Back-flashover Investigation of HV Transmission Lines Using Transient Modeling of the Grounding Systems

The article presents the transients analysis of the substation grounding systems and transmission line tower footing resistances which can affect to the back-flashover (BF) or overvoltage across insulator chain in an HV power systems by using EMTP-RV software. The related transient modeling of the grounding systems is based on a transmission line (TL) model with considering the soil ionization. In addition, different configuration of grounding system have been simulated to calculated the BF, including number of vertical grounding rod, length of rod, point of lightning current injection into the grounding grid and using two depth design of grounding system where the surface of substation under consideration is very small orit is necessary to bury the grounding grid in the rocky media, occasionally. The simulation results have shown that how the mentioned parameters can considerably affect inception of BF, and suitable design of grounding system can reduce damages caused by lightning

Analysis of heat and mass transfer during microwave drying of food products

Microwave (MW) drying is a rapid dehydration technique that can be applied to specific foods. Increasing concerns over product quality and production costs have motivated the researchers to investigate and the industry to adopt microwave drying technology. The advantages of microwave drying include the following: shorter drying time, improved product quality, and flexibility in producing a wide variety of dried products. Drying is influenced by heat and mass transfer between drying airflow and product, as well as the complex moisture transport processes which take place in the product.. This paper presents an analytical approach for the drying of potato. The laws of moisture content change in the food product as a function of mass transfer are used for the theoretical approach. The study gives a brief description of efforts made to obtain basic drying parameters under different microwave drying conditions. This computational method can be used as a tool for microwave drying of potato slabs more efficiency

Homotopy Analysis Method for a Fin with Temperature Dependent Internal Heat Generation and Thermal Conductivity

Abstract: In this paper, an approximate but very accurate solution of a fin with temperature dependent internal heat generation and temperature dependent thermal conductivity is formally obtained using a powerful analytical method called the homotopy analysis method (HAM). A comparative study is also made between the results obtained by means of the HAM and a numerical procedure based on the finite difference method with Richardson extrapolation. It is shown that the freedom of choice of the auxiliary parameter h gives way to adjust and control the convergence of the solution series, which can be considered as a fundamental difference between the homotopy analysis method and other existing methods. Results confirm that the temperature distribution in the fin with temperature dependent internal heat generation and temperature dependent thermal conductivity can be accurately predicted with the HAM solution

Experimental Study of Geometrical Effects With Internal Loop on Gas Hold up and Flow Pattern in Gas-Liquid Bubble Column Reactor

Abstract: The hydrodynamic of internal reactors with a riser diameter of 4cm and 5cm operating with air and water system have been experimentally investigated for a range of superficial gas velocity. Here we have used 2 internal loops with 4cm and 5cm internal diameter. For each velocity we have measured the gas hold up. The gas phased sparged in to the column by means of 4 different spargers with different number of holes in 1mm diameter. The results show that the gas distributer plays an important role on the evolution of the bubble size distribution in gas-liquid reactor. So one of the main subjects of the present work is to study the influence of sparger design