Bond graph model of a vertical U-tube steam condenser coupled with a heat exchanger

A simulation model for a vertical U-tube steam condenser in which the condensate is stored at the bottom well is developed in this paper. The U-tubes carrying the coolant are partially submerged in the stored condensate and thus the bottom well acts as a heat exchanger. The storage of hydraulic and thermal energies is represented using a coupled pseudo-bond graph model. Advection effects are modelled by considering reticulated segments of the tubes carrying coolant, over which condensation takes place. The developed model is of intermediate complexity and it is intended for use in observer based real time process supervision, which works by comparing the process behaviour to the reference model outputs. The simulation results obtained from the bond graph model are validated with experimental data from a laboratory set-up.     

Letter to the Editor: Smart Grid Initiatives in India

Abstract

The Indian power industry is one of the fastest growing sectors and needs a paradigm shift through next-generation automation to handle the operational challenges. Presently, the Indian power sector possesses a number of issues, such as minimizing transmission and distribution losses, power theft, inadequate grid infrastructure, low metering efficiency, and lack of awareness etc. This gap can only be bridged by bringing smart grid initiatives into the Indian power industry.     

Role of Prandtl number in the interaction phenomenon of surface radiation with an opposing mixed convection within a differential heated cavity

A numerical analysis has been done for opposing mixed convection resulting due to wall movement and buoyancy induced by a clockwise fluid motion in a differentially heated cavity. The effect of Prandtl number (Pr) and wall surface emissivity (?) has been investigated for different values of Richardson number. The net radiation method has been employed to simulate the effect of surface radiation. The energy equation along with its nonlinear boundary condition is treated with the Newton‐Raphson scheme. As momentum and energy equations are coupled with each other through their source terms, an iterative solution procedure is employed. A vorticity‐stream function formulation of the momentum equation has been adopted and solved by using an underrelaxation parameter of 0.45. The effect of Prandtl number with respect to the transformation of a multi‐cellular structure of streamline into a unicellular structure has been analyzed. For the same Richardson number (Ri) with an increase in Prandtl number, the flow and heat transfer phenomena changes from a buoyancy‐induced dominated flow to a shear‐induced dominated flow, which leads to some exciting results with respect to wall movement as well. Furthermore, the role of surface radiation in this respect has been emphasized. Nusselt number variation with the Prandtl number and surface emissivity has also been presented. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21003     

Round-to-channel section extrusion through linearly converging die: a three-dimensional analysis

Metal flow in the extrusion process is an important factor in controlling the mechanical properties of the extruded products. It is, however, difficult to predict the metal flow in three-dimensional extrusion of sections due to the involvement of re-entrant corners. The present work is an attempt to find an upper bound solution for the extrusion of channel section from round billet through the taper die. The rigid-perfectly plastic model of the material is assumed, and the spatial elementary rigid region (SERR) technique is presented for which the kinematically admissible velocity field is found out by minimizing the plastic dissipation of power. The presented analysis allows for specification of process control parameters and their relation to extrusion load, equivalent die angle, reduction ratios and friction factor.     

Joint strength prediction in a pulsed MIG welding process using hybrid neuro ant colony-optimized model

In this work, a pulsed metal inert gas welding (PMIGW) process is modeled by using a hybrid soft computing technique. Ant colony optimization (ACO) and back-propagation neural network (BPNN) models are combined to predict the ultimate tensile strength of butt-welded joints. A large number of experiments have been conducted, and comparative study shows that the hybrid neuro ant colony-optimized model produces faster and also better weld-joint strength prediction than the conventional back propagation model.     

Trichuris vulpis infection in an Indian tribal population

Stools from 28 of the 82 inhabitants on remote Little Andaman Island in India were examined for parasite eggs and cysts. Trichuris trichiura eggs were found in 27, Trichuris vulpis eggs in 5, Strongyloides stercoralis larvae in 3, hookworm eggs in 15, Entamoeba histolytica and Entamoeba coli cysts each in 9, Giardia lamblia in 6, Retortamonas sp. in 3, Iodoamoeba sp. in 2, and Chilomastix sp. in 2 stools. Ascaris lumbricoides eggs were not seen. The occurrence of T. vulpis eggs in 5 stools and the absence of A. lumbricoides eggs were considered unusual findings.     

Microstructural features of Cd0·8Zn0·2Te thin films studied by X-ray diffraction and electron microscopy

Thin films of synthesized Cd_0·8Zn_0·2Te have been deposited on glass substrate at different substrate temperatures. Different microstructural parameters like crystallite size, rms strain, dislocation density, stacking fault probability and stacking fault energy are determined by XRD, SEM, TEM and TED. XRD and XPS have been used to determine the composition. Variations of the microstructural parameters with film thickness and substrate temperature have been studied in order to obtain optimum growth condition for maximum particle size and least microstructural defects. An effort has been made to correlate the experimental results.     

Characterization of deformation instability in modified 9Cr–1Mo steel during thermo-mechanical processing

In this study, various existing instability criteria were employed to delineate the unstable flow regions in modified 9Cr–1Mo steel during hot deformation. Experimental stress–strain data obtained from isothermal hot compression tests, in a wide range of temperatures (1123–1373 K) and strain rates (10⁻³–10 s⁻¹), were employed to develop instability maps. The domains of these instability maps were validated through detailed microstructural study. It has been observed that Hart’s stability criterion, Jonas’s criterion and Semiatin’s criterion under-predicts the instability regions in the studied temperatures and strain rates regime. Gegel’s and Alexander’s criteria as well as Murty’s metallurgical instability criterion, on the other hand, found to over-predict the instability domains. The instability map developed based on Dynamic Materials Model criterion has been found to precisely predict the instability domains. This instability map revealed four major unstable domains. Microscopic examination in these domains revealed that the instability is manifested in the specimens either as localized deformation band primarily along one of the diagonal or inhomogeneous distribution of martensite lath in the prior austenite grains.