Electrical generator or motor structure – Dynamoelectric – Conducting fluid
Patent
1986-11-26
1988-11-15
Budd, Mark O.
Electrical generator or motor structure
Dynamoelectric
Conducting fluid
H02K 4400, G21D 702
Patent
active
047852097
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to the conversion of thermal energy to electrical energy using the magnetohydrodynamic principle which eliminates the turbine or engine used in conventional conversion systems.
In MHD generators a conducting fluid is caused to flow through a channel placed between the poles of an electromagnet. An electric current is induced in the fluid at right angles to botht he direction of fluid flow and the magnetic flux and is utilized by an external load connected across electrodes placed in contact with the fluid.
Existing MHD generators are of various types.
1. Plasma
A fuel/air mixture seeded with an ionizing element is burned to produce a high temperature conducting gas mixture (plasma) which is expanded through the MHD channel. Plasmas' are relatively poor conductors, even at the high operating temperatures employed (typically about 3000.degree. C.) and superconducting (magnets with flux densities up to 6T are required to boost output. Because of the high operating temperature and flux density, plasma generators can only be considered for large scale systems.
2. Liquid Metal
In this type the conducting fluid is a liquid metal used in conjunction with a seperate thermodynamic working fluid to move it through the MHD channel. As high temperatures are not required to impart conductivity to the fluid as is the case with plasma generators lower temperature heat sources and lower strength magnets can be utilized making these generators more suitable for small scale installations.
The two main types of such generators use a single phase or a two phase medium in the MHD channel.
Two Phase
The thermodynamic fluid is injected into hot liquid metal in a mixer ahead of the MHD channel. Combinations used or proposed are organic fluids and sodium-potassium eutectic mixtures for low temperature systems, water and tin for medium temperature systems, and helium and sodium or lithium for high temperature systems. The working fluid expands and the resultant two phase mixture of gas and liquid metal accelerates through the MHD channel producing electric power. From the MHD channel the mixture enters a nozzle where further acceleration occurs followed by separation of the components in a rotating separator. The metal passes through a diffuser which converts part of its kinetic energy to potential energy in the form of pressure sufficient to force it through the primary heat exchanger where it is reheated before returning to the mixer to continue the process.
From the separator the vapour or gas still at high temperature passes through a regenerator where a proportion of its sensible heat is transferred to the working fluid on route to the mixer. The partially cooled vapour or gas from the regenerator is then further cooled in a reject heat exchanger, vapour condensing to liquid which is pumped back to the mixer via the regenerator. In the case of a gaseous working fluid the cool gas from the reject heat exchanger is compressed and returned to the mixer via the regenerator.
The main problems with these forms of generators are that: easily converted to alternating current for general use because of the very low voltage and wide voltage and current swings. non-conductive vapour or gas bubbles in the liquid metal and the high temperature of the liquid metal.
Single Phase
One form of such a generator is described in U.S. Pat. No. 3,443,129 dated May 6th, 1969. It consists of a vertical U tube the limbs of which terminate in a tank, the tube and tank are filled with liquid metal. The liquid metal is heated at the bend of the U tube and a thermodynamic working fluid is injected into the metal at the base of one of the limbs. The working fluid vapourizes forming a two phase mixture which is less dense than the contents of the other limb and is thus forced upwards. The vapour and liquid metal separate in the tank whereby the vapour is then condensed and returned as liquid to the base of the first limb and the liquid metal runs into the second limb to maintain circulation.
A MHD channel forms part of the second
REFERENCES:
patent: 3102224 (1963-08-01), Maeder
patent: 3185871 (1965-05-01), Bodine, Jr.
patent: 3286108 (1966-11-01), Fouda-Bonardi
patent: 3350584 (1967-10-01), Brocher et al.
patent: 3430081 (1969-02-01), Zauderer
patent: 3453462 (1969-07-01), Hsu et al.
patent: 3549915 (1970-12-01), Prem
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