Question

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 second law efficiency of this process.

Answer #1

To solve this question we need to use property table of R134a refrigerant.

here not that we can not use constant specific heat capacity values of R134a because in process pressure and volume both varies with temperature.

see below the complete solution.

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...

A piston cylinder device contains 5 kg of Refrigerant 134a at
800 kPa and 70 C. The refrigerant is now cooled at constant
pressure until it reaches a saturated vapor state. How much heat
was lost in the process? Express your result in kJ and you may
ignore the negative sign.

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.

A piston - cylinder device, whose piston is resting on a set of
stops, initially contains 2 kg of air at 300 kPa and 27 degree C.
The mass of the piston is such that a pressure of 600 kPa is
required to move it. Heat is now transferred to the air until its
volume doubles.
a) Show the process on p - V and p - T diagrams.
b) Determine the work done by the air.
c) Determine the...

Frictionless piston-cylinder system.
Initially contains 167 L of saturated liquid
Refrigerant-134a.
The piston can move freely in such that it maintains pressure at
877 kPa, an Isobaric process.
The Refrigerant-134a is heated until its temperature rises to 70
℃
Determine:
The work was done during the process in (kJ) units?

A piston-cylinder contains 2 kg of refrigerant R-134a at
temperature -20 degrees Celsius and a quality of 20% is heated in
device until it reaches a saturated mixture with quality 60%. a)
Show process on a P-v and P-T diagram b) What is the pressure? c)
What is the change in volume? d) What is the change in the internal
energy? e) Redo the problem if the piston-cylinder assembly is
replaced with a rigid container.

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

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.

a plunger cylinder device contains 0.8 kg of water at 4 Mpa and
500 ° C, it begins to lose heat causing the piston to descend to a
set of stops inside the cylinder, at which point saturated steam is
obtained through an isobaric process. Cooling continues until the
cylinder contains water at 1 atm pressure. The heat transferred
during this process is kJ

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?

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