Increasing Saturation Temperature Research Articles

Numerical simulation study of boiling heat transfer of R290 flow in horizontal microtubes

Abstract R290 is considered to be an excellent alternative refrigerant for domestic air conditioners in the future. In this paper, CFD numerical simulation was used to obtain the flow field distribution of R290 in a micro-fine circular tube with an inner diameter of 2mm under a specific range of working conditions, and the effects of saturation temperature, mass flow density, heat flow density and tube type on the boiling heat transfer characteristics of R290 tube were investigated. The results show that the boiling heat transfer coefficient increases with the increase of saturation temperature, and the maximum value of the heat transfer coefficient increases by 8.1% when the saturation temperature increases from 284K to 286K. The boiling heat transfer coefficient increases with the increase of mass flow density, and the maximum value appears in the medium dryness range. The boiling heat transfer coefficient in the tube increases and then decreases when the heat flow density increases from 10 kW/m2 to 20 kW/m2 and increases faster at high heat flow density conditions. In addition, compared with the circular tube, the boiling heat transfer coefficient in the elliptical tube with an aspect ratio of 1.56 increases by 2.78% for R290 under the same flow area.

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.

Effect of Impurities on Solubility and Metastable Zone Width of Manganese Sulfate Monohydrate

AbstractRecovering manganese from waste batteries is an important issue to promote the development of new energy. Herein, nickel sulfate and cobalt sulfate, representative impurities in waste battery leachate, are selected to examine their influence on the crystallization thermodynamics and crystal nucleation of manganese sulfate monohydrate. This work assessed alterations in solubility and metastable zone width (MSZW) due to the presence of impurities. The results showed a decrease in manganese sulfate monohydrate solubility in water with increasing impurity concentrations of either nickel sulfate or cobalt sulfate. The effects of initial concentration, heating rate, and impurity concentration on MSZW demonstrated a consistent increase in MSZW as these factors increased. The MSZW data are fitted using the self‐consistent Nývlt‐like model and the classical 3D nucleation theory model. The results revealed a general increase in the nucleation rate constant, K, with increasing saturation temperature or decreasing nickel sulfate concentration. Conversely, the solid‐liquid interface energy, γ, generally decreases with increasing saturation temperature or decreasing nickel sulfate concentration. Based on the influence observed on the interface energy, a possible mechanism is proposed that suggests that impurities inhibit crystal nucleation through adsorption.

Insight into the nucleation behavior of tiamulin hydrogen fumarate methanol solvate in methanol-ethyl acetate binary mixtures

To investigate the nucleation behavior of tiamulin hydrogen fumarate methanol solvate (THFMS), the solubility, induction time, and metastable zone width (MSZW) of THFMS in methanol-ethyl acetate binary mixtures were measured. The nucleation potential model, which is based on the classical nucleation theory and correlates the induction time and MSZW, has been employed to deal with the experimental data and estimate the interfacial energy and the critical nucleation potential. The estimated values determined from the nucleation potential model are in accordance with the experimental values. The interfacial energy and the critical nucleation potential of THFMS steadily decrease with the increasing saturation temperature, whereas those of THFMS initially decrease and subsequently increase as the ethyl acetate content increases. The results demonstrate that an increase in saturation temperature leads to enhanced nucleation favorability, while the difficulty of nucleation initially decreases and then increases with increasing ethyl acetate content. Furthermore, the critical nucleation parameters, including the critical Gibbs free energy, the critical nucleus size, and the critical number of molecules in a nucleus, exhibit the same trend in alterations regarding both saturation temperature and ethyl acetate content.

Flow boiling heat transfer characteristics of zeotropic mixture CO2/R152a with large temperature glide in a 2 mm horizontal tube

The flow boiling characteristics of CO2/R152a zeotropic mixtures with three mass fractions (22.1/77.9, 47.4/52.6 and 65.3/34.7 wt.%) and the pure components in a 2 mm horizontal tube are experimentally studied. The flow boiling characteristics are tested in the range of temperature glide of 30.9∼38.3 °C, mass flux of 200∼400 kg/m2s, heat flux of 12∼36 kW/m2, and saturation temperature of 5∼15 °C. Flow patterns are observed and the flow pattern map is also described, and the heat transfer and pressure drop characteristics of working fluid are also conducted. Furthermore, a new correlation to predict the heat transfer coefficient of large temperature glide working fluid is proposed. The results show 7 types of flow patterns are recorded, showing the flowing characteristic between the conventional and microscale channel. The heat transfer coefficient of CO2/R152a increases slowly with vapor quality, and decrease rapidly when vapor quality reaches to the initial dryout vapor quality, which is lower than that of pure CO2. The mass transfer resistance and sensible heat resistance shows a severe deterioration effect on the flow boiling heat transfer due to the high temperature glide as the sensible heat accounts for 13.12∼15.44 % for the mixture CO2/R152a. The frictional pressure drop gradient of CO2/R152a increases with mass flux, and decreases with the increase of saturation temperature and mass fraction of CO2. Considering the mass transfer resistance and effects of non-negligible sensible heat contribution, a new heat transfer correlation is proposed, with the mean absolute deviation of 16.9 %, which shows an acceptable prediction accuracy compared with the reported data in the literatures.

Investigation into the effects of foaming variables on the cellular structure and expansion ratio of foamed TPU using response surface methodology

Thermoplastic polyurethane elastomer (TPU) foams were prepared using the high-pressure autoclave with supercritical fluid carbon dioxide (SC-CO2). The effects of foaming variables (i.e. saturation temperature, saturation pressure, and depressurization rate) on cellular structure and expansion ratio were investigated. The model between expansion ratio and foaming variables was constructed using the Box-Behnken design (BBD) of response surface methodology (RSM), and analysis of variance (ANOVA) was conducted to evaluate the validity and significance of the model. Finally, the interactive effects of foaming variables on the expansion ratio were investigated, and the expansion ratios of maximum and center point from numerical model were verified by experiment. The result showed higher saturation pressure and depressurization rate resulted in the more uniform cellular structure and higher cell density, however the higher saturation temperature resulted in the bigger cell and nonuniform structure. The ranges of average cell diameter and cell density were 15.26–45.4 μm and 0.32 × 108 to 6.24 × 108 cells/cm3, respectively. The model obtained using BBD of RSM was valid to predict the expansion ratio in the design window. The saturation temperature was the most important factor influencing the expansion ratio. With the increase of saturation temperature, the expansion ratio always increases in the design window. The maximum expansion ratio from numerical optimization was 4.91, which was located at saturation temperature 190°C, saturation pressure 12.51 MPa, and depressurization rate 5 MPa/s, and the corresponding experiment value was 4.56. The error between them was 7.13%.

Study on the nucleation kinetics of DL-methionine based on the metastable zone width of unseeded batch crystallization

The metastable zone width (MSZW) of DL-methionine aqueous solution for unseeded batch crystallization was measured by turbidity method. The spontaneous nucleation curves at different stirring rates (250 rpm, 350 rpm and 450 rpm) and cooling rates (18.0 K/h, 30.0 K/h and 42.0 K/h) were obtained by measuring the nucleation temperatures of solutions with saturation temperatures from 304.3 K to 341.9 K. The results show that the increase in saturation temperature and stirring rate makes the MSZW narrower. This is mainly because the enhanced mass transfer makes solute molecules more likely to collide and thus facilitate nucleation. Also the increase in cooling rate widen the MSZW for there is a time lag between nucleation and turbidity is detected. These data provide the operating boundary of crystallization and are important in production to obtain the desired crystal quality. Meanwhile, the nucleation kinetics is studied based on the MSZW data by five semi-empirical models in this work. And the interfacial energy between DL-methionine and water was determined, which decreases from 1.88 mJ·m2 to 0.99 mJ·m2 when temperature increases from 304.3 K to 341.9 K.

Enhanced pool boiling of propane on horizontal U-shaped tubes in a large-scale confined space

• The experimental data of propane pool boiling on a fin-enhanced tube was obtained. • The heat transfer coefficients demonstrated increasing with heat flux and saturation temperature. • The enhancement factors were found in the range of 1.25∼2.28. • Optimum correlations were validated to predict the experimental data within 11.48%. This paper aims to experimentally investigate the heat transfer characteristics of pool boiling on horizontal U-shaped tubes in a large-scale confined space. The saturation temperature ranges from 20 to 40°C and the heat flux varies from 2.5 to 10.5 kWm −2 . Two types of tubes with an outside diameter of 19.05 mm are tested: a smooth tube and a fin-enhanced tube with 0.4 mm fin height, 1220 fpm (fins per meter) and a 0.12 mm fin gap. The tubes are made of titanium with a length of 1165 mm. In case of pool boiling, the heat transfer coefficient for the tested tubes increases with increasing saturation temperature and heat flux. The fin-enhanced tube facilitates the bubble nucleation with the heat transfer coefficient enhancement factor varying in the range of 1.25∼2.28. Furthermore, the experimental heat transfer coefficients are compared with four correlations obtained in the open literature. R-J correlation and Copper correlation are found to be the optimum correlation for the smooth tube and the enhanced tube with the mean relative error of 10.93% and 11.48%, respectively. Findings from this study can supply a fundamental basis for validation and improvement propane heat transfer performances for the intermediate fluid vaporizer (IFV) engineering design.

Heat transfer and pressure drop characteristics of two phase flow in helical coils

This paper presents a review on heat transfer coefficient and pressure drop during condensation and boiling in helically coiled tubes. The geometric parameters such as coil diameter, coil pitch and operating parameters containing saturation temperature, system pressure, mass flux, heat flux and vapor quality have significant effects on the heat transfer characteristics. The frictional pressure drop during flow boiling increases with increasing vapor quality and mass flux, and decreases with increasing system pressure. Also, the effect of the curvature on the two-phase frictional multiplier is negligible. The frictional pressure drop in condensation increased with increasing average vapor quality and mass flux, and decreased with increasing saturation temperature. According to the results reported, heat flux had little effect on the pressure drop during condensation. Flow boiling heat transfer coefficient in helical coils of large diameter showed the similar characteristics and trend with the straight tube as the system pressure decreased. Lockhart-Martinelli parameter was generally preferred to be used by the authors as a function in the correlations to predict flow boiling heat transfer coefficient. There was a decrease in the average Nusselt number with increasing heat flux for the constant Dean number during condensation. This reduction in the average Nusselt number indicated that the turbulence effect created by the secondary flow in the helically coiled tubes eliminated the effects caused by the difference in density. The correlations used for determination of Nusselt number and pressure drop in helical coils with their major findings are presented in details.

Flow Regimes and Transitions for Two-Phase Flow of R152a During Condensation in a Circular Minichannel

Two-phase flow regimes were experimentally investigated during the entire condensation process of refrigerant R152a in a circular glass minichannel. The inner and outer diameters of the test minichannel were 0.75 and 1.50 mm. The channel was 500 mm long to allow observation of all the two-phase flow regimes during the condensation process. The experiments used saturation temperatures from 30 to 50°C, a mass flux of 150 kg/(m2·s) and vapor qualities from 0 to 1. The annular, intermittent and bubbly flow regimes were observed for the experimental conditions in the study. The absence of the stratified flow regime shows that the gravitational effect is no longer dominant in the minichannel for these conditions. Vapor-liquid interfacial waves, liquid bridge formation and vapor core breakage were observed in the minichannel. Quantitative measurements of flow regime transition locations were carried out in the present study. The experiments also showed the effects of the saturation temperature and the cooling water mass flow rate on flow regime transitions. The results show that the annular flow range decreases and the intermittent and bubbly flow ranges change little with increasing saturation temperature. The cooling water mass flow rate ranging from 38.3 kg/h to 113.8 kg/h had little effect on the flow regime transitions.

관경 변화에 따른 R-1234yf의 응축 압력강하에 관한 실험적 연구

In this study, the condensation pressure drop of R-1234yf according to the variation of the tube diameter is experimentally studied and it is intended to be provided as the basic data for the design of the condenser. The experiment measured the pressure drop of R-1234yf by changing the mass flow rate, saturation temperature, and tube diameter. It also compared with the pressure drop of R-134a under the same conditions. As a result, the pressure drop tends to increase as the mass flow rate increases and the tube diameter decreases. In addition, the pressure drop tends to decrease as the saturation temperature increases. As a result of comparing the experimental results and the pressure drop of R-134a, R-134a showed a larger tendency than R-1234yf. As a result of comparing the experimental results with the existing correlation equation, the correlation equation of Miyara et al showed the most similar prediction.

Insights into solvent-dependent nucleation behavior of benzoic acid from metastable zone widths

Currently, how the solvents and temperature affect the solution species and rate-determining step in the nucleation process, thus altering the nucleation behavior remains elusive. In this contribution, by employing metastable zone width (MSZW) experiments, the modified Sangwal’s theory and the molecular dynamic simulations, we explore nucleation behavior of benzoic acid (BA) in polar and non-polar solvents. We find that in methanol, the solid–liquid interfacial tension γ decreases with increasing the saturation temperature, in contrast, the value of γ increases with increasing the saturation temperature in chloroform. Furthermore, in the classical nucleation framework, we conclude that the critical nuclei size and critical Gibbs free energy monotonous decline as the driving force increases in methanol, which implies that the interfacial tension is independent of the driving force. On the contrary, the relationship between critical nucleation parameters and driving force indicates that the interfacial tension changes with the driving force in chloroform. By employing FTIR, we find that dimerization of BA is restricted in methanol, and BA always exists as the monomer even near the nucleation point, which implies that desolvation is the rate-determining step in the nucleation process. While in chloroform, we demonstrate that the form of monomers and dimers coexist in solution. As the saturation temperature increases, the equilibrium is broken and moves toward the monomer. It implies that the rate-determining step of the nucleation process of BA may change from molecular rearrangement to desolvation with increasing the saturation temperature in chloroform.

Flow boiling heat transfer and dryout characteristics of ammonia in a horizontal smooth mini-tube

A boiling two-phase flow heat transfer experimental system for ammonia in a horizontal smooth tube with an inner diameter of 3 mm was established. The purpose is to explore the characteristics of flow boiling and dryout phenomenon. The experimental conditions: heat flux density is 10–30 kW·m−2, the mass flux is 40–200 kg·m−2·s−1, the saturation temperature is −10–10 °C, and the range of vapor quality is 0.1–1. The results show that the dominant heat transfer in different flow patterns is different, intermittent flow with nucleate boiling, annular flow and mist flow with convective boiling; the increase of mass flux can reinforce the convective boiling, the heat flux density can enhance the nucleate boiling, the increase of saturation temperature has no significant effect on the nucleate boiling, but it can weaken the convective boiling. The increase of mass flux and heat flux density will increase the friction pressure drop, and the increase of saturation temperature can decrease the friction pressure drop. The dryout visualization results and attenuation of heat transfer show that the increase of saturation temperature, heat flux density and mass flux can decrease the initial vapor quality of dryout, which is consistent with the results of Mori et al. model. Compared with the experimental data, the existing two-phase flow correlations are not suitable for the post-dryout prediction for ammonia, and the Wojtan et al. model and Mori et al. model can provide a reference for the dryout prediction.

수평관 내 R-1234yf 응축 열전달 실험

Due to environmental problems around the world, HFC refrigerants have been used instead of CFC and HCFC refrigerants with high ODP in the field. But, these refrigerants are also subject to regulation due to their high GWP. Accordingly to cope with the phased regulatory planning of HFC refrigerants, related companies have developed HFO refrigerants with low GWP. Among HFO refrigerants, the working fluid R-1234yf (GWP:4) in this paper is similar in thermodynamic properties to R-134a (GWP:1300). The experiment results are summarized as follows. The condensation heat transfer coefficient of R-1234yf in the double tube heat exchanger increased with increasing mass flux and quality. The condensation heat transfer coefficient decreased with increasing saturation temperature, but at high mass flux and high quality, it had little effect on saturation temperature. As the temperature difference between the coolant and the refrigerant increased, the heat transfer coefficient tended to increase. The condensation heat transfer coefficient of R-1234yf is lower than that of R-134a in almost all quality. However, at low quality and low mass flux the condensation heat transfer coefficient of R-1234yf tended to be greater than R-134a. Due to the difference in refrigerant physical properties such as density, surface tension, and thermal conductivity of the two refrigerants. As a result, it is believed that this paper could be used as a foundation for the optimal design of condensers using R-1234yf.

Tube-in-Tube 미세관내 R-22 및 R-407C의 응축열전달 특성

This paper focuses on the results of an experimental study of condensation heat transfer coefficients with the refrigerants R-22 and R-407C, and looks at the pressure gradient and heat transfer coefficients of horizontal tube-in-tube heat exchangers with the use of small tubes with inner diameters of 4 mm, 3 mm and 2 mm, in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at an inlet saturation temperature of 35 to 45℃ and mass flux ranges from 200 to 600 kg/m²s. The use of an inner tube with a diameter of 4.0 mm resulted in a pressure gradient that was 2.5 times higher than that of an inner tube with a diameter of 8.0mm. In tube-in-tube HEX, the pressure gradients of R-22 measured higher than those of R-407C. The condensation heat transfer coefficients increase with an increase in mass flux, but they decrease with an increase in saturation temperature. Condensation heat transfer coefficients of R-407C were a little higher than those of R-22, and the condensation heat transfer coefficients of double tube HEX were about 40% higher than those of tube-in-tube HEX. The experimental results of this study were also compared with five existing correlations. New condensation heat transfer correlations were developed, and successfully predicted the experimental results with mean deviations of 10.6% and 10.1%, and average deviations are -0.92% and -0.31%, for R-22 and R-407C, respectively.

Pool boiling heat transfer on a reentrant cavity tube with R134a: Effects of saturation temperature under ice storage condition

This study focused on the effects of saturation temperature under ice storage condition in heating, ventilation, and air conditioning or related industry for the R134a boiling heat transfer coefficients (HTCs) of a newly designed reentrant cavity copper tube. Experiments were conducted at saturation temperature ranging from −6.0 °C to 6.0 °C with heat flux ranging from 10.0 kW/m2 to 65.0 kW/m2 and the tube was heated with ethylene glycol–water mixture. The nominal outside diameter of the test tube was 25.14 mm, and the length in the test section was 1000 mm. Experimental results showed that the maximum increase in HTCs varies between 18% and 58% with the increase in saturation temperature by 12 °C. The enhancement factor, which is the ratio of HTC of the enhanced tube to that of plain tube, reaches its maximum at each saturation temperature. With the increase in saturation temperature from −6.0 °C to 6.0 °C, the maximum value increases from 2.2 to 2.5, and the corresponding optimum heat flux decreases from 40.0 kW/m2 to 20.0 kW/m2. The HTC shows different varying rates for experimental heat flux smaller and larger than the optimum heat flux. An exponent-function-form correlation well-fitted with the distinctive change rule is developed with a predicted error less than ±5.0%. The current study can serve as reference for industrial design and future academic studies.

Nucleate boiling heat transfer of R-134a and R-134a/POE lubricant mixtures on smooth tube

The present study examines the influence of polyolester lubricant oil (POEA-68 and POEA-170) with R-134a on the nucleate pool boiling performance for a horizontal smooth tube. The heat flux ranges from 10 kW/m2 to 90 kW/m2 and the lubricant mass fraction varied from 1% to 10% at a saturation temperature of 10 °C, 0 °C and, −6 °C, respectively. The experimental results show that the heat transfer coefficient (HTC) of the pure refrigerant is increased with an increase in saturation temperature. But the presence of lubricant oil alters the HTC considerably. The addition of 3% POEA-68 lubricant shows the highest 29.3% HTC enhancement relative to pure refrigerant at a supplied heat flux of 70 kW/m2 and at a saturation temperature of 0 °C. Whereas for R-134a/POEA-170 lubricant mixture at 3% of mass fraction, the highest enhancement in HTC was around 26% at a supplied heat flux of 70 kW/m2 and −6 °C saturation temperature. The bubble size is reduced and the bubble density is increased appreciably with the addition of POE oil. It was observed that the HTC of lubricant-refrigerant mixtures differs appreciably with the variation of lubricant oi mass fraction (ω). The HTC first decreases at a very low mass fraction (ω≤1%), followed by an appreciable increase in the range of 1% ≤ ω ≤ 3%, and finally reveals a continuous decline for the higher mass fraction. The dramatic decrease in HTC for lubricant-refrigerant mixture is associated with mass transfer resistance and a significant increase in surface tension.

Experimental investigation on two-phase heat transfer of R-134a during vaporization in a plate heat exchanger with rough surface

New experimental data were presented on the effect of heat exchanger plate surface roughness, mass flux, average quality, heat flux, and temperature on the evaporative heat transfer coefficient (HTC) and frictional pressure gradient (FPG) of R-134 flowing in a plate heat exchanger (PHE). Three different plate surface roughness of 0.594 μm, 1.816 μm, and 2.754 μm, were used. A commercial herringbone PHE was tested under the counterflow arrangement. The experiments were done at the heat fluxes ranging between 5 and 15 kW/m2, the mass fluxes were between 67 and 96 kg/m2s, and the saturation temperatures ranging from 10 to 20 °C. The results showed that the HTC and FRG increased with increasing mass flux, heat flux, average quality and surface roughness. Conversely, they were slightly decreased with an increase in saturation temperature. The optimum thermal performance of a PHE appeared at high plate surface roughness and average quality by about 0.2. The correlations for predicting the Nusselt number and friction factor were proposed for practical applications.

Research on pressure drop characteristics of CO2 flow boiling based on flow pattern in horizontal Minichannel

The experimental study of the frictional pressure drop characteristics of flow boiling heat transfer of CO2 in a horizontal minichannel with an inner diameter of Φ1.5 mm was carried out. Experimental conditions: heat flux (7.5 ~ 30 kW•m−2), mass flow rate (50 ~ 600 kg•m−2•s−1), saturation temperature (−40 ~ 0 °C), vapor quality (0 ~ 1). The comparison between the experimental results and theoretical flow pattern diagrams shows that the change of heat flux has little effect on the frictional pressure drop at high vapor quality area, but it has a decisive effect on the dryout and mist flow areas. The mass flow rate is the most important factor affecting the frictional pressure drop which has a decisive effect on the flow pattern experienced during the heat transfer process. The saturation temperature has an important influence on the flow pattern transition characteristics and the friction pressure drop decreases with the increase of saturation temperature. The influence of vapor quality on the frictional pressure drop is mainly caused by the flow pattern change in the minichannel. The flow visualization study shows that the theoretical flow pattern diagram can better reflect the flow pattern of CO2 in the phase-change heat transfer process and the transition trend of flow pattern under different working conditions.

Experimental analysis of condensation heat transfer and frictional pressure drop in a horizontal circular mini channel

The present study aims to investigate the effect of working fluid, mass flux, vapour quality and saturation temperature on local condensation Heat Transfer Coefficient (HTC) and local Frictional Pressure Drop (FPD) in a horizontal circular mini-channel. The refrigerants HFO-1234yf and HFC-R134a have been used as a working fluids. The mass flux was varied from 200 to 800 kg/m2 s whereas two distinct saturation temperatures were used: 35 °C and 40 °C. The experimental analysis was carried out using horizontal circular single port mini-channel of hydraulic diameter 1 mm. During experiment, inlet condition of refrigerant was maintained to be saturated vapour. The results show that HTC and FPD increases with increase in vapour quality and mass flux whereas decreases with increase in saturation temperature. The experiment results of present study and previously published results are compared with various predictive models. Models which show minimum deviation from experimental results were used to develop new modified model to predict HTC with MARD of ± 15 % and FPD with MARD of ± 10 %.