Feng-Chen Li

Large-scale water desalination methods: a review and new perspectives

ABSTRACT In this paper, modern large-scale industrial water desalination technologies are briefly reviewed and a comparison between their technological characteristics and field of application is presented to indicate possible areas for technology advancement. In addition, recent developments in distillation processes and new desalination methods are introduced for relevant technologies, offering more accessible water supplies. The research was based on both work with analytic materials from large information agencies involved in the desalination industry and research carried out by individual authors and research institutions. The authors discuss the possibility of applying their own technology for water distillation, so called supercavitating evaporation. Analysis of the current situation indicates an increasing trend for reverse osmosis technology for water desalination, the rise of newer technologies and further limitation of thermal methods for heat utilization purposes.

Tunable Polarization Conversion and Rotation based on a Reconfigurable Metasurface

Polarization is an important property of electromagnetic (EM) wave and different polarization manipulations are required for varied optical applications. Here we report a reconfigurable metasurface which achieves both the polarization conversion and the polarization rotation in THz regime. The metasurface is reconfigured through the micro-electro-mechanical-systems (MEMS) actuation. The cross polarization transmittance from a linear polarized incidence is experimentally tuned from 0 to 28% at 2.66u2009THz. In addition, the polarization rotation angle is effectively changed from −12.8° to 13.1° at 1.78u2009THz. The tunable bi-functional metasurface for polarization conversion and the polarization rotation can be flexibly applied in various applications such as imaging, polarization microscopy and material analysis, etc.

Numerical simulation of the temperature effects on the performance of rotational supercavitating evaporator

With the application of supercavitation effect, a novel device named Rotational Supercavitating Evaporator (RSCE) has been designed for desalination. In order to study the effect of temperature on the performance of RSCE and then direct the experimental study on RSCE for the next step, numerical simulations are conducted on the supercavitating flows in RSCE under different temperatures and rotational speeds. The results show that the rotational speed, resistance moment and mechanical energy consumed by the rotational cavitator under the critical state with the largest supercavity, decrease with the increase of temperature. And the area and volume of the supercavity increase exponentially with the increase of temperature under the same rotational speed.

Numerical study of the characteristics of supercavitation on a cone in a stationary evaporator

Computation results of the supercavitation on a cone in a bounded axial cold water (20˚C) flow, obtained by ANSYS13 CFX and FLUENT, are found to correlate with experimental data. CFX solution has captured considerable backflow, and temperature gradient of 7˚C between free water stream and steam inside the supercavity, with the average water vapor temperature of supercavity volume equal to 17.8˚C, while FLUENT has revealed negligible temperature gradient, and the position of backflow vortex is different. Although we have used the same setup and appropriate meshes for both solvers, due to different cavitation models: mixture Rayleigh‐Plesset and Schnerr-Sauer, for CFX and FLUENT, respectively, we have found wide discrepancy in the resulted thermal, mass, and velocity flow fields. Understanding thermal, mass, and velocity fields of the supercavitating flow is important for the development of an industrial application of supercavitation for the design of the evaporators, open-type heat exchangers, coolers, deaerators, mixers, and chemical reactors. The CFX solver have been used for revealing the multiply factor response of the supercavitating flow on the temperature of source water, its inlet velocity, rate of steam extraction from the supercavity, and the degree of flow obstruction by the cavitator. This analysis goes beyond the presently referred experimental results, and the influences of the each factor on the supercavitating flow dynamics have been formulated in respect of the steam volume fraction, steam motion and effective temperature influence on the interphase heat mass transfer.

Dynamic control of particle separation in deterministic lateral displacement separator with viscoelastic fluids

We proposed an innovative method to achieve dynamic control of particle separation by employing viscoelastic fluids in deterministic lateral displacement (DLD) arrays. The effects of shear-thinning and elasticity of working fluids on the critical separation size in DLD arrays are investigated. It is observed that each effect can lead to the variation of the critical separation size by approximately 40%. Since the elasticity strength of the fluid is related to the shear rate, the dynamic control can for the first time be easily realized through tuning the flow rate in microchannels.

Solution of the Problem of Flow Past a Wing Profile Near the Interface

In this paper presente some approaches to solving the problems of flow past a wing profile near the interface. Studies on the flow in the vicinity of separation boundaries (solid walls and free surfaces) show that in a confined flow liquid turns into a bubble mixture of liquid and gas. This complicates the flow analysis and introduces additional losses resulting in impaired energy performance of the concerned mechanisms. In a general case the problem of a two-phase compressible flow around various types of vane mechanisms is substantially nonlinear (even under no-vortex flow assumption).

Design method of supercavitating pumps

The problem of effective supercavitating (SC) pump is solved, and optimum load distribution along the radius of the blade is found taking into account clearance, degree of cavitation development, influence of finite number of blades, and centrifugal forces. Sufficient accuracy can be obtained using the equivalent flat SC-grid for design of any SC-mechanisms, applying the grid effect coefficient and substituting the skewed flow calculated for grids of flat plates with the infinite attached cavitation caverns. This article gives the universal design method and provides an example of SC-pump design.

Numerical study on thermodynamic characteristics of rotational supercavitating evaporator

Rotational Supercavitating Evaporator (RSCE) has been proposed as a new technology for seawater desalination. However, thermodynamic characteristics of rotational supercavitation are still vacant. In this paper, numerical simulations are conducted on the supercavitating flows around a 3D rotating blade of RSCE with different rotational speeds and extraction pressures. Energy effect is taken into consideration in the simulation and thermodynamic characteristics of rotational supercavitation are obtained. Rotational supercavitation has a larger convective heat transfer coefficient than the boiling on a heated wall.

Numerical study on the performance of rotational supercavitating evaporator with optimized blade shape

Based on supercavitation effect, a novel device named Rotational Supercavitating Evaporator (RSCE) has been designed for desalination. In order to improve the performance of RSCE, the optimal design of three-dimensional blade shape is performed by utilizing the empirical formulae which have been validated before. Numerical simulation is then conducted on the supercavitating flow in RSCE with the optimized blade, and the supercavity dimension generated by rotational cavitator is obtained, which is further compared with the above- mentioned empirical formulae obtained by two-dimensional calculations. The results show that the supercavity length obtained by numerical simulation on the optimized blade increases with the increase of radius at first, and then decreases at larger radii, which is much smaller than the result of empirical formula at each radius.

Numerical simulation research on the optimization for blade shape of rotational supercavitating evaporator

Rotational Supercavitating Evaporator (RSCE) has been proposed as a new technology for seawater desalination. However, it lacks systematic researches on the blade shape of RSCE. In this paper, numerical simulations were conducted on the supercavities formed behind two-dimensional (2D) wedge-shaped cavitators of the RSCE. The cavitating flows around the 2D wedge-shaped cavitators with several certain wedge angles varied from 30 to 150 degrees under different cavitation numbers were simulated, and the empirical formulae of supercavity dimensions about cavitation number at corresponding wedge angles were obtained.