scholarly journals Modeling Strategies to Compute Natural Circulation Using CFD in a VHTR After a LOFA

2012 ◽  
Author(s):  
Yu-Hsin Tung ◽  
Richard W. Johnson ◽  
Ching-Chang Chieng ◽  
Yuh-Ming Ferng
Keyword(s):  
Heat Transfer ◽  
Natural Circulation ◽  
Department Of Energy ◽  
Full Potential ◽  
The Core ◽  
Triso Fuel ◽  
Flow And Heat Transfer ◽  
Local Symmetries ◽  
Fuel Particles ◽  
Global And Local

A prismatic gas-cooled very high temperature reactor (VHTR) is being developed under the next generation nuclear plant program (NGNP) of the U.S. Department of Energy, Office of Nuclear Energy. In the design of the prismatic VHTR, hexagonal shaped graphite blocks are drilled to allow insertion of fuel pins, made of compacted tristructural-isotropic (TRISO) fuel particles, and coolant channels for the helium coolant. One of the concerns for the reactor design is the effects of a loss of flow accident (LOFA) where the coolant circulators are lost for some reason, causing a loss of forced coolant flow through the core. In such an event, it is desired to know what happens to the (reduced) heat still being generated in the core and if it represents a problem for the fuel compacts, the graphite core or the reactor vessel (RV) walls. One of the mechanisms for the transport of heat out of the core is by the natural circulation of the coolant, which is still present. It is desired to know how much heat may be transported by natural circulation through the core and upwards to the top of the upper plenum. It is beyond current capability for a computational fluid dynamics (CFD) analysis to perform a calculation on the whole RV with a sufficiently refined mesh to examine the full potential of natural circulation in the vessel. The present paper reports the investigation of several strategies to model the flow and heat transfer in the RV. It is found that it is necessary to employ representative geometries of the core to estimate the heat transfer. However, by taking advantage of global and local symmetries, a detailed estimate of the strength of the resulting natural circulation and the level of heat transfer to the top of the upper plenum is obtained.

scholarly journals Numerical Investigation of Flow and Heat Transfer in a Rotor-Stator Cavity with Centripetal Carbon Dioxide Through-Flow

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2613
Author(s):  
Hu ◽  
Li ◽  
Fu ◽  
Gu ◽  
Ren ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Flow Parameter ◽  
Local Heat Transfer ◽  
Local Heat ◽  
The Core ◽  
Moment Coefficient ◽  
Flow And Heat Transfer ◽  
Through Flow ◽  
The Moment

A centrifugal carbon dioxide compressor is a kind of general machine with extensive applications. The geometry of the side chambers of the compressors can be determined by studying the rotor-stator cavity with centripetal through-flow. In this paper, numerical simulations were conducted to predict the characteristics of flow and heat transfer. Three different speeds of rotation and two axial gap widths were considered. The correlations of the core swirl ratios were determined by fitting the results for two axial gap widths. The amounts of the moment coefficients of the disk were predicted. In order to better analyze the temperature field, the radial distributions of the local heat transfer coefficient were numerically investigated. According to the simulation results, the average Nusselt number was found to be dominated by the turbulent flow parameter. It also seemed to be proportional to the moment coefficient at a fixed circumferential Reynolds number.

Study on Flow and Heat Transfer Characteristics of Different States of Water Under Natural Circulation

2014 ◽  
Author(s):  
Zhongyun Ju ◽  
Tao Zhou ◽  
Jingjing Li ◽  
Zejun Xiao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Supercritical Water ◽  
Natural Circulation ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

Software CFX is used to build a typical natural circulation loop to study flow and heat transfer characteristics of water vapor, the vapor-liquid two-phase and supercritical water under natural circulation. During the process of natural circulation, the variation of parameters, heat transfer coefficient and mass flow is compared. It is found that when formed a natural circulation, the steam has a lower mass flow and heat transfer coefficient, while the two parameters of two-phase and supercritical water are higher. Indicates that the heat transfer capability of steam is weak, the steam cannot transfer heat out opportunely when serious accidents take place. The two-phase water is of high heat transfer coefficient. Supercritical water is of strong exchange capacity, supercritical water under natural circulation is a promising flow pattern.

Flow and Heat Transfer Characteristics of a Natural Circulation Evaporative Cooling System for Electronic Components

2004 ◽  
Vol 126 (3) ◽  
pp. 317-324 ◽  
Author(s):  
Hiroshi Honda ◽  
ZhengGuo Zhang ◽  
Nobuo Takata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Test Section ◽  
Cooling System ◽  
Natural Circulation ◽  
Electronic Components ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Test Loop

Experiments were conducted to study the flow and heat transfer characteristics of a natural circulation liquid cooling system for electronic components. The test loop consisted of a horizontal test section, a horizontal evaporator, a vertical tube, a horizontal condenser, a rubber bag attached at the exit of the condenser, a downcomer, a mass flow meter, and a liquid subcooler. The loop height H was set at either 250 or 450 mm. FC-72 was filled in the test loop up to some level of loop height and the upper part was filled with air. During the operation of the cooling system, the rubber bag expanded and stored the mixture of generated vapor and air. Thus the inner pressure was maintained at atmospheric pressure. In the test section, a silicon chip with dimensions of 10×10×0.5 mm3 was attached at the bottom surface of a horizontal duct with dimensions of 10×14 mm2. A smooth chip and four chips with square micro-pin-fins with 150 to 300 μm in fin height were tested. The duct height s was set at 10 mm for most of the experiments. The cases of s=1 and 25 mm were also tested for one of the micro-pin-finned chips. For each H, the average flow rate of FC-72 was correlated well as a function of the static pressure difference between the two vertical tubes. All chips showed the boiling curve similar to that for pool boiling except that the critical heat flux was lower for the natural circulation loop. For all chips tested, the maximum allowable heat flux qmax increased monotonically with increasing liquid subcooling ΔTsub. Comparison of the results for s=1, 10 and 25 mm revealed that the highest qmax was obtained with s=10 mm. The values of qmax for s=1 and 25 mm were 36–46% and 87–90% of that for s=10 mm, respectively. The maximum value of qmax=56 W/cm2 was obtained by one of the micro-pin-finned chips at s=10 mm and ΔTsub=35 K.

Numerical Study of Developing Flow and Heat Transfer in a Wavy Passage

1999 ◽  
Vol 121 (4) ◽  
pp. 713-719 ◽  
Author(s):  
K. Stone ◽  
S. P. Vanka
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Spatial Location ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
The Core ◽  
Flow And Heat Transfer ◽  
Developing Flow ◽  
Energy Equations

Developing flow and heat transfer in a wavy passage are studied using a numerical scheme that solves the two-dimensional unsteady flow and energy equations. Calculations are presented for a wavy channel consisting of 14 waves. Time-dependent simulations have been performed for several Reynolds numbers. At low Reynolds numbers, the flow is steady in the complete channel. As the Reynolds number is progressively increased, the flow becomes unsteady. As a result of the unsteadiness, there is increased mixing between the core and the wall fluids, thereby increasing the heat transfer rate. With further increase in Reynolds number, the flow becomes unsteady at a much earlier spatial location.

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