Modeling and Parametric Simulation of Microplastic Transport in Groundwater Environments

Efforts to reduce the toxic effects of microplastics (MPs) on the environment have increased globally in recent years. However, the existing models used for the simulation of contaminant transport in groundwater are meant for dissolved substances, which is not suitable for studying MPs. Therefore, in this study, the transport of MPs in a saturated porous medium was modeled by establishing governing equations. Simulations were performed using the finite element method to examine the effects of the parameters of the governing equations on the transport of MPs. The results suggest that it is necessary to reduce the diffusivity of MPs and increase the water flow velocity, porosity, and first-order attachment coefficient to effectively contain this environmental hazard. From the simulation results, it can be derived that a combination of low diffusivity, fast water flow velocity, and high soil porosity may reduce the amount of MPs that are leaked into groundwater environments. The modeling and simulations performed in this study provide a clear understanding of the transport phenomena of MPs with applications in combating water pollution.

Electron Swarm Parameters and Dielectric Properties of the Superconducting Binary Mixtures of He-H2

In this study, the electron energy distribution function EEDF, the electron swarm parameters, the effective ionization coefficients, and the critical field strength (dielectric strength) in binary He-H2 gas mixture which used as cryogenic for high-temperature superconducting power application, are evaluated by using two-term approximation of the Boltzmann equation over the range of E/N ( the electric field to gas density) from 1 to 100 Td ( 1 Td=10-17 Vcm2) at temperature 77 K and pressure 2MPa, taking into account elastic and inelastic cross-section. Using the calculated EEDF, the electron swarm parameters (electron drift velocity, mean electron energy, diffusion coefficient, electron mobility, ionization and attachment coefficient) are calculated. At low reduced electric field E/N, the EEDF close Maxwellian distribution, at high E/N, due to vibrational excitation of H2 the calculated distribution function is non-Maxwellian. Besides, in the He-H2 mixture, it is found that increasing small amount of H2 enhances to shift the tail of EEDF to the lower energy region, the reduced ionization coefficient α/N. reduced effective ionization coefficient (α-η)/N) decreases, while, reduced attachment coefficient η/N, reduced critical electric field strength (E/N)crt. and critical electric field Ecrt. Increases, because of hydrogen’s large ionization cross-sections. The dielectric strength of 5% H2 in mixture is in good agreement with experimental values, it is found that dielectric strength depend on pressure and temperature. The electron swarm parameters in pure gaseous helium (He) and hydrogen (H2), in satisfying agreement with previous available theoretical and experimental values. The validity of the calculated values has been confirmed by two-term approximation of the Boltzmann equation analysis.

Ionization and Attachment Coefficients in C4F7N Gas Measured by the Steady-State Townsend Method

The normalized Townsend first ionization coefficient α/N and normalized attachment coefficient η/N in pure C4F7N were measured by using the steady-state Townsend (SST) method for a range of reduced electric fields E/N from 750 to 1150 Td at room temperature (20 °C). Meanwhile, the effective ionization coefficients are obtained. All SST experimental results show good agreement with pulsed Townsend (PT) experiment results. Comparisons of the critical electric fields of C4F7N with SF6 and other alternative gases such as c-C4F8 and CF3I indicate that C4F7N has a better insulation performance with a much higher normalized critical electric field at 959.19 Td.

The Analysis of the Testing Accuracy of the Anti-Force Rolling Brake Testing Platform

Many Factors influencing the testing accuracy are discussed according to the differences between the testing data of most of the domestic anti-force rolling brake testing platform. We try to get the theoretical analysis and be proved by experiment through the mechanical model. We focus on some respects just as attachment coefficient, tire pressure, vehicle moving and direction displacement which influencing the testing accuracy of the anti-force rolling brake testing platform.

Design and Simulation of Electric Pallet Truck Hydraulic Anti-Skid System

Based on electric pallet truck skids in the process of moving because of low road attachment coefficient, this paper proposed an anti-skid method by changing the proportion of enduring pressure between the driving wheel and trundles. Anti-skid control theory of the new method is researched and mathematical models of the main modules are established. Anti-skid control system is simulated by using AMESim and Matlab / Simulink software. Simulation results show that, this hydraulic anti-skid system can respond quickly and precisely.

Extended mixed-culture biofilms (MCB) model to describe integrated fixed film/activated sludge (IFAS) process behaviour

This paper presents how, in a calibration process, different assumptions regarding the standard Mixed-Culture Biofilms (MCB) model were able to match the average results at a continuous Johannesburg pilot plant (comprising two aerobic reactors, AE1 and AE2), but failed to match the batch test results of either the rate of endogenous carbonaceous oxygen uptake (OUR) or the rate of nitrate production (NPR). Under the first assumption, where attachment and diffusion of particulate components were not used, the OUR in the biofilm of the first aerobic reactor (AE1) was too low due to the absence of slowly biodegradable COD (XS) attachment flux. In a second assumption, where high diffusion and attachment coefficients were used, the NPR in the biofilm of the AE1 reactor exceeded the experimental value due to the high attachment flux used for nitrifiers (XA) and the low competition for space from XS and heterotrophic bacteria (XH). The only way to match all the experimental results was through the use of a higher attachment coefficient for XS in the first reactor (AE1), but this was considered unreasonable. Hence, an extended model was developed where a colloidal state, which interacts at the same time with the flocs and the biofilm through attachment-detachment processes, is distinguished. This model allowed the experimental results to be matched, but using the same value for the attachment coefficients of all particulate components.