A capillary tube is a long, narrow tube of constant diameter. The word
“capillary” is a misnomer since surface tension is not important in refrigeration
application of capillary tubes. Typical tube diameters of refrigerant capillary tubes
range from 0.5 mm to 3 mm and the length ranges from 1.0 m to 6 m.
The pressure reduction in a capillary tube occurs due to the following two
factors:
1. The refrigerant has to overcome the frictional resistance offered by tube
walls. This leads to some pressure drop, and