DEM-CFD Study on Fluid Flow Through Radial Layered Composite Packed Beds

The radial porosity generally have a higher value at the container wall than that in the core part. Consequently, the fluid flows are mal-distributed in packed bed with significant bypass flow at the wall, which lowers the convective heat transfer performance inside the packed bed. To overcome this drawback of packed bed, we developed an effective way to construct the radial layered composite packed bed, which can easily realize placing small particle at the near wall region and large spheres in the core region. Therefore, smaller pores forms close to the container wall and larger channels presented in the core part. This could result in a much homogenous radial porosity distribution, which is benefit to restrain the bypass flow near the wall. In present paper, the packing procedure is simulated by the discrete element method (DEM). Radial layered composite packed bed and traditional packed bed with uniform spheres are compared on radial porosity distribution. By altering the size of spheres ratios in the near wall region different radial layered packings are also generated and compared. Then, the geometries of these packed bed are imported into the computational fluid dynamics (CFD) simulation. The fluid flow inside the packed bed is investigated. It finds that the radial layered packed bed has a lower pressure drop with the ordered packing structure. And a much homogenous fluid flow distribution is obtained than the traditional, which is benefit for the heat removal inside the packed bed. This would be useful for the optimum design of packed bed in industry applications.

Uranium Enrichment Measurement Using Enrichment-Meter Approach

The 235U enrichment is one of the most important characteristics of nuclear materials for nuclear safeguards purposes. The multi-group γ-ray analysis method for uranium (MGAU) is an important non-destructive gamma spectroscopy method for 235U enrichment determination. Using that method, the typical measurement bias is below 3% for uranium material with abundance from 0.3 to 93 %. However, it is not applicable for the samples with thick container or without isotopic decay equilibrium. In this work, the enrichment meter method was studied with two uranium dioxide samples (235U abundance 0.71 % and 3.167 %). The nuclear materials spectra were measured using a planar high-purity germanium detector. Based on the specific gamma peak (185.71 keV) of relative high intensity, this traditional enrichment meter approach gives measurement bias more than 10 %. Thus, this work represents two objects: (1) an alternative approach which was investigated, where the calibration is performed through Monte Carlo simulation (MCNP5) instead of experiment in advance, as the measurement bias was reduced to be around 5 %. Thus, to use this approach, one should have the sample details, such as dimensions, chemical composition and container. (2) The influence of the container wall thickness on the measurement accuracy by Monte Carlo simulation. So, if the container wall thickness is not modeled correctly the measurement accuracy is influenced, which is investigated by simulation.

Preparation and Properties of TiB2 Coating against Erosion by Molten Al-12.07wt.%Si Alloy

TiB2 protective coating was prepared in the 310S container wall to improve the life of the container and achieve long-term protection purposes, and also studied the properties of TiB2 coating with anti-heat shock, mechanical and anticorrosion to molten Al-12.07%Si . The results showed that the anti-heat shock properties of the coating was good, bonding strength between coating and substrate was high, the corrosion resistance was improved under certain limited temperature, and the life of container was also remarkable enhanced.

Planting Depth Affects Root Form of Three Shade Tree Cultivars in Containers

Study was designed to evaluate impact of planting depth on root morphology inside nursery containers. Trees were planted shallow (13 mm) or deep (64 mm) into #3 Air-Pot™ containers, then shallow (0 mm) or deep (64 mm) into #15 containers prior to shifting them to their final #45 container size at the same depth. Trunk diameter (caliper) was significantly larger for both magnolia and maple planted shallow (13 mm) into #3, and then shallow into #15 containers when compared to planting deeper. However, differences were small and may not be relevant to a grower. No caliper or height differences among planting depths were found for elm. Presence of stem girdling roots in elm and magnolia growing in #45 containers increased with planting depth into # 3 containers. Downward re-orientation of main roots comprising the flare by #3 container wall, likely contributed to amount of roots growing over root flare. Maple root systems were not impacted by planting depth into #3 primarily due to adventitious root emergence from the buried portion of stem. Distance between substrate surface and top of root flare in finished #45 containers was not impacted by planting depth into #3 containers for any species. Planting elm and maple deeply into #15 led to more trunk-girdling by roots, a deeper root flare, and more roots growing over flare compared to planting shallow. Most root defects in all species were hidden from view because they were found below substrate surface. Presence of a visible root flare was not related to occurrence of root defects. Root balls on elm and maple were packed with roots which made it time consuming to remove substrate and roots above the root flare. Planting depth appears most crucial when shifting into #15 containers.

Root Ball Shaving Improves Root Systems on Seven Tree Species in Containers

Established forest trees planted from small containers are less stable at the point where roots fork, bend or branch as a result of deflection by container wall, but less is known about the post-transplant impact of root deflections resulting from growing trees in large containers. We either root pruned by shaving off the periphery of the #3 container root ball as it was planted into the #15 container or did not root prune on 5 tropical and 2 temperate tree species. Shaving did not affect trunk caliper or tree height on the seven species tested under the conditions of this study. Shaving removed the entire outer and bottom 2.5 cm (1 in) of the root ball and reduced or eliminated culls on five of seven species. The largest diameter roots on trees in #15 containers that were not root pruned when shifted from #3 containers were kinked, descended down the container wall, or circled at the position of the #3 container. These root defects were largely missing on trees with root balls that were shaved of peripheral roots when shifted into #15 containers. The largest roots on shaved trees grew more-or-less straight radially from the trunk. Shaving the root ball periphery and bottom is recommended to improve root ball quality by reducing root ball defects.