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

Water undergoes a constant‐volume process within a
piston–cylinder assembly from saturated liquid at 4 bar to a final
pressure of 50 bar. Kinetic and potential energy effects are
negligible. Determine the work and the heat transfer, each in kJ
per kg of water. [7 points]

Water, initially (state 1) a saturated liquid at
1100C, is contained in a piston-cylinder assembly. The
water undergoes a process to the corresponding saturated vapor
(state 2), during which the piston moves freely in the cylinder. If
the change of state is brought about by heating the water as it
undergoes an internally reversible process at constant pressure and
temperature, determine (a) heat transfer using first law of
thermodynamics in kJ/kg and (b) heat transfer using second law of
thermodynamics...

A piston-cylinder assembly containing 3 kg of an ideal gas
undergoes a constant pressure process from an initial volume of 48
m3 to a final volume of 30 m3 . During the
process, the piston supplies 1.2 MJ of work to the gas. The gas has
a constant specific heat at constant volume of 1.80 kJ/(kg∙K) and a
specific gas constant of 1.48 kJ/(kg∙K). Neglect potential and
kinetic energy changes.
a. Determine the initial specific volume of the gas in...

One kg of water in a piston-cylinder assembly
undergoes two processes in series from an initial state where p1 =
0.8 MPa, T1 = 500°C:
Process 1-2: Constant-pressure compression until the
volume is half of
the initial volume.
Process 2-3: Constant-volume cooling until the
pressure drops to 400 kPa.
Sketch the two processes in series on a p-v and T-v
diagram. Determine the work and heat transfer for both
processes.

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.

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]

A frictionless piston-cylinder device is filled with helium gas
at 300 kPa and 40 °C. A thermal reservoir at 95 °C is used to heat
the gas at constant pressure to a final temperature of 75 °C.
a) Determine the change in entropy per unit mass for the gas
during this process. Prove your answers to
b) and c) below quantitatively using entropy concepts or briefly
describe why you’re unable to evaluate.
b) Is this process internally reversible, irreversible,
impossible,...

Atmospheric pressure is 100 kPa in a system of cylinders and pistons.The mass of the piston is 4 kg and the area of the piston is 4.0 cm2. The following process takes place by external heat transfer. (Gravity acceleration is 10 m / s2).
1. Calculate the pressure inside the cylinder in kPa.
2. The cylinder contains 0.1 kg of water vapor, and the
temperature of the water vapor is 150oC. Find the volume and
internal energy of water vapor...

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