Reference no: EM132224635

Question 1. When a thermodynamic system undergoes a cycle

(a) the internal energy at the end of each cycle is zero
(b) the internal energy of the system is always increasing
(c) the internal energy of the system is always decreasing
(d) there is no net change in internal energy in the system.

Briefly explain your answer.

Question 2. A heat pump

(a) can deliver more heat to the hot reservoir than work delivered to it from the surroundings
(b) can deliver more heat to the hot reservoir than that taken from the cold reservoir
(c) must take more heat from the cold reservoir than it delivers to the hot reservoir
(d) must have a coefficient of performance of less than one.

Briefly explain your answer.

Question 3. Calculate the maximum theoretical thermal efficiency of a heat engine operating between heat reservoirs at 500°C and 50°C.

Question 4. State the second law of thermodynamics.

Question 5. In a quasistatic process involving heat transfer the temperature difference between the system and surroundings is always
(a) finite
(b) infinitesimal
(c) zero
(d) changing.

Briefly explain your answer.

Question 6. The Carnot cycle:

(a) consists of polytropic processes
(b) will convert all of the available heat energy into work
(c) establishes the maximum theoretical efficiency of a heat engine
(d) consists of internally reversible processes only.

Question 7. 0.8 kg of gas receives heat at constant pressure until its volume doubles. Calculate the change in entropy of the gas.
For the gas take c_p = 1.006 kJ kg^-1 K^-1 and cv = 0.717 kJ kg^-1 K^-1.

Question 8. An engine operating on the Otto cycle has a stroke length of 100 mm and a piston diameter of 50 mm. What is the maximum clearance volume which will give an air standard efficiency of 60%?

Question 9. A dual cycle operates with an air intake of 1 bar and 50°C. The compression ratio is 15:1 and the maximum pressures and temperatures reached in the cycle are 75 bar and 2200°C.

(a) Sketch a p-V and T-S diagram for the cycle.

(b) Calculate the pressure, specific volume and temperature at the end of each process in the cycle and complete the table below.

(c) Calculate the thermodynamic efficiency of the cycle.

Question 10. A single cylinder diesel engine produces an output torque of 75 Nm when running at 1600 revs min^-1. The indicated mean effective pressure in the cylinder is 5 bar and the piston diameter and stroke length are 150 mm and 250 mm respectively. Calculate :

(a) the mechanical efficiency of the engine

(b) the brake mean effective pressure.