Investigation of Transient Flow and Heat Transfer for Passive Nuclear Reactor Direct Safety Injection

2017 ◽  
Author(s):  
Yu Weng ◽  
Lang Liu ◽  
Yang Jiang ◽  
Hongfang Gu ◽  
Haijun Wang
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Pressure Vessel ◽  
Transient Flow ◽  
Reactor Vessel ◽  
Transient Processes ◽  
Continuous Change ◽  
Pressurized Water ◽  
Injection Flow ◽  
Flow And Heat Transfer

This paper describes a transient flow and heat transfer characteristics for a 1400MW passive pressurized-water reactor (PWR) direct vessel injection (DVI) system in different accident transient processes. The study components include reactor pressure vessel and a series reactor internal such as core barrel and radiation surveillance capsules, the flow channel include downcomer and lower plenum. Furthermore, the inject device is designed with special structures: first, a venturi type tube nozzle is connected to pressure vessel, second, a flow deflector is arranged in the downcomer which is facing the nozzle. This special structures will make the flow mixing and heat transfer very complicate and hard to predict. This study considers characteristics of the loops temperature and flow rate for both injection loop and reactor cold leg loop which are continuous change and long duration. Computational fluid dynamics (CFD) method is used in this study. Before this study, the physical model and numerical method are verified by an independent scaled model experiment. In this real reactor scale study, two typical accident transient processes are analyzed in this study, and temperature distribution on both reactor vessel and reactor internals are obtained. According to results analysis, the characteristics of heat distribution in downcomer were obtained: The injection fluid which is supposed to flow to core barrel is driven to the side of reactor vessel by the reflector. With the injection fluid flows in downcomer, the injection flow shape comes to a triangle. In addition, the transient results show that correlation degree of temperature distribution and injection flow character is gradually decreased with the increase of time history for passive injection. Overall, the exercise complements the activities in reactor safety analysis areas in understanding the origins of thermal load in reactor vessel, and being able to quantify them. Results of this study can be directly used by analyzing of reactor fatigue mechanics. (CSPE)

Mathematical Modeling of Transient Flow and Heat Transfer in Gas Stirred Molten Steel

2001 ◽  
Author(s):  
J. L. Xia ◽  
T. Ahokainen
Keyword(s):  
Heat Transfer ◽  
Molten Steel ◽  
Thermal Stratification ◽  
Transient Flow ◽  
Liquid Interface ◽  
Turbulent Dispersion ◽  
Steel Ladle ◽  
Bubble Liquid ◽  
Flow And Heat Transfer ◽  
Heat Transfer Correlations

Abstract Transient two phase flow and heat transfer in a gas-stirred steel ladle are numerically investigated. An Eulerian two fluid approach is used. The drag, lift and turbulent dispersion forces are taken into account for the interface interactions. Different interface heat transfer correlations such as Ranz-Marshall and Hughmark relations are used to examine the influence of heat transfer between gas-liquid interface on the flow. The flow pattern, the histories of both gas and molten steel temperatures, and the thermal stratification history are presented. Results show that gas injection can homogenize thermal field and result in a thermal stratification of about 2 °C only (not complete homogenization). The different heat transfer correlations examined for the bubble-liquid interface have negligible impact on the flow and thermal fields. Predictions are compared with experimental data measured in an industrial ladle and a reasonable agreement is achieved.

Heat transfer enhancement in microchannels using ribs and secondary flows

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Karthikeyan Paramanandam ◽  
Venkatachalapathy S. ◽  
Balamurugan Srinivasan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Study on the Influence of Safety Injection Rate on the Process of SBLOCA

2013 ◽  
Author(s):  
He Hui ◽  
Liang-ming Pan
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Pressure Vessel ◽  
Nuclear Reactor ◽  
Injection Rate ◽  
Relief Valve ◽  
Flow And Heat Transfer ◽  
Long Time ◽  
Nuclear Reactor Safety ◽  
Relap5 Code

After the nuclear accident of TMI-2, more and more researchers devote to the researches of SBLOCA. It is almost impossible for the large break LOCA depending on the probability of the accident during the reactor life cycle. But it is possible for SBLOCA, such as opening a relief valve for a long time. After reactor shutdown, reactor takes the form of directly safety injection, which has great effects on the flow and heat transfer of the reactor pressure vessel and it has influence on the process of the SBLOCA finally. In present work, an SBLOCA analytical model has been developed with RELAP5 code to analyze special design features at SBLOCA accident. The results are compared with the calculations from Westinghouse NOTRUMP code. This analytical model has also used to analyze the effects of different safety injection rate on the process of accident. The transient variation about some key parameters have been obtained. e.g. the temperature, pressure variations of core, void fraction of core. The results show that the rate of safety injection has significant influence on the process of SBLOCA and the characteristics about the heat transfer of pressure vessel. Different safety injection rates influence the nuclear reactor safety differently.

Flow and Heat Transfer Characteristics of a Novel Heat Exchanger

2013 ◽  
Author(s):  
Haolin Ma ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Transient Flow ◽  
Ansys Fluent ◽  
Tube Heat Exchanger ◽  
Flow And Heat Transfer ◽  
Narrow Slot ◽  
Slot Size ◽  
Tube Type

Computational fluid dynamics and heat transfer simulations are conducted for a novel shell-tube type heat exchanger. The heat exchanger consists of tube with a narrow slot oriented in the streamwise direction. Numerical simulations are conducted for the Reynolds number of 1500. The 3D turbulent flow in the tube bank region is modeled by k-ε Reynolds stress averaging method by employing ANSYS FLUENT. 3-D transient flow and heat transfer simulations are conducted to determine the flow structure and temperature profiles in the wake of cylinders in the first row and other rows. The effects of the slot size and the orientation and the arrangement of the cylinder in different configuration will be examined. The slotted tube heat exchanger improved heat transfer by more than 27% compare to the traditional shell-tube heat exchanger without slots. Enhancement in heat transfer is even higher at higher values of Reynolds number.

Flow and Heat Transfer Analysis of an Electro-Osmotic Flow Micropump for Chip Cooling

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
K. Pramod ◽  
A. K. Sen
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Analytical Model ◽  
Flow Rate ◽  
Maximum Flow ◽  
Back Pressure ◽  
Design Parameters ◽  
Chip Cooling ◽  
Flow And Heat Transfer ◽  
Electro Osmotic Flow

This paper reports theoretical and numerical analysis of fluid flow and heat transfer in a cascade electro-osmotic flow (EOF) micropump for chip cooling. A simple analytical model is developed to determine the temperature distribution in a two-dimensional (2D) single channel EOF micropump with forced convection due to a voltage difference between both ends. Numerical simulations are performed to determine the temperature distribution in the domain which is compared with that predicted by the model. A novel cascade EOF micropump with multiple microchannels in series and parallel and with an array of interdigitated electrodes along the flow direction is proposed. The simulations predict the maximum flow rate and pressure capability of one single stage of the micropump and the analytical model employs equivalent circuit theory to predict the total flow rate and back pressure. Each stage of the proposed micropump comprises sump and pump regions having opposing electric field directions. The various design parameters of the micropump includes the height of the pump and sump (h), number of stages (n), channel width (w), thickness of the channel wall or fin (r), and width ratio of the pump and sump (s:p) regions. Numerical simulations are performed to predict the effects of these design parameters on the pump performance which is compared with that predicted by the analytical model. The micropump is used for cooling cooling of an Intel® CoreTM i5 chip which produces a maximum heat of 95 W over an area of 3.75 × 3.75 cm. Based on the parametric studies a design for the cascade EOF micropump is proposed which provides a maximum flow rate of 14.16 ml/min and a maximum back pressure of 572.5 Pa to maintain a maximum chip temperature of 310.63 K.

In-Cylinder Heat Transfer Model for Diesel Engine Based on Improved Woschni Correlation

2014 ◽  
Vol 538 ◽  
pp. 175-178
Author(s):  
Xiao Ri Liu ◽  
Guo Xiang Li ◽  
Yu Ping Hu ◽  
Shu Zhan Bai ◽  
Kang Yao Deng
Keyword(s):  
Heat Transfer ◽  
Cfd Simulation ◽  
Transient Flow ◽  
Three Dimensional ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Three Dimension ◽  
Characteristic Parameters ◽  
Flow And Heat Transfer ◽  
Dimension Characteristic

Based on the Woschni correlation, a three dimensional in-cylinder heat transfer model is proposed, which develops Woschni correlation from zero dimension to three dimension. Characteristic parameters are proposed as transient flow and heat transfer parameters from in-cylinder CFD simulation, with further consideration of the influence of thermal conductivity, viscosity and Prandtl number. According to test data, the new correlation can be regressed. The new model costs little more calculation time, and it can satisfy the engineering demand.

Advanced Computational Modeling of Multiphase Boiling Flow and Heat Transfer

2010 ◽  
Author(s):  
Huiying Li ◽  
Sergio A. Vasquez ◽  
Peter Spicka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Volume Fraction ◽  
Nucleate Boiling ◽  
General Purpose ◽  
Phase Changes ◽  
Pressurized Water ◽  
Flow And Heat Transfer ◽  
Boiling Flow

Numerical simulation of boiling flow and heat transfer presents a number of unique challenges in both theoretical modeling and developing robust numerical methodology. The major difficulty arises due to the heat transfer and phase changes between heated walls and fluid (liquid and vapor). Furthermore, modeling of the liquid-vapor interfacial transfers of momentum, heat and mass proves to be equally challenging. The multiphase boiling modeling approach described in this paper has been found to be capable of addressing these issues and is therefore suitable for inclusion in an advanced general purpose CFD solver. In the present approach, boiling flows are modeled within the framework of the Eulerian multifluid model. The governing equations solved are phase continuity, momentum and energy equations. Turbulence effects can be accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic RPI model for nucleate boiling, and its extensions to non-equilibrium boiling and critical heat flux regime. A range of sub-models are considered to account for the interfacial momentum, mass and heat transfer, and flow regime transitions. An advanced numerical scheme has been developed for solving the model equations which can handle the heat partition between heated walls and fluid, provide for wall and interfacial mass transfer source terms in phase volume fraction equations, and address the coupling between the phase change rates and the pressure correction equation. The wall boiling models and numerical algorithm have been implemented in an advanced, general-purpose CFD code, FLUENT. Validations have been carried out for a range of 2D and 3D boiling flows, including pressurized water through a vertical pipe with heated walls, R-113 liquid in a vertical annulus with internal heated walls, a 3D BRW core channel geometry with vertical heated rods, and water in a vertical circular pipe under critical heat flux and post dry-out conditions. The results demonstrate that the wall boiling models are able to correctly predict the wall temperature and vapor volume fraction distribution. The predictions in all the cases are in reasonable good agreement with available experiments. Tests also indicate that the present implementation is fast and robust, as compared to previous approaches. All the cases are able to be simulated with the use of the FLUENT steady-state multiphase solver with reasonable numbers of iterations.

scholarly journals 3-D Conjugate Flow and Heat Transfer Calculations of a Film-Cooled Turbine Guide Vane at Different Operation Conditions

1997 ◽  
Author(s):  
Dieter E. Bohn ◽  
Volker J. Becker ◽  
Karsten A. Kusterer
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Leading Edge ◽  
Equilibrium Temperature ◽  
Flow And Heat Transfer ◽  
Cooling Method ◽  
Thermal Investigations ◽  
Transfer Method ◽  
Cooling Air ◽  
Operating Points

Film-cooling has become a widely used cooling method in present day gas turbines. Cooling gas ejection at the leading edge serves to protect the entire vane surface from contact with the hot gas. Thus, material temperatures must be reduced in order to guarantee an economically acceptable life span of the vane. Normally, thermal investigations are performed with frozen equilibrium temperature distributions for different operating points. Thus, the heat transfer interaction between the flow and the solid body is neglected. This influence is taken into account by a conjugate fluid flow and heat transfer method in the investigations to be presented. In the case of the aerodynamics, a solver for the 3-D full Navier-Stokes equations is employed. The numerical scheme works on the basis of an implicit finite volume method combined with a multi-block technique. In the 3-D numerical experiment to be presented, the influence of leading edge cooling gas ejection on the temperature distribution to the vane material is investigated. The cooling air is ejected through two slots at the leading edge. 3-D aerodynamic investigations performed by Bohn et al. (1996a) have shown the influence of complex 3-D flow phenomena, e.g. secondary flow, on the distribution of the cooling air along the vane surface. Furthermore, 3-D thermal investigations for one operation point with a realistic temperature ratio of cooling air flow and main flow were presented by Bohn et al. (1996b). The investigations were performed for three different flow angles in the non-ejection case and the film-cooled case in order to demonstrate the operation of the cooling method. The shift of the stagnation line significantly influences the cooling fluid distribution along the vane surface, something that has consequences for the thermal load of the vane. Furthermore, the results are compared to an investigation with a prescribed frozen equilibrium temperature distribution. It is shown that the vane temperature increases locally for over 10 K at different operating points. This increase is significant for the thermal design process and can only be detected using the conjugate fluid flow and heat transfer method.

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