Thermal Engineering, Refrigeration & Power

Design features of hermetically sealed refrigeration compressors:

• In a hermetic compressor, the motor and compressor are mounted on a common shaft and completely enclosed within a welded, gas-tight steel casing without external shaft seals, effectively eliminating the primary source of refrigerant leakage to the atmosphere.
• Lubrication is self-contained and simple (splash or forced internal oiling).
• Hermetic compressors are quieter due to internal spring suspension and acoustic muffling within the welded shell.
• The electric motor is internal, not external.

Performance definitions in cooling tower thermodynamics:

• Approach of a cooling tower is the temperature difference between the cold water leaving the cooling tower ($T_{out}$) and the ambient wet-bulb temperature ($T_{wb}$):
  $$\text{Approach} = T_{out} - T_{wb}$$
• Gradient is an informal rate of temperature change.
• Lift is static pumping height.
• The Range of a cooling tower (cooling range) is defined as the temperature difference between the warm water entering the cooling tower ($T_{in}$) and the cooled water leaving the tower basin ($T_{out}$):
  $$\text{Range} = T_{in} - T_{out}$$

Classification of idealized thermodynamic gas power cycles:

• Dual cycle supplies heat partly at constant volume and partly at constant pressure, and rejects heat at constant volume.
• Otto cycle supplies heat at constant volume and rejects heat at constant volume.
• The Atkinson cycle (invented by James Atkinson in 1882) is an ideal thermodynamic cycle where heat addition occurs at constant volume, expansion continues down to atmospheric pressure (longer expansion stroke than compression stroke), and heat rejection takes place at constant pressure.
• Diesel cycle supplies heat at constant pressure and rejects heat at constant volume.