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Problem 3: Electric melting
An electric melting furnace is used to melt copper scrap .The scrap is initially at 25oC .The overall power consumption is 300 kW.hr /ton of molten copper, when heated to a temperature of 1523 K. Estimate the thermal efficiency of this furnace . melting point of copper 1356 K, Latent heat of melting =
Solution:
To estimate thermal efficiency,one has to calculate theoretical power consumption in heating scrap from 298 K to 1523 K.
Power required = sensible heat required to raise scrap temperature from 298 K to 1356 K + Latent heat of melting + sensible heat to raise temperature of liquid copper from 1356 to 1523 K.
Power required theoretically = 208.5 kw-hr /ton of copper and thermal efficiency = 69.5%
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