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Browse complete papersAn ideal Otto cycle has a compression ratio of 9. The specific heat ratio is 1.4. The approximate air-standard efficiency is _________.
56.7%
58.5%
61.4%
65.2%
Correct answer
56.7%
A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 40 bar and \( 400^{\circ}C \). A fraction of steam is bled at 10 bar for regenerative feedwater heating. The condenser pressure is 0.8 bar. Pump work is neglected. What is the thermal efficiency of the cycle?
21.9%
25.3%
29.6%
36.4%
Correct answer
21.9%
A reversible heat engine converts one-sixth of the supplied heat into work. When the sink temperature is lowered to 70°C, the thermal efficiency becomes twice its original value. Determine the temperatures of the source and the sink.
420K and 350K
350K and 300K
490K and 300K
490K and 350K
Correct answer
420K and 350K
An air-standard Otto cycle has a thermal efficiency of 60%. The ratio of specific heats for the working fluid is \( \gamma = 1.5 \). Determine the compression ratio of the engine.
6.25
4.41
8.50
5.25
Correct answer
6.25
In a practical vapor compression refrigeration system, replacing a throttle valve with an isentropic expander will result in_______.
no change in performance
lower COP due to higher work requirement
same COP but higher refrigeration effect
higher COP due to work recovery
Correct answer
no change in performance
A vapor compression refrigeration system uses Freon-12 as the refrigerant. The evaporator operates at \( -10^{\circ}C \) and the condenser at \( 40^{\circ}C \). The system provides a cooling capacity of 150W. Given that the enthalpy of saturated vapor at \( -10^{\circ}C \) is \( 183kJ/kg \) and the enthalpy of saturated liquid at \( 40^{\circ}C \) is \( 74.5kJ/kg \), determine the mass flow rate of the refrigerant.
0.00098 kg/s
0.00138 kg/s
0.00215 kg/s
0.00360 kg/s
Correct answer
0.00098 kg/s
An ideal vapor compression refrigeration system operates with refrigerant R - 12. The refrigerant enters the compressor as dry saturated vapor at \( -15^{\circ}C \) and leaves the condenser as saturated liquid at \( 30^{\circ}C \). Compression is isentropic. Given that the enthalpy of dry saturated vapor at \( -15^{\circ}C \) is 344.93 kJ/kg, the enthalpy of saturated liquid at \( 30^{\circ}C \) is 228.54 kJ/kg, and the compressor exit enthalpy is 369.68 kJ/kg, determine the coefficient of performance (COP) of the system.
3.25
5.80
6.95
4.70
Correct answer
3.25
A rectangular plane surface, 2.5m wide and 4 m deep, is immersed in water such that its plane makes an angle of \( 40^{\circ} \) with the free surface. The upper edge of the plane surface is 2m below the free surface. Determine the position of the center of pressure, given that the density of the fluid is \( 1000kg/m^{3} \).
3.45m below the free surface
2.45m below the free surface
1.45m below the free surface
2m below the free surface
Correct answer
3.45m below the free surface
A plate is 0.04 mm away from a fixed plate and moves with a velocity of 0.8 m/s. The force required to maintain this speed is 3 N per \( m^{2} \). Find the viscosity of the fluid between the plates in \( N\ sec/m^{2} \)?
0.00030
0.00015
0.00045
0.00060
Correct answer
0.00030
Find the surface tension in a soap bubble of 50 mm diameter when the inside pressure is \( 3\ N/m^{2} \) above atmospheric pressure.
0.01675 N/m
0.0175 N/m
0.01875 N/m
0.01775 N/m
Correct answer
0.01675 N/m