Thermodynamic Processes and Refrigeration Cycle Components

Posted on Mar 25, 2025 in Chemistry

Item 5: Thermodynamic Processes

Isothermal Process: The substance changes state without changing its thermodynamic temperature.
Isobaric Process: The substance changes state without changing its pressure.
Isochoric Process: The substance changes state without changing its specific volume.
Isenthalpic Process: The substance changes state without changing its heat (enthalpy).
Isentropic Process: The substance changes state without changing its entropy.
Adiabatic Process: A process in which no heat transfer occurs between the surroundings and the system.

Subcooled Liquid: If energy is added as heat, the liquid temperature rises but it does not convert to vapor.
Saturated Liquid: If energy is added as heat, the liquid becomes steam.
Saturated Steam: Vapor at its condensation point.
Superheated Steam: Vapor that is not about to condense.

Boyle’s Law: If pressure (P1) is twice the pressure (P2), then volume (V1) is half the volume (V2).
Gay-Lussac’s Law: If (T2) is twice (T1), then (V2) will double (V1).
Charles’s Law: In a tank where the gas is at a lower temperature, the pressure will be lower; the higher the temperature, the greater the pressure.
Perfect or Ideal Gas: A gas that meets the previous laws with complete accuracy.

Compressor: Compresses a low temperature and vapor pressure to high pressure and temperature.
Condenser: A heat exchanger where the refrigerant in a state of superheated steam from the compressor is cooled to saturated vapor, then condensed to saturated liquid, and finally exits in a supercooled liquid state.
Expansion Device: (Implied)
Evaporator: A heat exchanger where the refrigerant absorbs heat from the enclosure to cool it until it reaches the saturated vapor state.
Cooling Capacity: The amount of heat extracted by the evaporator from the enclosure to cool it per unit of time.
Compressor Performance: The ratio between the minimum power required and the electric power actually absorbed by the compressor.

COP (Coefficient of Performance) of a Refrigeration Cycle: The ratio between refrigeration power and the power applied to work as a refrigerant by the compressor.
COP Compressor: The ratio between refrigeration power and the electric power absorbed by the compressor to compress the refrigerant flow (no unit).

Useful Overheating: Occurs at the end of the evaporator or the suction pipe installed inside the refrigerated space.
Not Useful Overheating: Occurs outside the refrigerated space or because of the refrigeration compressor motor.

Slightly increases compression work.
Increases the temperature of the compressor.
Increases the heating value released in the condenser.
The maximum aspirated volume decreases as a result of increased specific volume with temperature.

Place the thermometer at the outlet of the evaporator.
Place the gauge on the low-pressure side of the installation.
The difference between the measured temperature and the temperature corresponding to the evaporating pressure read on the gauge will indicate the overheating of the coolant.

The thermometer should be placed on the condenser outlet pipe once it has been cleaned.
The high-pressure gauge is used to determine the temperature of condensation through its temperature range.
Compare the temperature of condensation with that indicated by the thermometer at the outlet of the compressor.

Azeotropic Mixture: These refrigerant blends behave exactly like a pure refrigerant, but they have different physical characteristics.
Non-azeotropic Mixture: In contrast to azeotropes and pure refrigerants, the phase change at constant pressure does not happen at a constant temperature.
Bubble Temperature: The saturation temperature of saturated liquid.
Dew Point Temperature: The saturation temperature of saturated vapor.

To find the warming, compare the value obtained on the thermometer to the dew point temperature indicated on the low-pressure gauge.
Subcooling: Subtract the bubble temperature from the high-pressure gauge reading from the temperature indicated by the contact thermometer.