Question

# 1) A nozzle is a device for increasing the velocity of a steadily flowing stream of...

1) A nozzle is a device for increasing the velocity of a steadily flowing stream of fluid. At the inlet to a certain nozzle the enthalpy of the fluid is 3025 kJ/kg and the velocity is 60 m/s. At the exit from the nozzle the enthalpy is 2790 kJ/kg. The nozzle is horizontal and there is negligible heat loss from it.

(i) Find the velocity at the nozzle exit.

(ii) If the inlet area is 0.1 m2 and specific volume at inlet

is 0.19 m3/kg, find the rate of flow of fluid in kg/s.

(iii) If the specific volume at the nozzle exit is 0.5 m3/kg,

find the exit area of the nozzle.

2) In the turbine of a gas turbine unit the gases flow through the turbine is 17 kg/s and the power developed by the turbine is 14000 kW. The enthalpies of the gases at inlet and outlet are 1200 kJ/kg and 360 kJ/kg respectively, and the velocities of the gases at

inlet and outlet are 60 m/s and 150 m/s respectively.

(i) Calculate the rate at which the heat is rejected from the turbine.

(ii) Find also the area of the inlet pipe given that the specific

volume of the gases at inlet is 0.5 m3/kg.

3) Air flows steadily at the rate of 0.4 kg/s through an air compressor, entering at 6 m/s with a pressure of 1 bar and a specific volume of 0.85 m3/kg, and leaving at 4.5 m/s with

a pressure of 6.9 bar and a specific volume of 0.16 m3/kg. The internal energy of air leaving is 88 kJ/kg greater than that of the air entering. Cooling water in a jacket surrounding the cylinder absorbs heat from the air at the rate of 59 kJ/s. (i) Calculate the power required to drive the compressor and (ii) the inlet and outlet pipe cross-sectional areas.

4) Steam enters a turbine at 20 m/s and specific

enthalpy of 3000 kJ/kg and leaves the turbine at

40 m/s and specific enthalpy of 2500 kJ/kg. Heat

lost to the surroundings is 25 kJ/kg of steam as the

steam passes through the turbine.

5) A turbine, operating under steady-flow conditions, receives 5000 kg of steam per hour. The steam enters the turbine at a velocity of 3000 m/min, an elevation of 5 m and a specific enthalpy of 2787 kJ/kg. It leaves the turbine at a velocity of 6000 m/min, an elevation of 1 m and a specific enthalpy of 2259 kJ/kg. Heat losses from the turbine to the surroundings amount to 16736 kJ/h. Determine the power output of the turbine.

If the steam flow rate is 360000 kg/h, determine the

output from the turbine in MW.

6) A refrigerator operates on reversed Carnot cycle.

Determine the power required to drive refrigerator

between temperatures of 42oC and 4oC if heat at the

rate of 2 kJ/s is extracted from the low temperature

region.

7) In a winter season when outside temperature is

–1oC, the inside of house is to be maintained at

25oC. Estimate the minimum power required to run

the heat pump of maintaining the temperature.

Assume heating load as 125 MJ/h.

8) What would be maximum efficiency of engine that

can be had between the temperatures of 1150oC

and 27oC ?

9)A heat engine is supplied with 278 kJ/s of heat at a constant fixed temperature of 283°C and the heat rejection takes place at 5°C. The following results were reported :

(i) 208 kJ/s are rejected, (ii) 139 kJ/s are rejected, (ii) 70 kJ/s are rejected.

Classify which of the results report a reversible cycle or irreversible cycle or impossible results.

10) An air-standard Otto cycle has a compression ratio of 9. At the beginning of the compression process, the temperature is 20°C, and the pressure is 100 kPa. The heat added is 500 kJ/kg. Determine the cycle efficiency, work output, and the heat rejected.

11)An air-standard Otto cycle operates with a minimum temperature of 300 K and a maximum temperature of 1700 K. The compression ratio of the cycle is 7. At the beginning of the compression process, the pressure is 105 kPa. Calculate P, V, and T at each point in the cycle, the mean effective pressure, and the thermal efficiency of the cycle.

12)An air-standard Diesel cycle has a compression ratio of 22

and a cut-off ratio of 2.2. Determine the thermal efficiency of

the cycle.

13)An air-standard Diesel engine has 1000 kJ/kg added as heat.

At the beginning of the compression, the temperature is

20°C, and the pressure is 150 kPa. If the compression ratio is

20, determine the maximum pressure and temperature in

the cycle.

14)An ideal Stirling engine using air as the working fluid

operates between temperature limits of 300 and 2000 K.

Determine the thermal efficiency of the cycle.

15) Consider an ideal Ericsson cycle with air as the working

fluid executed in a steady-flow system. Air is at 270C and

120 kPa at the beginning of the isothermal compression

process, during which 150 kJ/kg of heat is rejected. Heat

transfer to air occurs at 1200 K. Determine the thermal

efficiency of the cycle and net work output per unit mass of

air.

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