V.K. Rohatgi

Gamma-ray attenuation method for void fraction measurement in fluctuating two-phase liquid metal flows

Void fraction measurements are made by the gamma -radiation attenuation method in mercury-air two-phase flow systems. To measure the void fraction with an accuracy of the order of 5%, the required gamma -ray source and the strength of the source is experimentally found for mercury-air two-phase flow systems of pathlength up to 80 mm using 137Cs and 60Co. This is achieved by comparing the simulated void fraction and the measured void fraction. Since the dynamic fluctuations affect the accuracy of the measurement, the dynamic effect is analysed by simulating void fraction fluctuations of different magnitude. If the fluctuation magnitude is known then the required correction can be applied to the measured void fraction. The measured void fraction is compared with the predicted values by a theoretical model available for the upward liquid metal-gas two-phase flow in pipes.

Relativistic electron beam heating of a hydrogen plasma in open confinement systems: Theoretical model

A one‐dimensional theoretical model for predicting the heating of a hydrogen plasma in open confinement systems by a relativistic electron beam is presented. Direct energy transfer of beam electrons via interaction with large amplitude waves of the two‐stream instability and Ohmic dissipation of plasma return current caused by classical and anomalous resistivities are considered as power input terms. For loss terms, various atomic processes and heat conduction mechanisms are considered. In the light of observed changes in the average scattering angle of the beam inside the plasma, criteria deciding the character of beam–plasma interaction and the estimation of direct power transfer are discussed. The numerical results are presented with a reference to the results of the beam–plasma heating experiments reported in the literature. Better agreement is observed between the experiment and the present analysis.

Measurement of temperature, electrical conductivity and ion density of seeded combustion plasmas

Abstract The combustion products of a fossil fuel with an additive of low ionisation potential constitute the working medium in open cycle MHD generators. The most important parameters which have a direct bearing on the performance of MHD generators (apart from gas dynamic parameters) are: (a) plasma temperature, (b) electrical conductivity (c) charged particle density. In this paper, we have studied these characteristic parameters of a potassium seeded LPG-O2 plasma as a function of stoichiometric coefficient, power rating of torch, seeding percentage in the plasma and water ballast on the seed solution. A few experiments were also done with caesium as seed. A suitable theoretical model developed has been used to cross-check the experimental results.

Power output characteristics of a finitely segmented faraday mhd generator

Abstract Accounting for the effect of finite segmentation of electrodes as a reduction of both the electrical conductivity of the working fluid and the Hall parameter, we have derived expressions of power density for a finitely segmented Faraday MHD generator with and without considerable electrode voltage drop. While calculating the actual loading factor through the electrode voltage drop, the latter has been estimated in a finitely segmented Faraday MHD generator with and without ash in the combustion products. The results have been discussed and compared with earlier results where the considered effects are not taken into account. It is found that the effects of finite segmentation of electrodes and the electrode voltage drop modify the power output characteristics significantly.

Quasi-three-dimensional analysis of a combustion MHD generator

Abstract A quasi-three dimensional code is developed for an MHD generator. Turbulent compressible steady state boundary layer equations near the electrode and insulator wall along with core region are explicitly solved for a seeded combustion plasma. Effects of leakage currents in the boundary layers and imperfect channel walls are included in the analysis. Accuracy and validity of the model is verified with experimental data. Effect of wall temperature, leakage currents and other parameters are analysed.

Radiation and ionizational nonequilibrium effects on the electron density in a nonequilibrium MHD generator duct

Abstract This paper presents an investigation of the radiation and ionizational nonequilibrium effects of charge carriers on the electron density across a nonequilibrium MHD channel. Using the generated and empirical velocity and temperature profiles, the steady and unsteady diffusion equations are solved numerically using an implicit finite difference technique. It is found that, as a result of the radiation effects during ionizational nonequilibrium processes, the electron density is more, in comparison with its equilibrium value, in the boundary layer region, whereas it is less than its equilibrium value in the core.

Analysis of voltage-drop near cold-electrodes of a combustion MHD generator

Abstract In this paper turbulent compressible boundary layer equations for mass, momentum and energy are solved near the cold electrode wall of a combustion MHD generator. Arcs are simulated by freezing the electron temperature (and hence electrical conductivity) to a temperature called T arc when gas temperature is less than T arc . Theoretical neare electrode drop for various current densities along the flow direction is analysed for various T arc temperatures and compared with experimentally obtained near electrode drop. It is found that the T arc temperature increases as a square root along the flow direction and has linear dependency on current density.

Two-Phase Flow Studies in Mercury-Air Liquid Metal MHD Generators

A two phase liquid metal MHD system consisting of Mercury and Air is built to study MHD Generator behaviour at high void fractions. Average void fraction, pressure, and voltage fluctuations and electrical continuity have been studied. It is found that all the frequency of fluctuations of pressure and voltage are within 100 Hz. There is an increase in the rate of electrical discontinuity between electrodes with increase in void fraction. Gamma ray technique using Cs-137 and Co-60 satisfactorily measures void fraction.

Radiative heat transfer from potassium seeded water gas combustion plasma

Abstract Radiative heat transfer calculations from a potassium seeded water gas combustion plasma have been made to estimate the radiative heat losses through the walls of a MHD channel. Both molecular combustion products and seed contribute significantly to the total radiation loss from a plasma. The spectral emission properties of CO 2 , H 2 O, CO and potassium have been taken into account. It has been shown that the contribution of CO to heat flux is very small and, thus, can be neglected. CO 2 and H 2 O are the primary contributors to the radiation from the combustion products. At MHD temperatures, 55–80% of the contribution to heat flux from the combustion products comes from bands lying up to 2.7 μm in the near infrared. It has been shown that accurate knowledge of absorption cross-section data is essential to predict the radiative heat transfer from potassium. It has been estimated that 25–30% of the total radiative heat flux is from the potassium seed.

Electric potential behaviour in segmented Faraday-type MHD generators

Abstract The potential distribution in the transverse cross-section of a segmented Faraday-type MHD generator is studied. The governing elliptic equation, derived with allowance for the finite electrode segmentation effect and nonuniformity of the gas in the channel, is solved numerically using the Alternating Direction Implicit method in the finite difference scheme, instead of the successive overrelaxation method. The computed potential distribution and the potential drops are found to compare well with experimental results. The potential drops at the electrodes are found to increase with increasing current density.