Numerical Simulation of an ADSS With Surface Heat Flux and Heat Generation Using FEM

2005 ◽  
Author(s):  
K. Arul Prakash ◽  
G. Biswas ◽  
B. V. Rathish Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Generation ◽  
Nuclear Reactors ◽  
Critical Conditions ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Critical System ◽  
Flow And Heat Transfer ◽  
Interest In Research

ADSS (Accelerator Driven Sub-critical System) nuclear reactors have evoked renewed interest in research because it operates in sub-critical conditions and transmutes nuclear wastes. Numerical investigation of fluid flow and heat transfer characteristics of an ADSS has been accomplished using a finite element method based on Streamline Upwind Petrov-Galerkin (SUPG) technique. The time-dependent governing equations for conservation of mass, momentum and energy are solved. The simulations have been carried out to predict the heat transfer in the spallation regime. The cases of beam window with heat flux prescription is analyzed in the absence and presence of heat generation in the liquid metal. At the first place, laminar regime of the flow is considered for the ADSS geometry. The Reynolds number of interest were varied over a specified range.

On Suddenly Expanding Non-Isothermal Pipe Flows of a Bingham Fluid

1999 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Heat Transfer ◽  
Newtonian Fluid ◽  
Transfer Problem ◽  
Numerical Technique ◽  
Complex Nature ◽  
Brinkman Number ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Pipe Expansion

Abstract The non-isothermal laminar flow of the Bingham non-Newtonian fluid through a sudden pipe expansion is investigated. The governing equations of conservation of mass, momentum and energy are solved using the finite-difference numerical technique. The effects of non-dimensional yield stress, Reynolds number, Prandtl number and Brinkman number on the flow and heat transfer characteristics are studied. The obtained results indicate the complex nature of the present non-Newtonian fluid flow and heat transfer problem and reveal new features not encountered in the case of Newtonian fluids.

Heat Flux and Variable Thermal Conductivity Effects on Casson Flow and Heat Transfer due to an Exponentially Stretching Sheet with Viscous Dissipation and Heat Generation

2016 ◽  
Vol 14 (1) ◽  
pp. 167-174 ◽  
Author(s):  
Ahmed M. Megahed
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Generation ◽  
Stretching Sheet ◽  
Variable Thermal Conductivity ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flow And Heat Transfer ◽  
Exponentially Stretching

AbstractIn this paper, we introduce a theoretical and numerical study for the effects of thermal buoyancy and constant heat flux on the Casson fluid flow and heat transfer over an exponentially stretching sheet taking into account the effects of variable thermal conductivity, heat generation/absorption and viscous dissipation. The governing partial differential equations are transformed into coupled, non-linear ordinary differential equations by using suitable transformations. Numerical solutions to these equations are obtained by using the fourth order Runge-Kutta method with the shooting technique. The effects of various physical parameters which governing the flow and heat treansfer such as the buoyancy parameter, the thermal conductivity parameter, heat generation or absorption parameter and the Prandtl number on velocity and temperature are discussed by using graphical approach. Moreover, numerical results indicate that the local skin-friction coefficient and the local Nusselt number are strongly affected by the constant heat flux.

Variable Property Effects in Simultaneously Developing Gaseous Slip-Flow in Rectangular Microchannels With Prescribed Wall Heat Flux

2010 ◽  
Author(s):  
Azad Qazi Zade ◽  
Metin Renksizbulut ◽  
Jacob Friedman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Knudsen Number ◽  
Thermophysical Properties ◽  
Slip Flow ◽  
Wall Heat Flux ◽  
Heat Transfer Characteristics ◽  
Rectangular Microchannels ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The effects of variable physical properties on the flow and heat transfer characteristics of simultaneously developing slip-flow in rectangular microchannels with constant wall heat flux are numerically investigated. A co-located finite-volume method is used in order to solve the mass, momentum and energy equations in their most general form. Thermophysical properties of the flowing gas are functions of temperature, while density and Knudsen number are allowed to change with both pressure and temperature. Different Knudsen numbers are considered in order to study the effects of slip-flow. Simulations indicate that the constant physical property assumption can result in under/over-prediction of the local friction and heat transfer coefficients depending on the problem configuration. Density and thermophysical property variations have significant effects on predicting flow and heat transfer characteristics since the gas temperature constantly changes as a result of the applied wall heat flux. Heat transfer coefficient is affected both due to the change in the velocity field and change in thermophysical properties. Also temperature dependence of the local Knudsen number can significantly alter the friction coefficients due to its strong dependence on slip conditions. The degree of discrepancy varies for different cases depending on the Knudsen number, and the applied heat flux strength and direction (cooling versus heating).

Buoyancy Driven Flow, Heat Transfer and Entropy Generation Characteristics for Different Heater Geometries Placed in Cryogenic Liquid: A CFD Study

2021 ◽  
pp. 1-20
Author(s):  
Someshwar Ade ◽  
Sushil Rathore
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Entropy Generation ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Cryogenic Liquid ◽  
Heat Generation Rate ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Abstract The present work reports 3D computational study of buoyancy driven flow and heat transfer characteristics for a localized heater (analogous to superconductor) submerged in cryogenic liquid nitrogen in an enclosure. Seven different heater geometries are considered and the effect of heater geometry on flow and heat transfer characteristics are illustrated. The heater is generating heat at a constant rate (W/m3). Continuity, momentum and energy equations are solved using finite volume method. Liquid flow and heat transfer features are demonstrated with the help of velocity vector and temperature contours. Rayleigh number, average Nusselt number, maximum vertical velocity of fluid flow, average velocity of fluid flow are the parameters which are considered for comparing seven different geometries of heater. Additionally, an analysis of the entropy generation owing to transfer of heat and friction due to fluid flow are reported. Furthermore, the dependency of average Nusselt number, maximum velocity of fluid, entropy generation owing to transfer of heat and fluid friction as a function of heat generation rate is illustrated graphically. The results of this study indicate that heater geometry can considerably affect the transfer of heat, fluid flow features and entropy generation under same heat generation rate in the heater. Highest average Nusselt number on heater surface is obtained when heater geometry is circular; whereas lowest value of total entropy generation in the domain is obtained when heater geometry is equilateral triangle.

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 Investigation on Heat Transfer to Supercritical CO2 in Vertical Annular Channel

2016 ◽  
Author(s):  
Zhenxing Zhao ◽  
Jun Wu ◽  
Fan Bai ◽  
Qi Xiao ◽  
Chunhui Dai ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Supercritical Fluid ◽  
Annular Channel ◽  
Outer Wall ◽  
Wall Heat Transfer ◽  
Heat Transfer Characteristics ◽  
Heat Transfer Deterioration ◽  
Flow And Heat Transfer ◽  
Wall Heating

The special fluid flow and heat transfer characteristics of supercritical CO2 in a vertical annular channel have been numerically investigated. The AKN k-ε model was selected to model the turbulent flow and heat transfer of supercritical fluid. The three heating types were individual outer-wall heating, simultaneous outer/inner walls heating and outer-wall heating (inner-wall cooling) separately. The local heat transfer coefficients were obtained to investigate the influence of inner-wall thermal boundary conditions, supercritical fluid mass flux, fluid temperature and flow direction on outer-wall heat transfer phenomenon. The mechanisms of abnormal heat transfer and primary influence factors were analyzed by the detailed information on the flow, turbulence and thermal fields. When the supercritical fluid is in the large-property-variation (LPV) region and flows upward, the inner-wall thermal boundary condition obviously affects the heat transfer characteristics of outer wall. When supercritical fluid flows downward, the inner-wall boundary condition hardly affects the heat transfer phenomena of outer wall. The increase of inner-wall heating heat flux will result in the larger deterioration region and heat transfer decline on outer wall when the other conditions remain unchanged. When the heat transfer deterioration also appears on the inner wall with the increase in the inner-wall heat flux, the outer-wall heat transfer no longer decreases, but the deterioration region abruptly increases. However, as inner-wall cooling heat flux increases, the heat transfer deterioration phenomenon on outer wall will weaken gradually.

scholarly journals Flow and Heat Transfer Characteristics of Supercritical N-Decane in Adjacent Cooling Channels with Opposite Flow Directions

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1071
Author(s):  
Dongpeng Jia ◽  
Ning Wang ◽  
Yu Pan ◽  
Chaoyang Liu ◽  
Shiwei Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Flow Direction ◽  
Heat Transfer Characteristics ◽  
Cooling Channels ◽  
Flow And Heat Transfer ◽  
Flow Asymmetry ◽  
Recirculation Zones ◽  
Flow Directions

To ensure the safety of a scramjet, an arrangement scheme of adjacent regenerative cooling channels with opposite flow directions is adopted to decrease the maximum wall temperature. Based on extended corresponding-state methods, the flow and heat transfer characteristics of supercritical n-decane in cooling channels with same and opposite flow directions under a pressure of 3 MPa are comprehensively investigated in this paper. Compared to adjacent cooling channels with same flow direction, the local maximum wall temperature in adjacent cooling channels with opposite directions is notably reduced. Moreover, the effects of the heat flux and gravity on the development of flow field are analysed. A pair of recirculation zones is found close to the bottom wall of the cooling channels along the flow direction, the scale of which greatly expands with increasing heat flux. Once the heat flux density reaches a critical value, a phenomenon of flow asymmetry occurs. In addition, the small recirculation zones induced by the buoyancy force narrow when the gravity and heat flux directions remain the same, and the gravity effect could inhibit the generation of small-scale vortices and flow asymmetry.

scholarly journals Numerical Study on the Flow and Heat Transfer Characteristics of a Second Throat Exhaust Diffuser According to Variations in Operating Pressure and Geometric Shape

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 532
Author(s):  
Seonghwi Jo ◽  
Sanghyeon Han ◽  
Hong Jip Kim ◽  
Kyung Jin Yim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Study ◽  
Geometric Shape ◽  
Oblique Shock Wave ◽  
Flow Section ◽  
Operating Pressure ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

A numerical study was conducted to investigate the flow and heat transfer characteristics of a supersonic second throat exhaust diffuser for high-altitude simulations. The numerical results were satisfactorily validated by the experimental results. A subscale diffuser using nitrogen was utilized to investigate starting pressure and pressure variation in the diffuser wall. Based on the validated numerical method, the flow and heat transfer characteristics of the diffuser using burnt gas were evaluated by changing operating pressure and geometric shape. During normal diffuser operation without cooling, high-temperature regions of over 3000 K appeared, particularly near the wall and in the diffuser diverging section. After cooling, the flow and pressure distribution characteristics did not differ significantly from those of the adiabatic condition, but the temperature in the subsonic flow section decreased by more than 1000 K. Furthermore, the tendency of the heat flux from the diffuser internal flow to the wall was similar to that of the pressure variations, and it increased with operating pressure. It was confirmed that the heat fluxes of the supersonic and subsonic flows in the diffuser were proportional to the operating pressure to the 0.8 and −1.7 power, respectively. In addition, in the second throat region after separation, the heat flux could be scaled to the Mach number ratio before and after the largest oblique shock wave because the largest shock train affected the heat flux of the diffuser wall.

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