Question

Q3. 5 kg of water at T = 20° C and P = 7 bar is isobarically heated such that ΔU = 5000 kJ. (i) Find the initial and final volumes (in m3 ). (ii) Find Q and W (in kJ). (iii) Show the initial and final states on p-υ and T-υ diagrams (not to scale), denoting by arrows the direction of the process. Label the ‘f’ (saturated liquid) and ‘g’ (saturated vapor) points. Also, indicate the values of υf and υg on the x-axis of both the p-υ and T-υ diagrams.

Q4. Water inside a closed, rigid tank is cooled from its critical point to a final pressure of 10 MPa. (i) Sketch the process on p-υ and T-υ diagrams. Label the saturated liquid and saturated vapor states. (ii) Find the quality of the water after cooling. (iii) Calculate the heat transfer in kJ/kg.

Q5. Water of mass 1 kg contained in a piston-cylinder configuration is initially in a saturated liquid state (state A) at 10 bar. The water undergoes the following thermodynamic cycle: AB -> The water is heated isobarically until the water is in a saturated vapor state. BC -> The system is then cooled isochorically until the pressure is 1 bar. CD -> The system is further cooled isobarically until υD= υA. DA -> The system is finally heated isochorically back to state A. (i) Sketch this cycle on p-υ and T-υ diagrams (not to scale), using arrows to indicate the direction of each process. (ii) For each of the four states A to D, write down p, T and υ. (iii) For each of the four processes, evaluate the work and heat transfer (in kJ). (iv) What is the thermal efficiency of this power cycle?

Q6 (Bonus). Water of mass 2 kg in a closed, rigid tank is initially in the form of a twophase liquid-vapor mixture. The initial temperature is 50° C. The mixture is heated until the tank contains only saturated vapor at 110° C. (i) Find the initial pressure, in kPa. (ii) Find the work for the process, in kJ. (ii) Find the heat transfer for the process, in kJ.

Answer 1