Ch14_2
New Problems
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Make sure to calculate your answers in SI units unless specified otherwise .
1) A heat engine withdraws heat at the rate of
W
from a heat reservoir. What is the power output of the engine if
W
of heat are released into the heat sink
(see sheet 16,21)
? Indicate with a positive (negative) sign whether the input heat is always smaller (larger) than the output heat.
2) A heat engine converts % of the input heat into mechanical work. How much heat is released into the environment when the engine does
kJ
of work
(see sheet 16,17)
? Indicate with a negative (positive) sign whether the the efficiency of the engine is always (not always) less than 1.
3) The temperatures of the heat reservoir and the heat sink of a heat engine are
o
C
and 350
o
C
respectively. What is the power output of the engine if it draws heat at a rate of
KW
from the heat reservoir and it's real efficiency is of the ideal efficiency
(see sheet 17,19)
? Indicate with a positive (negative) sign whether one can (cannot) calculate the real efficiency of the engine from the two temperatures alone.
4) The compressor of a refrigerator delivers
W
of power and withdraws
W
from the freezing compartment. How many
watts
heat are released into the kitchen
(see sheet 24)
? Indicate with a negative (positive) sign whether the amount of heat released is always (only sometimes) greater than the amount of heat withdrawn from the low temperature compartment.
5) A refrigerator withdraws heat from the freezing compartment at a rate of
W
which is times the compressor power. At which rate is heat released into the environment
(see sheet 24,27)
? Indicate with a positive (negative) sign whether the real "coefficient of performance" is always (sometimes) smaller than the ideal one.
6) A refrigerator in a room at
o
C
keeps the temperature in the freezing compartment at -2
o
C
. If the real "coefficient of performance" is the ideal one divided by and
W
are released into the room what is the power use of the compressor
(see sheet 24)
?
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