Evaluation of the Hall parameter of electrolyte solutions in thermosyphonic MHD flow

Abstract The objective of this work is to determine experimentally the Hall parameter of electrolyte solutions using a closed loop thermosyphonic magnetohydrodynamic flow. The upper and lower parts of the loop, which represent the heat sink and heat source of the system respectively, are constructed from copper pipe coated with varnish on the inside surface. The middle region, connecting the upper and lower parts of the loop, is made from plastic vertical pipes, with segmented copper electrodes placed vertically opposite to each other on each side of the loop plastic walls and connected as a Hall generator to measure the open circuit voltage. A transverse magnetic field is imposed in the middle non-conducting plastic-wall region by a set of permanent magnets. The magnets provide a magnetic field strength of up to 0.225 T, whereas the driving temperature difference between the hot and cold portion of the loop ranges from 10 to 80 °C. Measurements of the induced flow rate and induced open circuit voltage are reported as a function of driving temperature difference and magnetic field strength. The analytical one-dimensional model of Ghaddar [Int. J. Heat Mass Transfer 41 (8–9) (1998) 1075] is extended to account for the electrode design and the Hall effect pertinent to electrolyte solutions. The open circuit voltage is related to the driving temperature difference, flow characteristic, magnetic field strength, electrolyte electric properties and electrode design. The developed 1-D model and the measured open circuit voltage are used to evaluate the Hall parameter ( ωτ ), which is a property of the fluid of the electrolyte liquid. It is found that ωτ can be as large as 100 for electrolytes and causes a significant loss in power output at the electrodes due to electron drift in the fluid leading to generation of current in an axial direction at the expense of the current flowing in the transverse direction between the electrodes.