Using Hot Air to Create an Oven

5/21/2015

One of the most common application enquiries we get at STANMECH Technologies is about using air heaters to create an oven. Creating an oven is a logical use of air heaters but there are a few areas that require technical knowledge to ensure your oven achieves the desired end result. Below, we cover the 5 areas that require consideration when using hot air to create an oven.

1. The Air Volume Required

In order to efficiently transfer heat to the objects in the oven, it needs to be continually flushed with hot air. At STANMECH, we use a rule of thumb of 10 flushes per minute but it could be less depending on the details of the design. Calculating the volume of 10 flushes per minute gives a conservative number for the air volume required by the blower, helps ensures good heat transfer, and limits problems like temperature gradients and heat loss to the environment.
With air continually flushing the cavity venting becomes important. Intuitively people want to seal a system to eliminate air escaping to the environment but in this case you must ensure that the air has somewhere to go. The location of the venting is important and should be placed to encourage even distribution of the hot air in the chamber. We recommend partnering with a company that has experience creating hot air systems in order to ensure an even distribution of air within your oven.
The volume of hot air required becomes a simple calculation:

Volume of the oven

Desired flushes per minute

Required air volume/minute

2. The Energy Required

There are two major elements to the energy requirements of an oven:
1. Requirements to heat the flowing air to the desired temperature
2. Requirements to heat items in the oven to the required temperature
There is a difference between heat energy and temperature. The temperature is a design criteria whereas the heat energy (usually stated in kilowatts) is the input. For more information on this topic see our article on The Basics of Heat Calculations.

For details on how to calculate energy requirements see our page on Heat Requirement Calculations.

3. The Size and Shape of the Oven

Ovens come in all shapes and sizes and this can impact the type and number of heaters required. Most of the complexity comes when ovens get large.
The heater and blower choice becomes more important in larger ovens. Generally we recommend centrifugal blowers and open element heaters in order to generate the volume of hot air required. See our article on blowers and our whitepaper on heaters for more information.
Temperature gradients and hotspots can be problematic and may have to be solved by using multiple heaters.

4. Temperature Control

Each application has different requirements for how precisely the temperature needs to be controlled. The precision required changes the control method used. Tight acceptable temperature ranges will likely necessitate a closed loop control system. See our article Temperature Control of Air Heaters for more information.
Precise control requires careful consideration of thermocouple placement. This is especially true in large ovens where several control zones may be required. For more information on thermocouple placement see our article Thermocouples in Hot Air Systems.

5. Air flow distribution

Flowing air will want to move in a straight line unless forced to do otherwise. In order to achieve complete or even heating, there are times when mechanical solutions such as baffles or ducting must be used to redirect the hot air. We recommend seeking expert help with the design process to ensure your oven heats evenly.

Air heaters are an excellent candidate for building an oven but the design needs to be carefully considered. STANMECH Technologies has the expertise to make sure you get it right. Give us a call to discuss your application and ideas, we’ll help you figure out the next step in the design process and make sure you get equipment that will work for you. Contact your Technical Sales Representative.