The expansion process and devices

In all types of the refrigeration cycle there is a step where liquid refrigerant is expanded from the condensing pressure to the evaporating pressure. Refrigerant evapo-

rates and simultaneously cools down to the evaporation temperature.

The expansion device could be any type of restriction which exerts a pressure drop

on the fluid which is equal to the difference between the condensation and evaporation

pressure for the actual refrigerant flow rate.

Fluid dynamic theory teaches us that the pressure drop

Increases with: Increasing flow length

surface roughness

direction changes

Decreasing hydraulic diameter

Cross-section area.

Theoretically, all these parameters could be used to control the pressure drop but it

is difficult to imagine a device, which uses the surface roughness. Similarly, the number of directional changes and the flow length closely interrelated as are the hydraulic diameter, the cross section area and the de/acceleration.

2. Read the text again and correct the mistakes. Begin your answer with:

a) as far as I know,

b) as far as I remember,

c) as far as I understand.

1. In all types of the refrigeration cycle there is no step where liquid refrigerant is expanded

from the condensing pressure to the evaporating pressure.

2. Refrigerant evaporates and simultaneously heats to the evaporation temperature.

3. A pressure drop on the fluid is not equal to the difference between the condensation

and evaporation pressure for the actual refrigerant flow rate.

4. All these parameters could not be used to control the pressure drop.

5. The number of directional changes and the flow length are not closely interrelated.