P. Satyamurthy

A COMPARISON OF EXPERIMENTAL RESULTS AND FLUENT SIMULATIONS FOR VOID-FRACTION DISTRIBUTION IN A TWO-PHASE SYSTEM

Abstract This work focuses on the comparison between the results obtained by gamma-ray tomography (experimental) and the FLUENT code (simulation). The physical property targeted here is the void distribution in the riser leg of a mercury-nitrogen flow system. Multiplicative algebraic reconstruction technique (MART) algorithms have been used for the tomographic image reconstruction. A comparison of the predicted and the experimental results shows that experimental numbers are consistently lower than FLUENT predictions.

Two-fluid model studies for high density two-phase liquid metal vertical flows

Abstract Liquid metal magnetohydrodynamic power converters (LMMHD PC) have been recently proposed for electrical power generation. These systems contain two-phase vertical flows consisting of high density liquid metals and suitable gas–vapor. Optimum design of LMMHD power plants require accurate modeling of two-phase flows in the riser. A two-fluid model has been developed for this purpose. One-dimensional, steady state two-fluid flow equations consisting of conservation of mass, momentum of each phase along with auxiliary relations have been solved numerically by the Runge–Kutta method. Interfacial drag force corresponding to multi-bubble, churn turbulent and slug flow based on Ishii et al. and Taitel classification has been used. Effect of variation of void fraction and phase velocities of the fluids across the cross section of the pipe has been studied based on Ishii et al. model by modifying relative velocity and incorporating appropriate coefficients in the conservation equations. Bubble size at the mixer orifice exit has been calculated using the equations of Kumar et al. In order to verify the accuracy of the model, a nitrogen–mercury experimental system has been set up. Void profiles have been measured using gamma-ray attenuation method. Void fraction, slip and pressure at different locations were determined for the mass fluxes varying from 0.125 to 2.302 kg/sm2 for nitrogen and 5.52×103 to 12.26×103 kg/sm2 for mercury. The predicted values have been compared with the experimental data. The void fraction values matched well with the experimental data within 10% and within 20% when cross-sectional effects were included. The over all pressure values were within 13% and 8%, respectively, while the slip values deviated within 25% and 27%, respectively. In general, the model matched better with experimental data when the cross-sectional effects were not included. This is due to the high density of the liquid metal and relatively larger pipe diameter.

Void fraction profile measurements in two-phase mercury — nitrogen flows using gamma-ray attenuation method

A nonintrusive measurement system using gamma rays from a 60Co source is developed to measure the void fraction profile in a two-phase flow of a high-density liquid metal and nitrogen. The method is based on the attenuation of gamma rays along various chord lengths in the cross section of a pipe line. Both the chord segment inversion (CSI) method and the least squares solution (LSS) method were applied to obtain void fraction profiles from the data. The CSI method gave spurious oscillations in the void fraction profiles, which could be attributed to the Poisson corruption due to low count rate. On the other hand, the LSS method did not contain any oscillations. Experiments were performed in the vertical riser pipe of a gravitational-type liquid metal magnetohydrodynamic loop with mercury-nitrogen two-phase flow. Void fraction profiles were obtained for various flow rates at two locations in the riser pipe. The average void fraction obtained from the profile data was compared with the values predicted by empirical relations developed for vertical two-phase flows.

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.

A conceptual scheme for electrical power generation from nuclear waste heat using liquid metal magnetohydrodynamic energy converter

Abstract A novel conceptual scheme has been proposed for utilizing the nuclear waste for electrical power generation by using a Liquid Metal Magnetohydrodynamic Energy Converter (LMMHDEC). The heat released during interim storage of the vitrified nuclear waste is used for this purpose. Possible modifications in the canister design for obtaining a higher air outlet temperature have been suggested. The basic design details of the LMMHD gravitational type energy converter is presented, and based on this model, various important parameters of the LMMHDEC system, suitable for coupling to the nuclear waste, are obtained. The gross thermodynamic cycle efficiency varies from 4.9% at a cycle temperature of 450 K to 20.1% at a cycle temperature of 570 K. Detailed engineering and economic studies are yet to be undertaken. However, in view of the minor modifications that are required in the existing canister system, this study suggests that it is possible to generate electrical power from nuclear waste heat using a LMMHDEC.

Experimental study on the effect of insulating vane and interaction parameter on current and voltage in a liquid metal MHD generator

Abstract A room temperature air-mercury LMMHD system has been set up to study the end effects in the presence of an insulating vane in a single phase LMMHD generator. Currents and voltages have been measured for various load factors (0.3-1.0) with different flow rates of mercury, vane locations and different magnetic field interaction parameter values. The deviation between the predicted values of load voltage and current, based on the constant velocity model, and the experimental results has been explained in terms of flow modifications arising because of boundary layers and due to the simultaneous presence of axial current and axial gradient of the azimuthal magnetic field at the end regions of the generator.

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.

Measurement of high gas-stream temperature using dynamic thermocouples

Abstract The dynamic probe technique using the transient response of a thermocouple is one of the methods of measuring high temperature flowing gases. In this paper, the complete dynamic response of a thermocouple has been solved consisting of convective, conductive, and radiative terms. The solution has been used to arrive at correction factors for actual experimental data. The use of dynamic thermocouples in the measurement of temperature profiles has also been illustrated by experiment. The model is verified at lower temperatures using a bunsen flame.

Analysis of heat fluxes in the electrode walls of a combustion-driven MHD generator

Abstract A qualitative analysis is presented to explain the difference in the measured heat fluxes in the anode and cathode in the arc mode of current transfer of a combustion-driven MHD generator. It is shown that various surface phenomena that take place near the wall, like Debye voltage, thermionic work function and electron enthalpy, approximately account for the asymmetry in anode and cathode heat fluxes under the same current condition.

Analysis of combustion MHD generator using a coupled core-boundary layer model

Abstract A coupled core-boundary layer model, is used to analyze a combustion MHD generator. Turbulent compressible steady state boundary layer equations near the electrode and insulator wall, along with the core region, are explicitly solved for a seeded combusion plasma. Effects of current density on core parameters, velocity and temperature profiles in the electrode boundary layer are analyzed. Effect of MHD terms on heat flux, friction coefficient and boundary layer growth are discussed. Current and voltage distributions across the boundary layer are also discussed. Some of the predicted data is compared with experimental values.