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As a new type of waste heat conversion machine, the roots power machine can convert low-quality waste heat resources that are difficult to use into mechanical energy. In order to study the influence of tip clearance and radial clearance on the roots power machine, experimental studies were conducted with the roots power machine having different combination of tip and radial clearances and their influence on the performance of the roots power machine was examined. A parametric study was undertaken using CFD to find the sensitivity of these clearances in influencing the performance of roots power machine in the range of 0.2-0.5 mm. From the analysis, it was inferred that radial clearance was sensitive for clearance range of 0.25-0.5 mm and tip clearance in the range of 0.2-0.25 mm. Reduction in clearance from 0.5 mm to 0.2 mm caused an increase of 10.368 and 11.423% in mechanical and volumetric efficiency respectively. [ABSTRACT FROM AUTHOR]

In the current industrial production process, waste heat of low quality is seriously wasted. In order to effectively recover low-quality waste heat, the research group developed a small energy conversion device –Roots power machine. On this basis, the research group designed a low-quality waste heat efficient utilization system with the equipment as the core and successfully applied it to low-quality waste heat recovery. However, in the actual operation process, the system can not run stably due to the occasional fluctuation of the input gas source. In view of this, after the study of waste heat recovery system, the fluctuation of gas source can be controlled by different grades according to the degree of change. Fuzzy rules also divide variables into different grades to solve problems, and fuzzy control can convert continuous changes of airflow into discrete changes, which greatly reduces the complexity of the control system. Therefore, the research group proposed a control strategy based on fuzzy PID. The simulation results show that the adjustment time of fuzzy PID is within 7 s, and the adjustment effect is obviously better than that of traditional PID. The experimental results show that the speed deviation under the condition of air source fluctuation is within the speed fluctuation rate (±5%), and the speed deviation under the condition of sudden disturbance load is within the steady speed adjustment rate (±3.5%), both of which meet the requirements of indexes. Therefore, the fuzzy PID control strategy can further improve the stability of output speed, reduce airflow pulsation, and provide the possibility for grid-connected power generation. [ABSTRACT FROM AUTHOR]

Roots power machine has obvious advantages in low and medium temperature waste heat recovery. The existing roots power machine has the problem of internal flow field disturbance, which seriously affects the power generation efficiency of the power machine. In order to solve the problem of disturbance of the internal flow field of roots power machine, the traditional involute rotor roots power machine is improved, and the roots power machine based on negative displacement involute rotor is proposed. The structure model and turbulence model of roots power machine are constructed, and the internal flow field simulation of roots power machine is realized by CFD. The pressure contour and torque change of roots power machine before and after improvement are compared, and the experimental research on the improved structure is carried out. The results show that the intensity of flow field disturbance in the modified involute rotor roots power machine decreases, and the working performance of the roots power machine improves,which provides a reference for the structural improvement and performance optimization of roots power machine. [ABSTRACT FROM AUTHOR]

Roots-type engine is suitable for small power generation system fuelled by waste heat. The disorderly fluctuations of the waste heat source upstream of the power generation process and changes in external environmental factors cause the working parameters of the device to change, which makes the speed of roots engine unstable, and the output power quality of the system is not good. For this problem, this paper starts from the control structure and control strategy to improve the adjustment speed and anti-interference ability of the control system. In this contribution, the model transformation of the dynamic work unit of waste heat power generation device from engineering to theoretical model is performed, the temperature of working gas and the speed of output shaft of roots engine are determined as control objects, and the internal mode control strategy is introduced to optimize the controller of the system. Simulation results are in good agreement with the measurements, which verify that the optimized control system can effectively improve the following ability and anti-interference of the system, and shorten the response time. [ABSTRACT FROM AUTHOR]

At present, the traditional technology on waste heat resources recovery and utilisation can not achieve the economy and feasibility of low grade waste heat resources recovery, which caused serious waste of low grade waste heat resources. In order to break through the technical difficulties, the power device of professional matching low grade waste heat is proposed. The device is called the new roots-type engine. Theoretical calculation value is derived from the theoretical research and analysis of the generation device structure, working mechanism of engine, internal three-dimensional flow field numerical simulation and other factors. By setting up the test platform, the field test was carried out to obtain the test value. The theoretical calculated values are consistent with the experimental values in a large degree. This consistency can prove that the roots-type engine flow model and parameter calculation is reliable to a certain extent. This provides a strong theoretical basis and guidance for further engineering practice of rootstype engine waste heat recovery system. This has far-reaching significance for the recovery and utilisation of low grade energy. [ABSTRACT FROM AUTHOR]

Metal-assisted chemical etching (MaCE) of metallurgical-grade silicon (MG-Si) has improved the purity of MG-Si (~99%) to close to solar-grade (~99.9999%) by removing metal impurities during the successful preparation of porous silicon nanowires (SiNWs). A new etching principle is proposed to explain the different levels of chemical reduction between various metal impurities with pore formation during etching. This model provides chemical insights into the relationship between dissolved metal ions and pores evolved during the formation of SiNWs. [ABSTRACT FROM AUTHOR]

We report the transport properties of mechanically exfoliated few-layer SnSe2 flakes, whose mobility is found to be ~85 cm2 V-1 s-1 at 300 K, higher than those of the majority of few-layer transitional metal dichalcogenides. The mobility increases strongly with decreased temperature, indicating a phonon limited transport. The conductivity of the semiconducting SnSe2 shows a metallic behavior, which is explained by two competing factors involving the different temperature dependence of mobility and carrier density. The Fermi level is found to be 87 meV below the conduction band minima (CBM) at 300 K and 12 meV below the CBM at 78 K, resulting from a heavy n-type doping. Previous studies have found SnSe2 field-effect transistors to be very difficult to turn off. We find the limiting factor to be the flake thickness compared with the maximum depletion width. With fully depleted devices, we are able to achieve a current on-off ratio of ~105. These results demonstrate the great potential of SnSe2 as a two dimensional (2D) semiconducting material and are helpful for our understanding of other heavily doped 2D materials. [ABSTRACT FROM AUTHOR]

Wearable indoor localization can now find applications in a wide spectrum of fields, including the care of children and the elderly, sports motion analysis, rehabilitation medicine, robotics navigation, etc. Conventional inertial measurement unit (IMU)-based position estimation and radio signal indoor localization methods based on WiFi, Bluetooth, ultra-wide band (UWB), and radio frequency identification (RFID) all have their limitations regarding cost, accuracy, or usability, and a combination of the techniques has been considered a promising way to improve the accuracy. This investigation aims to provide a cost-effective wearable sensing solution with data fusion algorithms for indoor localization and real-time motion analysis. The main contributions of this investigation are: (1) the design of a wireless, battery-powered, and light-weight wearable sensing device integrating a low-cost UWB module-DWM1000 and micro-electromechanical system (MEMS) IMU-MPU9250 for synchronized measurement; (2) the implementation of a Mahony complementary filter for noise cancellation and attitude calculation, and quaternions for frame rotation to obtain the continuous attitude for displacement estimation; (3) the development of a data fusion model integrating the IMU and UWB data to enhance the measurement accuracy using Kalman-filter-based time-domain iterative compensations; and (4) evaluation of the developed sensor module by comparing it with UWB- and IMU-only solutions. The test results demonstrate that the average error of the integrated module reached 7.58 cm for an arbitrary walking path, which outperformed the IMU- and UWB-only localization solutions. The module could recognize lateral roll rotations during normal walking, which could be potentially used for abnormal gait recognition. [ABSTRACT FROM AUTHOR]

Cu2ZnSnS4 (CZTS) absorbers have been grown on Mo-coated glass substrates by the rapid thermal processing (RTP) sulfurization of stacked metallic precursor (CZT) films at different annealing temperatures ranging from 500 to 580°C for 5min in sulfur atmosphere. The effects of sulfurization temperature on the structural, morphological, chemical, and optical properties of the CZTS absorbers have been investigated. XRD and Raman studies reveal that the as-deposited stacked metallic precursor films consist of metal elements such as Zn, Sn and binary alloys such as Cu6Sn5, Cu3Sn and CuZn. The sulfurized CZTS absorber films have single phase polycrystalline kesterite crystal structure with dense morphology. At 580°C, the CZT metallic precursor film is fully sulfurized with Zn-rich and Sn-poor composition, and its bandgap energy is found to be 1.50eV. The solar cell fabricated with the CZTS absorber grown at an optimized sulfurization temperature of 580°C shows a conversion efficiency of ~5% for a 0.44cm2 area with V oc =561mV, J sc =18.4mA/cm2, and FF=48.2. [ABSTRACT FROM AUTHOR]