... Auteur(s) / Author(s). ARAYA Pablo E. (1) ; GREINER Miles (1) ; Affiliation(s) du ou des aute... more ... Auteur(s) / Author(s). ARAYA Pablo E. (1) ; GREINER Miles (1) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) University of Nevada, Reno Mechanical Engineering Department, Mail Stop 312, Reno, Nevada 89557, ETATS-UNIS Résumé / Abstract. ...
Volume 7: Operations, Applications and Components, 2008
... RAREFIED GAS Pablo E. Araya Research Assistant University of Nevada, Reno Mechanical Engineer... more ... RAREFIED GAS Pablo E. Araya Research Assistant University of Nevada, Reno Mechanical Engineering Department Mail Stop 312, Reno 89557 Phone: 775-784-7575 Email: [email protected] Miles Greiner Professor ...
Volume 7: Operations, Applications and Components, 2007
The current work is a scoping study to determine which heat transfer effects are significant in t... more The current work is a scoping study to determine which heat transfer effects are significant in the fuel/backfill gas region of spent nuclear fuel transport casks.
International Journal of Heat and Mass Transfer, 2009
The enhancement characteristics of heat transfer, through a transition scenario of flow bifurcati... more The enhancement characteristics of heat transfer, through a transition scenario of flow bifurcations, in asymmetric wavy wall channels, are investigated by direct numerical simulations of the mass, momentum and energy equations, using the spectral element method. The heat transfer characteristics, flow bifurcation and transition scenarios are determined by increasing the Reynolds numbers for three geometrical aspect ratios r = 0.25, 0.375, and 0.5, and Prandtl numbers 1.0 and 9.4. The transition scenarios to transitional flow regimes depend on the aspect ratio. For the aspect ratios r = 0.25 and 0.5, the transition scenario is characterized by one Hopf flow bifurcation. For the aspect ratio r = 0.375, the transition scenario is characterized by a first Hopf flow bifurcation from a laminar to a periodic flow, and a second Hopf flow bifurcation from a periodic to quasi-periodic flow. The periodic and quasi-periodic flows are characterized by fundamental frequencies x 1 , and x 1 and x 2 , respectively. For all the aspect ratios and Prandtl numbers, the time-average mean Nusselt number and heat transfer enhancement increases with the Reynolds number as the flow evolves from a laminar to a transitional regime. For both Prandtl numbers, the highest increase in the Nusselt number occurs for the aspect ratio r = 0.5; whereas, the lowest increases happen to r = 0.25. The increase of the Nusselt number occurs at the expense of a higher pumping power, which, for both Prandtl numbers, grows as the aspect ratio increases from r = 0.25 to r = 0.5 for reaching a specific Nusselt number. This enhancement is obtained without the necessity of high volumetric flow rates associated with turbulent flow regimes, which demand much higher pumping powers. Significant heat transfer enhancements are obtained when the asymmetric wavy channel is operated in the appropriate transitional Reynolds number range.
In the current work, numerical simulations and experiments of an 8×8 square array of heater rods ... more In the current work, numerical simulations and experiments of an 8×8 square array of heater rods within an aluminum enclosure have been performed. This geometry represents the region inside the channel of a boiling water reactor (BWR) fuel assembly between two consecutive spacer plates. The simulation model and the experimental apparatus can be oriented horizontally or vertically, to represent transport or storage configurations. The interior void is filled with air at ambient pressure conditions. All rods dissipate at the same heating rate. In the experiment, this is controlled using a variable power supply. The temperatures are measured in the experiment by thermocouples that are placed within the enclosure walls, on the endplates, and in 31 of the 64 heater rods at their axial mid-planes. The three-dimensional computational fluid dynamics (CFD) model is based on the dimensions of experimental apparatus. Natural convection/radiation simulations are performed using the Fluent package at the same average wall temperatures and rates of heat generation measured from the experiment. Simulation results of rod temperatures are compared to experimental results to assess the accuracy of the threedimensional computational fluid dynamics (CFD) simulations. Simulation results show good agreement with measured temperatures. Average simulated rod temperatures are lower than measured data by up to 1.2% in horizontal orientation and higher than measured by up to 1.3% in vertical orientation.
... Auteur(s) / Author(s). ARAYA Pablo E. (1) ; GREINER Miles (1) ; Affiliation(s) du ou des aute... more ... Auteur(s) / Author(s). ARAYA Pablo E. (1) ; GREINER Miles (1) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) University of Nevada, Reno Mechanical Engineering Department, Mail Stop 312, Reno, Nevada 89557, ETATS-UNIS Résumé / Abstract. ...
Volume 7: Operations, Applications and Components, 2008
... RAREFIED GAS Pablo E. Araya Research Assistant University of Nevada, Reno Mechanical Engineer... more ... RAREFIED GAS Pablo E. Araya Research Assistant University of Nevada, Reno Mechanical Engineering Department Mail Stop 312, Reno 89557 Phone: 775-784-7575 Email: [email protected] Miles Greiner Professor ...
Volume 7: Operations, Applications and Components, 2007
The current work is a scoping study to determine which heat transfer effects are significant in t... more The current work is a scoping study to determine which heat transfer effects are significant in the fuel/backfill gas region of spent nuclear fuel transport casks.
International Journal of Heat and Mass Transfer, 2009
The enhancement characteristics of heat transfer, through a transition scenario of flow bifurcati... more The enhancement characteristics of heat transfer, through a transition scenario of flow bifurcations, in asymmetric wavy wall channels, are investigated by direct numerical simulations of the mass, momentum and energy equations, using the spectral element method. The heat transfer characteristics, flow bifurcation and transition scenarios are determined by increasing the Reynolds numbers for three geometrical aspect ratios r = 0.25, 0.375, and 0.5, and Prandtl numbers 1.0 and 9.4. The transition scenarios to transitional flow regimes depend on the aspect ratio. For the aspect ratios r = 0.25 and 0.5, the transition scenario is characterized by one Hopf flow bifurcation. For the aspect ratio r = 0.375, the transition scenario is characterized by a first Hopf flow bifurcation from a laminar to a periodic flow, and a second Hopf flow bifurcation from a periodic to quasi-periodic flow. The periodic and quasi-periodic flows are characterized by fundamental frequencies x 1 , and x 1 and x 2 , respectively. For all the aspect ratios and Prandtl numbers, the time-average mean Nusselt number and heat transfer enhancement increases with the Reynolds number as the flow evolves from a laminar to a transitional regime. For both Prandtl numbers, the highest increase in the Nusselt number occurs for the aspect ratio r = 0.5; whereas, the lowest increases happen to r = 0.25. The increase of the Nusselt number occurs at the expense of a higher pumping power, which, for both Prandtl numbers, grows as the aspect ratio increases from r = 0.25 to r = 0.5 for reaching a specific Nusselt number. This enhancement is obtained without the necessity of high volumetric flow rates associated with turbulent flow regimes, which demand much higher pumping powers. Significant heat transfer enhancements are obtained when the asymmetric wavy channel is operated in the appropriate transitional Reynolds number range.
In the current work, numerical simulations and experiments of an 8×8 square array of heater rods ... more In the current work, numerical simulations and experiments of an 8×8 square array of heater rods within an aluminum enclosure have been performed. This geometry represents the region inside the channel of a boiling water reactor (BWR) fuel assembly between two consecutive spacer plates. The simulation model and the experimental apparatus can be oriented horizontally or vertically, to represent transport or storage configurations. The interior void is filled with air at ambient pressure conditions. All rods dissipate at the same heating rate. In the experiment, this is controlled using a variable power supply. The temperatures are measured in the experiment by thermocouples that are placed within the enclosure walls, on the endplates, and in 31 of the 64 heater rods at their axial mid-planes. The three-dimensional computational fluid dynamics (CFD) model is based on the dimensions of experimental apparatus. Natural convection/radiation simulations are performed using the Fluent package at the same average wall temperatures and rates of heat generation measured from the experiment. Simulation results of rod temperatures are compared to experimental results to assess the accuracy of the threedimensional computational fluid dynamics (CFD) simulations. Simulation results show good agreement with measured temperatures. Average simulated rod temperatures are lower than measured data by up to 1.2% in horizontal orientation and higher than measured by up to 1.3% in vertical orientation.
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