Further Details of a Numerical Analysis on the Thermal Hydraulic Effect of Wrapped Wire Spacers in Fuel Bundle

2020 ◽  
Vol 6 (3) ◽  
Author(s):  
Attila Kiss ◽  
Bence Mervay
Keyword(s):  
Heat Transfer ◽  
Fuel Assembly ◽  
High Performance ◽  
Transverse Velocity ◽  
Axial Direction ◽  
Optimal Choice ◽  
Strong Mixing ◽  
Fuel Rods ◽  
Ongoing Research ◽  
Fuel Bundle

Abstract The application of relatively simple and cheap wrapped wire spacer in the European supercritical water-cooled reactor (SCWR) (high-performance light water reactor (HPLWR)) has been proposed in order to provide enhanced heat transfer in the fuel assembly without unacceptable penalty in pressure loss. The wires cause twisting flow in the fuel assembly, which means the coolant not only flows straight in the axial direction but also has a significant transverse velocity component, and strong mixing between neighboring subchannels occurs. The aim of this ongoing research is to numerically investigate the effect of wrapped wire spacers on thermal hydraulics of the turbulent coolant flow and its heat transfer in a small bundle of four fuel rods. One bare and six-wired geometries with varying wire pitches (1–6 turn(s) of wires) have been studied. It was found that the wires generate significant amount of transverse velocity, decrease the wall temperature, and increase the heat transfer coefficient mostly in corner subchannels which were the hottest in bare geometry. Thus, the presence of wires enhances heat transfer where it is most needed. Temperature hot spots with moderate values have been identified on the cladding wall of fuel rods. Based on the results, a technically optimal choice of number of wire turns from thermal hydraulic sense has been proposed.

2D Natural Convection and Radiation Heat Transfer Simulations of a PWR Fuel Assembly Within a Constant Temperature Support Structure

2006 ◽  
Author(s):  
Pablo E. Araya Go´mez ◽  
Miles Greiner
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fuel Assembly ◽  
Heat Generation ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Radiation Heat Transfer ◽  
Radiation Heat ◽  
Fuel Rods ◽  
Water Reactor

Two-dimensional simulations of steady natural convection and radiation heat transfer for a 14×14 pressurized water reactor (PWR) spent nuclear fuel assembly within a square basket tube of a typical transport package were conducted using a commercial computational fluid dynamics package. The assembly is composed of 176 heat generating fuel rods and 5 larger guide tubes. The maximum cladding temperature was determined for a range of assembly heat generation rates and uniform basket wall temperatures, with both helium and nitrogen backfill gases. The results are compared with those from earlier simulations of a 7×7 boiling water reactor (BWR). Natural convection/radiation simulations exhibited measurably lower cladding temperatures only when nitrogen is the backfill gas and the wall temperature is below 100°C. The reduction in temperature is larger for the PWR assembly than it was for the BWR. For nitrogen backfill, a ten percent increase in the cladding emissivity (whose value is not well characterized) causes a 4.7% reduction in the maximum cladding to wall temperature difference in the PWR, compared to 4.3% in the BWR at a basket wall temperature of 400°C. Helium backfill exhibits reductions of 2.8% and 3.1% for PWR and BWR respectively. Simulations were performed in which each guide tube was replaced with four heat generating fuel rods, to give a homogeneous array. They show that the maximum cladding to wall temperature difference versus total heat generation within the assembly is not sensitive to this geometric variation.

Numerical Analysis of the Flow and Heat Transfer in the Sub-Channel of Supercritical Water Reactor

2013 ◽  
Author(s):  
Ajoy Debbarma ◽  
K. M. Pandey
Keyword(s):  
Heat Transfer ◽  
Fuel Assembly ◽  
Supercritical Water ◽  
High Performance ◽  
Flow Distribution ◽  
Diameter Ratio ◽  
Light Water Reactor ◽  
Water Reactor ◽  
Fuel Rod ◽  
Gap Width

Research activities are ongoing for High performance light water reactor (HPLWR) with square double rows fuel assembly to develop nuclear power plants with the purpose to achieve a high thermal efficiency and to improve their economical competitiveness. However, there is still a big deficiency in understanding and prediction of heat transfer in supercritical fluids. This paper evaluates three-dimensional turbulent flow and convective heat transfer in a single-phase and steady-state sub-channel of HPLWR by using general computational fluid dynamics code, Ansys 14 Fluent. The major concern using supercritical water as work fluid is the heat transfer characteristics due to large variations of thermal properties of supercritical water near pseudo-critical line. In order to ensure the safety of operation in High performance light water reactor (HPLWR), heat transfer deterioration (HTD) must be avoided. Numerical results prove that the RNG k-e model with the enhanced near-wall treatment obtained the most satisfactory prediction and lead to satisfactory simulation results. The HPLWR Square fuel assembly has many square-shaped water rods, Out of four types of sub-channels; three sub-channels SC-1, SC-2 and SC-3 are investigated (adjacent to the side of the moderator flow channels (SC-1) (moderator tube and assembly gap), central sub-channels formed by four fuel rods (SC-2), adjacent to the corner of the moderator tube (SC-3). Since coolant flow distribution in the fuel assembly strongly depends on the gap width between the fuel rod and water rod, fuel rod pitch to diameter ratio 1.1–1.4 with 8mm diameter are considered for simulation. Sub-channel analysis clarifies that coolant flow distribution becomes uniform when the gap width is set to 1.0 mm. was less than 620°C. Effects of various parameters, such as boundary conditions and pitch-to-diameter ratios, on the mixing phenomenon in sub-channels and heat transfer are investigated. The effect of pitch-to-diameter ratio (P/D) on the distributions of surface temperature and heat transfer coefficient (HTC) in a sub-channel, it was found that HTC increases with P/D 1.1 first and then decreases with increasing P/D ratio. Apart from the basic geometry sub-channel, a square sub-channel with a wire-wrapped rod inside has been chosen to investigate the “wire effect”.

Analysis of Heat Transfer Characteristics of Canadian SCWR Fuel Assembly Concept

2020 ◽  
Vol 6 (3) ◽  
Author(s):  
A. Nava Domínguez ◽  
Y. F. Rao ◽  
T. Beuthe
Keyword(s):  
Heat Transfer ◽  
Fuel Assembly ◽  
Heat Loss ◽  
Pressure Tube ◽  
Flow Tube ◽  
Code Model ◽  
Fuel Bundle ◽  
Tube Type ◽  
Gen Iv ◽  
Central Flow

Abstract Canada is participating in the Generation IV (Gen IV) International Forum with a main focus on the pressure-tube-type supercritical water-cooled reactor (SCWR) concept. The subchannel code ASSERT-PV modified for SCWR applications was used to design the SCWR fuel assembly, specifically the fuel bundle. Several assumptions were required to model the fuel assembly, including the perfect insulation of (i) the central flow tube (i.e., no heat transfer through the central tube) and (ii) the pressure tube (i.e., no heat loss to the moderator). These two assumptions were considered as conservative, but they were not analyzed or assessed for their validity or accuracy. ASSERT-PV was upgraded to model the heat loss to the moderator, and an external CATHENA system code model was coupled to ASSERT-PV to model the heat transfer to the central flow tube. This paper describes these additional heat transfer components, and presents an assessment of these two assumptions for their impact on the prediction of maximum fuel cladding temperature.

The Research on Scale of Cluster Fuel Assembly Spacer Grids

2010 ◽  
Author(s):  
Jie Chen ◽  
Bingde Chen ◽  
Hong Zhang
Keyword(s):  
Heat Transfer ◽  
Fuel Assembly ◽  
Cfd Simulation ◽  
Flow Instability ◽  
Flow Direction ◽  
Boundary Effect ◽  
Fuel Rods ◽  
Spacer Grids ◽  
Flow And Heat Transfer ◽  
Cfd Method

The existence of boundary walls will impact flow and heat transfer to some extent. The boundary walls decrease the lateral velocities and change the flow direction to form some eddies, so the flow instability increases. Besides, they stop the mass transfer between the inner areas and outside. For the spacer grids of cluster fuel assembly, in order to confirm the scale of simulation object or experiment noumenon, the first thing is to research the influence depth of boundary effect, and try to eliminate its influence to the concerned object or area. This paper is focused on the spacer grids of 7×7 scale, 5×5 scale and 3×3 scale, respectively. Computed with CFD method, the lateral velocities of corner areas and typical subchannels are compared. And then, the influence depth of boundary effect is confirmed as the distance of a range of fuel rods. Therefore, for the concerned subchannel of CFD simulation, there must be no less than a range of fuel rods in the periphery to mitigate, so the result is not affected by the boundary effect.

Methodology of Fluid Flow Evaluation in the Lower Core and in Fuel Assembly Legs of a PWR With Code_Saturne

2007 ◽  
Author(s):  
Christelle Le Maiˆtre-Vurpillot ◽  
Yvan Fournier
Keyword(s):  
Fluid Flow ◽  
Fuel Assembly ◽  
Transverse Velocity ◽  
Local Scale ◽  
Nozzle Geometry ◽  
Major Influence ◽  
Practical Reasons ◽  
Spacer Grid ◽  
Fuel Rods ◽  
Fuel Rod

In order to better understand the stresses to which fuel rods are subjected, we need to improve our knowledge of the fluid flow inside the core and the fuel assembly, and we are particularly interested in the first spacer grid region, as fuel rod fretting has sometimes been observed. It has been seen experimentally in previous years that rotating mixing grids on EDF’s lock-up (a fuel assembly section subjected to fluid flow, with 2 spacer grid and 2 mixing grids) could let to different vibration levels with some fuel assembly types. This seems to confirm that the influence of fluid flow is of primary importance for fuel rod vibration (and thus fretting). A series of calculations are thus run with our incompressible Navier-Stockes solver, Code_Saturne with a classical RANS turbulence model. We limit to a scale of few assemblies for practical reasons. At this scale, most of the features of the fuel rods, nozzles, and guides tubes are represented, though the geometry of the spacer grids is still much simplified, and details such as debris-trapping grids are ignored. We have analysed the axial and transverse velocities for configuration with different fuel assembly types, and calculated an approximation of efforts on individual fuel rods. Local scale results are mainly qualitative, but they already enable us to obtain a better understanding of the effect of nozzle shape or heterogeneous fuel assemblies on the fluid flow. The nozzle geometry (and fuel rod cap positions) have a major influence on the levels of transverse velocity attained. We have run a good number of sensitivity verifications and built a solid methodology, when defining these calculations. To better validate local scale calculations, EDF R&D has built a small lower fuel rod assembly mock-up “BORA 3×7” (3×3 assemblies with 7×7 rods each). This mock-up is being used to obtain the velocity data. The calculations described in this paper are not refined enough to be able to directly correlate fluid flow and fuel cladding fretting in a quantitative manner, but are a step in this direction and may already improve our understanding of the local loads and spatial load variations a fuel assembly is subjected to.

Enhancement of Heat Transfer in a Short Rectangular Channel with Substantial Deflection of Inlet Velocity from Axial Direction

2005 ◽  
Vol 36 (4) ◽  
pp. 311-318 ◽  
Author(s):  
R. Bunker ◽  
M. YA. Belen'kii ◽  
M. A. Gotovskii ◽  
B. S. Fokin ◽  
S. A. Isaev
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Axial Direction ◽  
Enhancement Of Heat Transfer ◽  
Inlet Velocity

APPLICATIONS OF NUMERICAL FLOW MODELLING TO HIGH-PERFORMANCE HEAT TRANSFER SURFACES

1998 ◽  
Author(s):  
Keith N. Atkinson ◽  
Radenko Drakulic ◽  
Morgan R. Heikal ◽  
Christopher A. McNab
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Flow Modelling

scholarly journals Numerical Evaluation of a HVAC System Based on a High-Performance Heat Transfer Fluid

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3298
Author(s):  
Gianpiero Colangelo ◽  
Brenda Raho ◽  
Marco Milanese ◽  
Arturo de Risi
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Cooling System ◽  
Electrical Energy ◽  
Simulation Software ◽  
Heat Transfer Fluid ◽  
Hvac System ◽  
Dynamic Simulations ◽  
Heating And Cooling ◽  
The University

Nanofluids have great potential to improve the heat transfer properties of liquids, as demonstrated by recent studies. This paper presents a novel idea of utilizing nanofluid. It analyzes the performance of a HVAC (Heating Ventilation Air Conditioning) system using a high-performance heat transfer fluid (water-glycol nanofluid with nanoparticles of Al2O3), in the university campus of Lecce, Italy. The work describes the dynamic model of the building and its heating and cooling system, realized through the simulation software TRNSYS 17. The use of heat transfer fluid inseminated by nanoparticles in a real HVAC system is an innovative application that is difficult to find in the scientific literature so far. This work focuses on comparing the efficiency of the system working with a traditional water-glycol mixture with the same system that uses Al2O3-nanofluid. The results obtained by means of the dynamic simulations have confirmed what theoretically assumed, indicating the working conditions of the HVAC system that lead to lower operating costs and higher COP and EER, guaranteeing the optimal conditions of thermo-hygrometric comfort inside the building. Finally, the results showed that the use of a nanofluid based on water-glycol mixture and alumina increases the efficiency about 10% and at the same time reduces the electrical energy consumption of the HVAC system.

The Infrared Characteristics of the Wall Temperature of Boiling Heat Transfer in Microchannel

2011 ◽  
Vol 383-390 ◽  
pp. 811-815
Author(s):  
Hu Gen Ma ◽  
Jian Mei Bai ◽  
Rong Jian Xie ◽  
Wen Jing Tu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Boiling Heat Transfer ◽  
Transfer Test ◽  
Axial Direction ◽  
Transfer Model ◽  
Micro Channel ◽  
Vapor Quality ◽  
Test Rig

In this paper, the boiling heat transfer test rig was designed and built, while the characteristics of boiling Heat Transfer of refrigerants in micro-channel was researched. The wall temperature of micro-channel was measured by TH5104 Infrared thermography. The results showed that there were obvious variations for wall temperature of micro-channel along the axial direction when boiling heat transfer occurred in the micro-channel. The temperature distribution affected obviously by the heat flux, mass flow rate; vapor quality and heat transfer model.

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