Chapter 5 Flashcards
(15 cards)
What is a heat engine?
Converts thermal energy to mechanical energy
In a Carnot Cycle, heat is absorbed in what step
Isothermal Expansion
If the change in entropy of the system is positive, then the process is?
It depends
An ideal heat engine operates at temperature 740 °F and -60 °F. Compute the actual efficiency.
<2/3
Entropy change for hot reservoir is?
negative
The coefficient of performance for a heat pump is given by
Qc/W
The heat of vaporization of water is 540 cal/kg. Calculate the change in entropy of 5 gram of water if it vaporized at normal boiling point in J/K
30.3
Thermal efficiency is
net Wout/Qin
The heat engine’s high temperature is 600 K and low temperature is 400 K. If the work done by engine is W, what is the heat output
2W
The change in entropy of the working substance in a heat engine is
Zero
An inventor claims to have devised an engine that produces 1200 Btu work while receiving 1000 Btu of heat during a single cycle of the engine such engine would violate
Both laws
A heat engine operates at 500 K and 250 K. It produces 10 kW of work per 30 kW of heat rejected. What is the thermal efficiency of the engine?
25 %
Soln: [10/(10+30)] x 100
The entropy change for a closed system which undergoes a cyclic process
must be Zero
The maximum thermal efficiency of a heat engine depends only upon
Temperature of the Reservoir
An insulated resistor has an electric current through it. The entropy of the resistor
Increases
