics. This study considers a simple but widely applicable fabrication method using a two simultaneous chemical reactions method to prepare the acid-salt mixed solutions to process the metal surfaces with surface deposition and surface etching to construct hierarchical micro-nano structures on the surface and then modify the surface with low surface-energy materials. Al-based and Cu-based superhydrophobic surfaces were fabricated using this method. The Al-based superhydrophobic surface had a water contact angle of 164° with hierarchical micro-nano structures similar to the lotus leaves. The Cu-based surface had a water contact angle of 157° with moss-like hierarchical micro-nano structures. Droplet condensation experiments were also performed on these two superhydrophobic surfaces to investigate their condensation characteristics. The results show that the Al-based superhydrophobic surface has lower droplet density, higher droplet jumping probability, slower droplet growth rate and lower surface coverage due to the more structured hierarchical structures.

Numerical simulation of bubble condensation using CF-VOF

In present study, subcooled boiling is simulated using color function volume of fluid (CF-VOF) method. For this purpose, energy equation and Tanasawa mass transfer model accompanied with some suitable source terms are implemented in OpenFOAM solver (interFoam). The surface tension between vapor–liquid phases is considered using continuous surface force (CSF) method. In order to reduce spurious current near interface, a smoothing filter is applied to improve curvature calculation. The variation of saturation temperature in vapor bubble with local pressure is considered with Clausius–Clapeyron relation. The numerical model is validated with one-dimensional Stefan problem.The shape and life time history of single vapor bubble condensation are verified with existing experimental data. Computational study shows bubble life time is nearly proportional with bubble size and it is prolonged at bubble swarm motion. The present study reveals some fundamental characteristics of single and multiple vapor bubble condensation and is expected to be instructive for further applications.

Heat transfer of bio-oil in a direct contact heat exchanger during condensation

Rapid quenching of volatiles in fast pyrolysis is important for achieving high yield and quality of the bio-oil product, but few studies have examined the condensation of volatiles and their related heat exchangers. Accordingly, we have studied the condensation characteristics of volatiles by varying heat transfer conditions in a direct contact heat exchanger. As the mass flow rate ratio of quenching oil to pyrolysis gas increased, the heat transfer rate and yield of bio-oil increased. The heat transfer rate and yield of bio-oil reached a maximum value at an intermediate air-to-quenching oil mass flow rate ratio. Additionally, the heat transfer rate and yield of bio-oil decreased as the temperature of the quenching oil increased. Experiments were also conducted to derive an empirical relationship for the volumetric heat transfer coefficient for direct contact heat exchangers.

Investigation of Bose Condensation in Ideal Bose Gas Trapped under Generic Power Law Potential in d Dimension

The changes in characteristics of Bose condensation of ideal Bose gas due to an external generic power law potential are studied carefully. Detailed calculation of Kim et al. (J. Phys. Condens. Matter 11 (1999) 10269) yielded the hierarchy of condensation transitions with changing fractional dimensionality. In this manuscript, some theorems regarding specific heat at constant volume CV are presented. Careful examination of these theorems reveal the existence of hidden hierarchy of the condensation transition in trapped systems as well.

Numerical simulation of condensation for R410A at a different saturation temperature in mini/micro tubes

ABSTRACTHeat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 0.25, 1, and 4 mm) at saturation temperatures Tsat = 310, 320, and 330 K are investigated numerically. Liquid–vapor interfaces and stream traces are also presented to provide a better understanding of the effect of saturation temperature on the condensation process inside micro tubes. The results indicate that local heat transfer coefficients and pressure drop gradients increase with increasing mass flux and vapor quality and with decreasing tube diameter and saturation temperature. Liquid film thickness also increases with increasing saturation temperature because of the lower surface tension at a higher saturation temperature. When gravity dominates the condensation process, a vortex with its core lying at the bottom of the tube is found in the vapor phase region. For annular flow regime at dh = 0.25 mm, the vortex disappears, and stream traces point from the symmetry plan to the liquid–vapor interface, where the vapor phase turns into the liquid phase. Numerical heat transfer coefficients and pressure drop gradients are compared with available empirical correlations. Two new models for heat transfer coefficients and frictional pressure drop gradients are developed based on the numerical work. A reasonable agreement between predicted and numerical results is obtained.