PROPERTIES OF PURE SUBSTANCES 99
Dharm
\M-therm/th3-2.p65
- In throttling process
(a)h 12 = h 2 (b)h 1 = h 2
(c)h 1 = h 2 +
h
Tfg
s (d)h^2 = h^1 +h
Tfg
s
(e) none of the above.- In isentropic process
(a)W = 2(u 2 – u 1 ) (b)W = (u 2 – u 1 )^2
(c)W = u 2 – u 1 (d)W = ()uu 21 −^12 /
(e) none of the above.
Answers - (d) 2. (a) 3. (b) 4. (c) 5. (d) 6. (b) 7. (b)
- (c) 9. (b) 10. (b) 11. (a) 12. (e) 13. (a) 14. (a)
- (a) 16. (b) 17. (c).
Theoretical Questions
- What is a pure substance?
- Draw and explain a p-T (pressure-temperature) diagram for a pure substance.
- What is a triple point?
- Explain with a neat diagram p-V-T surface.
- Does wet steam obey laws of perfect gases?
- Describe the process of formation of steam and give its graphical representation also.
- Explain the following terms relating to steam formation :
(i) Sensible heat of water, (ii) Latent heat of steam,
(iii) Dryness fraction of steam, (iv) Enthalpy of wet steam, and
(v) Superheated steam. - What advantages are obtained if superheated steam is used in steam prime movers?
- What do you mean by the following :
(i) Internal latent heat (ii) Internal energy of steam
(iii) External work of evaporation (iv) Entropy of evaporation
(v) Entropy of wet steam (vi) Entropy of superheated steam. - Write a short note on Mollier chart.
- Draw a neat sketch of throttling calorimeter and explain how dryness fraction of steam is determined ;
clearly explain its limitations. - Describe with a neat sketch a separating-throttling calorimeter for measuring the dryness fraction of
steam.
Unsolved Examples
- Find the specific volume, enthalpy and internal energy of wet steam at 18 bar, dryness fraction 0.9.
[Ans. 0.0994 m^3 /kg ; 2605.8 kJ/kg ; 2426.5 kJ/kg] - Find the dryness fraction, specific volume and internal energy of steam at 7 bar and enthalpy 2600 kJ/kg.
[Ans. 0.921 ; 0.2515 m^3 /kg, 2420 kJ/kg] - Steam at 110 bar has a specific volume of 0.0196 m^3 /kg, find the temperature, the enthalpy and the internal
energy. [Ans. 350°C ; 2889 kJ/kg ; 2673.4 kJ/kg]