MHD EFFECT ON NaK-NITROGEN TWO-PHASE FLOW AND HEAT TRANSFER IN A VERTICAL ROUND TUBE

The research and development of LMMHD energy conversion (EC) systems which started in the 1960s has already come a long way and is heading towards commercialization. Design and development of such systems has to deal with a number of questions relating to single- and two-phase flows of molten metals, including different patterns of two-phase flow, interphase, phenomena, heat transfer, performance of LMMHD components and compatibility of liquid metals with other fluids and with confinement materials. Liquid metal MHD (LMMHD) power conversion systems proposed many years ago are gaining increasing attention in their various proposed modes, consisting of single-phase or two-phase fluid flow for a wide range of heat sources, e.g. solar energy, waste heat, nuclear energy, etc. Liquid metal MHD (LMMHD) power systems have been recently proposed for direct electrical energy conversion of low grade thermal sources of energy, like solar energy. Solar-powered LMMHD power generation systems are very attractive regarding efficiency and cost per unit of installed power. Theoretical and experimental investigations carried out in the various aspects of these systems are presented. A state of the art review of activities in the solar-powered LMMHD power systems field which have taken place so far is described here.

Solar-assisted liquid metal MHD power generation: A state of the art study

Single-phase and two-phase magnetohydrodynamic pipe flow

An analytical model of a two‐phase liquid‐metal magnetohydrodynamic generator is developed. The model is based on the averaging equations governing the two‐phase flow in the channel of a liquid‐metal magnetohydrodynamic generator. The inhomogeneity of the distribution of the gas phase over the channel cross section is taken into account by introducing the correlation coefficients β1, β2, and β3: 〈αu〉 = β1〈α〉〈u〉, 〈σu〉 = β2〈σ〉〈u〉, 〈ρu〉 = β3〈ρ〉〈u〉. Expressions for these coefficients in terms of the correlation coefficient β1 are obtained. The calculated characteristics of the generator were compared with experimental data obtained at the Argonne National Laboratory. The comparison shows that the calculated and measured characteristics are in fairly good (±15%) agreement.

An analytical model of a two‐phase liquid metal magnetohydrodynamic generator

Characteristics of flow and heat transfer in air-mercury two-phase stratified flow under a vertical magnetic field

: An extensive series of experiments were performed in which the measured efficiency of two-phase liquid-metal MHD generators has been significantly increased by reducing dissipative boundary-layer current shunts. A series of experiments were performed in which a thin layer (0.0305 cm) of nitrogen was injected along the insulated walls of a constant-moving, conducting, liquid boundary layer. Preliminary water-nitrogen experiments were performed to study the effects of injector port geometry on boundary-layer control. Results of the experiments indicate that the liquid boundary-layer can be effectively displaced from the wall by the injection of nitrogen parallel to the insulator wall.

Experimental two-phase liquid-metal magnetohydrodynamic generator program

The Argonne National Laboratory ambient-temperature NaK-nitrogen facility was recently rebuilt for tests at higher liquid velocities and pressures The revised facility is described Recent runs with the same parameters as with the old facility showed better generator operation was obtained--the slip ratio was lower and the power level was higher Operation at higher liquid velocities showed still further reductions in slip ratio and increased generator efficiency The initial steps in a program to evaluate surface-active agents in the generator are described

Initial generator tests with revised ambient-temperature liquid-metal MHD facility

Testing of the second diverging-channel generator with the revised ambient-temperature NaK-N/sub 2/ facility has been completed. The primary goal of the revised facility, demonstrating reduced slip ratio (ratio of gas velocity to liquid velocity) with higher liquid velocity (flow rate), was accomplished. The reduction in slip ratio was dramatically demonstrated by a series of consecutive runs with varying flow rate (from 6 kg/s to 12 kg/s for the liquid). Substantial increases in generator efficiency were obtained with higher liquid flow rates. Experiments to demonstrate that good liquid-to-gas heat transfer exists in the generator were successfully completed. Good heat transfer is essential because it is the almost-constant-temperature expansion of the gas (vapor) in the generator that yields the higher system efficiencies for liquid-metal MHD power cycles. The feasibility of generating relatively-stable bubbles, hence, a foam, in liquid metals has been demonstrated. Photographic documentation of these phenomena, both motion and still pictures, was made. Surface tension measurements and foaming experiments have shown that viscosity is also a factor in promoting bubble formation and persistence. Wetting and contact angle measurements have been made for stainless steel and carbon steel immersed in eutectic NaK. An analytical study of the liquid shunt (wall) layer sizesmore » and losses has shown that these losses are not expected to be significant for large generators; less than 1.0 percent decrease in efficiency is anticipated. A two-phase pressure-gradient correlation developed for MHD flows has been shown to agree to within 20 percent with the generator data.« less

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G. Fabris

Papers

Experimental two-phase liquid-metal magnetohydrodynamic generator program

Experimental two-phase liquid-metal magnetohydrodynamic generator program

Initial generator tests with revised ambient-temperature liquid-metal MHD facility

Experimental two-phase liquid-metal magnetohydrodynamic generator program. Annual report, October 1976--September 1977