By far the most common mistake we see is confusion between the concepts of temperature and heat. The terms are often used in conversation as if they are the same thing. This can have big implications when choosing a heater or designing a hot air system.
Heat and temperature are related. When heat is added to a material, the temperature of the material increases. The amount the temperature increases depends on the material and the amount of heat energy applied.
Let’s define the two concepts in greater depth:
Heat is form of energy. It can be transferred from one body to another. It can be created by, or transformed into, other forms of energy. As heat is a form of energy it can be used to accomplish useful work and it is measured in units of energy (SI units: Joules).
Temperature is the measurement of hot or cold. It is a measurable quality of a substance. Temperature cannot be “added” to a material and cannot do work. When an object’s temperature decreases, the object has lost heat energy to its surroundings; when its temperature increases, it has absorbed heat energy from its surroundings.
Why does it matter?
The distinction between temperature and heat is important to understand when selecting an air heater or designing a system.
Let’s look at an example:
An application requires a block of metal to be heated to 200°C in a given amount of time.
A common misperception is that any heater that gets to over 200°C will work for this application. Since all of the Leister heaters can reach 650°C any one of them should be able to do the job. This is the trap of designing by temperature rather than by heat.
The important parameter is actually the heat energy that is required to raise the temperature of the metal to 200°C. This article provides an introduction to the basics of heat calculations. Once the amount of heat energy (in joules) required to raise the temperature of the material is known, this information can be combined with the time limit (in seconds) to find the required power (in joules per second better known as watts) for the application. Once the number of watts is known, an appropriate air heater can be chosen based on its power rating. Remember that no process is 100% efficient, so some amount of expected loss should be included in your calculation.
Still confused? Contact STANMECH so we can help.