Scientifically, thermodynamic is a study of heat or energy that affects living organism and all matters on earth. When learning about heat movement and its underlying fact, the best source of knowledge are those that were presented in this field of study.
Before getting into the discussion about the second law of thermodynamics, which directly relates to what happen inside the refrigeration system, it is required to study the characteristics of heat to understand how the process in this principle is taken into action. The following are the characteristics of heat or thermal energy.
1. Heat is Everywhere
Heat is present in all places and in all substances; this makes the earth go round. It gives life to all living organisms in our planet. With the presence of heat, natural processes occur in our environment. Plant grows; animals become alive and multiply including human beings.
For non-living things, heat affects the binding and breaking of its molecules and atomic structures to create chemical change, which may form other substances for some other purposes. For example, in welding or joining of metals, heat must be applied to melt that metal surface to alter its structure and connect other piece of metals.
In quantum theory, all matters are just form of energy that takes its physical form according to the level of vibration of its subatomic particles. This means that, whatever substance it might be, it could be a gas, solid or liquid, regardless of its chemical composition and properties, the one that make it exist is the thermal energy that it carries within.
This thermal energy or presence of heat creates the vibration of its minute particles to attract other particles and form molecules or the chemical composition of that particular matter. So, if heat is completely taken away, all natural processes may also stops including the existence of life.
2. Heat can Never be Destroyed
The theory that heat is present in all places is due to the fact that it can never be destroyed. It naturally exists in all bodies of matter at varying degree or level. When fire occurs and fire fighters stop the fire, it does not mean that heat has been eliminated or destroyed. It is just being dispersed and transferred into other bodies of matter where its presence creates no harm or any untoward effect.
When putting off a fire using water, the heat that burns the flammable material, has just been absorbed by the water and goes together with hydrogen and oxygen in the air. There is no way to destroy heat it can only be transferred from one place to another.
3. Heat can Never be Created
If heat can never be destroyed by any means, in the same way it can never be created. The only source of heat anywhere in this planet is the sun in our solar system. But by means of some mechanical or chemical processes, heat as a form of energy can be generated here on earth for some specific purposes.
Generating heat does not mean of producing it out of nowhere. It is simply allowing heat to travel into a certain medium or material to collect and increase its amount up to the level of intensifying it, where it can be used or converted into other forms of energy.
When creating a fire, heat is just being collected by using a flammable substance where it requires extreme heat in order to create chemical change on that material. The flame that is visible is just the physical appearance of heat collected in an extreme level.
4. Heat always Travels from Warmer Body to Colder Body
In the same way, heat moves in a bit similar manner. Heat also finds its way to equalize in all bodies of matter. Whenever there are two bodies with different temperatures, heat always travel from warmer body to colder body to make its presence equal in both bodies. This makes heat keeps on moving from one body to another every now and then.
The above figure shows the direction of heat movement when two bodies of matter at different temperatures are put together in a place with even more lower temperature. As you can see, heat flows from warmer body to colder body to equalize its presence.
Whenever it completely equalizes in all matters, that is the only time heat stops moving. But it never happens because as heat moves from one place to another, there are also factors that affect its presence to make a change on its level on every spot. This makes the heat constantly in motion as it seeks its way to find its equilibrium point.
The second law of thermodynamics was just mentioned in the above paragraph. It is one of the fundamental principles in the study of refrigeration and air conditioning. It tells that “heat always travel from warmer body to colder body” regardless of the phases of matter and this principle can never be altered or reversed by any means. To understand how heat moves from different bodies of matter, we need to study and understand the three methods of heat transfer.
3 Methods of Heat Transfer
One of the most evident examples of heat transfer via radiation is how the sun illuminates the earth. Heat travels in a form of light from the solar system through the atmosphere and reaches the surface of the earth it just a matter of seconds. This could result to increase in temperature for all objects here on earth, which are directly exposed to the heat of the sun.
Another example of heat transfer via radiation is when you put your hands near the flame when you cook something. As you do that, heat travels via radiation from the body of flame into the surface of your skin.
As we turn on the heater and open the faucet, hot water will start to flow. As it flows, the faucet also will become hot. In this scenario, the heat from the heater coil transfers to the faucet by means of convection. The flowing water which also becomes hot acts as a medium for heat to transfer into the faucet, which is made of metal.
Another example of convection is when you stand outside the building near the operating condensing unit of split ac system. That unit gives off heat via induced or forced air. When the air hits your body, you can feel that it’s hot. If you are wearing a gold necklace or a metallic watch, you can feel that it is also heating up.
In that case, the heat given off by the condenser transferred to your necklace or watch via convection. The air that conveys the heat to your body serves as a medium for heat to transfer.
When a piece of metal is fixed on a vise or anything that can hold it firmly, then heating up one end, heat will travel into the other end and to the vise. It means heat moves from point A to point B in the same body and by direct contact between two bodies.
In refrigeration system, these 3 methods of heat transfer occur simultaneously within the system during the heat absorption and extraction process. The following figure shows the three methods of heat transfer occurs simultaneously whenever there is a presence of heat.
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