PFC控制器芯片内部剖析

今天大多数电源供应商的目标都是获得接近一的功率因数(powerfactor),因此需要在交流/直流电源(AC/DC)前端采用PFC电路,该电路可将输出电压提高至高于最大交流线峰值电压的水平,通常达到直流385V。     

Thermal Performance Simulation of a Heat Pump Assisted Solar Desalination System for Kazakhstan Climatic Conditions

ABSTRACT

A numerical model has been proposed in this research work for predicting the energy performance of a heat pump assisted regenerative solar still using phase change heat storage materials such as paraffin wax and hydrate salt. The numerical model is based on energy and mass balance. The performance was simulated for Fort Sherchenko town in Kazakhstan. The performance comparison between the conventional solar still and heat pump assisted regenerative solar still with and without phase change materials are presented. Moreover, the influence of two different phase change materials on thermal performance of a heat pump assisted regenerative solar still are described. The numerical simulation results showed that heat pump assisted regenerative solar still is more energy efficient and produces better productivity when compared to the conventional simple solar still. The use of hydrate salt phase change heat storage material was found to be a good option for enhancing the performance of a heat pump assisted regenerative solar still.     

The possibility of dietary protective factors in duodenal ulcer. II. An investigation into the effect of pre-feeding with different diets and of instillation of foodstuffs into the stomach on the incidence of ulcers in pylorus-ligated rats

Rats pre-fed on a South Indian diet show a much higher incidence of ulceration of the stomach after pyloric ligation than those on a North Indian diet. Removing vegetables and pulses from the North Indian diet deprives it of its protective effect. Staple foodstuffs with a high buffer content (unmilled rice, unrefined wheat and a millet [ragi]) placed in the stomach after pyloric ligation are also protective, but those with a low buffer content (milled rice, tapioca, sorghum and maize) are not protective. Refined wheat, however, gives protection despite its low buffer content. The significance of these findings in relationship to the distribution of duodenal ulcer in India and Africa is discussed.     

WEDM of Mg/CRT/BN composites: Effect of materials and machining parameters

The current work presents a detailed exploration on real-time wire electric discharge machining (WEDM) experiments and grey relational analysis (GRA)–based multi-criteria optimization of material and machining characteristics for lowered surface roughness (R_a) and improvised material removal rate (MRR) of the newly developed magnesium/boron nitride/cathode ray tube (Mg/BN/CRT) hybrid metal matrix composites (MMCs). The composites were fabricated through powder metallurgy (PM) route by reinforcing silica-rich E-waste CRT panel glass powder crushed for different particle sizes (10, 30, and 50?µm) at various weight percentages (5%, 10%, and 15%) and with 2% boron nitride (BN). Taguchi-based orthogonal array procedure was utilized to formulate the experimental plan for WEDM considering reinforcement level and size, pulse on time (P_on), pulse off time (P_off), and wire feed (W_f) as the input process parameters. ANOVA results reveal that P_on and wt% of reinforcement has more effect on R_a and MRR than any other considered parameters. The developed mathematical model for R_a and MRR predicted values similar to that of experimental results. Multi-criteria optimization was done through GRA technique and the so recommended optimum parameter set furnishes higher MRR (22.34?mm³/min) and reduced R_a (2.87?µm).     

Special Features in Powder Preparation, Pressing, and Sintering of Uranium Dioxide

Nuclear ceramic grade UO₂ powders are usually prepared by the wet chemical ammonium diuranate route. The powders are pressed and sintered before incorporation into nuclear fuel assemblies. The processing is complex at all stages and the specifications are stringent. In powder preparation, slow addition of the precipitating reagent at a low temperature is recommended. The conditions for the drying of the precipitate, calcination and reduction are chosen to result in an agglomerate free, fine and porous powder that does not require milling or binder addition and is capable of being compacted and sintered to desired density with a homogeneous microstructure. The pressing conditions are chosen to give compacts that are free from defects such as cracking, chipping and end-capping. Sintering conditions are such that desintering, bloating, weathering and nitriding are avoided. Some insights that have been gained in powder preparation, pressing and sintering are presented in this paper. The relationship between powder characteristics and pressing and sintering properties is described.     

A twin unidirectional impulse turbine topology for OWC based wave energy plants – Experimental validation and scaling

The twin unidirectional turbine topology was recently proposed with the promise of very significant improvements in the energy capture in Oscillating Water Column (OWC) based wave energy plants. Here, we present the initial results of the experimental validation of the twin unidirectional impulse turbine topology. A scale model of the concept was built and tested using simulated bidirectional flow. The model consists of two 165 mm impulse turbines each individually coupled to 375 W grid connected induction machines. An oscillatory flow test rig was used to simulate bidirectional flow to test the model. The results of the experiments validate the concept of the twin turbine configuration. The proposed topology utilizes no moving parts and achieves more than 50% efficiency over a broad range of flow coefficients. A comparison with other competing turbines (viz, a twin Wells’ turbine, a linked guide vane impulse turbine and a fixed guide vane impulse turbine) is done, based on actual measurements in the Indian wave energy plant. The results from the experiments are scaled to evaluate the design features of a 50 GWh wave energy plant.     

There’s always the river: social and environmental equity in rapidly urbanising landscapes in India

In the pursuit of sustainable and liveable cities, Indian built environment practitioners and policy-makers are understandably focused on aspects of infrastructure, sanitation and health, given the significant urban problems of pollution and environmental degradation. However, there is limited empirical examination of Indian towns and cities as changing urban landscapes. To explore this, the paper examines the rivers in two rapidly urbanising Indian cities. It calls on interviews with practitioners, residents and users in Madurai and Ahmedabad, focusing on access and use of the river to explore social and environmental equity. The findings suggest that free, public and safe access to the rivers have reduced over time in both cities, for different reasons. Perceived environmental quality of both rivers has also worsened and the associated cultural meanings, held by riparian users, have changed. We suggest that urban river infrastructure should be reconceptualised to explore the feasibility and acceptability of a more holistic approach to understanding Indian riparian urban landscapes.     

Effects of insulating layer on the performance of thin film electroluminescent devices

Thin film electroluminescent devices were fabricated with active layer of ZnS:Mn and different insulators viz Sm₂O₃, Eu₂O₃, Na₃A1F₆, MgF₂, CeO₂ and SiO in MIS and MISIM structure. The threshold voltage for light emission in AC thin film electroluminescent devices of MIS and MISIM structures is found to depend on the dielectric properties of insulating materials. The observed threshold voltage for these devices and its variations for devices with different insulators are explained using the equivalent circuit for the device and the dielectric properties of the insulting material used for the preparation of device. Variation of threshold voltage with operating time is also studied for some of the devices.     

Growth and characterization of Zn1 – x Mg x S thin films for electroluminescent applications

:Mn thin films (x=0–0.30) were prepared by thermal co-evaporation of ZnS, Mg and Mn. The structural investigation shows the solid solution is formed in the Mg composition range x=0–0.25 and phase segregation occurs at higher Mg composition (x > 0.25). The optical band gap shows an increase with increase of Mg composition. The electroluminescent emission corresponding to the transition ion shows a blue shift with increase of Mg composition in the film. :Mn films could be used as an active layer in a.c. thin film electroluminescent (ACTFEL) devices for obtaining green emission color.