Refrigeration Cycle

Refrigeration Cycle vs Power Cycle

Power cycle:

• Objective: create work/power
• How: Take heat from hot source
• By-product: Give heat to cold source
  

Refrigeration cycle:

• Objective: Take heat from cold source
• How: Take work/power
• By-product: Generate heat
  

Recall 2nd law: Clausius Statement:

It is impossible to construct a device that operates in a cycle and produces no other effects than the transfer of heat from a cooler body to a hotter body.

Layman terms: If you want heat to go from cold to hot, you need to do work.

History

William Cullen:

• 1710-1790
• Scottish
• 1755: general concept

Oliver Evans:

• 1755-1819
• American
• 1805: closed vapor-compression refrigeration cycle

Jacob Perkins:

• 1766-1849
• American
• 1834: patent for vapor-compression refrigeration cycle

Examples:

Components:

Cycles:

Stages:

Compression:

• Compression of gases
• Isentropic

Heat exhaust/Condensation:

• Loose Heat
• Constant Pressure

Expansion:

• Pressure reduction
• Adiabatic (not always isentropic)
• Air-Standard Cycle: $s=const$ $h\downarrow$
• Vapor Compression Cycle: $h=const$ $s\uparrow$

Heat intake/Evaporation:

• Gains Heat
• Constant Pressure

Air-Standard Refrigeration Cycle

Extensions:

2-Stages:

Concept:

• Large $T$ difference
• One fluid
• One cycle
• Two stages
  

Cascade System:

Concept:

• Very large $T$ difference
• two fluids
• Two cycles
  

Applications:

Liquefaction of gases:

• Linde-Hampson system