ELECTRICAL HEATING

ELECTRICAL HEATING:- Electric heating is any process in which electrical energy is converted to heat. An electric heater is an electrical device that converts electric current to heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy.

Application:- 1. Domestic purposes – Hot plates for cooking Room heaters Immersion heaters for water heating Electric irons Electric toasters Electric ovens for baking etc.

2. Industrial purposes – Melting of metals Moulding of glass Heat treatment processes Baking of insulators Enamelling of copper wires etc.

Mathode of electrical heating:- Direct resistance heating:- in this mathod of heating,current is passed through the body to be heated.

Mathod of direct resistance heating:- Resistance welding. In electrod boiler for heating water. Salth bath fernace.

Indirect resistance heating in this mathod of heating current is passed through a high resistance wire know as heating elament. In this mathod heat produse is proportional to losses. Heat so developed is transferred to from heating element to the body to be heated.

Mathod of indirect resistance heating:- Room heater. Immersion water heater. Restance ovens. In matelic strip used in starter.

Introduction of induction heating Induction heating is a process which is used to bond, harden or soften metals or other conductive materials. For many modern manufacturing processes, induction heating offers an attractive combination of speed, consistency and control. Induction heating is a non-contact heating process. It uses high frequency electricity to heat materials that are electrically conductive. Since it is non-contact, the heating process does not contaminate the material being heated. It is also very efficient since the heat is actually generated inside the workpiece. This can be contrasted with other heating methods where heat is generated in flame or heating element, which is then applied to the workpiece. For these reasons Induction heating leads itself to some unique applications in industry.

How Induction heating works? It helps to have a basic understanding of the principles of electricity. When an alternating electrical current is applied to the primary of a transformer, an alternating magnetic field is created. A source of high frequency electricity is used to drive a large alternating current through a coil. This coil is known as the work coil. See the picture opposite.

In a basic induction heating setup shown at right, a solid state RF power supply sends an AC current through an inductor (often a copper coil), and the part to be heated (the workpiece) is placed inside the inductor. The inductor serves as the transformer primary and the part to be heated becomes a short circuit secondary. When a metal part is placed within the inductor and enters the magnetic field, circulating eddy currents are induced within the part. The passage of current through this coil generates a very intense and rapidly changing magnetic field in the space within the work coil. The workpiece to be heated is placed within this intense alternating magnetic field. Depending on the nature of the workpiece material, a number of things happen...

Alternative industrial heating method Flame heating Resistance heating Traditional ovens and furnaces

Advantages of induction heating Cleanliness Maximize productivity Improved product quality Extended fixture life Environmentally sound Reduce energy consumption

Advantages Absence of flue gases. Ease of control. Better working conditions. Very high efficiency of utilization. Uniform heating. No limit to upper maximum temperature.

Dielectric heating:- The heating of non-metallic materials,such as wood,plastics or ceramics, use can be made of thr dielectric loos. Supply frequency are used as 10-50MHz. Voltage needed me be as high as 20Kv. Overall efficiency of dielectrical heating is about 50%.

Dielectric heating diagram:-

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