Question

3. A rigid vessel of volume 0.86 m3 contains 1 kg of steam at a pressure of 2 bar. Evaluate the specific volume, temperature, dryness fraction, internal energy, enthalpy, and entropy of steam. The steam is heated to raise its temperature to 150°C. Show the process on a sketch of the p–v diagram, and evaluate the pressure, increase in enthalpy, increase in internal energy, increase in entropy of steam, and the heat transfer. Evaluate also the pressure at which the steam becomes dry saturated.

4. Ten kg of water at 45°C is heated at a constant pressure of 10 bar until it becomes superheated vapour at 300°C. Find the change in volume, enthalpy, internal energy and entropy.

Answer 1

Answer on Question #73331, Physics / Molecular Physics | Thermodynamics

4. Ten kg of water at $45{}^{\circ}\mathrm{C}$ is heated at a constant pressure of 10 bar until it becomes superheated vapour at $300{}^{\circ}\mathrm{C}$. Find the change in volume, enthalpy, internal energy and entropy.

Solution:

From steam tables, corresponding to $45{}^{\circ}\mathrm{C}$,

$$v_1 = v_{f1} = 0.001010 \, \mathrm{m}^3 / \mathrm{kg};$$ $$h_1 = h_{f1} = 188.4 \, \mathrm{KJ/kg};$$ $$s_1 = s f_1 = 0.638 \, \mathrm{KJ/kg} \, \mathrm{K}$$

From steam tables, corresponding to 10 bar and $300{}^{\circ}\mathrm{C}$,

$$h_2 = 3052.1 \, \mathrm{KJ/kg};$$ $$s_2 = 7.125 \, \mathrm{KJ/kg} \, \mathrm{K};$$ $$v_2 = 0.258 \, \mathrm{m}^3 / \mathrm{kg};$$

Change in Volume:

$$V = 10 \left(0.258 - 0.001010\right) = 2.5699 \, \mathrm{m}^3.$$

Change in Enthalpy:

$$h = 10 \left(3052.1 - 188.4\right) = 28637 \, \mathrm{KJ}.$$

Change in Entropy:

$$S = 10 \left(7.125 - 0.638\right) = 64.87 \, \mathrm{KJ/K}.$$

Change in Internal energy:

$$U = m \left[ \left(h_2 - h_1\right) - \left(p_2 v_2 - p_1 v_1\right) \right]$$ $$U = m \left[ \left(h_2 - h_1\right) - p_1 \left(v_2 - v_1\right) \right]$$ $$U = 10 \left[ \left(3052.1 - 188.4\right) - 1000 \left(0.258 - 0.001010\right) \right] = 26067.1 \, \mathrm{KJ}.$$

Answer: $2.5699 \, \mathrm{m}^3$; 28637 KJ; 26067.1 KJ; 64.87 KJ/K.

Answer provided by https://www.AssignmentExpert.com