Numerical investigation for the suitable choice of bubble diameter correlation for EMMS/bubbling drag model

Mesoscale bubbles exist inherently in bubbling fluidized beds and hence should be considered in the constitutive modeling of the drag force.The energy minimization multiscale bubbling(EMMS/bubbling)drag model takes the effects of mesoscale structures(i.e.,bubbles)into the modeling of drag coefficient and thus improves the coarse-grid simulation of bubbling and turbulent fluidized beds.However,its dependence on the bubble diameter correlation has not been thoroughly investigated.The hydrodynamic disparity between homogeneous and heterogeneous fluidization is accounted for by the heterogeneity index,H_(d),which can be affected by choice of bubble diameter correlation.How this choice of bubble diameter correlation influences the model prediction calls for further fundamental research.This article incorporated seven different bubble diameter correlations into EMMS/bubbling drag model and studied their effects on H_(d).The performance of these correlations has been compared with the correlation used previously by EMMS/bubbling drag model.We found that some of the correlations predicted lower Hd by order of a magnitude than the correlation used by the original EMMS/bubbling drag.Based on such analysis,we proposed a modification in the EMMS drag model for bubbling and turbulent fluidized beds.A computational fluid dynamics(CFD)simulation using two-fluid model with the modified EMMS/bubbling drag model was performed for two bubbling and one turbulent fluidized beds.Voidage distribution,time averaged solid concentration and axial solid concentration profiles were studied and compared with the previous version of the EMMS/bubbling drag model and experimental data.We found that the right choice of bubble diameter correlations can significantly improve the results for CFD simulations.

Quantifying effects of soil heterogeneity on groundwater pollution at four sites in USA

Four sites located in the north-eastern region of the United States of America have been chosen to investigate the impacts of soil heterogeneity in the transport of solutes(bromide and chloride)through the vadose zone(the zone in the soil that lies below the root zone and above the permanent saturated groundwater).A recently proposed mathematical model based on the cumulative beta distribution has been deployed to compare and contrast the regions'heterogeneity from multiple sample percolation experiments.Significant differences in patterns of solute leaching were observed even over a small spatial scale,indicating that traditional sampling methods for solute transport,for example the gravity pan or suction lysimeters,or more recent inventions such as the multiple sample percolation systems may not be effective in estimating solute fluxes in soils when a significant degree of soil heterogeneity is present.Consequently,ignoring soil heterogeneity in solute transport studies will likely result in under-or overprediction of leached fluxes and potentially lead to serious pollution of soils and/or groundwater.The cumulative beta distribution technique is found to be a versatile and simple technique of gaining valuable information regarding soil heterogeneity effects on solute transport.It is also an excellent tool for guiding future decisions of experimental designs particularly in regard to the number of samples within one site and the number of sampling locations between sites required to obtain a representative estimate of field solute or drainage flux.

Ecological niche modelling of a critically endangered species Commiphora wightii (Arn.) Bhandari using bioclimatic and non-bioclimatic variables

Background The aim of this study is to examine the effects of four different bioclimatic predictors(current,2050,2070,and 2090 under Shared Socioeconomic Pathways SSP2-4.5)and non-bioclimatic variables(soil,habitat heterogeneity index,land use,slope,and aspect)on the habitat suitability and niche dimensions of the critically endangered plant species Commiphora wightii in India.We also evaluate how niche modelling affects its extent of occurrence(EOO)and area of occupancy(AOO).Results The area under the receiver operating curve(AUC)values produced by the maximum entropy(Maxent)under various bioclimatic time frames were more than 0.94,indicating excellent model accuracy.Non-bioclimatic characteristics,with the exception of terrain slope and aspect,decreased the accuracy of our model.Additionally,Maxent accuracy was the lowest across all combinations of bioclimatic and non-bioclimatic variables(AUC=0.75 to 0.78).With current,2050,and 2070 bioclimatic projections,our modelling revealed the significance of water availability parameters(BC-12 to BC-19,i.e.annual and seasonal precipitation as well as precipitation of wettest,driest,and coldest months and quarters)on habitat suitability for this species.However,with 2090 projection,energy variables such as mean temperature of wettest quarter(BC-8)and isothermality(BC-3)were identified as governing factors.Excessive salt,rooting conditions,land use type(grassland),characteristics of the plant community,and slope were also noticed to have an impact on this species.Through distribution modelling of this species in both its native(west-ern India)and exotic(North-east,Central Part of India,as well as northern and eastern Ghat)habitats,we were also able to simulate both its fundamental niche and its realized niche.Our EOO and AOO analysis reflects the possibility of many new areas in India where this species can be planted and grown.Conclusion According to the calculated area under the various suitability classes,we can conclude that C.wight-ii’s potentially suitable bioclimatic distribution under the optimum and moderate classes would increase under all future bioclimatic scenarios(2090>2050≈current),with the exception of 2070,demonstrating that there are more suitable habitats available for C.wightii artificial cultivation and will be available for future bioclimatic projections of 2050 and 2090.Predictive sites indicated that this species also favours various types of landforms outside rocky environments,such as sand dunes,sandy plains,young alluvial plains,saline areas,and so on.Our research also revealed crucial information regarding the community dispersion variable,notably the coefficient of variation that,when bioclimatic non-bioclimatic variables were coupled,disguised the effects of bioclimatic factors across all time frames.