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[Audio] UNIT-3 HEATING AND WELDING. UNIT-3 HEATING AND WELDING.

[Audio] Introduction -Advantages of electric heating Modes of heat transfer Methods of electric heating Resistance heating Arc furnaces Induction heating Dielectric heating Electric welding – types Resistance welding Arc welding Power supply for arc welding Radiation welding..

[Audio] Electric Heating Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. This process is done by using Joule's Law of heating. Electric heating is based on the principle, when an electric current passes through the heating element or the coil then due to the resistance or the properties it induces heat. Joule's Law states that when a current flows in a conductor the amount of heat generated is proportional to current, resistance, and time in the current flowing..

[Audio] Formula of Heat H α I². (RT) (I, R, and T are variables) H= (1/ J).I²RT (where J is a Joule's Constant) R – Resistance in ohms , T- time in seconds & I – current in amperes R – Resistance in ohms , T- time in seconds & I – current in amperes The joule's constant J is defined as the number of work units that furnishes one unit of heat when converted completely into heat. The value of J= 4.2 joules/cal. 1 Kcal = 4186 Joules According to Joule's law : I²RT= work done in joules when through a resistor of R ohms, I Ampere of current is maintained for T seconds..

[Audio] The specific heat capacity of a substance is the quantity of heat needed to raise the temperature of a unit quantity of the substance by one degree. Calling the amount of heat added Q calories, which will cause a change in temperature ∆T to a weight of substance W, at a specific heat of material Cp, then Q = W x Cp x ∆T. If Mass= 200 grams , Cp = 1 cal/ g °C , calculate H required to raise temperature from 20° C to 100 ° C . Ans: 16000 calories.

Advantages of electric heating. Cleanliness: It completely eliminates dust and ash and keeps the surroundings clean. No pollution : Due to the absence of fur gases, there is no risk and contamination of the atmosphere. Ease of control: It is possible to control and regulate the temperature accurately either manually or fully automatically. This is not possible with non-electrical heating. Uniform heating: The charge can be heated uniformly throughout whether the charge is conducting or non-conducting material. High efficiency: The overall efficiency of electric heating is high since the heat can be produced directly with the charge itself. Low attention : Electric heating generally does not require continuous attention. Localized heating: A particular job can be heated up to a particular depth for heat treatment..

Better working conditions : Electric heating produces no irritating noise. High Temperature: A particular job can be heated up to a particular depth for heat treatment. High temperature: High temperature can be obtained by electric heating (the only thing is the heating element should withstand the heat). Less floor area is required : Due to the compactness of the electric furnace, the floor area required is less. No carrying expense : The heat can be developed at or close to the point of use..

Modes of heat transfer. What is Heat Transfer?. According to thermodynamic systems, heat transfer is defined as “The movement of heat across the border of the system due to a difference in temperature between the system and its surroundings.” Interestingly, the difference in temperature is said to be a ‘potential’ that causes the transfer of heat from one point to another..

Modes of Heat Transfer- Conduction, Convection, Radiation.

Types of Heat Transfer.

[Audio] Conduction It is defined as the heat transfer directly between neighboring atoms or molecules. Usually, it is heat transfer through a solid. For example, the metal handle of a pan on a stove becomes hot due to convection. Touching the hot pan conducts heat to your hand. Conduction Equation Q = [K ∙ A ∙ (Thot – Tcold)] / d Where Q is heat transfer per unit time K is the coefficient of thermal conductivity of the substance A is the area of heat transfer Thot is the temperature of the hot region Tcold is the temperature of the cold region d is the thickness of the body.

Convection Convection is heat transfer via the movement of a fluid, such as air or water. Heating water on a stove is a good example. The water at the top of the pot becomes hot because water near the heat source rises. Another example is the movement of air around a campfire. Hot air rises, transferring heat upward. Meanwhile, the partial vacuum left by this movement draws in cool outside air that feeds the fire with fresh oxygen..

Convection Equation. Q = h c ∙ A ∙ (T s – T f ). Q is the heat transfer per unit time h c is the coefficient of convective heat transfer A is the area of heat transfer T s is the surface temperature T f is the fluid temperature.

Radiation It is the emission of electromagnetic radiation. While it occurs through a medium, it does not require one. For example, it’s warm outside on a sunny day because solar radiation crosses space and heats the atmosphere. The burner element of a stove also emits radiation. However, some heat from a burner comes from conduction between the hot element and a metal pan. Most real-life processes involve multiple forms of heat transfer..

Radiation Equation. P = e ∙ σ ∙ A· (Tr – Tc) 4. P is the net power of radiation A is the area of radiation Tr is the radiator temperature Tc is the surrounding temperature e is emissivity σ is Stefan’s constant (σ = 5.67 × 10 -8 Wm -2 K -4 ).

[Audio] Methods of electric heating In electric heating there are various methods by which heat can be produced, the heat can be produced by passing the current through resistance or by initiating an arc between two current-carrying electrodes or by using the principle of induction or by using dielectric heating, etc. Bombardment by some high energy particles like α, β, γ, and x-rays or accelerating ions can produce heat on a surface..