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The negative effect of an air gap layer presented between the membrane and cooling plate on air gap membrane distillation (AGMD) performance was diminished largely by inserting a water gap membrane distillation (WGMD) module in series. The new design of air-gap–water-gap membrane distillation (AG-WG)MD was evaluated experimentally by comparing with an AGMD system under different operating conditions. In theory, mass and heat transfer in the new (AG-WG)MD and imitative AGMD systems were analyzed. Experimental outcomes showed that a new (AG-WG)MD design profoundly enhanced flux (Pd) and gained output ratio (GOR), and greatly decreased energy consumption (STEC) and heat input (EH.I). At a concentration of 5,000 mg/L, coolant temperature of 20 °C, and flow rate of 18 L/h, Pd was promoted by 76.26%, 40.84%, 35.45%, 30.91%, and GOR by 46.38%, 33.46%, 31.27%, 26.65%, in addition to STEC being reduced about 55.63%, 46.81%, 43.66%, 38.30%, and EH.I around 31.31%, 25.84%, 23.53%, 20.55%, from the AGMD to (AG-WG)MD system at feed temperatures of 50 °C, 60 °C, 70 °C, and 80 °C, respectively. The outcomes proved that the AGMD performance could be significantly promoted by integrating with WGMD in a combined MD system. This combination increased the temperature difference across the membrane and decreased thermal-concentration boundary layers for the AGMD system.

The low flux and high energy consumption problems of the conventional three-stage air-gap membrane distillation (AG-AG-AG)MD system caused by the low temperature difference between hot and cold feed at both sides of the membrane and high boundary layer thickness were solved successfully by replacing one of the three stages of air gaps by a water gap. The novel three-stage air-gap–water-gap membrane distillation (AG-AG-WG)MD system reduced energy consumption and increased flux due to efficient internal heat recycling by virtue of a water-gap module. Heat and mass transfer in novel and conventional three-stage systems were analyzed theoretically. Under a feed temperature of 45 °C, flow rate of 20 l/h, cooling temperature of 20 °C, and concentration of 340 ppm, the (AG-AG-WG)MD promoted flux by 17.59% and 211.69%, and gained output ratio (GOR) by 60.57% and 204.33% compared with two-stage (AG-WG)MD and one-stage AGMD, respectively. This work demonstrated the important role of a water gap in changing the heat and mass transfer where convection heat transfer across the water gap is faster by 24.17 times than conduction heat transfer through the air gap. The increase in flux and GOR economized the heating energy and decreased waste heat input into the system. Additionally, the number of MD stages could increase the achieving of a high flux with operation stability.

A high-stability flat-top pulsed magnetic field (FTPMF) is strongly needed for some scientific studies, such as nuclear magnetic resonance and specific heat measurement. This paper presents a new linear flat-top regulation bypass circuit to generate a high-stability FTPMF based on a battery bank power supply. The bypass circuit consists of insulated-gate bipolar transistors (IGBTs) in parallel that operate in the active region and are free of switch ripples. To achieve precise control of the IGBT current, the influence of the Miller effect and the nonlinearity of the IGBT's transfer characteristic are studied in detail. Then, a dual-feedback loop is designed and analyzed. A prototype consisting of a 1000 V/30 kA battery bank and a bypass circuit of 1700 V/3600 A IGBTs is developed. An FTPMF with a field/duration of 23.370 T/100 ms and a stability of 64.2 ppm has been achieved.

In this paper, a kind of poly(vinylidene fluoride) (PVDF) porous heat exchange tube (HET) was prepared via non-solvent induced phase separation (NIPS) method. This porous HET possessed an ultra-thin dense skin layer of 2 μm. Since the thermal conductivity of water is higher than that of PVDF, filling the pores with water can significantly improve the heat performance of the porous HET. A full plastic double-pipe air gap membrane distillation (AGMD) module was fabricated with the porous HETs and PVDF hollow fiber membranes. In the AGMD process, the wetting treatment can make the membrane distillation flux (J) and the gained output ratio (GOR) increased by 30%. During the long-term stability test, the maximum conductivity of distillate water was only 17.2 μS/cm. The experimental results demonstrated that the porous HET can be applied for the AGMD process to treat high saline brine, and the ultra-thin dense layer can prevent the leakage of saltwater.

In this paper, an innovative method for generating high stability flat-top pulsed magnetic field (FTPMF) based on battery power supply is proposed. The system including a bypass circuit and a divider resistor is developed. The bypass circuit is in parallel with the magnet to form a parallel branch, with which the divider resistor is in series. Different from traditional application, the IGBT in bypass circuit work in linear area, as a controllable constant current source, rather than in the switch mode. The current of bypass circuit can be adjusted by the driving voltage of IGBTs to achieve the continuously regulation of the voltage division ratio between divider resistor and magnet. The current of magnet can maintain stability with feedback control, and high stability flat-top pulsed magnetic field can be obtained. The prototype has been developed, and the experiment was conducted, which proved that the high stability current can be achieved by this way.