In certain professions it is necessary to make use of so-called capillary tubes. These devices fulfill different functions depending on where they are used. For example, you can use them in refrigeration system as in clinical laboratories. So, if you want to know what its utilities are, in this article we will explain it to you.
What is the capillary tube used for?
Generally speaking, capillary tubes are made of metal, such as copper or stainless steel, but in other cases, they are glass. They get their name because they have a very narrow internal diameter circular section, very similar to the thickness of a hair, which can range from 0.5 mm to 3 mm. In addition, it is important to know that depending on the context and area where it is used, it fulfills very varied functions.
Fluids are conducted through the capillary tube and the capillarity phenomena. The latter is essential to know the property of a substance. In this way, the pressure with which a liquid passes from one end to the other can be controlled, which is very useful in refrigerant circuits. That is, it acts as an expansion device, decreasing the pressure and temperature of the substance in question.
On the other hand, capillary tubes in the laboratory are used to perform different tests. These allow to analyze certain parameters, for example, the hematocrit. With a capillary tube, the components of blood can be separated, such as erythrocytes, white blood cells, platelets and serum. In the same way, it allows coagulation tests to be carried out.
How does a capillary tube work?
The function of the capillary tube is reduce pressure and temperature of the refrigerant liquid that comes from the condenser through the fluid pipe. In this way the correct feed is provided to the evaporator.
Depending on the diameter and length of the capillary, the resistance to the passage of the fluid inside is determined. In addition, it conditions the amount of content that passes through it. The higher the resistance and the pressure drop, the lower the flow rate of the tube. When the length of the capillary is narrower, then the resistance will be lower and therefore the flow rate will increase accordingly. It is important that there is a pressure difference between the two ends of the capillary so that the liquid passes through there.
What are the principles of operation of capillary tubes?
Depending on your application, several are the features that play a key role in its use. For refrigeration systems, where the flow is constant, it is governed by the principle of throttling. Thanks to this your passage is restricted, which allows a pressure drop by causing the local loss of the same.
On the other hand, in these tubes the phenomenon of capillarity is manifested, which is typical of fluids. It also defines the ability of a liquid to move up or down the walls of the capillary, which in turn depends on the fluid surface tension that he owns The narrower the tube, the greater the suction of the liquid and the height reached. Unlike what happens in a wide one, where the length or column of the substance will be less.
What is capillary tube in refrigerators?
It consists of a narrow diameter tube, made of copper or stainless steel. And they fulfill the function of expansion systems. Well, it allows the liquid that serves as a refrigerant lose the big pressure with the one that comes from the compressor.
What is the function of the capillary tube in refrigeration?
It’s used in small power refrigeration machines, since it works as an expansion device. This causes a fluid to pass from a place of high pressure and temperature, to another place with lower pressure and temperature.
This tube connects to the suction pipe. Thus forming a heat exchanger, which allows the fluid circulating through the capillary to be cooled. The goal of this is to keep it in a liquid state despite the pressure loss. Also, depending on the length of this tube, the head loss is determined. This will cause the refrigerant to exit the condenser is at the proper evaporation pressure and temperature. In the compressor, such a fact will be the opposite.
So, when the ambient temperature is high, it happens that the condensing pressure will also be high. This will cause the pressure in the capillary to drop at its end, which results in an increase in the flow rate to the evaporator. When this overfeed occurs on the evaporator, there is a decrease in superheat.
On the other hand, if the refrigerant is not completely liquid, then the flow will be reduced. In this way, less cooling of the evaporator is caused, and greater overheating of the refrigerant that reaches the compressor. In short, if it weren’t for this artifact, then the evaporation process would be slower, which in the long run, will damage the compressor by receiving the condensed refrigerant.
Characteristics and properties of capillary tubes in refrigerators
When we talk about the refrigeration system, these devices must meet certain parameters. The main characteristics to take into account in your choice and application for this type of use are its internal diameter and its length.
The internal part can measure from 0.63 mm to 3 mm. While, the maximum length reached is 304.8 cm.
In turn, the capillary tubes are chosen taking into account the following aspects such as the capacity of the HP compressor of the equipment. On the other hand, it also depends on the cooling capacity in Btu/h. And finally, it should be taken into account, the type of application for which it is intended (if it is for refrigeration, freezing or air conditioning) together with the type of refrigerant used.
What is a capillary tube in chemistry laboratories?
Unlike those used for refrigerants, in the chemical context they are made of glass. They are small in diameter and short in length. This property is used to see the effects of capillarity. Which is a characteristic that all liquids have.
The latter is defined as the ability of a fluid to rise through the walls of a tube. The process is carried out thanks to the forces that act between the surface of the material and the liquid. These associated phenomena are known as adhesion and cohesion.
What are the applications of the capillary tube in fluid handling?
In a chemical laboratory they are used to measure and calculate the melting point of a substance. This refers to the moment in which it goes from a solid state to a liquid one (it is molten).
In another context, they are also used to determine clinical parameters. For example, knowing the hematocrit of a blood sample from a patient. In this sense, it also allows calculating the coagulation time and performing various types of tests in different diseases. Such is the case of diabetes, febrile states or cancer.
In turn, the capillary tube performs two functions. The first is related to the melting point of a substance. For which, the temperature at which this phenomenon occurs, called the melting point, is measured. In this case, the capillary tube is filled with the material to be melted and then heated until it begins to occur.
On the other hand, it also fulfills the function of represent the properties of a liquid substance. That is, it is used to measure the density and viscosity of liquids. To do this, the capillary tube is filled with the fluid and the time it takes to flow through its interior is calculated. Density is determined by measuring the amount of mass that passes through the device in a given time. Whereas, the viscosity is calculated by means of Poiseuille’s law.