Question

In a cylinder/piston arrangement, air is compressed in a
reversible polytropic process to a final state of 800 kPa, 500 K.
Initially air is at 110 kPa and 25^{o}C. During the
compression process heat transfer takes place with the ambient
maintained at 25^{o}C. Assume air as an ideal gas (R =0.287
kJ/kg) and has constant specific heats of C_{p} = 1.004
kJ/kgK and C_{v} = 0.717 kJ/kgK. If the mass of air in the
cylinder is 0.1286 kg, determine

a) the polytropic exponent *n,*

b) the final volume of the air,

c) the work done by the air,

d) the heat transfer and

e) the total entropy generation for the process.

Answer #1

A piston cylinder device contains air with a volume of 0.05 m3
at 25oC and 100 kPa pressure. The gas is now compressed to a final
temperature of 95oC at 250 kPa. This compression is polytropic and
follows PVn=constant.
a. Determine how much boundary work was added to the gas [in
kJ]
b. How much heat was added or removed from this system during
this process? [in kJ]

A piston cylinder device contains 0.15 kg of air initially at 2
MPa and 350 C. First, the air expands isothermally to a pressure of
500 kPa. Then, it is compressed polytropically back to the initial
pressure (2 MPa) with a polytropic exponent of 1.2. Find the work
performed or introduced by or to the air for each process. Express
it both times in kJ.

A 0.2 m3 piston-cylinder initially contains 400 K air. A heavy
frictionless piston maintains a pressure of 500 kPa abs. Then, a
weakness in the cylinder wall blows out and creates a hole. Air
escapes through the hole until the piston drops far enough to cover
the hole. At that point, the volume is half the initial volume.
During this process, 75 kJ of heat is transferred to the 100 kPa,
300 K surroundings. Using Cp = 1.005 kJ/kg-K and...

Air was compressed (polytropic process) from p1= 100kPa and T1=
293Kto p2= 0.3MPa and v2=0.2803m3/kg. The isentropic exponent of
the gas and specific gas constant are 1.4 and 287 J/(kgK),
respectively. Determine (a) polytropic exponent, (b) heat and work
of this process, (c) change of internal energy, (d) change of
entropy of air,if mass of air is 2kgand air can be treated as ideal
gas.Additionally,(e) draw the process on the p-v and T-s
diagrams.You can round temperature to one decimal...

Air expands in a polytropic process (n = 1.35) from 2 MPa and
1200 K to 150 kPa in a piston/cylinder. Determine per
unit mass of air the work produced and the heat transferred during
the expansion process in kJ/kg.

Steam, initially at 700 lbf/in.2, 550°F undergoes a
polytropic process in a piston–cylinder assembly to a final
pressure of 2200 lbf/in.2 Kinetic and potential energy
effects are negligible.
Determine the heat transfer, in Btu per lb of steam, for a
polytropic exponent of 1.4,
(a) using data from the steam tables.
(b) assuming ideal gas behavior.

5 kg of air in a piston cylinder assembly undergoes a Carnot
power cycle. Heat is received at temperature?1=727°C and rejected
at ?3=27°C.During the heat input process, the pressure changes from
?1=1200kPa to ?2=900kPa, respectively. Assume the air behaves as an
ideal gas with constant specific heats.
Determine:
a.pressures [kPa] at beginning and end of the isothermal heat
rejection process (?3,?4)
b.heat transfer from high temperature source [kJ]
c.thermal efficiency
d.net work output for cycle [kJ]

Your new engine design consists of a piston cylinder
arrangement. The engine operates with mostly air and a small amount
of fuel. The system undergoes a cycle. The initial Pressure and
temperature are p1= 1bar and T1= 27°C. The system undergoes a power
cycle consisting of the following process:
Process
1-2
constant volume to a pressure, P2 of 4 bars
Process
2-3
expansion of pv=constant
Process 3-1
constant-pressure compression
Draw the system and pv diagrams
If P2 is 4...

Air in a closed piston cylinder device is initially at 800 K and
at 250 kPa.
The air undergoes a process until it is at 2200 K and at 750
kPa.
What is the change in the air's specific entropy during
this process (kJ/kgK)?

A mass of one kg of water within a piston–cylinder assembly
undergoes a constant-pressure process from saturated vapor at 500
kPa to a temperature of 260°C. Kinetic and potential energy effects
are negligible. For the water:
a) Evaluate the work, in kJ,
b) If the work is 30 kJ, evaluate the heat transfer, in kJ,
c) If the heat transfer is negligible, evaluate the entropy
production in kJ/K
d) Determine if the process is reversible, irreversible, or
impossible.

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