Question

Air in a piston-cylinder device undergoes an isobaric expansion process from 280 K and 245 kPa to 880 K. This is achieved by adding heat to the system under quasi-equilibrium conditions. What is the work done by the air during this process? (Use the appropriate sign convention.) What is the amount of heat transferred for this process? (Use the appropriate sign convention.) Considering the actual variation in the specific heat of air during the process, what is the change in entropy of the air per unit mass? Given that the environment surrounding the piston-cylinder is at 1160 K, how much entropy is generated from this process?

Answer #1

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
piston-cylinder device contains 3.2 kg of air at 400 kPa and 10°C.
Heat is transfered to air and the piston is allowed to expand at
constant pressure until its temperature reaches 50°C. The work done
during this expansion process is: Use kj units

An ideal gas initially at 350 K undergoes an isobaric expansion
at 2.50 kPa. The volume increases from 1.00 m3 to 3.00 m3 and 13.0
kJ is transferred to the gas by heat. (a) What is the change in
internal energy of the gas? kJ (b) What is the final temperature of
the gas?

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 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.

An insulated piston–cylinder device initially contains
20 L of air at 140 kPa and 27 °C. Air
is now heated for 10 min by a 100-W resistance heater placed inside
the cylinder. The pressure
of air is maintained constant during this process, and the
surroundings are at 27 °C and 100 kPa.
Determine the exergy destroyed during this process.

0.75 kg of refrigerant-134a at 120 kPa and 20°C
initially fills a piston-cylinder device. Heat is now transferred
to the refrigerant from a source at 150°C, and the piston which is
resting on a set of stops, starts moving when the pressure inside
reaches 140 kPa. Heat transfer continues until the temperature
reaches 90°C. Assuming the surrounding to be at 25°C and 100 kPa,
determine (a) the work done, (b) the heat transfer, (c) the exergy
destroyed, and (d) the...

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 25oC. During the
compression process heat transfer takes place with the ambient
maintained at 25oC. Assume air as an ideal gas (R =0.287
kJ/kg) and has constant specific heats of Cp = 1.004
kJ/kgK and Cv = 0.717 kJ/kgK. If the mass of air in the
cylinder is 0.1286 kg, determine
a)...

A 0.2 m3 piston/cylinder contains air at 400 K and
400 kPa and receives heat from a constant temperature heat source
at 1300 K. The piston expands at constant pressure to a
volume of 0.6 m3. Determine the change of availability
of the system.

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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