CFD Study on Specifics of Flow and Heat Transfer in Vertical Bare Tubes Cooled With Water at Supercritical Pressures

2017 ◽  
Author(s):  
Alexander Zvorykin ◽  
Nataliia Fialko ◽  
Sherenkovskyi Julii ◽  
Sergey Aleshko ◽  
Natalia Meranova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Cfd Simulation ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Coolant Temperature ◽  
Flow And Heat Transfer ◽  
Medium Mass ◽  
Experimental Values

The paper presents results of a study on flow and temperature fields in bare tubes cooled with SuperCritical Water (SCW). This study is based on a Computational Fluid Dynamics (CFD) simulation with the FLUENT code for upward flows in vertical tubes with heated length of 4 m and an inner diameter of 10 mm. Operating conditions were: Mass flux – G ≈ 500 and 1000 kg/m2s; heat flux – q = 189 – 826 kW/m2; and inlet coolant temperature – Tin = 320–360°C. CFD predictions were compared with experimental data in this study. All three heat-transfer regimes: 1) normal heat transfer; 2) improved heat transfer; and 3) deteriorated heat transfer; were considered. The obtained results show that within normal and improved heat transfer CFD predicts experimental values reasonably well. However, within conditions of deteriorated heat transfer CFD predictions are less satisfactory. The CFD outcomes of the heat flux effect on the flow and heat transfer of SCW are presented. Specifics of flow within the pseudocritical region (i.e., approximately ±25°C around a pseudocritical point) are discussed. The buoyancy effect is investigated by axial velocity profiles at the medium mass flux of 500 kg/m2s and heat flux of 287 kW/m2.

Simulation on the Flow and Heat Transfer Characteristics of Confined Bubbles in Micro-Channels

2012 ◽  
Author(s):  
Qingming Liu ◽  
Björn Palm ◽  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Phase Interface ◽  
Working Fluid ◽  
Initial Shape ◽  
Thin Film Evaporation ◽  
Flow And Heat Transfer ◽  
Vof Model ◽  
Micro Channels

3D simulations on confined bubbles in micro-channels with diameter of 1.24 mm were conducted. The working fluid is R134a with a mass flux range from 125kg/m2s to 375kg/m2s. The VOF model is chosen to capture the 2 phase interface while the geo-construction method was used to re-construct the 2-phase interface. A heated boundary wall with heat flux varying from 15kW/m2 to 102kW/m2 is supplied. The wall temperature was calculated. The effects of mass flux and heat flux are studied. The shape of the bubble was predicted by the simulation successfully and the results show that they are independent of the initial shape. Both thin film evaporation and micro convection enhance the heat transfer. However, the micro convection which is caused by bubble motion has greater contribution to the total heat transfer at the stage of bubble growth studied.

Main Results of Na-K Alloy Boiling Investigation

2002 ◽  
Author(s):  
G. A. Sorokin ◽  
G. P. Bogoslovskaya ◽  
E. F. Ivanov ◽  
A. P. Sorokin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Modeling ◽  
Liquid Metal ◽  
Critical Heat Flux ◽  
Liquid Metals ◽  
Operating Conditions ◽  
Coolant Temperature ◽  
Low Velocity ◽  
Experimental Conditions

Boiling experiments on eutectic sodium-potassium alloy in the model of fast reactor subassembly under conditions of low-velocity circulation carried out at the IPPE call for further investigations into numerical modeling of the process. The paper presents analysis of pin bundle liquid metal boiling, stages of the process, its characteristics (wall temperature, coolant temperature, flow rate. pressure void fraction and others), that allowed the pattern map to be drawn. The problem of conversion of the data gained in Na-K mock-up experiments to in-pile sodium reactor operating conditions is analyzed here, as well as thermodynamic similarity of liquid metal coolants and eutectic Na-K alloy. Data on bundle boiling in Na-K are presented in comparison with those in different liquid metals. Analysis of data on liquid metal heat transfer in cases of pool boiling, boiling in tubes, in slots, and in pin bundles, as well as data on critical heat flux in tubes was performed and discussed in the paper. The relationship for calculation of critical heat flux in liquid metal derived by the authors is presented. Results of numerical modeling of liquid metal boiling heat transfer during accident cooling of reactor core applied to experimental conditions of going from forced to natural circulation are presented, too.

Numerical Study of the Effects of Different Buoyancy Models on Supercritical Flow and Heat Transfer

2013 ◽  
Author(s):  
X. Y. Xu ◽  
T. Ma ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Mass Flux ◽  
Wall Heat Flux ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Temperature Prediction ◽  
Flow And Heat Transfer

Due to the dramatic changes in physical properties, the flow and heat transfer in supercritical fluid are significantly affected by buoyancy effects, especially when the ratio of inlet mass flux and wall heat flux is relatively small. In this study, the heat transfer of supercritical water in uniformly heated vertical tube is numerically investigated with different buoyancy models which are based on different calculation methods of the turbulent heat flux. The applicabilities of these buoyancy models are analyzed both in heat transfer enhancement and deterioration conditions. The simulation results show that these buoyancy models make few differences and give good wall temperature prediction in heat transfer enhancement condition when the ratio of inlet mass flux and wall heat flux is very small. With the increase of wall heat flux, the accuracy of wall temperature prediction reduces, and the differences between these buoyancy models become larger. No buoyancy model can currently make accurate wall temperature prediction in deterioration condition in this study.

scholarly journals Experimental investigation on evaporation of R407C in a single horizontal smooth tube

2017 ◽  
Vol 7 (2 (S)) ◽  
pp. 266
Author(s):  
M. D. Hambarde ◽  
Ramakant Shrivastava ◽  
S.R. Thorat ◽  
O.P. Dale
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Mass Flux ◽  
Test Section ◽  
Flow Boiling ◽  
Horizontal Tube ◽  
Operating Conditions ◽  
Montreal Protocol ◽  
Vapor Quality

Due to higher ozone layer depletion potential of HCFC refrigerant, R22 which has been mostly used in house hold refrigeration will be phased out by 2020 as per Montreal Protocol and UNFCCC Regulations. R407C, a zeotropic refrigerant from HFC category is a promising refrigerants in place of R22. Performance evaluation of R407 is required to enhance its application in house hold refrigeration. Hence an experimental investigation is carried out to understand the heat transfer characteristics during flow boiling of R407C in a smooth horizontal tube of 13.386 mm inner diameter and 2m length. The experiment is performed under the operating conditions; (i) mass flux range 100 to 300 kg s-1m-2; (ii) heat flux within range 2 to 7 kWm-2; (iii) temperature range at inlet to test section -100C to +100C; (iv) average vapor quality within test section from 0.05 to 0.95.The effect of heat flux, mass flux, vapor quality, temperature glide on heat transfer coefficient, during evaporation of R407C are examined.

Experiment and CFD Simulation of Boiling Heat Transfer Coefficient of R410A in Minichannels

2015 ◽  
Vol 23 (04) ◽  
pp. 1550032 ◽  
Author(s):  
Nguyen Ba Chien ◽  
Kwang-Il Choi ◽  
Jong-Taek Oh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Saturation Temperature ◽  
Boiling Heat Transfer Coefficient

This study performed a comparison between experimental and computational fluid dynamic (CFD) simulation results of boiling heat transfer coefficient of R410A in a small tube. The experimental data were obtained in the horizontal circular tubes of 3.0[Formula: see text]mm inner diameter, the length of 3000[Formula: see text]mm including: mass flux and heat flux in a range from 300[Formula: see text]kg/m2s to 600[Formula: see text]kg/m2s and from 5[Formula: see text]kW/m2 to 10[Formula: see text]kW/m2, respectively, and the saturation temperature constantly kept at 20[Formula: see text]C. In the simulation procedure, the Eulerian multiphase with wall boiling were obtained. The effects of mass flux and heat flux on the heat transfer coefficient of R410A were analyzed. The comparative data between CFD and experiment was also illustrated.

Experimental Study on Heat Transfer to Supercritical CO2 Flowing in Vertical Upward Tube at Medium Mass Flux

2017 ◽  
Author(s):  
Qian Zhang ◽  
Huixiong Li ◽  
Xiangfei Kong ◽  
Jun Zhang ◽  
Xianliang Lei ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Mass Flux ◽  
Temperature Peak ◽  
Buoyancy Effect ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Medium Mass ◽  
The Heat Transfer Coefficient

An experimental study was performed on heat transfer characteristics of supercritical pressure CO2 (SC-CO2) flowing at medium mass flux conditions in a vertically-upward tube of 16 mm inner diameter at the Heat Transfer and Flow test loop of Supercritical CO2 (HTF-SCO2) in Xi’an Jiaotong University. Experimental parameters included the pressure ranging from 7.5 to 10.5 MPa, the mass flux of 400–600 kg/m2s, and the heat flux of 20–100 kW/m2. Based on the experimental data, effects of mass flux, heat flux and operation pressure on heat transfer characteristics of SC-CO2 were thoroughly discussed. With the decrease of mass flux and increase of heat flux, heat transfer characteristics of SC-CO2 becomes worse and worse. The wall temperature rises to high levels with the occurrence of a wall temperature peak and the wall temperature peak also rises remarkably with the decrease in mass flux and increase in heat flux. Especially, effect of pressures on the heat transfer of SC-CO2 was found to be quite different from that previously reported in literature. When the heat flux is low (such as 30 kW/m2), the HTD was diminished with the increase in pressures, but when the heat flux is up to 50 kW/m2, the HTD is surprisingly intensified by the increase of pressure. The buoyancy effect was considered to explain this distinct influence of pressure on the heat transfer of SC-CO2 by employed a non-dimensional parameter Bu. With the increase of pressure, buoyancy effect was diminished owing to the decrease of density difference between fluids near the wall and the center. When heat flux was lower, the Bu was located between 5×10−6 and 10−4, where buoyancy effect impaired heat transfer, so the heat transfer coefficient increased by rising pressure. But when heat flux was larger, the Bu was above 10−4, where buoyancy effect began to enhance heat transfer, as a result, the heat transfer coefficient was reduced by weakened buoyancy effect because of the increase of pressure. (CSPE)

CFD Simulation of Supercritical LNG Heat Transfer in a Horizontal Tube of an Intermediate Fluid Vaporizer

2017 ◽  
Author(s):  
Shuangqing Xu ◽  
Xuedong Chen ◽  
Zhichao Fan
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Horizontal Tube ◽  
Small Mass ◽  
Maximum Deviation ◽  
Average Deviation ◽  
Flow And Heat Transfer ◽  
Reliable Design

A three-dimensional computational fluid dynamics (CFD) model has been established for the simulations of supercritical LNG heat transfer in a horizontal tube of an intermediate fluid vaporizer (IFV). The influences of inlet pressure and mass flux on heat transfer have been studied. The predictive capabilities of different heat transfer coefficient (HTC) correlations, which is vital for the economic and reliable design of an IFV, have been evaluated. The results indicate that the Jackson correlation gives more accurate HTC predictions for supercritical LNG at the relatively small mass flux, with a maximum deviation of 10% and an average deviation of 6%; while for the cases with larger mass flux, a modification to the Jackson-Hall correlation works well. Detailed flow and heat transfer characteristics and buoyancy effect have also been analyzed. The reported findings would provide insight into the supercritical LNG vaporization process and give guidance to the design optimization of an IFV.

Numerical Research of Film Boiling Heat Transfer Around a Vertical Short Cylinder With Flat or Hemispherical Ends

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Rubén Arévalo ◽  
Alberto Abánades ◽  
Luis Rebollo
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Vertical Cylinder ◽  
Operating Conditions ◽  
Film Boiling ◽  
Loss Of Coolant Accident ◽  
Computational Fluid Dynamics Cfd ◽  
Experimental Values ◽  
The Individual ◽  
Abnormal Operating Conditions

Film boiling is a heat transfer mechanism that might appear in different processes, such as cryogenics, metallurgical, and nuclear reactors during abnormal operating conditions, as happens during a loss of coolant accident. In this research, film boiling around a finite vertical cylinder was studied by means of computational fluid dynamics (CFD) simulations, considering six cases that include three different levels of surface temperature and two different shapes of the cylinder ends: flat and hemispherical ends. Volume of fluid (VOF) method for the treatment of multiphase flow was used, and a user-defined function was programed to consider the exchange of mass and energy between the phases. The simulations were performed with a vertical cylinder of 32 mm in diameter and 32 or 64 mm in high for flat ends or hemispherical ends, respectively, placed in a two-dimensional axisymmetric domain of 0.125 m × 0.25 m. Results obtained for the heat flux show a periodic fluctuating behavior in time as a consequence of periodical variations in the thickness of the vapor film around the cylinder. A wavy liquid–vapor interface is observed as is reported in the experimental works. The simulations results are compared with the experimental values reported in literature as well as with values obtained from correlations. The results show that the computational code used captures reasonably well the physics involved in the film boiling, being obtained that average heat flux to the case of hemispherical ends is 15.6% higher than for the case of flat ends, versus 15.2% showing experiments and 1.6% calculated combining correlations for the individual surfaces. It shows that use of correlations in this way is not appropriate in film boiling because it does not take into account the interactions between the different surfaces.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

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