Linear analysis of plasma pressure-driven mode in reversed shear cylindrical tokamak plasmas

The linear behavior of the dominant unstable mode(m=2,n=1)and its high order harmonics(m=2n,n≥2)are numerically investigated in a reversed magnetic shear cylindrical plasma with two q=2 rational surfaces on the basis of the non-reduced magnetohydrodynamics(MHD)equations.The results show that with low beta(beta is defined as the ratio of plasma pressure to magnetic field pressure),the dominant mode is a classical double tearing mode(DTM).However,when the beta is sufficiently large,the mode is driven mainly by plasma pressure.In such a case,both the linear growth rate and mode structures are strongly affected by pressure,while almost independent of the resistivity.This means that the dominant mode undergoes a transition from DTM to pressure-driven mode with the increase of pressure,which is consistent with the experimental result in ASDEX Upgrade.The simulations also show that the distance between two rational surfaces has an important influence on the pressure needed in mode transition.The larger the distance between two rational surfaces,the larger the pressure for driving the mode transition is.Motivated by the phenomena that the high-m modes may dominate over low-m modes at small inter-resonance distance,the high-m modes with different pressures and q profiles are studied too.

Pressure-driven mold filling model of aluminum alloy melt/semi-solid slurry based on rheological behavior

The pressure-driven mold filling ability of aluminum alloy melt/semi-solid slurry is of great significance in pressure casting processes,and the rheological behavior of the alloy has a crucial effect on the mold filling ability according to fluid dynamics.In this work,a pressure-driven mold filling model is first proposed based on the rheological behavior of the alloys.A356 alloy is employed as an example to clarify the rheological behavior of aluminum alloys,which obeys the power law model and is affected by temperature.The rheological behavior of the alloy in semi-solid state is modelled with the coupling of shear rate and temperature.The stop of mold filling attributes to the pressure loss which is caused by the viscosity during the flow of the melt/semi-solid slurry.Pressure loss caused by viscous flow and heat transfer between the alloy and the mold are calculated and coupled during the mold filling of the melt/semi-solid slurry.A pressure-driven mold filling model of aluminum alloy melt/semi-solid slurry is established based on steady-state rheological behavior.The model successfully predicts the filling length of melt/semi-solid slurry in pressure casting processes.Compared with the experimental results,the model can provide a quantitative approach to characterize the pressure-driven mold filling ability of aluminum alloy melt.The model is capable of describing the stop filling behavior of other aluminum alloys in pressure casting processes with corresponding rheological parameters and heat transfer coefficient.

The Development of a Renewable-Energy-Driven Reverse Osmosis System for Water Desalination and Aquaculture Production

Water and energy are closely linked natural resources - the transportation, treatment, and distribution of water depends on low-cost energy; while power generation requires large volumes of water. Seawater desalination is a mature technology for increasing freshwater supply, but it is essentially a trade of energy for freshwater and is not a viable solution for regions where both water and energy are in short supply. This paper discusses the development and application of a renewable-energy-driven reverse osmosis （RO） system for water desalination and the treatment and reuse of aquaculture wastewater. The system consists of （1） a wind-driven pumping subsystem, （2） a pressure-driven RO membrane desalination subsystem, and （3） a solar-driven feedback control module. The results of the pilot experiments indicated that the system, operated under wind speeds of 3 m s-~ or higher, can be used for brackish water desalination by reducing the salinity of feedwater with total dissolved solids （TDS） of over 3 000 mg L-1 to product water or permeate with a TDS of 200 mg L-~ or less. Results of the pilot experiments also indicated that the system can remove up to 97% of the nitrogenous wastes from the fish pond effluent and can recover and reuse up to 56% of the freshwater supply for fish pond operation.