# Steam at 8 bar and 0.9 dryness fraction. solved problem

#### A spherical vessel of 0.9 m3 capacity contains steam at 8 bar and 0.9 dryness fraction. Steam is blown off until the pressure drops to 4 bar. The valve is then closed and the steam is allowed to cool until the pressure falls to 3 bar. Assuming that the enthalpy of steam in the vessel remains constant during blowing off periods, determine : (i) The mass of steam blown off ; (ii) The dryness fraction of steam in the vessel after cooling ; (iii) The heat lost by steam per kg during cooling.

A spherical vessel of 0.9 m3 capacity contains steam at 8 bar and 0.9 dryness fraction. Steam is blown off until the pressure drops to 4 bar. The valve is then closed and the steam is allowed to cool until the pressure falls to 3 bar. Assuming that the enthalpy of steam in the vessel remains constant during blowing off periods, determine :

(i) The mass of steam blown off ;

(ii) The dryness fraction of steam in the vessel after cooling ;

(iii) The heat lost by steam per kg during cooling.

1. Using steam tables, determine the mean specific heat for superheated steam :
(i) at 0. 75 bar, between 100°C and 150°C ;
(ii) at 0.5 bar, between 300°C and 400°C.

2. A pressure cooker contains 1.5 kg of saturated steam at 5 bar. Find the quantity of heat which must be rejected so as to reduce the quality to 60 % dry. Determine the pressure and temperature of the steam at the new state.

3. A spherical vessel of 0.9 m3 capacity contains steam at 8 bar and 0.9 dryness fraction. Steam is blown off until the pressure drops to 4 bar. The valve is then closed and the steam is allowed to cool until the pressure falls to 3 bar. Assuming that the enthalpy of steam in the vessel remains constant during blowing off periods, determine :

(i) The mass of steam blown off ;

(ii) The dryness fraction of steam in the vessel after cooling ;

(iii) The heat lost by steam per kg during cooling.

4. If a certain amount of steam is produced at a pressure of 8 bar and dryness fraction 0.8. Calculate :

(i) External work done during evaporation.

(ii) Internal latent heat of steam.

5. A quantity of steam at 10 bar and 0.85 dryness occupies 0.15 m3. Determine the heat supplied to raise the temperature of the steam to 300°C at constant pressure and percentage of this heat which appears as external work. Take specific heat of superheated steam as 2.2 kJ/kg K.