DieselShip's Online Content Library

Q1. From 3.2 bar, 0.13 m³ and 470 K a mass of 0.308 kg of air is expanded polytropically to 2.5 bar, 0.158 m³ and 447 K.

The system is then heated undergoing isobaric (constant pressure) process to its original temperature.

(a) Calculate EACH of the following:

(i) the final volume; (2)

(ii) the polytropic index of expansion; (3)

(iii) the net work; (3)

(iv) the net heat; (5)

(v) the total change in entropy. (3)

Note: C_V, C_P and R are 718 J/kgK, 1005 J/kgK and 287 J/kgK respectively.

Q2. The ratio of compression of an engine working on the otto cycle is 4.3:1.

At the beginning of compression, the temperature is 31℃ with a pressure of 0.99 bar.

The maximum cycle pressure is 16.78 bar,

(a) Sketch a pV and Ts graph of the cycle. (2)

(b) Calculate EACH of the following:

(i) the temperature at all points; (9)

(ii) the air standard efficiency of the cycle; (2)

(iii) the mean effective pressure. (3)

Note: For air C_V = 0.718 J/kgK and C_P = 1.005 J/kgK.

Q3. A single-acting, TWO stage reciprocating air compressor is designed for minimum

work with perfect intercooling, and the LP cylinder has a volumetric efficiency of 91%.

The compressor delivers 4.8 kg/min of air from an initial condition of 1.0135 bar and 8℃.

In EACH stage the clearance volume is 5% of the respective swept volume, and the index for all compressions and expansions is n = 1.25.

The speed of rotation is 360 r/min.

(a) Sketch the cycle on a pressure-volume diagram. (2)

(b) Determine EACH of the following:

(i) the delivery pressure; (5)

(ii) the power; (5)

(iii) the volume induced per cycle. (4)

Note: For air C_V = 0.718 kJ/kgK and C_P= 1.005 kJ/kgK

Q5. A vapour compression refrigeration system using R134a operates between the pressures of 2.006 bar and 4.8833 bar.

It enters the compressor with 10 K of superheating and compressed through a compressor with an isentropic efficiency of 82%.

No undercooling takes place in the condenser.

(a) Draw the cycle on Pressure-specific enthalpy and Temperature-specific entropy diagrams. (2)

(b) Calculate EACH of the following;

(i) the temperature leaving the compressor; (11)

(ii) the coefficient of performance. (3)

Q6. Saturated steam at a pressure of 0.38551 bar enters into the heat exchanger. The rate of heat transfer is 75 MW.

The condenser has a total of 12000 tubes arranged in a single pass. EACH tube has an outside diameter of 16 mm and a length of 3.7 m.

Cooling water enters the tubes at a temperature of 25℃ and leaves at 41℃.

Determine EACH of the following:

(a) the mass flow rate of steam; (4)

(b) the mass flow rate of cooling water; (2)

(c) sketch a diagram of temperature change across the heat exchanger; (2)

(d) the logarithmic mean temperature difference; (4)

(e)the overall heat transfer coefficient, based on the tube outside area. (4)

Note: The C_p of water is 4.18 kJ/kgK

Q7. A Natural gas consists of the following volumetric composition, Ethane (C₂H₆) (50%) and Ethene (C₂H₄) (50%).

(a) Determine EACH of the following:

(i) the Stoichiometric volume of air, for the complete combustion of 1 m³; (9)

(ii) the percentage volumetric analysis of the exhaust gas products. (5)

(b) Describe the Low Calorific Value (LCV). (2)

Note: The Composition of air is 21% O₂ and 79% N₂.

Q8. A single stage impulse turbine has a mean blade diameter of 580 mm, and the speed of rotation is 10560 rev/min. The nozzle angle is 18 degrees to the plane of rotation and the steam leaves the nozzles at 829 m/s. The blade velocity coefficient is 0.9 and there is no axial thrust.

For a steam mass flow rate of 0.15 kg/s, determine EACH of the following:

(a) the velocity of the blades; (2)

(b) the blade inlet angle; (6)

(c) the blade outlet angle: (4)

(d) the power output. (4)

Q9. A horizontal pipe carrying fresh water tapers from 200 mm diameter to 100 mm diameter. The volumetric flowrate is 0.055 m³/s.

(a) Calculate EACH of the following:

(i) the velocities at both points; (4)

(ii) find the mass flow rate; (2)

(iii) determine the pressure difference between the two points. (5)

(b) A pipe bends through an angle of 45 degrees in the vertical plane. At the inlet it had an area of 0.002 m² and pressure 800 kPa. At the exit it has area 0.0008 m² and pressure 300 kPa.

Calculate the vertical and horizontal forces due to the pressure only. (5)