Energy

Question 1

What is the first law of thermodynamics

Answer 1

U = Q - W. This suggests energy can neither be created nor destroyed and will either become work or heat.

Question 2

What is the second law of thermodynamics

Answer 2

A device operating continuously cannot only export work from an isolated source of heat. In this case it means that the Q in 1st law cannot be 0 and that U=/=W.

Question 3

What does the second law of thermodynamics apply to perpetual motion machine

Answer 3

Perpetual motion machines cannot exist since the energy supplied to a device cannot be 100% converted into work and will be lost to the thermal sink. The energy lost to heat cannot be be recovered either.

Question 4

What is the grade of an energy flow

Answer 4

As the energy flows through a process its grade deteriorates

Question 5

What is a measure of the grade of an energy flow

Answer 5

exergy. A measure of how much an energy flow can be in theory be converted back into mechanical power in its conditions.

Question 6

Give two examples where the exergy is 100%

Answer 6

A pulley and chemical energy. ( energy stored in chemical bonds is all available)

Question 7

What does exergy of thermal sources depend on

Answer 7

temperature of the sources

Question 8

What is primary energy efficiency

Answer 8

A measure of energy efficiency that measures a ratio of useful energy to the energy input + the energy required to deliver and produce that energy

Question 9

what is the carnot efficiency

Answer 9

1-Tc/Th. This is also equal to the ratio of work to heat energy supplied

Question 10

What is a heat pump

Answer 10

The opposite of a heat engine, it uses work to move heat from the colder source to the hotter source. Heat engine does work when moving heat from hot source to cold source