wAn electrical heater capable of generating 10,000 W is to be designed. The heating element is to

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wAn electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire, having an electrical resistivity of 80 × 10??6 ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260?C. The heat transfer coefficient at the outer surface is expected to be no less than 1720 W/(m2 K) in a medium whose maximum temperature is 93?C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.GIVENA stainless steel wire with electrical heat generationHeat generation rate (QG) = 10,000 WElectrical resistivity (ρ) = 80 ×10??6 ohms-cmMaximum temperature of stainless steel (Tmax) = 1260?CHeat transfer coefficient ( hc ) = 1700 W/(m2 K)Maximum temperature of medium (T??) = 93?CVoltage (V) = 9 or 12 VASSUMPTIONSVariation in the thermal conductivity of stainless steel is negligibleThe system is in steady-stateConduction occurs in the radial directiononly

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Principles of heat transfer

ISBN: 978-0495667704

7th Edition

Authors: Frank Kreith, Raj M. Manglik, Mark S. Bohn

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