1. Mixing up heat and temperature
The most commonly made mistake when designing a hot air system is the confusion of heat and temperature. While the terms are often used interchangeably, by definition they are very different. Heat relates to the amount of energy that is required in order to raise the temperature of a material or change its state (i.e. water changing from a liquid to a gas). Temperature is usually a specific design criteria or limitation, such as the melting point of a material or a temperature above which the material will degrade. When designing a process heat system both are important, however temperature is a design variable and heat is a calculated output.
2. Making equipment choices without sufficient investigation
Choosing the right equipment for a hot air system is a complex task that requires a thorough application analysis. Simplistic choices are often made without enough examination of the key design elements. For example, a system may be designed considering only the required target temperature while ignoring the amount of heat or type of air supply required. This results in the wrong equipment being specified and a system that does not work. Read our article about using hot air to create an oven as an example of the complexity of designing a hot air system.
3. Over-specifying precision
We commonly see application outlines where the required temperature range is very tightly constrained. There are times when the temperature must be tightly controlled but in many cases the specified acceptable range is unnecessarily small. The result is an overly complex and expensive system. Read our article about temperature control of air heaters for more information about control options.
4. Mixing up air flow, velocity, and pressure
These words should not be used interchangeably, they are distinct aspects of a system’s air supply. Flow is the volumetric air flow produced and is particularly important when a space needs to be filled with hot air. Velocity is the speed the air is moving and is important when the process requires the air to physically impact an object. Pressure is the force per unit area the air exerts and becomes important in overcoming impediments in the air path. Read our article about this topic for more information.
5. Trying to control the wrong temperature
Many systems utilize a closed-loop control system for temperature. A common error is the incorrect placement of the temperature sensor (thermocouple, etc.). Incorrectly positioning the temperature sensor results in the wrong temperature being monitored and controlled. This can cause problems for temperature sensitive processes. Read our article about thermocouples in hot air systems for tips on placement.
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