Q17. An air standard Diesel cycle has minimum pressure and temperature of 1 bar and 300 K respectively. The maximum pressure and temperature are respectively 80 bar and 2000 K.
(a) Sketch the cycle on p-V and T-s diagrams.
(b) Calculate for the cycle EACH of the following:
(i) the thermal efficiency
(ii) the specific work output.
Note: For air, γ = 1.4 and = 1.005 kJ/kg K.
Q12. Benzene (C6H6) is burned in 10% excess air and the combustion products contain 0.03 kg of CO for each kg of fuel burned.
(a) Formulate the full combustion equation per kmol of fuel for the conditions stated.
(b) Calculate the percentage dry gas analysis by volume.
Note: Relative atomic masses: H = 1; C = 12; N = 14; O = 16
Air contains 21% Oxygen by volume.
Q3. Steam enters a turbine at a pressure of 50 bar and a temperature of 440°C, and leaves at a pressure of 0.12 bar with a dryness fraction of 0.92. It is then fully condensed without undercooling, and the condensate passes through two direct mixing feed heaters before being fed to the boiler. The high pressure bled steam is at a pressure of 15 bar and a temperature of 280°C, and the low pressure bled steam is at a pressure of 1.5 bar and a temperature of 120°C. The feed water leaves each feed heater at the saturation temperature of the bled steam.
Calculate EACH of the following:
(a) the mass of bled steam supplied to each feed heater, per kg of steam entering the turbine
(b) the work output of the turbine, per kg of steam entering the turbine.
Q16. A reversed Carnot refrigeration cycle uses R134a. The refrigerant is dry and saturated at the end of compression, and leaves the condenser as saturated liquid. The cycle operates between temperatures of -5°C and 40°C.
(a) Sketch the cycle on p-h and T-s diagrams.
(b) Determine EACH of the following:
(i) the dryness fraction at compressor inlet
(ii) the coefficient of performance
(iii) the refrigerating effect per kg.
(c) Give TWO reasons why such a cycle is unlikely to be used in practice
Q15. An LNG carrier has two spherical tanks each of diameter 45 m. They contain liquefied gas at a temperature of 163°C. The tanks are insulated with a 300 mm thickness of material of thermal conductivity 0.04 W/m K. The outside surface heat transfer coefficient is 8 W/m2 K, and the temperature of the surrounding air is 35°C. The thermal resistances of the inside surface film and of the tank wall may be disregarded. The latent heat of evaporation of the gas is 515 kJ/kg. The density of the liquid is 460 kg/m3.
(a) Calculate the total heat transfer rate to the tanks.
(b) Estimate the percentage of the cargo which boils off each day.
Q15. (a) Sketch the p-V diagram for a two-stage reciprocating air compressor, indicating the area(s) which represent the work saved by intercooling.
(b) In a two-stage reciprocating air compressor, the LP suction pressure is 1 bar, the LP delivery and HP suction pressure is 4 bar, and the HP delivery pressure is 15 bar. The LP suction temperature is 289 K and the HP suction temperature is 305 K. The index of compression and expansion is 1.28. Calculate EACH of the following:
(i) the indicated work per kg
(ii) the heat removed in the intercooler per kg
(iii) the isothermal efficiency.
Note: For air, R = 0.287 kJ/kg K and Cp = 1.005 kJ/kg K.
Username or email address *Required
Password *Required
Note: Entering wrong username in the login form will ban your IP address immediately. Entering wrong password multiple times will also ban your IP address temporarily.
Log in
Lost your password? Remember me
No account yet?
