Question

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.

Answer #1

A gas undergoes a process in a piston–cylinder assembly during
which the pressure-specific volume relation is
pv1.2 = constant. The mass of the gas
is 0.4 lb and the following data are known: p1
= 160 lbf/in.2, V1 = 1
ft3, and p2 = 300
lbf/in.2 During the process, heat transfer from
the gas is 2.1 Btu. Kinetic and potential energy effects are
negligible. Determine the change in specific internal energy of the
gas, in Btu/lb.
Δu=

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.

Entropy From Steam Tables
A piston-cylinder assembly contain 2 kg of water. The water is
initially at the pressure of 0.5 MPa and the temperature of 300°C.
The water is cooled down at constant pressure process until it is a
saturated vapor. Determine the change in the entropy of the
system.

Oxygen gas is contained in a piston cylinder assembly at an
initial pressure of 1000 kPa and expands from 0.2 m3 to 1.0 m3 by a
process where PV = constant. The gas has an internal energy change
of -200 kJ. Calculate the work (kJ) and the heat transfer (kJ) done
during the process.

1 kg of water in a piston cylinder arrangement is initially in a
saturated liquid state at 1 bar. It undergoes expansion at constant
pressure due to external heat supply to it, to a final state of
saturated vapor.
(i) What is the initial temperature of water in C? (a) 93.50 (b)
96.71 (c) 99.63 (d) 111.4 (e) 12.2
(ii) What is the change in enthalpy of water (kJ/kg-K)? (a)
417.46 (b) 2258.0 (c) 2675.5 (d) 2506.1
(iii) What is...

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)...

Carbon dioxide (CO2) is compressed in a
piston–cylinder assembly from p1 = 0.7 bar,
T1 = 280 K to p2 = 14 bar.
The initial volume is 0.2 m3. The process is described
by pV1.25 = constant.
Assuming ideal gas behavior and neglecting kinetic and potential
energy effects, determine the work and heat transfer for the
process, each in kJ, using constant specific heats evaluated at 300
K, and data from Table A-23.

H3.3 A frictionless piston-cylinder device contains 2 kg of H2O
initially at T1 = 300◦C and p1 = 5 bar. The device is cooled at
constant pressure until the volume is ∀2 = 0.5 m3 . Assume a
quasiequillibrium process which occurs slowly with no acceleration
as the piston moves. Kinetic and potential energy effects are
negligible. Determine: a. work [kJ] during process (indicate
magnitude and direction) b. heat transfer [kJ] during process
(indicate magnitude and direction)

Ammonia contained in a piston–cylinder assembly, initially
saturated vapor at T1 = 4°F, undergoes an isothermal process to a
final specific volume v2 = 5.2 ft3/lb. Determine the final
pressure, in lbf/in2, and the final quality, x2.

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...

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