Closed System Energy Balance Example
5.0 kg of water is heated from 110oC to
400oC at a constant pressure of 200 kPa.
Determine the amount of heat transfer.
Closed System Energy Balance Example
A freely moving piston-cylinder device
contains hydrogen at 1000 kPa and 50°C.
The initial volume of the system is 2 L and it
is heated until the volume reaches 10 L.
Determine the amount and direction of
heat transfer, in kJ.
Closed System Energy Balance Example
A freely moving piston cylinder device initially
contains 3 kg saturated liquid water at 150C. An
electric resistance heater is placed in the tank and is
turned on for 15 min until the volume triples.
Determine…
a. The initial volume of the tank
b. The final temperature
c. The electrical power of the heater, in kW
Closed System Energy Balance Example
A student living in a 4 m x 6 m x 6 m dorm room
turns on a 150 W fan before leaving for 10 hours on
a hot summer day. Assume that all windows and
doors are well sealed and the that the walls are
adiabatic. When the student left, the temperature
of the room was 25oC and the pressure was 100 kPa.
Determine the temperature when the student
returns.
Energy Balance Example
The power goes out at your brewery due to an
overheated transformer, shutting down your
fermentation cooling mechanism. Consider a 25
m3 cylindroconical vessel that is full with a
product at 10oC, specific heat of 3.4 kJ/kg.K, and
density of 1025 kg/m3. Assuming that the sum of
heat gains from the surroundings and conversion
from fermentation is 4 kW, determine the
temperature after 4 hours. How would the 4 kW
load change over time?
Closed System Energy Balance Example
Two tanks are separated by a partition. Initially, one
tank contained 2 kg of steam at 1 Mpa and 300oC
while the other contained 3 kg of a saturated
mixture (water) at 150oC with a quality of 50%. The
partition is removed, the two sides mix and reach
equilibrium. The final pressure of the mixture is 300
kPa. Determine the temperature and quality of the
steam (if mix) at the final state and the amount of
heat loss from the tanks.
Closed System Energy Balance Example
A mass of 5 kg of saturated liquid-vapor mixture
water is contained in a piston-cylinder device at 125
kPa. Initially, 2 kg is in liquid phase. Heat is
transferred to the system until the pressure reaches
300 kPa, at which time the piston rises from a set of
stops. Heat transfer increases until the volume
increases by 20%. Determine the initial and final
temperatures, the mass of liquid when the piston
starts moving and the work done. Plot on a P-v.