Question

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.

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=

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.

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.

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.

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...

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.

4.58 Air enters a compressor operating at
steady state with a pressure of 14.7 lbf/in^2, a temperature of 808
F, and a volumetric flow rate of 18 ft /s. The air exits the
compressor at a pressure of 90 lbf/in^2 Heat transfer from the
compressor to its surroundings occurs at a rate of 9.7 Btu per lb
of air flowing. The compressor power input is 90 hp. Neglecting
kinetic and potential energy effects and modeling air as an ideal
gas,...

Air enters a compressor operating at steady state at 15.4
lbf/in^2, 80°F with a volumetric flow rate of 424 ft^3/min and
exits at 176.4 lbf/in^2, 260°F. Heat transfer occurs at a rate of
6800 Btu/h from the compressor to its surroundings. Assuming the
ideal gas model for air and neglecting kinetic and potential energy
effects, determine the power input, in hp.

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)

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