This article extends in various directions of our previous studies related to gas flow in long rectangular cross-section microchannels. In the present article, the mass flow rate of various gases ...through microchannels with different aspect ratios, and various surface coatings (Au and SiO
2
) and surface roughnesses (from 0.9 to 12 nm) is measured under isothermal conditions. Previously, we developed a method to calculate the mass flow rate through rectangular microchannels that allows taking into account the real dimensions of the rectangular channel cross-section. In the present article, this method was applied to extract the velocity slip and tangential momentum accommodation coefficients in the frame of the Maxwell diffuse-specular scattering kernel. An extension of the previous approach is also proposed in the present paper. This extension allows considering the possible difference in properties (roughness or material) between the vertical and horizontal channel walls by introducing different accommodation coefficients for each wall. By applying the new method, we can extract a single accommodation coefficient for all the channel walls under the assumption of homogeneous material and roughness and two different accommodation coefficients for the horizontal and vertical walls in the case when the two walls have different properties (roughness or material).
•Basket/rail gap width effect on temperature in the TN-32 dry cask is investigated.•Basket thermal expansion and shift under storage and drying conditions are modeled.•Peak cladding temperature is ...sensitive to gap width and vacuum drying pressures.•Basket shifts may be detected through cask outer surface temperature measurements.•Basket/rail gap size must be considered for accurate cask temperature prediction.
This paper investigates the effect of the variation in the gap width between the basket and rails on predicted temperatures in the TN-32 dry storage cask. Two-dimensional (2D) cross-section models of the TN-32 containing thirty-two spent nuclear fuel assemblies generating 30.5 kW of thermal energy are constructed. Storage and vacuum drying pressures, a range of basket/rail gap widths, and shifting of the basket from the cask center, are considered. The simulations include surface-to-surface radiation and gas conduction (including rarefaction), but do not consider natural convection due to the 2D assumption. Results show that the peak cladding temperature, TPC, increases as the gap width increases and as the pressure decreases to vacuum drying (rarefied) levels. As a result, analysis using the nominal unloaded design gap width may overpredict TPC by up to 40 °C under storage conditions and up to 75 °C under vacuum drying conditions. The sensitivity of TPC on pressure is found to decrease as the gap width decreases, and as the basket shifts from the cask center. This paper demonstrates that reducing the uncertainty in the basket/rail gap width by, for example, calculating predictable thermal expansion, and/or statistically quantifying unpredictable manufacturing tolerances and basket shifting, may significantly reduce the uncertainty of peak cladding temperature prediction.
The temperatures of internal components within spent nuclear fuel (SNF) packages must be predicted to ensure they remain within specified limits. These packages have multiple millimeter-scale gaps ...whose widths are affected by predictable and unpredictable factors. The thermal resistance across these gaps is proportional to their width and it is relatively large because the thermal conductivity of the gas within the packages is significantly lower than that of the metal components. Prior numerical research has demonstrated that variations in gap widths can result in peak cladding temperature varying by as much as 68 °C. In this work, a three-dimensional computational fluid dynamics model of the TN-32B SNF package that employs effective fuel region and gap properties is constructed. Forty steady-state simulations are performed for varying widths of nine different gaps within their possible ranges using the Latin Hypercube Sampling method. The best estimate of temperatures and their uncertainties at 63 SNF fuel locations are compared with measurements acquired from the High Burnup Spent Fuel Data project, where other researchers collected temperature data from a TN-32B SNF cask. The results showed that predicted temperatures have 95%-confidence-level interval uncertainties ranging between ±12 °C and ±21 °C due to uncertainties in the gap widths. Most of the measured temperatures, including the peak cladding temperature, are within the confidence intervals of the predicted ones. A proposed linear correlation between the simulated fuel temperatures and gap widths recreated 95% of the simulation results within ±1.6 °C. This correlation highlighted that uncertainty in the width of the Basket/Rail gap near the package periphery accounts for approximately half of the total temperature uncertainty.
•Effects of gap width variations on temperatures in the TN-32 B cask are studied.•A global UQ method based on the LHS technique is used.•Effect of natural convection on temperature results is also investigated.•Cask temperatures varied by ±12 °C to ±22 °C due to variations of the gap widths.•A new linear regression model to predict cask temperature is proposed.
•Experimentally-validated CFD simulations of heated rods within a pressure vessel under rarefaction condition are presented.•The model is similar to a used nuclear fuel within two consecutive spacer ...grids subjected to vacuum drying.•The rarefaction effect causes the heater rods' temperature to increase in the slip regime compared to the continuum regime.•The rarefaction effect has to be taken into account to predict used nuclear fuel temperatures during vacuum drying operation.
A temperature-jump thermal resistance, based on results from Lin & Willis 1979, was implemented at the gas/solid interfaces of a three-dimensional computational fluid dynamics model of a 7 × 7 array of heated rods within a square-cross-section pressure vessel filled with rarefied dry helium. This configuration is relevant to the vacuum drying of used nuclear fuel canisters. Simulations were performed for a range of rod heat generation rates, boundary temperatures, and gas pressures in the continuum and rarefied-gas-slip regimes. Experiments conducted by the current authors were used to measure rod and enclosure temperatures for the same conditions, to validate the simulations. For all measurement locations and experiments, the measured rod-to-boundary temperature differences varied from 12 °C to 102 °C. The simulated differences correlated linearly to the measured differences, closely following variations for different locations and experiments, but exhibited random variations from the best-fit line. In the slip regime, the predicted rod-to-boundary temperature differences were systematically 0.9 °C smaller than the measured values (less than half of the thermocouple uncertainty), and 95% of the simulated differences were less than 2.5 °C from the best-fit line (14% larger than the rod thermocouple uncertainty). The temperature-jump thermal resistance model will be useful for predicting temperatures during vacuum drying operations.
•Experimental data of slip-flow rarefied gas heat transfer in a configuration similar to a used nuclear fuel assembly are presented.•The rarefaction effect causes the temperature of the heater rods ...to considerably increase in the slip regime compared to the continuum regime.•The rarefaction effect has to be taken into account to predict used nuclear fuel temperatures during the vacuum drying operation.•Data presented in this paper are suited for benchmarking computational models of heat transfer at low-pressure conditions.
The goal of this work is to obtain experimental data that can be used to validate computational models that quantify the effect of gas rarefaction on heat transfer during vacuum drying of used nuclear fuel transport/storage canisters. An experimental apparatus is constructed, consisting of a 7 × 7 array of electrically heated rods held by spacer plates near their ends and contained within a square cross-section helium-filled pressure vessel. Thermocouples are used to measure heater rod, spacer plate, and enclosure temperatures for a range of rod heat generation rates, helium pressures in the continuum and rarefied-gas slip regimes, and different thicknesses of insulation outside the enclosure, which increases the apparatus temperatures. The results shows that the temperature difference between the enclosure and the rods increases by less than 4% when the pressure decreases within the continuum regime (from ~ 105 to 5700 Pa). However, it increases by up to 78% in the slip regime (~5700 to 65 Pa), due to the temperature-jump thermal resistance at the gas/solid interfaces. Random variation in the measured temperatures, caused by configuration and measurement errors, is less than 1.1℃, which makes this data well suited for benchmarking computational methods for calculating heat transfer and temperatures in used nuclear fuel canisters under vacuum drying conditions.
Hydrogen (H2) gas stands at the forefront of next-generation energy, offering unparalleled combustion efficiency with minimal carbon emissions. H2 is also an important marker of many H2-related ...physiochemical processes in industries or medical practices (e.g., H2 release in the thermal runaway of lithium-ion battery and the biodegradation of magnesium (Mg) implants in human body). The development of high-performance H2 sensors is paramount for not only ensuring safety across various stages of H2 production, storage, transportation, and utilization, and also monitoring many critical steps in industrial or medical processes. Among the multitude of sensing technologies, chemiresistive sensors, particularly those utilizing noble metals such as Pd and Pt, or metal-oxide-semiconductor (MOS) materials like SnO2 and ZnO, have emerged as promising candidates, because these sensing materials can specifically and sensitively react with H2 to result in their conductivity change allowing for the detection of H2 gas. These materials offer not only exceptional performance metrics, but also cost-effectiveness, compact design, low power consumption, and ease of operation. In our review, for each type of chemiresistive sensors (noble-metal-based or MOS-based), we reviewed the fundamental sensing principles, and then summarized representative strategies that researchers developed in the last few years to improve specific aspects of sensing performance (e.g., sensitivity, selectivity, humidity tolerance, response time, hysteresis, etc.). In the summarization of each catalog of representative strategies, we emphasized why such strategies can improve specific sensing performance parameters. We hope that this review can help researchers gain valuable insights into this field and motivate them to explore and further advance the development of H2 sensors for broader applications.
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In this work, we developed composites of palladium-decorated tin dioxide (PdSnO2) and halloysite nanotubes (HNTs) by adding different amounts of HNTs as additives into PdSnO2, and investigated how ...the different amounts of HNTs in the composites and the different hydrogen (H2) carrying gases (air and helium (He)) could affect the H2 sensing performance of such composites (PdSnO2-HNT). Through the sensing-performance characterization using H2 carried by air, it was found that PdSnO2 with an appropriate small amount of HNTs (i.e., 2 % of PdSnO2 mass) can improve the sensing performance with respect to limit of detection (LOD) and response/recovery time. Further, the optimal PdSnO2-HNT composite as a sensor was tested to detect H2 in He. The testing results indicated that the composite can detect H2 in He, but its performance parameters (i.e., the profile of calibration curve, LOD, and response time) are different from those of such a sensor in detecting H2 in air. Moreover, the composite still presented better sensing performance than PdSnO2 without HNTs in detecting H2 in He. Possible reasons for the effects of HNT and H2-carrying gas on the sensing performance of PdSnO2-HNT-based sensors were discussed. We believe that this study provides valuable insights into the functionality and the adaptability of PdSnO2-HNT-based H2 sensors in diverse operational conditions.
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•Novel PdSnO2-HNT composites developed for enhanced H2 sensing applications.•Investigation of HNT additives on the sensing performance of PdSnO2 materials.•Characterization of H2 sensing performance in both air and helium environments.•Improved sensing performance observed with a small amount of HNTs in PdSnO2.
•New boundary conditions were developed which allow for a given heat flux at the surface calculate a surface temperature.•The boundary conditions were numerically implemented and validated in ...correlation with experimental data.•Analytical expressions for the temperature distribution were derived in slip and free molecular flow regimes.•The proposed conditions can be applied to evaluate a surface temperature when a heat flux at the surface is known.
In many applications, the heat flux at the surface is known instead of the surface temperature. In addition, in some applications, like vacuum drying or high altitude flights, the pressure is below atmospheric pressure, so the rarefaction effects become important, and therefore, the Navier-Stokes-Fourier equations fail to predict gas thermal behavior. In this paper, a constant heat flux boundary condition is developed and implemented in the frame of the Shakhov model kinetic equation, with the possibility to simulate the diffuse-specular reflexion of the molecules from the surface. The developed technique is implemented for the simulation of gas heat transfer in a two concentric cylinders configuration, similar to vacuum drying of used nuclear fuel canisters. The numerical results obtained using developed approach are compared with experimental data of heat transfer through rarefied gas between two concentric cylinders.
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