Heat-Transfer at Supercritical Pressures

2010 ◽  
Author(s):  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Power Plants ◽  
Cooling System ◽  
Nuclear Reactors ◽  
Turbine Blades ◽  
Convection Heat Transfer ◽  
Steam Generators ◽  
Capital Costs ◽  
The 1950S

The first works devoted to the problem of heat transfer at supercritical pressures started as early as the 1930s. E. Schmidt and his associates investigated free-convection heat transfer to fluids at the near-critical point with the objective of developing a new effective cooling system for turbine blades in jet engines. In the 1950s, the idea of using supercritical “steam”-water appeared to be rather attractive for steam generators / turbines to increase thermal efficiency of fossil-fired power plants. Intensive work on this subject was mainly performed in the former USSR and in the USA in the 1950s–1980s. Therefore, the most investigated flow geometry at supercritical pressures is circular tubes with water as the coolant. Currently, using supercritical “steam” in fossil-fired power plants is the largest industrial application of fluids at supercritical pressures. At the end of the 1950s and the beginning of the 1960s, some studies were conducted to investigate the possibility of using supercritical water as a coolant in nuclear reactors. Several concepts of nuclear reactors were developed. However, this idea was abandoned for almost 30 years, and then regained momentum in the 1990s as a means to improve the performance of water-cooled nuclear reactors. Main objectives of using supercritical water in nuclear reactors are increasing the efficiency of modern nuclear power plants, which is currently 30–35%, to circa 43–50%, and decreasing operational and capital costs by eliminating steam generators, steam separators, steam dryers, etc. Therefore, objectives of the current paper are to assess the work that was performed and to understand specifics of heat transfer at supercritical pressures.

Exploring the Use of Alumina Nanofluid as Emergency Coolant for Nuclear Fuel Bundle

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
A. S. Chinchole ◽  
Arnab Dasgupta ◽  
P. P. Kulkarni ◽  
D. K. Chandraker ◽  
A. K. Nayak
Keyword(s):  
Heat Transfer ◽  
Nuclear Fuel ◽  
Nuclear Reactor ◽  
Cooling System ◽  
Nuclear Reactors ◽  
Electrical Heating ◽  
High Dose ◽  
Potential Candidate ◽  
Alumina Nanofluid ◽  
Core Cooling

Abstract Nanofluids are suspensions of nanosized particles in any base fluid that show significant enhancement of their heat transfer properties at modest nanoparticle concentrations. Due to enhanced thermal properties at low nanoparticle concentration, it is a potential candidate for utilization in nuclear heat transfer applications. In the last decade, there have been few studies which indicate possible advantages of using nanofluids as a coolant in nuclear reactors during normal as well as accidental conditions. In continuation with these studies, the utilization of nanofluids as a viable candidate for emergency core cooling in nuclear reactors is explored in this paper by carrying out experiments in a scaled facility. The experiments carried out mainly focus on quenching behavior of a simulated nuclear fuel rod bundle by using 1% Alumina nanofluid as a coolant in emergency core cooling system (ECCS). In addition, its performance is compared with water. In the experiments, nuclear decay heat (from 1.5% to 2.6% reactor full power) is simulated through electrical heating. The present experiments show that, from heat transfer point of view, alumina nanofluids have a definite advantage over water as coolant for ECCS. Additionally, to assess the suitability of using nanofluids in reactors, their stability was investigated in radiation field. Our tests showed good stability even after very high dose of radiation, indicating the feasibility of their possible use in nuclear reactor heat transfer systems.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

Change of Thermal Conductivity and Cooling Performance for Water Based Al2O3-Surfactant Nanofluid with Time Lapse

2018 ◽  
Vol 26 (01) ◽  
pp. 1850009 ◽  
Author(s):  
Man Bae Kim ◽  
Hong Gen Park ◽  
Chang Yong Park
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Cooling System ◽  
Pure Water ◽  
Sodium Dodecyl ◽  
Convection Heat Transfer ◽  
Sodium Dodecyl Benzene Sulfonate ◽  
Time Lapse ◽  
Convection Heat ◽  
Conductivity Enhancement

An experimental research was performed to study the effect of time lapse on the change of water-Al2O3 nanofluid thermal conductivity and its convection heat transfer. The size of Al2O3 nanoparticle size was 20[Formula: see text]nm and 70[Formula: see text]nm, and initial volumetric concentration range was from 0.5% to 3%. A surfactant was added to the nanofluid and the change of thermal conductivity and convection heat transfer was also measured. The surfactant was Sodium Dodecyl Benzene Sulfonate (SDBS) and its mass fractions in the nanofluid were from 0.5% to 3.0%. Thermal conductivity of water and nanofluid was measured by the transient hot wire method. The accuracy of the measurement method was confirmed by the measurement error with 0.92% for distilled water at 20[Formula: see text]C. The thermal conductivity of the nanofluid without SDBS increased up to 11.3% and the enhancement decreased with time lapse. The reduction of thermal conductivity enhancement with the time lapse could be retarded by the addition of SDBS and its effect became higher with the increase of its mass fraction. The convection heat transfer characteristics of the nanofluid was measured in a small cooling system. Compared with pure water, nanofluid convection heat transfer could be enhanced but higher pressure drop also occurred. Compared with the convection heat transfer enhancement for the nanofluid without SDBS, the addition of SDBS decreased the enhancement at the initial stage of the experiment, but it could retard the reduction of convection heat transfer with time lapse.

Recent Trends of Impingement Cooling System Enhancement for Gas Turbine

2013 ◽  
Vol 465-466 ◽  
pp. 496-499
Author(s):  
Mohd Firdaus Bin Abas ◽  
Abdullah Aslam ◽  
Hamidon bin Salleh ◽  
Nor Adrian Bin Nor Salim
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Turbine Blades ◽  
Impinging Jets ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Jet ◽  
Rib Turbulators ◽  
Recent Trends ◽  
Plate Distance

Efforts have been given to improve the turbine blades ability to withstand high temperature for a long period of time by implementing effective cooling system. There are many aspects that should be considered when implementing impingement cooling. This paper will only cover two trending aspects in impingement cooling implementation; the jet-to-target plate distance and the application of ribs in promoting better impingement cooling performance. For target plate distance to impingement jet diameter value, H/d > 1, the area-averaged Nusselt number also decreases as the H/d value increases. This may have been due to a reduction of the amount of momentum exerted by the impinging jets onto the target plate. For H/d < 1, the results have been proven otherwise. Heat transfer in impingement/effusion cooling system in crossflow with rib turbulators showed higher heat transfer rate than that of a surface without ribs because the ribs prevent the wall jets from being swept away by the crossflow and increase local turbulence of the flow near the surface. It could be concluded that both H/d ratio and ribs installation play an important role in enhancing impingement cooling systems heat transfer effectiveness.

An investigation of a novel cooling system for chilled food display cabinets

2005 ◽  
Vol 219 (2) ◽  
pp. 157-165 ◽  
Author(s):  
G. G. Maidment ◽  
J. F. Missenden ◽  
T. G. Karayiannis ◽  
F Wang
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Convective System ◽  
Transfer System ◽  
The Novel ◽  
Heat Transfer Mechanism ◽  
Difference Model ◽  
Capital Costs ◽  
Cooling Mechanism ◽  
Heat Transfer System

The modern retail cabinets that are used for chilling and displaying food in shops are described in this paper. The deficiencies of the purely convective heat transfer mechanism used to cool food in modern cabinets are highlighted. A novel heat transfer system that provides an integrated conductive/convective cooling mechanism is then proposed. A purpose-developed finite difference model and its application in the study of the novel cooling system are presented in this paper. The model was used to evaluate the performance of the mechanism compared with the conventional convective system. The results indicate that the proposed novel system can provide improved heat transfer, which contributes to lower core food temperatures of approximately 2.5−3.5 K. This can lead to significant reductions in energy and capital costs as well as improvements in food quality and shelf-life. Furthermore, the use of this cooling system could avoid the requirement for electric defrost, which is energy-intensive.

An Analytical Investigation of Free Convection Heat Transfer to Supercritical Water

1970 ◽  
Vol 92 (3) ◽  
pp. 345-350 ◽  
Author(s):  
E. S. Nowak ◽  
A. K. Konanur
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Free Convection ◽  
Supercritical Water ◽  
Thermophysical Properties ◽  
Convection Heat Transfer ◽  
Analytical Investigation ◽  
Convection Heat ◽  
Free Convection Heat ◽  
Vertical Flat Plate

Heat transfer to supercritical water (at 3400 psia in the pseudocritical region) by stable laminar free convection from an isothermal, vertical flat plate was analytically investigated. The actual variations with temperature of all or some of the thermophysical properties of supercritical water were taken into consideration. Fair agreement was found between the analytical values of this paper and existing experimental data.

Heat Transfer to Supercritical Water in Smooth-Bore Tubes

1965 ◽  
Vol 87 (4) ◽  
pp. 477-483 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
C. R. Kakarala
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Supercritical Water ◽  
Convection Heat Transfer ◽  
Physical Property ◽  
Transfer Coefficients ◽  
Property Variation ◽  
Wide Range ◽  
Fully Developed Turbulent Flow ◽  
Data Points

Local forced convection heat-transfer coefficients for supercritical water flowing inside smooth-bore tubes were obtained experimentally over a range of pressures (3300 to 6000 psia) and bulk temperatures (167 to 1068 F). Because the thermophysical properties of supercritical fluids change rapidly with temperature in the pseudocritical range, conventional forced convection correlations were unable to fit the data. However, a satisfactory correlation for fully developed turbulent flow was obtained by properly modifying the conventional nondimensional model to account for the physical property variation across the boundary layer. Out of 2951 data points, 95 percent lie within ±15 percent of the correlation. It was also found that the same equation correlated supercritical pressure heat-transfer data of carbon dioxide over a wide range of conditions with good accuracy.

Natural Convection Heat Transfer in Horizontal Cylindrical Cavities: A Computational Fluid Dynamics (CFD) Investigation

2013 ◽  
Author(s):  
Daniele Ludovisi ◽  
Ivo A. Garza
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Power Plants ◽  
Convection Heat Transfer ◽  
Weather Conditions ◽  
Freezing Temperature ◽  
Cold Weather ◽  
Pipe Surface ◽  
Cfd Models ◽  
Different Diameters

Many processes in power plants involve the storage and transfer of fluids including water in outdoor pipelines. Under extreme cold weather conditions, water can freeze if allowed to cool down to the freezing temperature. Installing insulation and maintaining adequate flow rate can sometimes prevent problems. However, during extended non-processing times, there are circumstances where cool down cannot be avoided and heat tracing along the piping becomes a necessity. In many instances, the need for the installation of heat tracing is simply determined based on pipe size. However, by performing accurate calculations, it is possible to determine if the need for heat tracing is real or not, thus saving on installation and maintenance costs. Correlations for the estimation of the heat transfer coefficient in horizontal cavities are not sufficiently documented in literature. In the present work, two-dimensional CFD models are used to investigate the natural convection in water-filled horizontal pipes of different diameters. The analysis has been carried out based on the assumption of a uniform pipe surface temperature. The Nusselt number is estimated as a function of the Rayleigh number and shown not to be strongly dependent on the Prandtl number. The analysis and the results of the numerical investigation are presented and compared to experimental data and other correlations available in literature. The documented correlation has an expanded range of applicability to high and low Rayleigh numbers, is supported by numerical and experimental results and is expressed in a simple form.

Implicit Model Equation for Hydraulic Resistance and Heat Transfer including Wall Roughness

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Eckart Laurien
Keyword(s):  
Heat Transfer ◽  
Hydraulic Resistance ◽  
Supercritical Water ◽  
Nuclear Power ◽  
Power Plants ◽  
Supercritical Pressure ◽  
Wall Roughness ◽  
Layer Model ◽  
Two Layer Model ◽  
Analytic Prediction

Heat transfer to water at supercritical pressure within the core of a supercritical water reactor must be predicted accurately to ensure safe design of the reactor and prevent overheating of the fuel cladding. In the previous work (Laurien, 2012, “Semi-Analytic Prediction of Hydraulic Resistance and Heat Transfer for Pipe Flows of Water at Supercritical Pressure,” Proceedings of the International Conference on Advances in Nuclear Power Plants, ICAPP’12, Chicago, June 24–28), we have demonstrated that the wall shear stress and the wall temperature can be computed in a coupled way by a finite-difference method, taking the wall roughness into account. In the present paper, the classical two-layer model, consisting only of a laminar sublayer and a turbulent wall layer, is extended toward the same task. A set of implicit algebraic equations for the wall shear stress and the wall temperature is derived. It is consistent with the well-established Colebrook equation for rough pipes, which is included as a limiting case for constant properties. The accuracy of the prediction for strongly heated pipe flow is tested by comparison to experiments (Yamagata et al., 1972, “Forced Convective Heat Transfer to Supercritical Water Flowing in Tubes,” Int. J. Heat Mass Transfer, 15(12), 2575–2593) with supercritical water. The high accuracy and the generality of Laurien (2012) “Semi-Analytic Prediction of Hydraulic Resistance and Heat Transfer for Pipe Flows of Water at Supercritical Pressure,” Proceedings of the International Conference on Advances in Nuclear Power Plants, ICAPP’12, Chicago, June 24–28 are not achieved, but with the help of correction factors, the two-layer model has a potential for improved predictions of the hydraulic resistance and the heat transfer of pipe and channel flows at supercritical pressure.

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