Question

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 the change in entropy of water (kJ/kg-K)? (a) 1.3026 (b) 7.3594 (c) 6.0568 (d) 8.6620

Answer #1

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.

A vertical, insulated piston cylinder is filled with saturated
liquid H2O at 50 kPa. A stirrer moves rapidly inside the cylinder
until 22% of the H2O (by mass) evaporates. Determine the net work
done (in kJ/kg), the change in entropy during this process (in
kJ/kg-K) and the entropy generated during this process (in
kJ/kg-K).

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.

A piston-cylinder device initially contains 75 g of saturated
water vapor at 340 kPa . A resistance heater is operated within the
cylinder with a current of 0.6 A from a 300 V source until the
volume doubles. At the same time a heat loss of 7 kJ occurs.
Part A)Determine the final temperature (T2).
Part B)Determine the duration of the process.
Part C)
What-if scenario: What is the final
temperature if the piston-cylinder device initially contains
saturated liquid water?

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 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...

An insulated cylinder is initially divided into halves by a
frictionless, thermally conducting piston. On one side of the
piston is 1 m3 of a gas at 300 K, 2 bar. On the other
side is 1 m3 of the same gas at 300 K, 1 bar.The piston
is released and equilibrium is attained, with the piston
experiencing no change of state. Employing the ideal gas model for
the gas, determine
(b) the final pressure, in bar.
(c) the amount...

A piston-cylinder contains 25 g of saturated water vapor and
kept at 300 kPa. We add to the saturated water vapor an amount of
electrical work of 7.2 kJ (via a resistance heater).
Simultaneously, we lose 3.7 kJ from the water.
1.Show the path on a PV diagram.
2.Determine the change in internal energy, the PV work, and the
enthalpy of the system.
3.Determine the final temperature of the system

1-kg water in a frictionless piston-cylinder device is initially
at 250°C and 300 kPa (state
1). A total of 700 kJ of work is done ON the water
in order to isothermally reduce its volume to
1/20 of its initial volume (state 2). Determine the magnitude and
direction of the heat transfer
involved in this process.
Answer: -1147 kJ.

500 kg of saturated liquid at 11 MPA is heated at constant
pressure until it reaches a temperature of 450 C find the
following: a. enthalpy entropy and specific volume at the end of
the process b. change in entropy in kj/kg k of the process c.
amount of heat needed for the process

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