43 & 44 Eput(2)

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Parul Institute of Engineering & Technology:

Parul Institute of Engineering & Technology Subject Code : Name Of Subject : Electrical Power Utilization Name of Unit : Electrical Heating and Welding Topic : Name of Faculty : Name of Students : (i) PATEL PARTH R.(43) ( ii)PATEL NIRAVKUMAR(44)

ELECTRICAL POWER UTILIZATION AND TRACTON:

ELECTRICAL POWER UTILIZATION AND TRACTON

Topic:

Topic Resistance heating Methods Requirement of heating element Design of heating element Method of temperature control

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Resistance heating Resistance heating is based upon the I 2 R effect .this method of heating has widely applications such as heat treatment of metals, drying and baking of potteries ,staving of enameled ware and commercial and domestic cooking. There are two method of resistance heating. Direct resistance heating Indirect resistance heating

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Direct Resistance Heating

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In this method of heating, the material or change to be heated is taken as resistance And current is passed through it. The charge may be in the form of powder or a liquid Two electrodes are immersed in the charge and connected to the supply in case of availability of direct current. The current flows through the charge and heat is produced. This method has high efficiency since heat is produced in charge itself. This method of heating is used on salt bath furnaces and in the electrode boiler for heating water .

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Indirect Resistive Heating

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In this method of resistive heating, the current is passed through a wire or other high resistance material forming a heating element. The heat is proportional to I 2 R loss produced in the heating element is delivered to the charge by one or more of the mode of transfer of heat viz. conductive convection and radiant. For industrial process , where a large amount of charge is to be heated ,the heating element is kept in the cylinder surrounded by jacket containing the charge .

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Design of Heating Element The following two formulae will  help us to calculate the diameter of wire under certain Capacity and Voltage. Where: d — Diameter of heating wire, mm p — Resistivity of heating wire ,Ω· mm2/m P — Power per phase, KiloWatts U — Voltage ,Volts W — Surface loading ,W/ cm2 L — Length of heating wire, m

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We have two formulas to define the width and thickness of strip heating element. t—thickness of strip (mm) Kt—coefficient of thickness b—width of strip Kb—coefficient of width P—capacity/power (W) ω—surface area loading (W/cm2) U—Voltage (V) Ct—Temperature-Resistance Factor

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Requirements of a heating element • It should have melting point greater than furnace temperature. • It should not react with the atmosphere of the furnace. Commonly furnace atmospheres are oxidizing, reducing and may contain water vapor. • It should be resistant to thermal and mechanical shock. • It should have enough resistivity. Resistivity is the ability of a material to inhibit flow of current in presence of applied voltage.

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Method of temperature control Temperature can be controlled by switching the various combinations of groups of resistance used in the ovens or furnace in following ways Use of variable Number of Element. Change of connections .

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1 . Use of variable Numbers of elements : In this method. The numbers of heating elements in working are changed ; so total power input or heat developed id changed . This method does not provide uniform heating unless the number of heating element in the circuit at any particular instance are distributed over the surface area , which requires complicated wiring.

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2. Change of connections : In this method the elements are arraneged to be connected either all in series or all are in parallel or combination of both or in delta by means of switching at different instants according to the requirement.This is the simplest and most commonly used methods of temperature control.

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