Flow and heat transfer in a bidisperse gas–solid system with freely moving spheres are simulated by particle‐resolved direct numerical simulation (PR‐DNS). Gas–solid coupling is enforced by the ...direct‐forcing immersed boundary method. Compard with the DNS database, it is found that the existing polydisperse drag correction model developed from static systems combined with various monodisperse drag models underestimates the drag force on dynamic arrays of particles. The existing Nusselt number correction model developed from static systems combined with various monodisperse models overestimates the Nusselt number of dynamic arrays of particles. Sensitivity analysis indicates that the effects of the granular temperature on the drag force and Nusselt number are negligible. Novel polydisperse drag and Nusselt number models are derived based on the database. The advantages of the derived polydisperse drag and Nusselt number models are demonstrated and confirmed by comparing the results of the computational fluid dynamics–discrete element method using various drag and Nusselt number models with experimental or additional PR‐DNS data.
Film cooling is essential for protecting substrate materials from the hot gases in turbomachines. Recent experiments have explored the effects of compound angles for the 7-7-7 film cooling hole, a ...baseline shaped film cooling hole developed at the START lab. However, differences in facility conditions, manufacturing process uncertainties, uncertainties in flow conditions, and the absence of internal cooling hole measurements necessitate further investigation to fully understand the impact of compound angles and the associated flow physics. This study presents direct numerical simulations (DNS) for the baseline 7-7-7 shaped film cooling hole, examining a range of compound angles and flow conditions paralleling those in prior lab experiments. The data gleaned offers insights into the flow dynamics within and in the vicinity of the cooling hole, particularly in areas proximate to the wall. Our findings indicate that increasing the compound angle adversely affects adiabatic cooling efficiency. A detailed analysis reveals that this decline in efficiency is primarily due to hot gas intrusion into the cooling hole, the elevation of the cooling jet from the wall, and intensified secondary flows at higher compound angles. Additionally, the DNS data reveals a logarithmic scaling in the laterally averaged mean velocity profile and a self-similarity in temperature profiles beyond a certain distance from the cooling hole.
We present a proof-of-concept for the adaptive mesh refinement method applied to atmospheric boundary-layer simulations. Such a method may form an attractive alternative to static grids for studies ...on atmospheric flows that have a high degree of scale separation in space and/or time. Examples include the diurnal cycle and a convective boundary layer capped by a strong inversion. For such cases, large-eddy simulations using regular grids often have to rely on a subgrid-scale closure for the most challenging regions in the spatial and/or temporal domain. Here we analyze a flow configuration that describes the growth and subsequent decay of a convective boundary layer using direct numerical simulation (DNS). We validate the obtained results and benchmark the performance of the adaptive solver against two runs using fixed regular grids. It appears that the adaptive-mesh algorithm is able to coarsen and refine the grid dynamically whilst maintaining an accurate solution. In particular, during the initial growth of the convective boundary layer a high resolution is required compared to the subsequent stage of decaying turbulence. More specifically, the number of grid cells varies by two orders of magnitude over the course of the simulation. For this specific DNS case, the adaptive solver was not yet more efficient than the more traditional solver that is dedicated to these types of flows. However, the overall analysis shows that the method has a clear potential for numerical investigations of the most challenging atmospheric cases.
Gaskets play a significant role in the thermal insulation of refrigerators. Previous studies mainly focused on how to obtain the heat and moisture transfer load of a given gasket, but lacked ...appropriate structural improvement measures and their effect on the heat leakage load and energy consumption of refrigerators. In this paper, the heat transfer analysis of an original gasket was conducted via numerical simulation. It was found that the main thermal insulation weaknesses of the original gasket are gasket-cold air, gasket-outer shell of the cabinet, gasket-inner lining of door and gasket-hot air. Thus, adding an auxiliary-airbag to the original gasket and a comprehensive new-design gasket were proposed to improve the thermal insulation. Compared with the original gasket, the numerical simulation results showed the heat leakage loads of the auxiliary-airbag and new-design gasket were reduced by 18.44 % and 27.49 %. The total heat leakage loads of refrigerators equipped with improved gaskets were reduced by 4.46 % and 6.64 %. The effect of two structurally improved gaskets on the refrigerator energy consumption was experimentally studied. The repetitively measured results showed the energy consumption of refrigerators with the auxiliary-airbag and the new-designed gasket were reduced by 0.93 % and 3.19 %. The reason why the reduction in refrigerator energy consumption is lower than the reduction in heat leakage load is due to the difficulty in achieving the designed assembly state of the gasket during actual installation. Based on the holdings of refrigerators around the world, it is estimated that the refrigerators energy consumption can be reduced by 106.776 billion kWh per year and carbon emissions can be reduced by 12.74 million tons per year when using the new-design gasket proposed in this study.
•A method to determine the thermal insulation weaknesses of the gasket is proposed.•Comprehensive structural improvements to reduce gasket heat load are proposed.•Thermal insulation improvement of gaskets will decrease refrigerator temperature.•Energy consumption of refrigerators with new-design gaskets is reduced by 3.19 %.
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•High concentrations of pollutants were present in runoff flowing through tailings.•Metals have strong migration ability in TCLP environment.•The cumulative release of Mn, Zn, Co, and ...Ni was larger.•Seepage affects the chemical fraction of metals in tailings.•Mn has posed a serious threat to groundwater.
The continued growth in demand for mineral resources has led to a large amount of mining wastes, which is a major challenge in the context of carbon neutrality and climate change. In this study, runoff migration, batch leaching, and column experiments were used to investigate the short-, medium-, and long-term leaching of heavy metals from legacy tailings, respectively; the cumulative metal release kinetic equations were established, and the long-term effects of tailings leaching were verified by HYDRUS-1D. In runoff migration experiments, surface dissolution of tailings and the co-migration of adsorbed soil particles by erosion were the main carriers in the early stages of leachate formation (Mn ∼ 65 mg/L and SO42- up to 2697.2 mg/L). Batch leaching tests showed that the concentration of heavy metals in soil leached by acid rain were 0.1 ∼ 22.0 μg/L for Cr, 0.7 ∼ 26.0 μg/L for Cu, 4.8 ∼ 5646.0 μg/L for Mn, 0.3 ∼ 232.4 μg/L for Ni, and 1.3 ∼ 448.0 μg/L for Zn. The results of column experiments indicated that some soluble components and metals with high mobility showed a significant decreasing trend at cumulative L/S ≤ 2. Additionally, the metals have higher leaching rates under TCLP conditions, as shown by Mn > Co > Zn > Cd > Ni > Cu > Pb > Cr. The fitting results of Langmuir equation were closer to the cumulative release of metals in the real case, and the release amounts of Mn, Zn, Co, and Ni were higher with 55, 5.84, 2.66, and 2.51 mg/kg, respectively. The water flow within tailings affects the spatial distribution of metals, which mainly exist in relatively stable chemical fractions (F3 + F4 + F5 > 90 %) after leaching. Numerical simulation verified that Mn in leachate has reached 8 mg/L at a scale of up to 100 years. The research results are expected to provide technical basis for realizing the resource utilization of tailings in the future.
The interior oceans of several icy moons are considered as affected by rotation. Observations suggest a larger heat transport around the poles than at the equator. Rotating Rayleigh‐Bénard convection ...(RRBC) in planar configuration can show an enhanced heat transport compared to the non‐rotating case within this “rotation‐affected” regime. We investigate the potential for such a (polar) heat transport enhancement in these subglacial oceans by direct numerical simulations of RRBC in spherical geometry for Ra = 106 and 0.7 ≤ Pr ≤ 4.38. We find an enhancement up to 28% in the “polar tangent cylinder,” which is globally compensated by a reduced heat transport at low latitudes. As a result, the polar heat transport can exceed the equatorial by up to 50%. The enhancement is mostly insensitive to different radial gravity profiles, but decreases for thinner shells. In general, polar heat transport and its enhancement in spherical RRBC follow the same principles as in planar RRBC.
Plain Language Summary
The icy moons of Jupiter and Saturn like for example, Europa, Titan, or Enceladus are believed to have a water ocean beneath their ice crust. Several of them show phenomena in their polar regions like active geysers or a thinner crust than at the equator, all of which might be related to a larger heat transport around the poles from the underlying ocean. We simulate the flow dynamics and currents in these subglacial ocean by high‐fidelity simulations, though still at less extreme parameters than in reality, to study the heat transport and provide a possible explanation of such a “polar heat transport enhancement.” We find that the heat transport around the poles can be up to 50% larger than around the equator, and that the believed properties of the icy moons and their oceans would allow polar heat transport enhancement. Therefore, our results may help to improve the understanding of ocean currents and latitudinal variations in the oceanic heat transport and crustal thickness on icy moons.
Key Points
The polar heat transport in spherical rotating Rayleigh‐Bénard convection experiences an enhancement by rotation
The influence of rotation differs at low latitudes: the heat flux is reduced and compensates the polar enhancement on the global average
In combination, this strengthens the latitudinal variation between polar and equatorial heat flux for Prandtl numbers larger than unity
Soil characteristics play an important role in distribution of light non-aqueous phase liquid (LNAPL) spilled from buried pipeline, and enhanced understanding of distribution is significant to the ...effective design of soil and groundwater remediation strategies. Therefore, distribution of diesel in soils with different porosity and temperature on the temporal evolution of the diesel migration following the saturation profiles of the two-phase flow in soils were investigated in this study. The diffusion ranges, areas and volumes in both the radial as well as in axial directions of leaked diesel in soils with different porosity and temperature increased with time. Soil porosities played an important role in the distributions when soil temperatures had no effect on distributions of diesel in soils. The distribution areas were 0.385 m2, 0.294 m2, 0.213 m2, and 0.170 m2 at 60 min when the soils porosities were 0.1, 0.2, 0.3, and 0.4, respectively. The distribution volumes were 0.177 m3, 0.125 m3, 0.082 m3, 0.060 m3 at 60 min when the soils porosities were 0.1, 0.2, 0.3, and 0.4, respectively. But the distribution areas were 0.213 m2 at 60 min when the soil temperatures were 286.15 K, 296.15 K, 306.15 K and 316.15 K, respectively. The distribution volumes were 0.082 m3 at 60 min when the soil temperatures were 286.15 K, 296.15 K, 306.15 K and 316.15 K, respectively. The calculation formulas of distribution areas and volumes of diesel in soils with different porosity and temperature for developing prevention and control strategies in the future were fitted. The seepage velocities of diesel changed sharply around the leakage port and decreased from about 4.9 m/s to 0 within a few millimeters in soils with different porosity. Additionally, the diffusion ranges of leaked diesel in soils with different porosity were different, indicating that soil porosity had a significant impact on seepage velocities and pressures. The seepage velocities fields and pressures fields of diesel in soils with different temperature were same at the leakage velocity of 4.9 m/s. And the study could provide some supports for determination of the safety zone and formulation of emergency response plans for LNAPL leakage accidents.
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•The model of two-phases diesel and gas in soils was established by ANSYS soft to study the diffusion of diesel in soils with different porosity and temperature for the first time.•The calculation formulas of distribution areas and volumes of diesel in soils for developing prevention and control strategies were fitted.•The seepage velocities and pressures fields were studied and it's first time to prove that there's no effect for distribution of diesel in soils with different temperature.
Statistically steady supersonic deflagrations are numerically investigated in narrow channels with strong thermal expansion and heat loss. Four modes of flame propagation are observed, namely, ...extinction, low-speed deflagration, high-speed deflagration, and DDT. It is determined that larger thermal expansion facilitates initiation of high-speed deflagrations while the heat loss can suppress the transition to detonation. The high-speed deflagration mode is shown to be the result of the dynamic balance between thermal expansion and wall heat loss. The limits of high-speed deflagration in terms of the thermal expansion and heat loss coefficients are determined. The statistically steady oscillatory high-speed deflagrations propagate at average velocities close to half of the CJ detonation velocity. The dynamics of the flame front and shock waves are visualized using numerical schlieren. Periodic acceleration and deceleration of the leading shock are identified, and the mechanism of DDT suppression is elucidated.
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