- MHD Generation Definition: MHD power generation is a process that directly converts thermal energy into electrical energy, bypassing mechanical stages, making it highly efficient.
- Faraday’s Principle: The principle of MHD generation relies on Faraday’s law of electromagnetic induction, where movement of a conducting fluid through a magnetic field induces electrical current.
- System Types: MHD systems can be classified into open and closed cycle systems, each using different methods for circulating the working fluid.
- Efficiency Advantage: MHD generation is noted for its high efficiency and rapid achievement of full power output, surpassing many conventional generation methods.
- Operational Reliability: With no moving mechanical parts, MHD generators experience minimal mechanical losses and maintain high reliability and lower operational costs.
MHD generation, also known as magneto hydrodynamic power generation, directly converts heat energy to electrical energy without intermediate mechanical conversion. This process achieves substantial fuel economy by eliminating the steps of mechanical energy production and its subsequent conversion to electrical energy.
History of MHD Generation
The concept of MHD power generation was introduced for the very first time by Michael Faraday in the year 1832 in his Bakerian lecture to the Royal Society. He in fact carried out an experiment at the Waterloo Bridge in Great Britain for measuring the current, from the flow of the river Thames in earth’s magnetic field.
This experiment laid the groundwork for MHD generation. Over the years, extensive research followed, and by August 13, 1940, MHD generation became the accepted method for converting heat directly into electrical energy without mechanical intermediaries.
Principle of MHD Generation
The principal of MHD power generation is very simple and is based on Faraday’s law of electromagnetic induction, which states that when a conductor and a magnetic field moves relative to each other, then voltage is induced in the conductor, which results in flow of current across the terminals.
As the name implies, the magneto hydro dynamics generator shown in the figure below, is concerned with the flow of a conducting fluid in the presence of magnetic and electric fields. In conventional generator or alternator, the conductor consists of copper windings or stripswhile in an MHD generator the hot ionized gas or conducting fluid replaces the solid conductor.
A pressurized, electrically conducting fluid flows through a transverse magnetic field in a channel or duct. Pair of electrodes are located on the channel walls at right angle to the magnetic field and connected through an external circuit to deliver power to a load connected to it. Electrodes in the MHD generator perform the same function as brushes in a conventional DC generator. The MHD generator develops DC power and the conversion to AC is done using an inverter.
The power generated per unit length by MHD generator is approximately given by,
Where, u is the fluid velocity, B is the magnetic flux density, σ is the electrical conductivity of conducting fluid and P is the density of the fluid.
It is evident from the equation above, that for the higher power density of an MHD generator there must be a strong magnetic field of 4-5 tesla and high flow velocity of conducting fluid besides adequate conductivity.
MHD Cycles and Working Fluids
The MHD cycles can be of two types, namely
- Open Cycle MHD.
- Closed Cycle MHD.
The detailed account of the types of MHD cycles and the working fluids used, are given below.
Open Cycle MHD System
In the open cycle MHD system, highly heated and pressurized atmospheric air passes through a strong magnetic field. Coal is burned in a combustor at approximately 2700°C and 12 ATP, mixed with pre-heated air from plasma. Potassium carbonate is added to enhance electrical conductivity. The ionized gas, now more conductive, is accelerated through a nozzle and across the MHD generator’s magnetic field, creating an electric current as ions move toward the electrodes. This expended air is then exhausted, marking the system’s operation as an open cycle.
Closed Cycle MHD System
As the name suggests the working fluid in a closed cycle MHD is circulated in a closed loop. Hence, in this case inert gas or liquid metal is used as the working fluid to transfer the heat. The liquid metal has typically the advantage of high electrical conductivity, hence the heat provided by the combustion material need not be too high. Contrary to the open loop system there is no inlet and outlet for the atmospheric air. Hence, the process is simplified to a great extent, as the same fluid is circulated time and again for effective heat transfer.
Advantages of MHD Generation
The advantages of MHD generation over the other conventional methods of generation are given below.
- Here only working fluid is circulated, and there are no moving mechanical parts. This reduces the mechanical losses to nil and makes the operation more dependable.
- The temperature of working fluid is maintained by the walls of MHD.
- It has the ability to reach full power level almost directly.
- The price of MHD generators is much lower than conventional generators.
- MHD has very high efficiency, which is higher than most of the other conventional or non-conventional method of generation.
