Question

High-pressure (HP) steam is produced from water that is initially at room temperature and pressure using two heaters in series and a compressor. Water enters the first heater (heating duty of 25 kw), producing water-steam mixture, which subsequently enters the second heater to produce saturated steam. The steam is eventually compressed to 13.15 bar by a 32-hp compressor (assume 70% adiabatic efficiency). If the mass flow rate of the water (steam) is 220.5 lb/h, calculate: a) Vapour fraction at the outlet of the first heater b) Heating duty of the second heater c) Temperature of the produced HP steam

assume room temp is 27'C or 300K?

what more information? thats the question i got from the lecturer

Answer 1

For calculating vapor fraction at outlet of heater you need the outlet pressure and temperature to calculate specefic volume of liquid and vapor from steam table. Also you have to calculate volume of liquid. Divide this volume by specific volume , you will gel volume of liquid at outlet and similarly calculate volume of vapor. Now to calculate vapor fraction, divide calculated vapor volume by total volume of vapor and liquid .

For calculating heating duty of second heater you need latent heat of vaporization, Cp, it's outlet temperature (as inlet temperature of second heater is nothing but the outlet temperature of first heater).

For calculating outlet temperature of adiabatic compressor you need inlet temperature, pressure and outlet pressure, Cp,

For this first calculate (T2/T1)=(P2/P1)^(R/Cp).

Using above equation calculate T2 reversible.

Now calculate Workdone reversible = Cp*dT.

Now, workdone irreversible

= (work reversible)/efficiency

Yo will get irreversible workdone.

Now Workdone = Cp* dT.

Put workdone irreversible, Cp and T1 and calculate T2.

Hope this will be helpful and expected amswer to your question.