Comparison of Reynolds average Navier-Stokes turbulence models in numerical simulations of the DC arc plasma torch

Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.

Interactions of fluoroquinolone antibiotics with sodium hypochlorite in bromide-containing synthetic water:Reaction kinetics and transformation pathways

Seven popular fluoroquinolone antibiotics(FQs)in synthetic marine aquaculture water were subject to sodium hypochlorite(NaClO)disinfection scenario to investigate their reaction kinetics and transformation during chlorination.Reactivity of each FQ to NaClO was following the order of ofloxacin(OFL)>enrofloxacin(ENR)>lomefloxacin(LOM)>ciprofloxacin(CIP)?norfloxacin(NOR)>>pipemedic acid(PIP),while flumequine did not exhibit reactivity.The coexisting chlorine ions and sulfate ions in the water slightly facilitated the oxidation of FQs by NaClO,while humic acid was inhibitable to their degradation.The bromide ions promoted degradation of CIP and LOM,but restrained oxidation of OFL and ENR.By analysis of liquid chromatography with tandem mass spectrometry(LC-MS/MS),eight kinds of emerging brominated disinfection byproducts(Br-DBPs)caused by FQ S were primarily identified in the chlorinated synthetic marine culture water.Through density functional theory calculation,the highest-occupied molecular orbital(HOMO)and the lowest-unoccupied molecular orbital(LUMO)characteristic as well as the charge distribution of the FQs were obtained to clarify transformation mechanisms.Their formation involved decarboxylation,ring-opening/closure,dealkylation and halogenation.Chlorine substitution occurred on the ortho-position of FQs's N4 and bromine substitution occurred on C8 position.The piperazine ring containing tertiary amine was comparatively stable,while this moiety with a secondary amine structure would break down during chlorination.Additionally,logK_(ow)and log BAF of transformation products were calculated by EPI-Suite^(TM)to analyze their bioaccumulation.The values indicated that Br-DBPs are easier to accumulate in the aquatic organism relative to their chloro-analogues and parent compounds.