Q1. A. Calculate the internal energy and enthalpy of 1 kg of air occuping 0.05 m (cubic) at 20 bar. If the internal energy is increased by 120 kJ as the air is compressed to 50 bars, calculate the new volume, Cp and Cv.
B. The pressure in a steam main is 12 bars. A sample of steam is drawn off and passed through a throttling calorimeter, the pressure and temperature at exit from the calometer being 1 bar and 140 degree C respectively. Calculate the dryness fraction of the steam in the main, stating any assumptions made in the throttling process.
Q2.
A. Air at 40 degree Celsius enters a mixing chamber at a rate of 225 kg/s where it mixes with air at 15 degree Celsius entering at a rate of 540 kg/s. Calculate the temperature of the air leaving the chamber, assuming steady slow conditions. Assume that the heat loss is negligible.
B. The temperature in a vessel is 36 degree Celsius and the proportion by mass of air to dry saturated steam is 0.1. What is the pressure in the vessel in bar and in mm of mercury vacuum? The barometric pressure is 760 mm Hg.
Q3.
A. 1 kg of steam undergoes a reversible isothermal process from 20 bar and 250 degree C to pressure of 30 bar. Calculate the heat. Flow and stating whether it is supplied or rejected and sketch the process on a T-s Diagram.
B. An air standard dual-combustion cycle has a mean effective pressure of 10 bar. The minimum pressure and temperature are 1 bar and 17 degree Celsius respectively, and the compression ratio is 16/1. Calculate the maximum cycle temperature when the cycle efficiency is 60%. The maximum cycle pressure is 60 bar.
Q4. A. In the actual combustion of benzene in an engine the A/F ratio was 12/1. Calculate the analysis of the wet product of combustion.
B. A thermometer inserted into an air steam flowing at 33.5 m/s records a temperature of 15 degree Celsius; the static pressure in the thermometer bulb is brought to rest adiabatic ally calculate:
i. The true static temperature of the air;
ii. The stagnation pressure of the air.
Q5.
A. A reaction turbine is supplied with steam at 60 bars and 600 degree Celsius. The condenser pressure is 0.07 bar. If reheat factor can be assumed to be 1.04 and the stage efficiency is constant throughout at 80%, calculate the steam flow required for a diagram power of 25000 kW.
B. A four cylinder four stroke diesel engine has a bore of 212 mm and a stroke of 292 mm. At full load at 720 rev/min the bmep is 5.93 bar and the specific fuel consumption is 0.226 kg/kW h. The air-fuel ratio as determined by exhaust gas analysis is 25/1. Calculate the break thermal efficiency and the engine. Atmospheric conditions are 1.01 bar and 15 degree Celsius and Q net v, for the fuel may be taken as 44200kJ/kg.
Q6.
A. A heat pump using ammonia as the refrigerant operates between saturation temperatures of 6 and 38 degree Celsius. The refrigerant is compressed isentropic ally from dry saturation and there is 6K of under cooling in the condenser calculate.
i. The COP hp
ii. The mass flow of refrigerant per kilowatt power input;
iii. The heat available per kilowatt power input
B. Calculate the rate of heat transfer per unit surface area by radiation between two brick walls a short distance a part when the temperature of the surface are 30 degree Celsius and 15 degree Celsius. The emissivity of brick may be taken as 0.93, and the surface may be assumed to be gray.