Calculations of Combined Radiation and Convection Heat Transfer in Rod Bundles Under Emergency Cooling Conditions

1976 ◽  
Vol 98 (3) ◽  
pp. 414-420 ◽  
Author(s):  
K. H. Sun ◽  
J. M. Gonzalez-Santalo ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Radiation Heat Transfer ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Operation Conditions ◽  
Water Reactors ◽  
Core Cooling

A model has been developed to calculate the heat transfer coefficients from the fuel rods to the steam-droplet mixture typical of Boiling Water Reactors under Emergency Core Cooling System (ECCS) operation conditions during a postulated loss-of-coolant accident. The model includes the heat transfer by convection to the vapor, the radiation from the surfaces to both the water droplets and the vapor, and the effects of droplet evaporation. The combined convection and radiation heat transfer coefficient can be evaluated with respect to the characteristic droplet size. Calculations of the heat transfer coefficient based on the droplet sizes obtained from the existing literature are consistent with those determined empirically from the Full-Length-Emergency-Cooling-Heat-Transfer (FLECHT) program. The present model can also be used to assess the effects of geometrical distortions (or deviations from nominal dimensions) on the heat transfer to the cooling medium in a rod bundle.

Design and Simulation of a Novel Thermoelectric Micro-Device with Electrodeposited Bi-Te Alloys

2018 ◽  
Vol 281 ◽  
pp. 788-794
Author(s):  
S. Guo ◽  
Ning Su ◽  
Fu Li ◽  
Da Wei Liu ◽  
Bo Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Output Power ◽  
Short Circuit ◽  
Maximum Output Power ◽  
Convection Heat Transfer ◽  
Open Circuit ◽  
Maximum Output ◽  
Transfer Coefficients

A novel thermoelectric micro-device was designed with n-type and p-type Bi-Te materials alloys via a template electrodeposition process. The glass template including 250 holes in 10×10 mm2with a thickness of 200~ 400 µm. The diameter of the holes is 50~ 80 µm and the distance of adjacent centers of the holes is 200 µm. According to the design, the performance of heat transference and thermoelectric energy generation are simulated by COMSOL Multiphysics. In order to simplify model, there are 16 units in total, and each unit is made up of 16 (4 × 4) pillars. In the simulation, the largest temperature difference is 7.8K on the conditions of 500 W/m2K in convection heat transfer coefficients and the maximum output potential of the module is 21.7 mV. The maximum output power achieved 96.9 µW under 500 W/m2K of heat transfer coefficient and 10 mA of current. Under ideal conditions, the value of open circuit voltage and maximum output power increases to nine times as the model, but short circuit current remains the same. When the heat transfer coefficient is 500 W/m2K and the current density is 10 mA, the maximum output power of the actual product achieved 871.7 µW.

Forced Convection Heat Transfer From a Uniformly Heated Sphere

1962 ◽  
Vol 84 (2) ◽  
pp. 133-140 ◽  
Author(s):  
W. S. Brown ◽  
C. C. Pitts ◽  
G. Leppert
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Sphere Diameter ◽  
Transfer Coefficients ◽  
Number Range ◽  
Average Heat

An approximate analytical solution is presented for the variation of the local heat-transfer coefficient over the forward half of a uniformly heated sphere. Experimental measurements with water over a Reynolds number range of 5000 to 480,000 and a Prandtl number range of 2.2 to 6.8 give local coefficients which are in good agreement with analytical results. Average heat-transfer coefficients for the uniformly heated sphere are slightly higher than similar results reported earlier [1] for an isothermal sphere. The effect of variations of heat flux on the average heat-transfer coefficient is correlated in a manner similar to that which was used for the isothermal data. Three different duct sizes were used in the experiment to determine the effect of this variable, and the correlations which are presented are based on duct-to-sphere diameter ratios of 2, 2.67, and 4.

Improved Correlation for Natural Convection Heat Transfer From Inclined Cylinders Having Different Emissivities

1999 ◽  
Author(s):  
Jeffrey C. Stewart ◽  
William S. Janna
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

Abstract The purpose of this study was to develop an improved correlation for natural convection heat transfer from inclined cylinders having different emissivities. The angle of cylinder inclination varied from horizontal to vertical in 15° increments. The heat transfer coefficient was obtained experimentally with the cylinder in a state of constant heat flux. Three surface finishes were used in the experiment, which consisted of polished copper, black paint, and aluminum paint. The heat transfer coefficients in all cases varied from 1.21 to 1.65 BTU/(hr·ft2·R) [6.87 to 9.37 W/(m2·K)]. Rayeigh numbers for all experiments varied from 1.31 × 103 to 2.23 × 103. The heat transfer coefficient decreased for each cylinder with an increasing angle of inclination (from horizontal to vertical). The goal of this study was to produce Nusselt-Rayleigh number correlations for each cylinder, and then ultimately produce a single equation that can be applied for all emissivities. The Rayleigh number included a geometry term to account for the inclination of the cylinder. The form of the equation that best represented the data was a power law equation.

The Effects of Blade Passing on the Heat Transfer Coefficient of the Overtip Casing in a Transonic Turbine Stage

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Steven J. Thorpe ◽  
Roger W. Ainsworth
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Turbine Stage ◽  
Transfer Coefficients ◽  
Time Resolved ◽  
Turbine Engine ◽  
Transonic Turbine

In a modern gas turbine engine, the outer casing (shroud) of the shroudless high-pressure turbine is exposed to a combination of high flow temperatures and heat transfer coefficients. The casing is consequently subjected to high levels of convective heat transfer, a situation that is complicated by flow unsteadiness caused by periodic blade-passing events. In order to arrive at an overtip casing design that has an acceptable service life, it is essential for manufacturers to have appropriate predictive methods and cooling system configurations. It is known that both the flow temperature and boundary layer conductance on the casing wall vary during the blade-passing cycle. The current article reports the measurement of spatially and temporally resolved heat transfer coefficient (h) on the overtip casing wall of a fully scaled transonic turbine stage experiment. The results indicate that h is a maximum when a blade tip is immediately above the point in question, while the lower values of h are observed when the point is exposed to the rotor passage flow. Time-resolved measurements of static pressure are used to reveal the unsteady aerodynamic situation adjacent to the overtip casing wall. The data obtained from this fully scaled transonic turbine stage experiment are compared to previously published heat transfer data obtained in low-Mach number cascade-style tests of similar high-pressure blade geometries.

The Effects of Blade Passing on the Heat Transfer Coefficient of the Over-Tip Casing in a Transonic Turbine Stage

2006 ◽  
Author(s):  
Steven J. Thorpe ◽  
Roger W. Ainsworth
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Turbine Stage ◽  
Transfer Coefficients ◽  
Time Resolved ◽  
Turbine Engine ◽  
Transonic Turbine

In a modern gas turbine engine the outer casing (shroud) of the shroudless high-pressure turbine is exposed to a combination of high flow temperatures and heat transfer coefficients. The casing is consequently subjected to high levels of convective heat transfer, a situation that is complicated by flow unsteadiness caused by periodic blade-passing events. In order to arrive at an over-tip casing design that has an acceptable service life it is essential for manfacturers to have appropriate predictive methods and cooling system configurations. It is known that both the flow temperature and boundary layer conductance on the casing wall vary during the blade-passing cycle. The current article reports the measurement of spatially and temporally resolved heat transfer coefficient (h) on the over-tip casing wall of a fully-scaled transonic turbine stage experiment. The results indicate that h is a maximum when a blade-tip is immediately above the point in question, while lower values of h are observed when the point is exposed to the rotor passage flow. Time-resolved measurements of static pressure are used to reveal the unsteady aerodynamic situation adjacent to the over-tip casing wall. The data obtained from this fully-scaled transonic turbine stage experiment are compared to previously published heat transfer data obtained in low-Mach number cascade style tests of similar high pressure blade geometries.

scholarly journals Experimental and Numerical Study of Free Convection Heat Transfer Around the Junction of Circular Cylinder and Heated Vertical Plate

2020 ◽  
pp. 631-643
Author(s):  
Hamid Malah ◽  
Yurii S. Chumakov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Circular Cylinder ◽  
Transfer Coefficient ◽  
Vertical Plate ◽  
Numerical Study ◽  
Symmetry Plane ◽  
Convection Heat Transfer ◽  
Validity And Reliability ◽  
Transfer Coefficients

The present study investigates the effects of a circular cylinder on the three-dimensional characteristics of free convective heat transfer. The circular cylinder is mounted horizontally on a heated vertical plate and is categorized as high aspect ratio obstacle, which means the height of cylinder is comparable to its diameter. The obtained results are provided for the laminar flow regime. In addition, during numerical study the governing differential equations are solved around the Grashof number equals to 3 108. In order to illustrated the regions of high gradients of temperature, the flow temperature is shown in terms of non-dimensional contours and diagrams. At the near junction region in upstream of cylinder, by description of heat transfer coefficients represented to the temperature gradients at intended points, the effects of cylinder emplacement on the heat transfer rate is surveyed. As expected, the value of the buoyancy-induced heat transfer coefficient increases at the cylinder junction in the upstream side. The maximum value of heat transfer coefficient is seen at the symmetry plane of study domain, which is corresponded to the location of horseshoe vortex system core. Finally, by deviation calculating between numerical and experimental results also by analysis of the experimental method uncertainty the validity and reliability of numerical and experimental approaches are proved

Critical Heat Flux on Curved Calandria Vessel of Indian PHWRs During Severe Accident Condition

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
P. K. Verma ◽  
P. P. Kulkarni ◽  
P. Pandey ◽  
S. V. Prasad ◽  
A. K. Nayak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Nuclear Power ◽  
Cooling System ◽  
Severe Accident ◽  
Water Reactors ◽  
Curved Section

Abstract In pressurized heavy water reactors (PHWRs), during an unmitigated severe accident, the absence of adequate cooling arising from multiple failures of the cooling system leads to the collapse of pressure tubes and calandria tubes, which may ultimately relocate to the lower portion of the calandria vessel (CV) forming a debris bed. Due to the continuous generation of decay heat in the debris, it will melt and form a molten pool at the bottom of the CV. The CV is surrounded by calandria vault water, which acts as a heat sink at this scenario. In-vessel corium retention (IVR) through the external reactor vessel cooling (ERVC) is conceived as an effective method for maintaining the integrity of a calandria vessel during a severe accident in a nuclear power plant. Under the IVR conditions, it is necessary to ensure that the imparted heat flux due to melt is less than the critical heat flux (CHF) at the bottom of the calandria vessel wall. To evaluate the thermal margin for IVR, experiments are performed in a prototypic curved section of calandria vessel (25o sector) of calandria vessel to determine the CHF, heat transfer coefficient, and its variation along with the curvature of calandria vessel. The effect of moderator drainpipe on CHF and the heat transfer coefficient has also been evaluated. It has been observed that the imparted heat flux is much less than the CHF at the bottom of the calandria vessel.

Evaluation of Heat Removal During the Failure of the Core Cooling for New Critical Assembly

2018 ◽  
Author(s):  
Yuta Eguchi ◽  
Takanori Sugawara ◽  
Kenji Nishihara ◽  
Yujiro Tazawa ◽  
Kazufumi Tsujimoto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Core Temperature ◽  
Cooling System ◽  
Design Criterion ◽  
Heat Transfer Analysis ◽  
Rectangular Lattice ◽  
The Core ◽  
Core Cooling

The Japan Atomic Energy Agency (JAEA) has been conducting the research and development (R&D) on accelerator-driven subcritical system (ADS) as a dedicated system for the transmutation of long-lived radioactive nuclides. To foster the R&D of ADS, the Transmutation Physics Experimental Facility (TEF-P) in the J-PARC project has been planned to build by JAEA [1]. The TEF-P is used minor actinide (MA) fuel which has large decay heat, so during the failure of the core cooling system, the evaluation of the core temperature increase is important. This study aims to evaluate the natural cooling characteristics of TEF-P core and to achieve a design that does not damage the core and the fuels during an accident (the failure of the core cooling system). The experiments using mockup device was performed to validate the heat transfer characteristics in the empty rectangular lattice tube. It was obtained that the actual heat transfer coefficient of empty rectangular lattice tube was about 2.2 times larger than the theoretical free convection model. It was also confirmed that the insertion of any block into the empty rectangular lattice tube could achieve the higher heat transfer coefficient. Using the heat transfer coefficient obtained by experiment results, thermal analysis was performed by the three-dimensional heat transfer analysis. As a result, the calculation results showed that the maximum core temperature will be 294 °C which is less than the design criterion of temperature, 327 °C. It was presented that the design condition which the core temperature will be below the design criterion during the failure of the core cooling system through this study.

Measurement of Heat Transfer Coefficient Distributions and Flow Field in a Model of a Turbine Blade Cooling Passage With Tangential Injection

2006 ◽  
Author(s):  
John P. C. W. Ling ◽  
Peter T. Ireland ◽  
Neil W. Harvey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Cooling System ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Cooling Passage

In certain regions of turbine aerofoils, cooling system designers need to cool the blades with convection systems that provide high heat transfer coefficients. The present research has investigated a circular cooling passage with tangential injection suitable for a blade leading edge. The heat transfer coefficients are measured using the conventional transient heat transfer, liquid crystal technique. The results are compared to the data from steady state experiments performed by Hedlund et al. [1]. The cooling system performance is compared in detail to average data from earlier tangential injection experiments and to local heat transfer coefficient expected from a normal impingement system. The vortex flow field was also studied by numerical prediction and near-wall velocity measurements. The investigation of the flow structure has led to understanding of flow mechanisms responsible for the high heat transfer coefficient. The vortex flow field was also investigated using computational fluid dynamics and with hot wire anemometry. The latter near wall measurements were combined with the law of the wall and Colburn analogy to validate the flow and heat transfer measurements.

Experimental and Numerical Simulation of a Synthetic Jet for Cooling of Electronics

2011 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Mark North ◽  
Tianhong Cui
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Large Scale ◽  
Cooling System ◽  
Synthetic Jet ◽  
Computational Results ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
Heat Transfer Coefficients

Compared to traditional continuous jets, synthetic jets have specific advantages, such as lower power requirement, simpler structure, and the ability to produce an unsteady turbulent flow which is known to be effective in augmenting heat transfer. This study presents experimental and computational results that document heat transfer coefficients associated with impinging a round synthetic jet flow on the tip region of a longitudinal fin surface used in an electronics cooling system. Unique to this study are the geometry of the cooled surface and the variations in geometry of the jet nozzle or nozzles. Also unique are measurements in actual-scale systems and in a scaled-up system, and computation. In the computation, the diaphragm movement of the synthetic jet is a moving wall and the flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. The effects of different parameters, such as amplitude and frequency of diaphragm movement and jet-to-stagnation-line spacing, are recorded. The computational results show a good match with the experimental results. In the experiments, an actual-scale system is tested and, for finer spatial resolution and improved control over geometric and operational conditions, a large-scale mock-up is tested. The three approaches are used to determine heat transfer coefficients on the fin on and near the stagnation line. Focus is on the large scale test results and the computation. Application to the actual-size cases is discussed. The dynamically-similar mock-up matches the dimensionless Reynolds number, Stokes number, and Prandtl number of the actual setting with a scale factor of 44. A linear relationship for heat transfer coefficient versus frequency of diaphragm movement is shown. Heat transfer coefficient values as high as 650 W/m2K are obtained with high-frequency diaphragm movement. Cases with different orifice shapes show how cooling performance changes with orifice design.

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