ANALYTICAL AND EXPERIMENTAL STUDY OF A THERMOSYPHONIC CLOSED LOOP MHD GENERATOR

摘要

A direct energy conversion from thermal to electrical is experimentally and analytically verified in using a thermosyphonic hydromagnetic bottom-heated closed loop flow as an electrical generator. A workable model of the generator is designed and built using salt and water solution as the working electrically-conducting fluid. The design calculations of the MHD generator and the range of parameters involved are based on an analytical 1-D model that predicts the induced electric current as a function of the magnetic field strength and the driving temperature difference. The upper and lower parts of the loop, which represent the heat sink and heat source of the system, are constructed from copper pipe coated with varnish on the inside. The middle region, connecting the upper and lower parts of the loop, is made up from plastic vertical pipes, with copper electrodes placed vertically opposite to each other on each side of the loop plastic walls. A transverse magnetic field is imposed in the middle non-conducting plastic- wall region, through a careful design of a set of electromagnets with minimum circuit reluctance. The electromagnet provided a magnetic field strength of 0.1 T, where as the driving temperature difference between the hot and cold portion of the loop ranged from 10-70°C. Preliminary results show that the open-circuit induced voltage increases with increased electrical conductivity of the salt and water solution. The electrodes placed in the up going flow have given higher open circuit voltage than the electrodes present in the down going flow. Experimental results are compared with the prediction of the developed 1-D model for a pipe loop. The measured data were of the same order and the discrepancy was attributed to the electrical conductivity variation with temperature and to the 2-D natural convection and boundary layer effects in the insulated region.