Capillary tube in Refrigerator & A.C.

How to calculate the length of capillary tube used in Refrigeration & A.C.?

Questions by kanthasami   answers by kanthasami

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Capillary tubes are used to control pressure & temp in refrigerating unit. They are commonly used in domestic refrigerators. It is used to increase the performance of refrigerator in addition to other components like strainer and drier.
It consists of a tube with very thin diameter and some times in a coil shape. The length of the capillary tube depends on the unit to be served, the refrigerant used and other physical considerations.

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Since the pressure on the two sides of the capillary equalizes when the refrigeration plant is stopped, one should not overcharge the system with the refrigerant. Due to this reason the receiver is also not installed in the refrigeration system with the capillary. If the system is overcharged the discharge pressure from the compressor will be high and the compressor would get overloaded. Thus the refrigerant charge in the refrigeration and air conditioning systems with the capillary tube is critical.

The technician should be very careful while brazing the capillary to the condenser and the evaporator coil. Since the diameter of the capillary is very small the capillary may get blocked if the brazing is done deep inside. Brazing the capillary requires lots of expertise and patience.

In most of the cases, when the fresh refrigerant is charged into the refrigerator or the deep freezers, the capillary of the system should also be changed. This is because when the machine is stopped some oil particles may clog the capillary as the refrigerant leaks to the atmosphere.

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S J Dreyer

  • Feb 12th, 2015

No I am sorry, I can not answer the question to. I would however like to ask the persons that answered the question, If they read the question properly. Obviously someone that ask the question how do you calculate the length of a capillary tube needs to know how to calculate the length of the capillary tube not how it works. Is there no one in the world than can help us on this question? My thumb-suck method for domestic fridges using a 1/5 compressor and a 0.06 capillary is 2.8 to 3.2 meters. working from the smallest size in liters to the largest case used.

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Altamash Shaikh

  • Jun 20th, 2016

How to calculate the length of capillary tube used in Refrigeration & A.C.?

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Baren Kumar Baidya

  • Jul 15th, 2016

Special Rules of condenser and Evaporator and Capilary tube need for a Refrigerator and Freezer system.
By: Baren Kumar Baidya
B.Sc in Mechanical Engineering.(DUET)

Step -1: Find out Compressor power (watt)
Find out volume of Refrigerator (Ft3)
Example, A Refrigerator has a length 20 inch, wide 20 inch and height 60 inch.
So, Volume = 20 x 20 x 60 =24,000 inch3
Or, 24,000/ 1728 = 13.89 ft3
Now, exact inside volume of the refrigerator = 13.89 x .45 = 6.25 ft3
For, 1 ft3 volume need 23 watt compressor power.
So, total compressor power need= 23 x 6.25 = 143.75 watt

Step-2: Find out length of condenser tube.
For condenser tube diameter, 3/16 inch
For 3-watt compressor power need 1 feet condenser tube
Now, for 143.75 watt compressor need 143.75/3 = 47.91 ft condenser tube.

Step-3: Length need of evaporator tube .
For evaporator tube diameter 5/16 inch
For 4-watt compressor power need 1-feet evaporator tube
Now, for 143.75-watt compressor power need 143.75/ 4 = 35.94 ft evaporator tube.

Step-4: For 100 watt compressor power need 9 inch capillary tube (diameter 30 thou), but increase the compressor power (watt) the length of capillary tube decrease gradually.

Step-5: Need of evaporator tube in the Deep freeze and Refrigerator.

If the refrigerator bigger than deep-refrigerator so 15% evaporator coil use in refrigerator and 85% use in deep-freeze.
Furthermore, if the refrigerator and deep-freezer are equal to each other, then 10% evaporator coil is need for Refrigerator section and 90% use for deep-freezer.

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Nimesh Gajjar

  • Sep 29th, 2016

Barensir, for referring this calculation which book I have to refer?

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  • Nov 30th, 2019

is 9 inch for 100 watt correct?
is it enough?

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