ASSIGNMENT Me PDF
ASSIGNMENT Me PDF
ASSIGNMENT Me PDF
1. A utility runs a Rankine cycle with a water boiler at 3.0 MPa and the cycle has the
highest and lowest temperatures of 450C and 45C respectively. Find the plant
efficiency and the efficiency of a Carnot cycle with the same temperatures.
2. A steam power plant operating in an ideal Rankine cycle has a high pressure of 5 MPa
and a low pressure of 15 kPa. The turbine exhaust state should have a quality of at least
95% and the turbine power generated should be 7.5 MW. Find the necessary boiler exit
temperature and the total mass flow rate.
3. A smaller power plant produces steam at 3 MPa, 600oC in the boiler. It keeps the
condenser at 45 oC by transfer of 10 MW out as heat transfer. The first turbine section
expands to 500 kPa and then flow is reheated followed by the expansion in the low
pressure turbine. Find the reheat temperature so the turbine output is saturated vapor. For
this reheat find the total turbine power output and the boiler heat transfer.
4. A steam power plant operates with a boiler output of 20 kg/s steam at 2 MPa, 600C. The
condenser operates at 50C dumping energy to a river that has an average temperature of
20C. There is one open feedwater heater with extraction from the turbine at 600 kPa and
its exit is saturated liquid. Find the mass flow rate of the extraction flow. If the river
water should not be heated more than 5C how much water should be pumped from the
river to the heat exchanger (condenser)?
5. Consider an ideal steam regenerative cycle in which steam enters the turbine at 3.0 MPa,
400C, and exhausts to the condenser at 10 kPa. Steam is extracted from the turbine at
0.8 MPa for an open feedwater heater. The feedwater leaves the heater as saturated
liquid. The appropriate pumps are used for the water leaving the condenser and the
feedwater heater. Calculate the thermal efficiency of the cycle and the net work per
kilogram of steam.
6. A closed feedwater heater in a regenerative steam power cycle heats 20 kg/s of water
from 100C, 20 MPa to 250C, 20 MPa. The extraction steam from the turbine enters the
heater at 4 MPa, 275C, and leaves as saturated liquid. What is the required mass flow
rate of the extraction steam?
7. Steam enters the turbine of a power plant at 5 MPa and 400C, and exhausts to the
condenser at 10 kPa. The turbine produces a power output of 20000 kW with an
isentropic efficiency of 85%. What is the mass flow rate of steam around the cycle and
the rate of heat rejection in the condenser? Find the thermal efficiency of the power plant
and how does this compare with a Carnot cycle. All the components are ideal exceptthe
turbine
7. A diesel engine has a bore of 0.1 m, a stroke of 0.11 m and a compression ratio of 19:1
running at 2000 RPM (revolutions per minute). Each cycle takes two revolutions and has
a mean effective pressure of 1400 kPa. With a total of 6 cylinders find the engine power
in kW and horsepower, hp.
8. At the beginning of compression in a diesel cycle T = 300 K, P = 200 kPa and after
combustion (heat addition) is complete T = 1500 K and P = 7.0 MPa. Find the
compression ratio, the thermal efficiency and the mean effective pressure.
Refrigeration
1. A refrigerator using R-134a is located in a 20C room. Consider the cycle to be ideal,
except that the compressor is neither adiabatic nor reversible. Saturated vapor at -20C
enters the compressor, and the R-134a exits the compressor at 50C. The condenser
temperature is 40C. The mass flow rate of refrigerant around the cycle is 0.2 kg/s, and
the coefficient of performance is measured and found to be 2.3. Find the power input to
the compressor and the rate of entropy generation in the compressor process.
2. Consider a two-stage compression refrigeration system operating between the pressure
limits of 0.8 and 0.14 MPa. The working fluid is refrigerant-134a. The refrigerant leaves
the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.32
MPa. Part of the refrigerant evaporates during this flashing process, and this vapor is
mixed with the refrigerant leaving the low-pressure compressor. The mixture is then
compressed to the condenser pressure by the high-pressure compressor. The liquid in the
flash chamber is throttled to the evaporator pressure and cools the refrigerated space as it
vaporizes in the evaporator. Assuming the refrigerant leaves the evaporator as a saturated
vapor and both compressors are isentropic, determine (a) the fraction of the refrigerant
that evaporates as it is throttled to the flash chamber, (b) the amount of heat removed
from the refrigerated space and the compressor work per unit mass of refrigerant flowing
through the condenser, and (c) the coefficient of performance.