Temperature Measurement of an Array of Heated Rods Subjected to Vacuum Drying Conditions

2017 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Temperature Jump ◽  
Maximum Temperature ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Used Nuclear Fuel ◽  
Experimental Apparatus ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Drying Conditions ◽  
Low Pressures

During vacuum drying of used nuclear fuel canister, helium pressure is decreased to as low as 67 Pa to promote evaporation and removal of water remaining in the canister following draining operation. At low pressures associated with vacuum drying, there is a temperature jump (thermal resistance) between the solid surfaces and helium in contact with them. This temperature jump increases as the pressure decreases (rarefied condition), which contributes to the fuel assembly’s temperature increase. It is important to keep the temperature of the fuel assemblies below 400°C during vacuum drying to ensure their safety for transport and storage. In this work, an experimental apparatus consisting of a 7×7 array of electrically heated rods maintained between two spacer plates and enclosed inside a square cross-section stainless steel pressure vessel is constructed to evaluate the temperature of the heater rods at different pressures. This geometry is relevant to a BWR fuel assembly between two consecutive spacer plates. Thermocouples are installed in each of the 49 heater rods, spacer plates and enclosure walls. They provide a complete temperature profile of the experiment. Different pressures and heat generation relevant to vacuum drying conditions are tested. The results showed that the maximum temperature of the heater rods increases as the pressure decreases. The results from these experiments will be compared to computational fluid dynamics simulations in a separate work.

Temperature Jump Measurement at Stainless Steel and Helium Interface: Application to Used Nuclear Fuel Vacuum Drying Process

2018 ◽  
Author(s):  
Cody Zampella ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Stainless Steel ◽  
Nuclear Fuel ◽  
Temperature Jump ◽  
Rarefied Gas ◽  
Maximum Temperature ◽  
Vacuum Drying ◽  
Stainless Steel Surface ◽  
Concentric Cylinders ◽  
Experimental Apparatus ◽  
Fuel Assemblies

Vacuum drying of nuclear fuel canisters may cause the temperature of fuel assemblies to considerably increase due to the effect of gas rarefaction at low pressures. This effect may induce a temperature-jump at the gas-solid interfaces. It is important to predict the temperature-jump at these interfaces to accurately estimate the maximum temperature of the fuel assemblies during vacuum drying. The objective of this work is to setup a concentric cylinders experimental apparatus that can acquire data to benchmark rarefied gas heat transfer simulations, and determine the temperature-jump coefficient at the interface between stainless steel surface and helium gas. The temperature-jump is determined by measuring the temperature difference and heat flux across a 2-mm gap between the concentric cylinders that contains rarefied helium and compare the results to analytical calculations in the slip rarefaction regime.

Experimentally Benchmarked Computational Fluid Dynamics Simulations of a 7×7 Array of Heated Rods Within a Square-Cross-Section Enclosure Filled With Rarefied Helium

2017 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cross Section ◽  
Heat Generation ◽  
Maximum Temperature ◽  
Helium Pressure ◽  
Nuclear Fuel Assembly ◽  
Jump Model ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Computational fluid dynamics simulations of a 7×7 array of heated rods within a square-cross-section enclosure filled with rarefied helium are performed for heat generation rates of 50 W and 100 W and various helium pressures ranging from 105 to 50 Pa. The model represents a section of nuclear fuel assembly between two consecutive spacer plates inside a nuclear canister subjected to during vacuum drying process. A temperature jump model is applied at the solid-gas interface to incorporate the effects of gas rarefaction at low pressures. The temperature predictions from simulations are compared to measured temperatures. The results showed that when helium pressure decreased from 105 to 50 Pa, the maximum temperature of the heater rod array increased by about 14 °C. The temperatures of the hottest rod predicted by simulations are within 4°C of the measured values for all pressures. The random difference of simulated rod temperatures from the measured rod temperatures are 3.33 °C and 2.62 °C for 100 W and 50 W heat generation rate.

Temperature Prediction of a TN-32 Used Nuclear Fuel Canister Subjected to Vacuum Drying Conditions

2018 ◽  
Author(s):  
Megan Higley ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Nuclear Fuel ◽  
Heat Generation ◽  
Fluid Dynamic ◽  
Surface Radiation ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Spent Fuel ◽  
Pressurized Water ◽  
Used Nuclear Fuel ◽  
Drying Conditions

In this work, a geometrically-accurate two-dimensional (2D) computational fluid dynamic (CFD) model of a used nuclear fuel cask, that can contain up to 32 pressurized water reactor (PWR) used nuclear fuel (UNF) assemblies, is constructed. This model is similar to the TN-32 cask employed in the ongoing high-burnup (HBU) Spent Fuel Data Project lead by the Electric Power Research Institute (EPRI). This model is used to predict the peak cladding temperature under vacuum drying conditions. Due to the symmetry of the cask, only one-eighth of the cross-section is modeled. Steady-state simulations that include the temperature-jump boundary conditions at the gas-solid interfaces are performed for different heat generation rates in the fuel regions and a range of dry helium pressures, from ∼105 to 100 Pa. These simulations include conduction within solid-gas regions and surface-to-surface radiation across all gas regions. The peak cladding temperatures are reported for various heat generation rates and rarefaction conditions, along with the maximum allowable heat generation that brings the cladding temperatures to the radial hydride formation limit. The results showed that the decrease of helium pressure significantly increased the temperature of the cladding material compared to the atmospheric pressure condition.

Temperature Prediction of a Used Nuclear Fuel Cask With Different Gas Backfills

2020 ◽  
Author(s):  
Megan Higley ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner
Keyword(s):  
Heat Generation ◽  
Temperature Jump ◽  
Generation Rate ◽  
Spent Fuel ◽  
Heat Generation Rate ◽  
Ansys Fluent ◽  
Used Nuclear Fuel ◽  
Computational Fluid Dynamics Cfd ◽  
Project Lead ◽  
Low Pressures

Abstract In this work, a two-dimensional (2D) geometrically-accurate model of the TN-32 cask is generated in ANSYS/Fluent to investigate the effect of backfill gases and their pressures on the peak cladding temperature (PCT). This model is similar to the cask being used in high-burnup (HBU) spent fuel data project lead by the Electric Power Research Institute (EPRI). Helium, nitrogen, argon, and water vapor fill gases are investigated at pressures ranging from atmospheric (∼105 Pa) to 100 Pa. Steady-state computational fluid dynamics (CFD) simulations that include the effect of gas rarefaction (temperature-jump) at the gas-solid interfaces are conducted. The PCT as a function of heat generation rate and pressure is reported as well as the heat generation rate that brings the cladding temperature to the radial hydride formation limit. The results show that there are competing effects between the temperature-jump and the thermal conductivity of the gas to increase the fuel rods’ temperature. The low pressures increased the PCT, with the increase being most significant for the helium backfill.

Experimentally-Benchmarked Computational Fluid Dynamics Simulations of an Array of Heated Rods Within a Square-Cross-Section Helium-Filled Pressure Vessel

2016 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Narayana R. Chalasani ◽  
Miles Greiner
Keyword(s):  
Cross Section ◽  
Heat Generation ◽  
Pressure Vessel ◽  
Radiation Heat Transfer ◽  
Used Nuclear Fuel ◽  
Nuclear Fuel Assembly ◽  
Experimental Apparatus ◽  
Induced Motion ◽  
Dynamics Simulations ◽  
Square Array

An experimental apparatus was constructed, consisting of an 8×8 array of electrically-heated rods held in a square array by stainless-steel spacer plates near their ends. The rod/plate assembly was enclosed within a square-cross-section helium-filled aluminum pressure vessel and the rods were oriented vertically. The apparatus simulates the region between two consecutive spacer plates of a used nuclear fuel assembly within a vertical dry storage canister. Rod, spacer plate, and enclosure wall temperatures were measured using thermocouples in a matrix of nine experiments with total rod heat generation rates of 100, 300, and 500 W, and nominal helium pressures of 1, 2, and 3 atm. Steady-state simulations representing the experiment were performed, which include heat generation within the rods, conduction within the solid elements, as well as buoyancy-induced motion within, and natural convection and radiation heat transfer across, helium-filled regions. These were compared to the experimental results to assess the accuracy of the computational model for a range of boundary conditions. The comparison between the simulated and measured data showed that the simulations systematically under predict the hotter rod temperatures and over predict the cooler ones. Linear regression showed that 95% of the simulated temperatures are within 4.26°C of the correlation values.

scholarly journals Experimental approach for the analysis of the flow behaviour in the stator of a real centripetal turbine

2020 ◽  
pp. 146808742091628 ◽  
Author(s):  
José Galindo ◽  
Andrés Omar Tiseira Izaguirre ◽  
Luis Miguel García-Cuevas ◽  
Natalia Hervás Gómez
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Internal Flow ◽  
Quality Data ◽  
Normal Operation ◽  
Radial Turbine ◽  
Experimental Apparatus ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Very High

During normal operation, radial turbines may work in off-design conditions. Off-design conditions may be characterised by very low expansion ratios, very high expansion ratios, very low rotational speeds or very high rotational speeds. All of these cases are difficult to characterise experimentally due to high experimental uncertainties or a lack of capabilities in the system feeding pressurised air to the turbine. Also, there are two- and three-dimensional computational fluid dynamics simulations at these operating points but could not be accurate enough due to high turbulence effects, flow detachment and shock wave generation. With a lack of high-quality data, experimental or computational, to fit the reduced-order turbine models used in zero- and one-dimensional engine simulations, there are large uncertainties associated to their results in off-design conditions. This work develops an experimental facility able to characterise the internal flow of radial turbine stators in terms of pressure and velocity fields at off-design and regular working conditions. The facility consists of an upscaled model of a radial turbine volute and stator fed with air in pressure- and temperature-controlled conditions, so different sensors can be used inside it with the least amount of flow disturbance. The different restrictions considered in the design of the upscaled model are presented, and their effects in the final experimental apparatus capabilities are discussed. A preliminary comparison between computational fluid dynamics simulations and experimental data shows encouraging results.

Comparison of DSMC and CFD Models of Heat Transfer in a Rarefied Two-Dimensional Geometry

2018 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner ◽  
Stefan K. Stefanov
Keyword(s):  
Heat Transfer ◽  
Rarefied Gas ◽  
Complex Geometry ◽  
Direct Simulation Monte Carlo ◽  
Accurate Method ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Two Dimensional ◽  
Dsmc Method ◽  
Cfd Simulations

During vacuum drying of used nuclear fuel (UNF) canisters, helium pressure is reduced to as low as 67 Pa to promote evaporation and removal of remaining water after draining process. At such low pressure, and considering the dimensions of the system, helium is mildly rarefied, which induces a thermal-resistance temperature-jump at gas–solid interfaces that contributes to the increase of cladding temperature. It is important to maintain the temperature of the cladding below roughly 400 °C to avoid radial hydride formation, which may cause cladding embrittlement during transportation and long-term storage. Direct Simulation Monte Carlo (DSMC) method is an accurate method to predict heat transfer and temperature under rarefied condition. However, it is not convenient for complex geometry like a UNF canister. Computational Fluid Dynamics (CFD) simulations are more convenient to apply but their accuracy for rarefied condition are not well established. This work seeks to validate the use of CFD simulations to model heat transfer through rarefied gas in simple two-dimensional geometry by comparing the results to the more accurate DSMC method. The geometry consists of a circular fuel rod centered inside a square cross-section enclosure filled with rarefied helium. The validated CFD model will be used later to accurately estimate the temperature of an UNF canister subjected to vacuum drying condition.

scholarly journals Aerodynamic analysis of uphill drafting in cycling

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Scientific Literature ◽  
Sensitivity Analyses ◽  
Air Resistance ◽  
Wind Tunnel Measurements ◽  
Aerodynamic Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

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