The three types of heat transfer are of interest to HTV specialists. The guide below will help expand your knowledge on key terminologies of our industry:
In this article, we’re going to get a little scientific. The good news is that it will help you gain a more in-depth understanding of HTV. Let’s get started: Conduction, convection, and radiation are the three ways in which heat, one form of energy, is transferred from one object or medium to another. At the molecular level, heat transfer is related to the way molecules, atoms and electrons collide with each other as temperature changes. In general, heat will transfer from an object of higher temperature to an object of lower temperature. Nature loves equilibrium, therefore, higher energy particles (hotter temperature) move towards lower energy particles (cooler temperature) to create equilibrium. This affects how pieces of metal heat up or how drinks cool down or how the sun transmits heat to the earth. These changes in heat can be measured with precision measuring instruments for industrial purposes. Here is how each method of heat transfer works.
Heat Transfer by Conduction
Conduction mostly happens in solids and, among solids, metals are the best conductors of heat. In solids, the particles are closer together and they cannot move freely within a given material. Now, when two items at different temperatures are in contact with one another, heat flows from the hotter object to the cooler object until the two objects are at the same temperature. The particles with higher energy at the point of contact tend to vibrate faster and collide with the lower energy particles of the cooler item in the same way that billiard balls collide. On collision, the faster molecules lose some of their energy to the slower moving cooler particles. The slower-moving particles begin to move faster as they gain more energy. They, in turn, impart some of the energy to the neighboring slow-moving cooler particles. Gradually the cooler item heats up while the hotter item cools down. This will continue until the level of heat in the previously hotter item is the same as the level of heat in the previously cooler item.
A very good example of heat conduction is when you are cold and you hold a mug of hot coffee. Gradually your hands heat up as well. Another example is the transfer of heat from an iron to clothes when you press the clothes.
Heat Transfer by Convection
Have you ever wondered how you boil water in the kettle? Convection is the method of heat transfer in liquids and gases. The particles of water in contact with the kettle get heat from the kettle through conduction (water is a moderate conductor of heat). Now, the heated particles of water move upwards because they are free to move (molecules of water are further apart than in solids). As the warmer molecules move up in a current, their place is taken over by the colder water molecules which move down. Those colder molecules are also heated up through the conduction of heat and also move up. This process creates currents of upward movement of warm molecules and downward movement of cooler molecules. The process continues until the water is all heated up to the boiling point and begins to produce steam.
The same process happens with air. As the earth is heated by the sun, it transfers the heat to the air in touch with it. The heated air molecules rise, as they are less dense and more buoyant and their place is taken by the heavier cooler air molecules. This also creates convection currents. This process continues until the air itself becomes very hot.
Heat Transfer by Radiation
Radiation is the transfer of heat from a hot object without any intervening medium. No contact is necessary for heat to be transferred in this case. The transfer happens in the form of electromagnetic radiation. On the electromagnetic spectrum, heat is infra-red radiation. A hot object emits this infra-red radiation or energy from its surface and the heat increases the temperature of any matter that absorbs it.
One example of radiation is the transmission of heat from the sun which does not require any medium. However, all objects emit and absorb radiation and will continue to do so until the absorption and emission of energy become equal.
Measurement of Heat Flux
Conductive, convective and radiative heat flux (the flow of heat per unit of area per unit of time) can be measured directly using heat flux sensors or indirectly using temperature sensors. Heat flux sensors measure heat passing through the sensor surface. The indirect method relies on the relationship between heat flux, temperature difference, and absolute thermal resistance.
Manufacturing, heating, ventilation and air-cooling industries rely heavily on thermodynamics, the principles of heat transfer and accurate measurement of heat flux. They use the right instruments for measuring heat flux.
Information is power – with the above in mind, the building blocks for your knowledge in this industry has just become stronger and more complete!