Oven Air Flow Requirement

Have you looked at the oven specifications?

Is there a reason that you suspect that the air flow is deficient?

There are formula, but you'll need to know lots about your fans.

Actually, there is no deficient air flow, it was just I want to reduce the Fan speed in order to save power. I would like to check how far I can go to achieve the desired CFM.

Can you please let me know, what all parameters are required about fans?

The truth comes out. You are trying to squeeze every penny you can.

Don't waste time and money in a foolish attempt to "save" money.

The methods used to reduce fan speed will probably cost far more that any savings you will see.

How do you propose to reduce fan speed? What will you do for varying oven loads?

What makes you think that some air flow calculations you don't understand anyway will allow you to reduce energy consumption?

Just turn down the fan speed until you start to get defective product.

The GA.'s seem to be exhausted. This is one. Eventually you might be able to experiment a bit with restricting the fan's inlets. (panel to restrict surface)

That is a cheap and easy way to gather information about your process conditions. There might be danger involved:

1. When the panel gets sucked in the inlet.

2. When the heather is electric, it might not get enough heat transferred and burn down.

You are Guru, but still Guru should be open to learn the new things and should not discard with pre-conceived notions.

The fact is that such type of practices are already followed in many of Toyota plants, and I have detailed case study for that. The saving is achieved by using VFDs. There is a plenty of saving specially if the operation is 24x7. If you are interested I can share the calculation of "savings".

The fans are running at Full RPM (1440), we are already in a stage at which by reducing the speed to 1300 RPM, our ROI is in approx 18 months. And we don't have any problem in product quality.

My question in this forum was just to know if there is any such calculation available, which can let me know the baseline.

@ lyn if you really know the formulas please let me know,.

The title of Guru merely means that I have wasted my time been posting here for more than 500 times. It means nothing else.

I don't know how to give you the formula you desire, if such a formula even exists.

I do not believe that such a calculation exists.

Maybe someone here can suggest a formula that will tell you at what point the air flow ceases to produce a satisfactroy product.

You seem to have established two points on a line. How I do not know. Perhaps you are an MBA. That would explain it.

You may have to resort to trial and error.

Good luck. I have no more to add, including magic formula.

I think this would vary according to material and process.....the equalization of temperature is usually for a drying process, the type of material and it's properties and initial moisture content and goal of process, would all come into play...Drying something too fast, or too slow, each may have undesired consequences.....so while there may be a standard for general use ovens, for purpose process requirements I think would be unique....just as would be temperature and time of process....

A poster should give information before he makes such statements. It always returns in this forum as if we have a crystal ball.

I have designed ovens for drying and exhausting solvent based coatings on high speed speed web coating machines, even without supporting rollers in it at 240m/min speed at 3 meter wide.

I just wanted to save you some time and money to do product tests. Combined with anemometers and differential air pressure measurement equipment, it can bring you were you want. A piece of cardboard to start you up is probably cheaper than installing perhaps 20 VFD's?

Oven design is based on:

safety related

1. Nature of products (and persons if applicable): flashing off solvents requires to work far under the LEL or your oven becomes a powerful bomb.

2. Filter load, if installed and safety level applied.

load related:

3. How much material goes in the oven and to what temperature it has to heated to dry and cure a product in your case.

4. Time the material remains in the oven to have the process finished.

5. Direction, air speed, relative humidity of the air to condition at the start.

VFD's in fans can lead to a loss of pressure when used under the design speed.

I gave a few points away now. Thanks for letting me now you are drying cars. Perhaps from paint, water based or solvent based or you handle perhaps powder coatings or all combined? Data, figures etc...

The Guru status you get with trying to poke information out of your nose, instead of having access to necessary information.

You ask for formulas:

There are just formulas, there are formulas to calculate the losses in the piping, but with what you provide I can only refer to a good engineering handbook becaue of what I state here.

Perhaps you might provide a bit more information?

You refer to Toyota, but not to the process. Different products and processes require different equipment and settings. You savings however will be more when mastering the heat (content) than playing fan games with VFD's. Power bill related.

Sounds like you just have a convection oven. Eliminated the air movement is counterproductive

Q ΔT = K. (I.e., flow x temperature change is constant). From the acceptable temperature variation, you can then calculate the needed air flow per fan. If you can reduce flow by 20%, you can save ~48% of the fan power.

G.A.

Have the fans on a frequency drive, and try different settings.

Mr. Jain,

I have gone through various comments, disagree with Gurus and appreciate your thinking to think from basics and improve operations. That is the difference between Engineer and Scientist.

In your case, the fans must have been designed for maximum load of oven.

And for such a large over, there could be PLC and Temperature sensors (RTD TC etc.) to regulate temperature.

I can suggest you to build a logic on following lines, discuss with Shop floor Manager (say paint shop if it for paint dryer or heat treatment shop if this for heat treatment or foundry shop if this is for drying/ curing of moulds etc), write the program and try

- Monitor amount of heaters in load if this cuts down to below 50%

AND

Temperature do not exceed in a particular Chamber/Section of oven above Max. limit - 'x' :

Reduce Speed of fans in that section. Regulate speed using PID controller of PLC to achieve desired results.

To regulate speed you can use VFD.

You will definitely save lot of rupees in a continuous process industry.

Keep thinking for improvement - never get discouraged from Negative Gurus.

Best of luck

Ramesh Kapur Faridabad

The only point to get an idea of the relative size of the oven is a reference to TOYOTA that arrived accidentally and.

You come up with a practical solution at a maximal price tag and without any safety built in.

A tunnel oven in a bread factory is also big, as is a tile oven or a oven where tanks are glass injected (boiler- heaters), to name a few. The Electrostatic paper oven I referred to before is 48 meter long and has 142 separate air sections, and the oven in the lab of 1 m3 is called a big oven too. All is relative.

If you read everything as stated, you as engineer or scientist (fill out as you wish) should ask for more info too. The three lines the OP provides have nothing substantial to tell.

>>>IF<<< the oven is used for painting and solvents are applied it is not waiting for if mixture ignites but when, considered you start experimenting with the air supply. We just try to feed or sometimes provoke to get some needed info.

Read the posts once again perhaps?

Keep playing with it and keep records then the data may become a formula for that particular sized oven..

I think simple procedure to get uniform temperature within section is to provide dampers and adjust each dampers equally then might be your problem may solve.

But cost saving yes u r right u can provide VFD