will the superheated steam obeys the perfect gas laws. because in our power plant the hp steam before going to the superheater the pressure is 124 bar and temp is 330deg but after coming out of the super heater the temp increases up to 560deg but in pressure there is no change. but according to Charles law temp is directly proportional to pressure so if temp increases means the pressure should also increase. but there is no such thing happening.

 

Steam is not a perfect gas; it is not even an ideal gas! That's why we use steam tables and Moliere charts.

Even so, Charles law would still permit the pressure to remain constant (actually it will decrease passing through the superheater) as long as the volume increased. The perfect gas equation is PV = mRT. The only parameter in that equation that is defined as a constant is R.
The steam does expand through the superheater, and since it is flowing from the drum to the superheated steam outlet, there is a pressure drop across the superheater, so the outlet pressure is less than the drum pressure.

 

Ideal or not, time is a factor to consider. The mass of the steam will remain the same but the velocity will increase with the volume. I wasn't sure about the steam being an ideal gas.

 

Charles law only applies to closed systems (containers) at equilibrium and ideal gases

your superheater is an open system, with an inlet and outlet conditions, governed by the amount of heat input and the pressure losses,

you must perform a mass and energy balance on the system, with the steam properties as auxiliary data

with steam, use the steam tables

a mechanical engineering hand book is a good resource, use it

 

you're not comparing apples with apples.

steam before the superheater is saturated, after the superheater is ..... superheated.

the superheater is increasing the dryness fraction