1- A piston cylinder device contains nitrogen with initial volume, temperature, and pressure of 0.1 m3, 25 °C, and 150 kPa, respectively. The nitrogen is then compressed up to 1 MPa when its temperature reaches 150 ˚C. If the compression energy (in the form of work) added to the system is 20 kJ, calculate the amount of heat transfer during the process and comment on its direction (find nitrogen specific heats attached if required)
2- 1 kg of saturated water vapour at 100 °C in a syst em becomes saturated liquid water by losing heat to its surrounding ambient (at 25 °C), while the pressure of the system remains constant. Answer the following questions by considering that the surrounding ambient receives this heat reversibly (the process within the system may not be reversible):
a) Calculate the total entropy change of the system and the surrounding ambient. (Mark 2.5)
b) Considering the answer to part (A) and discuss if this process is possible or not (Mark: 1)
c) By running a Carnot Cycle between the system (at 100 °C) and ambient (at 25 °C), how much heat is rejected to the ambient surro unding the system? (Mark: 2.5)
3- Calculate the efficiency of a Rankine cycle that uses water as working fluid and evaporator and condenser are operating at 2 MPa and 10 kPa, respectively. Assume that water leaves the evaporator at saturated vapour condition. (Mark: 5)
Also discuss the possible options that can be considered for increasing the efficiency of this Rankine cycle (Mark: 2)
4- A well-insulated 2-m3 rigid tank contains saturated ammonia at 40 ˚C. Initially the tank contains 50% (volume based) of this ammonia in liquid form and the rest (50%) in vapour form. The valve (on the tank) is opened, discharging ammonia vapour (not liquid) until the temperature reaches 10 ̊C. How much is the mass of discharged ammonia vapour? (Mark: 8) (see ammonia’s properties attached if required).