Single-layer Bed Research Articles

Predicting the crushing behavior of pebbles: Theoretical model and experiment verification

In this paper, a theoretical model is established to describe pebble-crushing behavior, and the fractal theory was introduced to describe the relationship between original particles and fractures. Considering the size effect and random variation of crushing strength, the Weibull theory was used to characterize the strength variation, and the correlation between the Weibull modulus and fractal dimension was derived. The impact test was performed to verify the established theoretical model’s validity. Results showed that the theoretical model was verified to be valid for crushing behavior description, and the slope of the fitted straight line could be used to calculate the fractal dimension, which is the most critical parameter in fractal theory and could describe the extent of crushing in the pebble bed. The crushing behavior of pebble beds under impact loading was also studied, and test results identified limited evidence of fractal dimension limitation as the impact times increased. The crushing degree could not increase by only increasing the impact times. The extent of crushing had a limitation at a certain drop height. The evolution rate of crushing behavior negatively correlated with total impact energy, and the extent of crushing changed more drastically in a single-layer bed. The established theoretical model and findings presented in this paper add to our understanding of granular material physics, especially the mechanism of particle crushing behavior in a packed bed for fusion blankets.

Process evaluation and kinetic analysis of 3D-printed monoliths comprised of CaO and Cr/H-ZSM-5 in combined CO2 Capture-C2H6 oxidative dehydrogenation to C2H4

In this study, dual-function materials (DFMs) comprised of CaO and Cr/H-ZSM-5 were formulated in 3D-printed monolithic structures and investigated in a combined process for capture and utilization of CO2in oxidative dehydrogenation of C2H6 to C2H4 (CO2-ODHE). Various formulation strategies were employed to fabricate these DFM structures. Two bed designs were considered: i) a layered-bed in which adsorbent (CaO) and catalyst were printed separately and stacked on top of each other, and ii) a single-layer bed where the adsorbent-catalyst materials were 3D-printed into a singular monolith and loaded into the bed as DFMs. Between these, the layered-bed displayed enhanced performance as compared to the composite DFMs, as this configuration generated a 3.73 mmol/g CO2 adsorption capacity, 42.5% C2H6 conversion, 90.6% C2H4 selectivity and 38.6% C2H4 yield compared to 2.4 mmol/g CO2 adsorption capacity, 37.9% C2H6 conversion, 89% C2H4 selectivity and 33.8% C2H4 yield in the best singular monolith configuration. The enhanced performance of this configuration was attributed to a higher degree of adsorptive site accessibility and a lesser degree of active site blockage from intraparticle binding (as evident from the textural properties). This work also assessed the effects of monolith cell density on CO2 adsorption and utilization for ODHE by varying the cells per square inch (cpsi) from 200 to 600 cpsi. These experiments revealed that increasing the cell density from 200 to 600 cpsi enhanced the overall mass transfer coefficient from 0.40 × 10-2 to 1.01 × 10-2 s-1 due to a sizable enhancement in film mass transfer between the two geometric designs. Such enhancement improved the C2H4 selectivity and yield to 92 and 45.1% in the 600 cpsi sample. As such, this work also indicated that higher cell densities lead to better performance of the layered-bed configuration, where the optimum configuration is separate stacking of the adsorbent and catalyst phases. Overall, these findings provide a deeper understanding of DFM materials, bed configuration, and establish a groundwork which can be used to optimize their structures for CO2 adsorption-reaction processes.

Wave Damping over a Multilayered, Permeable Seabed

Abstract In this study, a wave-damping rate was derived for waves propagating over a multilayered, permeable seabed of finite depth. For a single-layer bed, a monogram is presented for the relationship between the wave-damping rate and the relative water depth for various depths of the permeable bed. The derived damping rate was used in the extended mild-slope equation to calculate wave dissipation over the permeable bed. For a single-layer bed, the result from the extended mild-slope equation model was compared with the result from the integral equation method and showed good agreement. The extended mild-slope equation model was also used to examine the wave transmission over a permeable shoal with a various number of layers, each with a different permeability. In general, short waves are more influenced by the permeability of the shoal than long waves unless the water depth is so great that the influence of the permeable bed on the surface water waves disappears. For a multilayered bed, the influences o...

Experimental Study on a New Dual-Layer Granular Bed Filter for Removing Particulates

A new dual-layer granular bed filter for hot gas cleanup was invented and studied experimentally. Fine sand, 0.5-1 mm grain size and about 1350kg/m^3 bulk density, was used as the lower layer of the filter. Expanded perlite particles, 2-5 mm grain size and about 70kg/m^3 bulk density, was used for the upper layer of the filter in this study. It was confirmed that the sizes and densities of these two media matched well; the binary media remained in complete segregation during regeneration by fluidization. Test results show that the filtration of the expanded perlite particle layer was characterized as ”deep bed filtration.” Filtration of the fine sand layer was ”surface cake filtration.” The expanded perlite particle layer contributed about 90% to the bed dust capacity, but only about 20% to the total bed pressure drop, which increased the bed dust capacity ten fold compared to a single-layer bed of the same sand and the same total bed pressure drop. The dust cake on the surface of the fine sand layer raised the collection efficiencies to over 99.99%.

Determination of the settlement of a multilayer bed by its replacement with a single-layer bed

Solutions are presented for determination of bed settlement for a computational scheme in the form of a linearly deformable half space with replacement of a multiple-by a single-layer bed with the average compression modulus, or layer-by layer summation of the settlement of homogeneous layers.

Pressure-Swing Adsorption Using Layered Adsorbent Beds with Different Adsorption Properties: I—Results of Process Simulation

A simulation study was conducted on layered-bed pressure-swing adsorption, PSA, processes with adsorbents that differ in their adsorption properties. As an example, an oxygen, O2, vacuum-swing adsorption, VSA, process was analyzed to investigate relationships between process performance and adsorption properties of the adsorbents used. For two adsorbents with identical nitrogen-to-oxygen, N2/O2, selectivity but different N2 and O2 capacities, placing the high-capacity adsorbent at the product end and the low-capacity adsorbent at the feed end of the adsorption bed gives a better performance than the case of reversing layering of these adsorbents. However, for two adsorbents with different values of N2/O2 selectivity but identical N2 capacity, changing the bed-layer configuration does not show a significant difference in O2-VSA performance. The advantages of layering a high-capacity adsorbent on product end of the bed are demonstrated by an examination of the N2-loading difference in a VSA cycle. The modeling study also reveals an effect of cycle features (e.g., equalization step) on the effectiveness of using layered-bed configurations in VSA/PSA processes. It suggests that layering appropriately two adsorbents with different adsorption properties could result in better VSA/PSA-process performance than using a single-layer bed with either of the two adsorbents.

Effects of human trampling on marine rocky shore communities

The effects of human trampling on two marine intertidal communities were experimentally tested in the upper-shore algal-barnacle assemblage and mid-shore mussel bed communities. On two shores, we trampled experimental plots 250 times every month for a year, and then allowed plots to recover for a further year. Results from the upper shore community showed that foliose algae were susceptible to trampling, and suffered significant declines shortly after trampling started. Canopy cover remained high in untrampled control plots. Barnacles were crushed and removed by trampling. Algal turf was resistant to trampling, and increased in relative abundance in trampled plots. In general the algal-barnacle community recovered in the year following trampling. In the mussel bed community, mussels from a single layer bed were removed by trampling, By contrast, mussels at a second site were in two layers, and only the top layer was removed during the trampling phase. However, mussel patches continued to enlarge during the recovery phase, so that by the end of the second year, experimental plots at both sites had lost mussels and bare space remained. Mussel beds did not recover in the 2 years following cessation of trampling. Control plots lost no mussels during the trampling and recovery phase. Barnacle and algal epibionts on mussels were significantly reduced by tramping. Overall, trampling can shift community composition to an alternate state dominated by low profile algae, and fewer mussels.