Effect of Buoyancy on the Mechanism of Heat Transfer Deterioration of Supercritical Water in Horizontal Tubes

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Xianliang Lei ◽  
Huixiong Li ◽  
Yifan Zhang ◽  
Weiqiang Zhang
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Thermophysical Properties ◽  
Supercritical Pressure ◽  
Axial Position ◽  
Bulk Fluid ◽  
Heat Transfer Deterioration ◽  
Horizontal Tubes ◽  
Pressure Water

In order to get insights into the mechanisms governing the heat transfer deterioration (HTD) of supercritical water, systematical numerical simulations were carried out in the present study for the flow and heat transfer of supercritical pressure water in horizontal smooth tubes. The numerical results were found in very good agreement with the corresponding experimental data, validating the reliability and accuracy of the numerical model and the computational method. It was found that from these profiles along the top generatrix of the wall of the horizontal tube, there exists a thin fluid layer in which the thermo-physical properties of the fluid, including the specific heat capacity, thermal conductivity, density and viscosity, all approach its minimum at a roughly identical axial position of the tube with the increasing of the bulk fluid enthalpy along the flow direction. The maximum wall temperature of the top generatrix, obviously show the occurrence of HTD. It was especially interesting that the axial position of the maximum top generatrix wall temperature (HTD position) just coincided with the axial positions of the minimum of the above-mentioned thermophysical properties in the near top generatrix layer, which reveals the inherent connection between the HTD and the minimum value of the above-mentioned thermophysical properties of the supercritical water. It was concluded that the HTD of supercritical water in horizontal tubes was evidently due to the vertical stratification and the accumulation of light supercritical pressure fluid (very high enthalpy but low density) in the near top generatrix region. Also, the HTD phenomena under supercritical condition was similar to that of the film boiling of the subcritical pressure water. This result clearly reveals why the axial position of the HTD occurred on the top wall of horizontal tubes (with bulk fluid enthalpy of roughly 1750 kJ/kg) is axially far ahead of the position corresponding to the critical point of the supercritical water (with bulk fluid enthalpy of roughly 2150 kJ/kg) in terms of the bulk fluid enthalpy.

Pseudoboiling Heat Transfer to Supercritical Pressure Water in Smooth and Ribbed Tubes

1970 ◽  
Vol 92 (3) ◽  
pp. 490-497 ◽  
Author(s):  
J. W. Ackerman
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heated Surface ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Pressure Water ◽  
Supercritical Pressure Water

Investigations of heat transfer to supercritical pressure fluids have been going on for some time, and correlations have been developed for both free and forced-convection conditions. In these investigations, unpredictable heat transfer performance has sometimes been observed when the pseudocritical temperature of the fluid is between the temperature of the bulk fluid and that of the heated surface. The unusual performance has been attributed to many causes, but one for which more evidence is being collected is that of a pseudofilm-boiling process similar to film boiling which occurs at subcritical pressures. This paper, which is an extension of work reported earlier on forced-convection heat transfer to supercritical pressure water, presents experimental evidence which suggests that a pseudofilm-boiling phenomenon can occur in smooth-bore tubes. During the period from 1963–1966, tubes with ID’s from 0.37 to 0.96 in. were tested at pressures from 3300–6000 psia and at heat fluxes and mass velocities in the range of interest in steam-generator design. The effects of heat flux, mass velocity, tube diameter, pressure, and bulk fluid temperature on both the occurrence and characteristics of pseudofilm boiling are discussed. Results of a second series of tests conducted in 1967, which show that ribbed tubes suppress pseudofilm boiling at supercritical pressure much like they do film boiling at subcritical pressures, are also discussed.

Analysis of Updated SuperCritical Water Heat Transfer Correlations for Vertical Bare Tubes

2010 ◽  
Author(s):  
Sarah Mokry ◽  
Sahil Gupta ◽  
Amjad Farah ◽  
Krysten King ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Thermophysical Properties ◽  
Vertical Tube ◽  
Large Set ◽  
Conservative Approach ◽  
Bulk Fluid ◽  
Heat Transfer Correlations ◽  
Vertical Tubes ◽  
Bare Tube

In support of developing SuperCritical Water-cooled Reactors (SCWRs), studies are currently being conducted for heat-transfer at supercritical conditions. This paper presents an analysis of heat-transfer to SuperCritical Water (SCW) flowing in bare vertical tubes as a first step towards thermohydraulic calculations in a fuel-channel. A large set of experimental data, obtained in Russia, was analyzed. Two updated heat-transfer correlations for forced convective heat transfer in the normal heat transfer regime to SCW flowing in a bare vertical tube were developed. It is expected that the next generation of water-cooled nuclear reactors will operate at supercritical pressures (∼25 MPa) with high coolant temperatures (350–625°C). Currently, there are no experimental datasets for heat transfer from power reactor fuel bundles to the fuel coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations obtained with bare tube data can be used as a conservative approach. The analyzed experimental dataset was obtained for SCW flowing upward in a 4-m-long vertical bare tube. The data was collected at pressures of about 24 MPa for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. The values for mass flux ranged from 200–1500 kg/m2s, for heat flux up to 1250 kW/m2 and inlet temperatures from 320–350°C. The Mokry et al. correlation was developed as a Dittus-Boelter-type correlation, with thermophysical properties taken at bulk-fluid temperatures. Alternatively, the Gupta et al. correlation was developed based on the Swenson et al. approach, where the majority of thermophysical properties are taken at the wall temperature. An analysis of the two updated heat-transfer correlations is presented in this paper. Both correlations demonstrated a good fit (±25% for Heat Transfer Coefficient (HTC) values and ±15% for calculated wall temperatures) for the analyzed dataset. Thus, these correlations can be used for preliminary HTC calculations in SCWR fuel bundles as a conservative approach, for SCW heat exchangers, for future comparisons with other independent datasets and for the verification of computer codes for SCWR core thermohydraulics.

Investigation of Characteristic-Temperature Approaches for Heat-Transfer Correlations at Supercritical Conditions

2013 ◽  
Author(s):  
Sarah Mokry ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Characteristic Temperature ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Supercritical Conditions ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients ◽  
Bare Tube

It is expected that the next generation of water-cooled nuclear reactors will operate at supercritical pressures (∼25 MPa) and high coolant temperatures (350–625°C). In support of the development of SuperCritical Water-cooled Reactors (SCWRs), research is currently being conducted for heat-transfer at supercritical conditions. Currently, there are no experimental datasets for heat transfer from power reactor fuel bundles to the fuel coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations obtained with bare-tube data can be used as a conservative approach. A number of empirical generalized correlations, based on experimentally obtained datasets, have been proposed to calculate Heat Transfer Coefficients (HTCs) in forced convective heat transfer for various fluids, including water, at supercritical pressures. These bare-tube-based correlations are available in various literature sources. There have been a number of methods applied to correlate heat transfer data. The most conventional approach, which accounts for property variations in the data, is to modify the classical Dittus-Boelter equation for forced convection. However, analysis and comparison of these correlations has shown that differences in HTC values can be up to several hundred percent. In general, the familiar correlations of Dittus-Boelter and Bishop et al. have used the bulk-fluid temperature approach for characteristic temperature properties evaluations. However, at high heat fluxes, fluid near the tube-wall will have a temperature close to that of the wall temperature. This might be significantly different from the bulk-fluid temperature. Therefore, another approach can be used based on the wall temperature as the characteristic temperature. The Swenson et al. correlation is based upon this approach. Finally, a third approach has been considered in which the film-temperature is used as the characteristic temperature (Tf = (Tw+Tb) / 2). McAdams et al. based their correlation for annuli on this approach. Therefore, the objective of this paper is to evaluate the three characteristic temperature approaches, (1) Bulk-fluid temperature approach; (2) Wall-temperature approach; and (3) Film-temperature approach, and determine which characteristic temperature method can most accurately predict supercritical water heat transfer coefficients. Both classical correlations and more recently developed correlations are considered in this investigation.

Supercritical Water Heat Transfer in a Vertical Bare Tube

2008 ◽  
Author(s):  
Yevgeniy Gospodinov ◽  
Sarah Mokry ◽  
Pavel Kirillov ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Test Section ◽  
Bulk Fluid ◽  
Transfer Data ◽  
Normal Heat ◽  
Bare Tube

This paper presents selected results on heat transfer to supercritical water flowing upward in a 4-m-long vertical bare tube. Supercritical water heat-transfer data were obtained at pressures of about 24 MPa, mass fluxes of 200 – 1500 kg/m2s, heat fluxes up to 884 kW/m2 and inlet temperatures from 320 to 350°C for several combinations of wall and bulk-fluid temperatures that were below, at or above the pseudocritical temperature. In general, the experiments confirmed that there are three heat-transfer regimes for forced convective heat transfer to water flowing inside tubes at supercritical pressures: (1) normal heat-transfer regime characterized in general with heat transfer coefficients (HTCs) similar to those of subcritical convective heat transfer far from critical or pseudocritical regions, which are calculated according to the Dittus-Boelter type correlations; (2) deteriorated heat-transfer regime with lower values of the HTC and hence higher values of wall temperature within some part of a test section compared to those of the normal heat-transfer regime; and (3) improved heat-transfer regime with higher values of the HTC and hence lower values of wall temperature within some part of a test section compared to those of normal heat-transfer regime. These new heat-transfer data are applicable as a reference dataset for future comparison with supercritical-water bundle data and for a verification of scaling parameters between water and modeling fluids. Also, these HTC data were compared to those calculated with the original Dittus-Boelter and Bishop et al. correlations. The comparison showed that the Bishop et al. correlation, which uses the cross-section average Prandtl number, represents HTC profiles more correctly along the heated length of the tube than the Dittus-Boelter correlation. In general, the Bishop et al. correlation shows a good agreement with the experimental HTCs outside the pseudocritical region, however, overpredicts the experimental HTCs within the pseudocritical region. The Dittus-Boelter correlation can also predict the experimental HTCs outside the pseudocritical region, but deviates significantly from the experimental data within the pseudocritical region. It should be noted that both these correlations cannot be used for a prediction of HTCs within the deteriorated heat-transfer regime.

On Calculating Heat Transfer and Pressure Drop of Supercritical-Pressure Coolants

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Vladimir A. Kurganov ◽  
Yuri A. Zeigarnik ◽  
Irina V. Maslakova
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Thermophysical Properties ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Transfer Deterioration ◽  
Normal Heat ◽  
Turbulent Flow Structure ◽  
Heat Loads

Specific features of thermophysical properties of single-phase supercritical-pressure (SCP) coolants and typical ranges of their thermodynamic state that determine heat-transfer regularities are presented. A brief analysis of the existing concepts on SCP-coolants heat transfer under turbulent flow in tube is given. Typical features of normal and deteriorated heat-transfer regimes are described. The simple classification of deteriorated heat-transfer regimes at high heat loads that make it possible to distinguish the causes and appraise a degree of heat-transfer deterioration danger is proposed. The results from the studies of the hydraulic-resistance structure under the regimes of normal and deteriorated heat transfer are considered and the conditions, when a one-dimensional (1-D) (homogeneous) flow model can be used in hydraulic calculations, are revealed. Using sounding measurements data, the interrelation between heat-transfer deterioration and radical changes in the averaged turbulent flow structure due to fluid thermal acceleration and Archimedes forces effects is analyzed. The recommendations on calculating normal heat transfer with an account of refined standards on thermophysical properties of water and carbon dioxide are presented. The review and analysis of the existing criteria for forecasting heat-transfer deterioration and assessing the boundaries of the normal heat-transfer range are given, and the correlations for describing deteriorated heat transfer are presented.

Analysis of Computational Fluid Dynamics Code FLUENT Capabilities for Supercritical Water Heat-Transfer Applications in Vertical Bare Tubes

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Amjad Farah ◽  
Glenn Harvel ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Additional Information ◽  
Turbulent Models ◽  
Multidimensional Effects

In this paper, the computational fluid dynamics (CFD) code FLUENT was used to predict wall-temperature profiles inside vertical bare tubes with supercritical water (SCW) as the cooling medium, to assess the capabilities of FLUENT for SCW heat-transfer applications. Numerical results are compared to experimental data and current one-dimensional (1D) models represented by existing heat-transfer empirical correlations. Wall-temperature and heat-transfer coefficients were analyzed to select the best model to describe the fluid flow before, at, and after the pseudocritical region. k−ϵ and k−ω turbulent models were evaluated in the process, with variations in the submodel parameters such as viscous heating, thermal effects, and low-Reynolds-number correction. Results of the analysis show a fit of ±10% for wall temperatures using the SST k−ω model within the deteriorated heat-transfer regime and less than ±5% within the normal heat-transfer regime. The accuracy of the model is higher than any empirical correlation tested in the mentioned regimes and provides additional information about the multidimensional effects between the bulk-fluid and wall temperatures.

Preliminary Investigation of Heat-Transfer Correlation for Upward Flow of CO2 at Supercritical Pressure

2013 ◽  
Author(s):  
Eugene Saltanov ◽  
Igor Pioro ◽  
Glenn Harvel
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Supercritical Water ◽  
Preliminary Investigation ◽  
Convection Heat Transfer ◽  
Theoretical Models ◽  
Supercritical Pressure ◽  
Operational Parameters ◽  
Bulk Fluid ◽  
Wide Range

The development of Generation IV nuclear reactors is an ongoing worldwide interdisciplinary effort. Canada is involved with the development of the SuperCritical Water-cooled Reactor (SCWR). One of the numerous engineering challenges associated with this development is to ensure intensive and stable heat transfer to SuperCritical Water (SCW) in a core. It is very important to develop sophisticated theoretical models to improving understanding of physical processes behind forced-convective heat transfer and its deterioration in near-critical region. However, not all turbulent models implemented in Computational Fluid Dynamics (CFD) codes are applicable to heat transfer at supercritical pressures. Additionally these codes should be first tuned on the basis of experimental data and, after that, used in similar calculations. Therefore, there is still a great reliance on 1D heat-transfer correlations for preliminary calculations. Performing experiments in SCW is extremely expensive due to the high temperatures and pressures involved. Therefore, it is reasonable to study the general properties of SuperCritical Fluids (SCF) by running experiments with modelling fluids; for example, carbon dioxide, which is widely used as a modeling fluid. In view of this, there is a need to compile a large database that will include experimental data on forced-convection heat-transfer to SuperCritical (SC) CO2 within a wide range of operational parameters. To date, a part of this database has been produced. It contains the bulk-fluid and wall temperatures of CO2 flowing upward in a vertical bare tube. CO2 is at supercritical pressure and the bulk-fluid and wall temperatures are below or above the pseudocritical temperature at the inlet of the test-section. Therefore, the objectives of this paper are: 1) to propose a correlation in a standard non-dimensional form, which will generalize data within ±25%; 2) to compare this correlation with the most recent, as well as previous 1D correlations for SC CO2 and SCW (appropriate scaling is performed).

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