15) Regenerator receives hot flue gases at  and cold air at  , the flue gases leave at  and the air is preheated to  . As estimated 15% of the heat given up by the flue gases is heat lost to the regenerator surroundings, and the rest (85%) is recovered in the preheated air. It may be assumed for estimating purposes that  for flue gases and  for air, independent of temperature. Estimate over all thermal efficiency, efficiency limit, and relative efficiency for this heat exchange operation.
Suppose now that the depth of the regenerator is increased to 2.5 times in such a way to double the heat exchange area while keeping constant the over-all heat transfer coefficient  .The quantities and entering temperatures of the flue gases and air will be kept the same. Heat losses are same as that in a). Estimate for the enlarged regenerator (a) air preheat temperature, (b) over-all thermal efficiency and relative thermal efficiency
16) The exit gas composition from a  charged furnace is  . The air blast is  of product Fe. The hot metal contains 5%C. Calculate
a) Quantity of active carbon in kg| ton Fe
b) Total carbon in kg
17) 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 =
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