Capillary tube

November 1, 2021

The capillary tube is a tool that we can explain initially using plants as an example, specifically how plants transport water and minerals through their roots and to the tips of the leaves.

The method that the plants developed to carry out this action is to make the water reach the top of their leaves through very narrow tubes that go from the roots to the top of the plants , the narrower the tube, the higher it will arrive at the plant. In this way they manage to make the water flow throughout the plant without wasting energy of any kind.

Knowing this we can give way to the most technical and precise explanations with which this laboratory instrument is described.

What is the Capillary Tube?

The Capillary Tube, named for the similarity of the narrow tube with the diameter of a hair , is a material used in laboratories that, in principle, in terms of its structure, it can be seen that it is an extremely thin tube, which generally has some marks representing the unit of measurements.

The function of the capillary tube is to represent the effects of the capillarity of a liquid substance, this effect is present in the tube, by sucking the liquid for no apparent reason, taking it to a certain height within the narrow tube.

What happens is that liquids, water being the most used liquid, tend to adhere to what they have around them, and due to the narrowness of the tube, it manages to adhere and rise above the normal water level.

An example of this is when a cloth or napkin is wet, the water has contact with a specific point, but by capillarity, it adheres and extends as far as gravity or the water source itself allows.

What is the Capillary Tube for?

The capillary tube offers a clear visual representation of two different activities or experiments. We have the capillarity effect, through which we can appreciate the cohesion of the liquids on the walls of the tube and how high they can go depending on the diameter of the tube.

We can see this in laboratories as an experiment, in which we can appreciate the different reactions that different liquids exposed to the same experiment can have, some liquids will present an increase in the level of the substance inside the capillary tube and others a decrease in it. versus the level of the liquid outside the tube.

On the other hand, taking a different approach from the previous one, they also serve to know the melting point of multiple substances . That is, it serves to measure the temperature at which certain substances melt.

How does the Capillary Tube work?

As we have already mentioned, it has two uses within the laboratory which are to facilitate the measurement of the melting point of substances. This is done by crushing or pulverizing the material and introducing it into the tube until it reaches a total height of 3 millimeters before being heated.

The heating process consists of starting with a temperature 5 degrees lower than the temperature that is estimated to be necessary to melt the material, increasing 1 degree every minute until the substance is completely melted.

We also have the most didactic use, which is to experiment with the capillarity of fluids, which is achieved by introducing water into a container in which the capillary tube is located so that the same cohesion property of the liquid adheres to the walls of the narrower tube and go as far as gravity allows.

This experiment can be contrasted when using capillary tubes of different diameters , because the narrower the higher the liquid will reach, or otherwise, the lower it will be with respect to the level of the liquid outside the tube. This type of case, in which the results are contrary to those of water compared to the same experiment, occur with substances such as mercury

Capillary Tube Uses

The capillary tube has two functions, one related to casting materials and the other to representing the properties of a liquid substance, so it also has two ways of being used, each one corresponding to a different result.

  • Melting point materials

For this we will have to crush the material in question to pulverize it and then introduce it into the tube until filling a measure of 3 millimeters in height. After this, we must heat the tube up to about 5 degrees before the melting point that we have calculated, making the heat rise 1 degree every minute until we reach the melting point of the material.

  • Capillarity of liquids

In this case we will have to use a container together with the capillary tube. In the container we will pour an amount of the liquid that we want to test, and then introduce the tube into the container. It is important that the liquid does not exceed the middle of the capillary tube , in order to appreciate how the capillarity of this liquid is manifested

In this exercise what we want to see is if the liquid inside the tube is higher than the level of the liquid outside the tube or if it is lower.

Knowing this, it is shown that its use is quite practical, and that just by knowing what will happen we can work with this laboratory tool to obtain our own conclusions and data on both the properties of the liquid we want to test, and the solid materials we want. melt.

Types of Capillary Tubes

Initially this instrument was used in laboratories to carry out experiments and tests, even so, the structure of the capillary tube was implemented for the mechanical area , specifically for refrigeration. For this reason we can speak of two types of capillary tubes.

  • Laboratory capillary tube

As mentioned in the previous points, the laboratory capillary tube is used for experiments or tests for materials, in one of the experiments we work with liquid materials to appreciate the effect of capillarity. While with the other experiment we detect the necessary degree of heat to melt certain materials.

  • Capillary cooling tube

It maintains the structure of being a very small diameter tube, such as a laboratory one, but made of copper rather than glass or plastic. This tube is located between the condenser and the evaporator of a refrigerant circuit.

The tube is responsible for measuring or restricting the flow of liquid that starts from the condenser and goes to the evaporator, thanks to the strong resistance and friction generated by the diameter and length of the tube that creates a constriction causing the pressure of the liquid to be minimized .

The benefit of being a single piece, eliminates the mechanical parts, thus preventing any of the moving parts from being damaged, making it a widely used option in many models of refrigeration circuits .

We have two types of capillary tubes, which, although their functions are very different from each other, maintain the same physical structure, which is the key to the operation of both types, one as a tool or instrument in laboratories and the other as a fundamental piece. for machine cooling.

Capillary Tube Features

Visually, the capillary tube is an extremely thin tube in presentations of 1 millimeter in diameter, also with models of smaller or larger diameters. Its name comes from its resemblance to the thickness of a hair.

Physically the tube can be made of materials such as glass, copper or other metallic alloys . We can also find tubes with measurements marked on the back of it, in units of grams or millimeters for accuracy in experiments.

On the other hand, tubes designed for refrigeration have a simpler design, which is that of a narrow diameter tube made of copper, since the other components of the refrigerant circuit are those that take advantage of this characteristic of the capillary tube.

Importance of the Capillary Tube

The importance of the capillary tube lies mainly in its use , or in what this tool is for. It is an important instrument in the laboratory, since with it we can make scientific demonstrations through experiments on the qualities of different liquid substances and the different reactions under the same exercise.

Also, in the same laboratory area it receives importance by facilitating the measurement of the melting point of solid materials, using small amounts of it and introducing it into the capillary tube and then heating it. By working in small chunks we can get the data without the need for larger and clunky equipment.

This is an extremely simple and practical instrument , just reading a little about its function and how to use it will be enough to put some science into practice, experiment personally and know how liquids react to this capillary test and with a little more knowledge provide the necessary heat to melt certain materials.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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