Generally the diameter of the capillary tube varies from 0.6 mm-2.2mm, while length of the capilary tube is around 0.3-4 m. The size of the capilary tube depedns on type of rhe refrgerant used, suction pressure, delivery pressure, power required by the compressor, and capacity of compressor.
The data is being assumed
A R-12 system operates between 1.83 bar and 9.65 bar. The enthalpy at the begining of compression (h1) is 181.94 k J/kg, while at the end of compression (h2) is 209.3 k J/kg,Total enthalpy of refrigerant before evaporator= 74.77 kJ/kg; Obtain the length of capillary tube of inner diameter 1.8 mm for 0.5kW compressor.
Compressor work per unit area = w= h2-h1= 209.3-181.94= 27.4 kJ/kg;
Compressor capacity for 0.5kW= mqcx3600=(0.5/27.4) 181.94-74.77)3600=
7040 kJ/kg
From log graph, (variation of compressor capacity with the length of capillary tube for different refrigerants), length of the capillary tube can approximately be estimaed by knowing the diamter of the capillary tube. After conducting experiment, exact size of the capillary tube can be determined.
Ref:
Refrigeration and Air Conditioning By Manohar Prasad; New Age International Pub. Limited, New Delhi, 2010