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so that the pressure in the fluid is a linear function of the volume (p = a + bV). The internal energy
of the fluid is given by the following equation
U = 42 + 3.6 pV
where U is in kJ, p in kPa, and V in cubic metre. If the fluid changes from an initial state of
190 kPa, 0.035 m3 to a final state of 420 kPa, 0.07 m3, with no work other than that done on the
piston, find the direction and magnitude of the work and heat transfer.
Taking γ = 1.4 calculate the following.
i. The final temperature.
ii. The work transfer.
iii. The change in internal energy.
.14. A closed system of constant volume experiences a temperature rise of 25°C
when a certain process occurs. The heat transferred in the process is 30 kJ. The specific heat at
constant volume for the pure substance comprising the system is 1.2 kJ/kg°C, and the system
contains 2.5 kg of this substance. Determine :
(i) The change in internal energy ;
(ii) The work done.
The power developed by a turbine in a certain steam plant is 1200 kW. The
heat supplied to the steam in the boiler is 3360 kJ/kg, the heat rejected by the system to cooling
water in the condenser is 2520 kJ/kg and the feed pump work required to pump the condensate
back into the boiler is 6 kW.
Calculate the steam flow round the cycle in kg/s
1. In a system, executing a non-flow process, the work and heat per degree
change of temperature are given by
dW
dT
= 200 W-s/°C and dQ
dT = 160 J/°C
What will be the change of internal energy of the system when its temperature changes
from
T1 = 55°C to T2 = 95°C ?
7. A cylinder containing the air comprises the system. Cycle is completed as
follows :
(i) 82000 N-m of work is done by the piston on the air during compression stroke and
45 kJ of heat are rejected to the surroundings.
(ii) During expansion stroke 100000 N-m of work is done by the air on the piston.
Calculate the quantity of heat added to the system.
4. When a stationary mass of gas was compressed without friction at constant
pressure its initial state of 0.4 m3 and 0.105 MPa was found to change to final state of 0.20 m3 and
0.105 MPa. There was a transfer of 42.5 kJ of heat from the gas during the process.
How much did the internal energy of the gas change ?
7. An air compressor commences compression when the cylinder contains 12 g at a pressure is 1.01
bar and the temperature is 20o
C. The compression is completed when the pressure is 7 bar and
the temperature 90o
C.
The characteristic gas constant R is 287 J/kg K. Assuming the process is reversible and
polytropic, calculate the index of compression and the work done.
Gas fills a cylinder fitted with a frictionless piston. The initial pressure and volume are 40 MPa
and 0.05 dm3 respectively. The gas expands reversibly and polytropically to 0.5 MPa and 1 dm3
respectively. Calculate the index of expansion and the work done
