Refrigeration and heat pump

Question 1

Answer 1

Question 2

Answer 2

Question 3

The reversed Carnot cycle is the most efficient refrig. cycle operating between TL and TH. It is not a suitable model for refrigeration cycles since processes 2-3 and 4-1 are not practical because Process 2-3 involves the compression of a liquid–vapor mixture, which requires a compressor that will handle two phases, and process 4-1 involves the expansion of high-moisture-content refrigerant in a turbine.

Answer 3

Both COPs increase as the difference between the two temperatures decreases, that is, as TL rises or TH falls.

Question 4

Answer 4

Question 5

An actual vapor-compression refrigeration cycle differs from the ideal one owing mostly to the irreversibilities that occur in various components, mainly due to fluid friction (causes pressure drops) and heat transfer to or from the surroundings.

Answer 5

DIFFERENCES
Non-isentropic compression
Superheated vapor at evaporator exit
Subcooled liquid at condenser exit
Pressure drops in condenser and evaporator
The COP decreases as a result of irreversibilities.

Question 6

GAS REFRIGERATION CYCLES
The reversed Brayton cycle (the gas refrigeration cycle) can be used for refrigeration.

Answer 6