Table of Contents
Electrical heating is process in which electrical energy is converted in to heat. Electrical heater is their examples which convert electrical energy in to heat. Heat is required for both domestic and industrial use. In industries heat is used to melt metal, to mould glass, enamelling of copper, welding in all these process we require heat in industry. In domestic it is also used for cooking, water heating, room heating and many more. All these purposes of heating can be fulfilled by electricity.
Methods of electrical heating:
- Power frequency heating
- High frequency heating
Electrical resistance heating is popular heating process that uses effect to operate. We can obtain about 1000° C temperature by using this method.
Resistance heating can be used in:
- Heat treatment of metals like (annealing, hardening)
- Storing of enamelled ware
- Commercial and domestic cooking
Direct resistance heating:
The temperature range of direct resistance heating is up to 1000° C. In this method the current directly flow through the substance from which we will produce heat. The substance which we heat is called charge in heating system. The charge means a substance will provide path for the flow of electric current. The heat will be produce inside the charge. Due to which the efficiency of the system will be increase. Resistance welding and electrode boiler are the example of direct resistance heating.
Indirect resistance heating:
In this type of heating electrical energy is passed through the heating element. The heat will be produce due to ohmic loss which is also called I2R loss and this heat will be transfer to the substance which we want to heat. For example if we want to heat water this heat will be transfer to the water. The example of indirect heating is emerging water heater, electrical cooking heater ovens, heat treatment system of metal and room heater. In room heater the current flow through the heater element and this heat transfer in the room by radiation.
Electric arc heating is a process in which electric arc is used to melt the metal. We obtain 2000° C temperature in this process.
Direct arc heating:
The temperature range in arc heating is from 3000° C to 3500° C. High temperature is obtained from the arc and the arc is formed by the two electrodes which has sufficient potential difference or it is between the one electrode and the charged cell. Electric furnace where arc is produce in electrode and charged cell is called direct arc furnace.
The direct arc heating consists of circular furnace whose inner surface is coated with refractory material. The refractories are heat insulating material. So that at high temperature the furnace not damage. In furnace depth we kept charge material. Generally the charge material is in pieces form.
The material which is to be heated or melt is known as charge. The large size director furnace operates by three phase AC. We used three electrodes in it and in case of single phase supply we will use two electrodes. There will be some gap between the electrode and the charge material on which length of arc depend. When we give supply at the electrodes medium between the charge and electrode is ionized and becomes conducting material and the current starts flowing as arc. Due to tremendous arc heat is generates due to high temperature charge starts to melt and impurities in the molten charge come at the surface and will form a layer which is known as slag. We can slant the furnace according to the need so that the impurities can be removed and we can collect pure metal.
- To increase or decrease the length of the arc we moved the electrodes upward and downward by the motor
- To control the voltage of the arc a transformer is used with tapping in the primary winding
- About 2000° C temperature reaches in direct arc furnace
- Arc remains in contact with the charge known as direct arc heating
Indirect arc heating:
In electrical furnace where the heat is producing between two electrodes and heat is generate in the arc. The heat is transfer to the charge then this is called indirect heating. The charge will itself behave like an electrode.
The construction of the indirect arc heating is almost similar to that of the direct arc heating. The main difference in it is that the arc will produce between the two electrodes. Due to the arc heat will be generated and the heat will be transfer to the charge through radiation process. The charge will start heating or melting. When the charge will be heated the slag of the metal will come at the surface and will be removed and pure metal is to be collected.
The induction heating works on the electromagnetic induction. Due to the electromagnetic induction eddy currents will be generated. This eddy current will be used for the generation of the heat. High frequency will be used for heating. The material that is to be heated is known as work piece or charge. The coil wound around the material is known as work coil.
A coil is wound on the work piece and the alternating current will flow through the coil usually this coil is made up of copper. When the current will flow in the coil magnetic field will be produced when the magnetic flux cut the metal piece the emf will be induced in the metal. From the Faraday law of electromagnetic induction we know that when alternating magnetic flux will cut the stationary conductor emf will be induced in the conductor. So here we also have a stationary charge. The magnetic flux which is produced due to the coil due to which emf will be induced in the charge. When the emf will be induced in the charge due to which a current will flow in the metal piece which is known as eddy current. There is no useful work of the eddy current. This current is dissipated in form of heat and charge material is heated. Thus due to eddy current we heated the metallic material. As it is operated by eddy current so it is also known as eddy current heating.
Direct induction heating:
In direct induction heating the current is induced in the charge and this is induces due to the current around the charge. Due to the charge inherit resistance heat will be produce. The example of direct induction heating is induction furnace and eddy current heater.
Indirect induction heating:
In this type of heating the heat element in the furnace is heated due to the current induce in it. The current is induced due to source coil mutual induction and this heat is transfer to the charge by radiation and convection. The example of indirect induction heating is indirect induction ovens used for melting of metals.
Advantages of induction heating:
- Induction heating is quick and clear
- There are no wastage of heat in the induction heating because the heat is directly produce in the charge
- Temperature control method is very easy
Application of induction heating:
- Brazing and welding
- Steed hardening
A Dielectric material is an insulator that can be polarized by applied electric field. For example if we have a dielectric material in which we have orientation of molecules randomly organized inside the material. When we will pass electric field through it the molecules will be in proper order and this is happen due to polarization which can be done with the help of an external electric field. This property will be used to generate heat. An important property of dielectric is its ability to support an electrostatic field while dissipating minimum energy in form of heat. A dielectric material is an efficient supporter of electrostatic fields but and is poor conductor of electricity. Examples of dielectrics are glass, mica, plastic, air etc.
Insulation materials like wood, plastic, ceramic to heat it uniformly is very difficult. For this case we used high frequency capacitive heating should be employ. The dielectric material is connected between two electrodes and this dielectric behaves like a capacitor. The high frequency current can pass through capacitor and will cause uniform heating in material. The frequency that is applied in dielectric heating is very maximum in the range of 10 KHz to 50 KHz. The efficiency of this system is very less.
Infrared heating is a system or appliance that provides heat by thermal radiation to get a better understanding of how thermal radiation work we will consider sun which emits infrared rays or thermal radiation that travels apart approximately 93 million miles through cold dark space. When it reaches the earth surface it is then absorbed by the objects and converted in to heat. Heated objects that emits this energy in the form of conduction, convection or radiation. Heating the surrounding air through the use of the electromagnetic spectrum. The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. It includes gamma radiation, x-rays, ultra violet, visible light, infrared, microwaves and radio waves. Like the sun energy radiant heat energy is emitted in the form of electromagnetic waves in the infrared band which is located next to the visible light band on the electromagnetic spectrum. These same operating principles apply for manufactured infrared heating appliance.
This is the most inefficient method of the heating. This is simplest form of heating the electromagnetic radiation comes from the incandescent bulb and these electric radiation is focussed on the surface which we want to heat. This method is usually used for
- Paint stoving
- Softening of thermoplastic sheets
The infrared heating has many advantages like:
- The heating is very spontaneous and rapid
- Compactness of heating unit means the setup require for infrared heating require very less space
- There is huge flexibility in the design
- It is comparatively a safe method
Electrical heating advantages:
- Electrical heat is dirt free
- Electrical heat is free from flue gases no need of exhaust system
- It is economical as compare to other heating system. It running and installation cost is very less
- We can easily control temperature in it
- We can design automatic system against abnormality in heating
- Efficiency of the system is very high
- Noise free
- Starting is quite faster
Selection of heater for room:
In winter season everyone need heater to warm them. Room heater is also called space heater. There are different types of brands, qualities and features of electric heaters.
Room heater on the basis of heating technology and methods we divide it in three major types:
- Infrared electric heater which is also known as halogen or quartz heater
- Fan room heater which is also known as blower, ceramic or convection heater
- Oil filled room heater
Infrared room heaters:
These heaters consist of halogen tube due to which it gives both heat and light. It works like a camp fire because it can warm a limited area. If the room size is large it will not work properly but if the room size is small it will work. This is the reason it consume less electricity. It does not contain fan due to which it does not produce any sound.
Fan room heater:
This heater consist of fan whose air is heated with the heating element ceramic coil. When the air flow from the fan then it is pass through the heating element. Due to which the room becomes warm. This is used in large space and is safe to use. It consumes less electricity and it also consist of thermostat with the help of which we can set the temperature. When the room becomes warm it will stop and when the room is cold it will start automatically.
Oil filled room heater:
it takes time to warm the room but when we off the heater the room will not cool quickly this is the property of this heater. It consist of oil when it start working the oil will also warm and when the air is passed through it the air will also be warm. Another quality of this heater is that it does not decrease the oxygen level and it can warm large room easily. This type of heater is expensive and it also consumes maximum electricity.
According to the size we can select heater for the room as given in the chart:
|20 square feet||250|
|40 square feet||500|
|60 square feet||750|
|80 square feet||1000|
|100 square feet||1250|
|120 square feet||1500|
|140 square feet||1750|
|160 square feet||2000|