Copper Capillary Tubes

Copper Capillary Tubes

Capillary copper tube is one of the most commonly used throttling devices in the refrigeration and the air conditioning systems. The capillary tube is a copper tube of very small internal diameter. It is of very long length and it is coiled to several turns so that it would occupy less space. The internal diameter of the capillary tube used for the refrigeration and air conditioning applications varies from 0.5 to 2.28 mm (0.020 to 0.09 inches). Capillary tube used as the throttling device in the domestic refrigerators, deep freezers, water coolers and air conditioners.

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How Capillary Tube Works?

When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary. In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary.

The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary. Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it.

In the normal working conditions of the refrigeration plant there is drop in pressure of the refrigerant across the capillary but when the plant stops the refrigerant pressure across the two sides of the capillary equalize. Due to this reason when the compressor restarts there won’t be much load on it. Also, due to this reason one cannot over-charge the refrigeration system with the refrigerant and no receiver is used.

The capillary tube is non-adjustable device that means one cannot control the flow of the refrigerant through it as one can do in the automatic throttling valve. Due to this the flow of the refrigerant through the capillary changes as the surrounding conditions changes. For instance as the condenser pressure increases due to high atmospheric pressure and the evaporator pressure reduces due to lesser refrigeration load the flow of the refrigerant through the capillary changes. Thus the capillary tube is designed for certain ambient conditions. However, if it is selected properly, it can work reasonably well over a wide range of conditions.

The length of the capillary of particular diameter required for the refrigeration applications cannot be found by fixed formula rather it is calculated by the empirical calculations. Some approximate length required for certain application is found out and it is then corrected by the experiments.


Important Points to Remember when Installing Refrigeration Plants with Capillary Tube

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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Advantages of copper pipes:
1. Lightweight, with good thermal conductivity and high low-temperature strength. Commonly used in the manufacturing of heat exchange equipment (such as condensers). It is also used for assembling low-temperature pipelines in oxygen production equipment. Copper pipes with small diameters are commonly used for conveying pressurized liquids (such as lubrication systems, oil pressure systems, etc.) and as pressure measuring pipes for instruments.
2. Copper pipes have strong and corrosion-resistant properties, making them the preferred choice for modern contractors to install water pipes, heating, and cooling pipes in all residential commercial buildings.
3. Copper tube combines many advantages in one body: it is strong and has the high strength of ordinary metals; At the same time, it is more prone to bending, twisting, cracking, and breaking than ordinary metals, and has a certain degree of frost heave and impact resistance. Therefore, once installed, copper water pipes in water supply systems in buildings are safe and reliable to use, and even do not require maintenance and upkeep.
Disadvantages of copper pipes: As far as copper pipes are concerned, their high price is their biggest disadvantage, and they are currently the most high-end water pipes. They are usually installed using welding technology and will not leak for a lifetime. The connection at the copper pipe interface mainly depends on the level of construction technology and has high requirements for construction quality.

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