Second Law of Thermodynamics

Question 1

Thermal energy reservoir

Answer 1

A hypothetical body with a relatively large thermal energy capacity that can supply or absorb finite amounts of heat without undergoing any change in temperature

Question 2

Thermal source

Answer 2

A reservoir that supplies energy in the form of heat

Question 3

Thermal sink

Answer 3

A reservoir that absorbs energy in the form of heat

Question 4

Heat engines

Answer 4

Devices that convert heat to work

Question 5

Heat engines typically: (4)

Answer 5

1. Receive heat from a high-temperature source
2. Convert part of this heat to work
3. Reject the remaining waste heat to a low temperature sink
4. Operate on a cycle

Question 6

Thermal efficiency (heat engine)

Answer 6

• A measure of performance for the heat engine

- Represents the fraction of heat input that is converted to net work output

Question 7

Working fluid

Answer 7

The fluid to and from which heat is transferred to while undergoing a cycle

Question 8

Second Law of Thermodynamics

Answer 8

• A heat engine cannot operate by exchanging heat with a single reservoir (KP)
• A refrigerator cannot operate without a net work input from an external sources (C)

Question 9

Second Law (follow-ons)

Answer 9

1. No heat engine can have a thermal efficiency of 100%
2. For a power plant to operate in a cycle, the working fluid must exchange heat with the furnace (source) and the environment (sink)

Question 10

Refrigerator

Answer 10

A device that transfers heat from a low-temp source to a high-temp sink
-heat engine in reverse

Question 11

Coefficient of performance

Answer 11

Provides a measure of the efficiency of a refrigerator or heat pump

Question 12

Heat pump

Answer 12

• Device that transfers heat from a low-temp source to a high-temp sink
• Operates on same cycle as refrigerator, but differs in objective
• Objective: maintain a heated space at a high temp

Question 13

Reversible process

Answer 13

• A process that can be reversed without leaving a trace on the surroundings
• Possible only when net heat and net work exchange between system and surroundings is zero

Question 14

Types of reversible processes

Answer 14

• Internally reversible
• Externally reversible
• Totally reversible

Question 15

The Carnot Principles

Answer 15

1. The efficiency of an irreversible heat engine is always less than a reversible one, operating between the same two reservoirs
2. The efficiencies of all reversible heat engines operating between the same two reservoirs is the same