Mass transfer drying

[khalilmaalej]

Hello, I have a room in an industrial machine which is used to dry mechanical parts after washing them
I want to use a fan mounted at the top which will blow air at very high speed and therefore there will be diffusion of water from the rooms but the problem is that I cannot calculate this speed.
I attach below a picture of the room



Thank you

[dedeleco]

I notice that it is not diffusion, but the evaporation of water in an air, which must be dry, not saturating, because otherwise nothing will dry at all, like a day of intense rain.
Without heating at all, the flow rate is extremely variable depending on the day and the place: in Brittany by drizzle, non-breaking by blowing on it to death and in the Sahara, hyper dry, drying in a second!

What are the parts exactly, with what surface, smooth or porous with how much water, ??
Because it's very different.
What dimensions of surface to dry, etc ...
In extreme cases algae or a thick terry towel, coming out of the water, requires much more (kilos of water) than washed aluminum parts.
The amount of water to be loaded, sets the amount of air and its flow, which are a function of the humidity level.

Air temperature is important; at 40 ° C or 50 ° C, it will dry as in the Sahara.

Read wikipedia and google for: dew point, dew point, evaporation, water vapor pressure, partial pressure, humidity, drying, vapor pressure, etc ... and learn the lessons on this basic physics.

So the fan speed is a function of these precise conditions and the nature of what you are drying: water in principle, but if it is paint, it is the same physics, but with very different properties, in pressure and vapor pressure, with also the dangers of solvents not to be discharged outside !!

So specify carefully !!

[Fakir]

The answer is in the definition of saturated vapor pressure: The saturated vapor pressure or vapor pressure is the pressure at which the gas phase of a substance is in equilibrium with its liquid or solid phase. It depends exclusively on the temperature.
http://fr.wikipedia.org/wiki/Pression_d ... ns_l.27air

By circulating the air, this pressure is lowered by replacing it with dry air, which evaporates the liquid.

In practice, this calculation will be done from the Antoine equation (http://fr.wikipedia.org/wiki/%C3%89quation_d%27Antoine) which will give the parameters of the water and by the calculation sheet of the following file (http://www.cheresources.com/flammable.pdf)

Small conversion to be made between mmHg and bar.

Good little math exercise.

[khalilmaalej]

Thank you for your answers, the pieces I want to dry are brass neck pieces that do not have a single shape but generally they are cylindrical with grooves or holes

In fact I understand well that the temperature plays a very important role in this phenomenon but me I want first of all to calculate the speed of the air supplied by the ventilator at an ambient temperature then if the result is illogical then I must add a heating element to increase the temperature in the room
So maybe my question will become as follows:
How can I calculate the speed of the incident air on the surface to be dried for a temperature of 20 ° C?

Thank you very much

[Fakir]

How can I calculate the speed of the incident air on the surface to be dried for a temperature of 20 ° C?

Air speed is not the determining factor. It is the renewal of the air. The calculation is in the elements transmitted in my previous post.

Good luck

[chatelot16]

there is not enough data to calculate the speed

is speed the right criterion?

I would rather seek the flow ... from the amount of water contained in the parts to be dried

how to know the quantity of water? it strongly depends on the shape and size of the pieces ... the way it is placed, well separated or piled up

what is the drying requirement ... apparent drying so as not to look wet ... or perfect drying which can last much longer

Isn't it stupid to consume too much energy for a powerful ventilator which must turn a long time to brew cold air

it may be more economical to heat a little to ventilate less

what is the context of your thing ... in the industry there is often waste heat easy to recover for drying

[phil53]

Working a little in this area, I advise you to take outside air and push it inside with the largest possible volume.
Even if the outside air is humid, if there is no mist it is not saturated.
Otherwise in the past they used drafts to dry, it is longer but it consumes nothing.

[elephant]

I have the impression that it is better to suck the air than to blow it on the parts.

[dedeleco]

Thank you for your answers, the pieces I want to dry are brass neck pieces that do not have a single shape but generally they are cylindrical with grooves or holes

In fact I understand well that the temperature plays a very important role in this phenomenon but me I want first of all to calculate the speed of the air supplied by the ventilator at an ambient temperature then if the result is illogical then I must add a heating element to increase the temperature in the room
So maybe my question will become as follows:
How can I calculate the speed of the incident air on the surface to be dried for a temperature of 20 ° C?

Thank you very much

For this kind of parts, the best is to mop them with towels or tea towels, to empty the blind holes and the grooves that keep the water or to shake them in all directions to drain them well by emptying these holes full of water, and then a few minutes in fairly dry air (max humidity 50 to 60%) passing over it slowly, is enough to dry them with the little water that remains on it. Brass does not absorb water.
It's the same as drying dishes !!
Otherwise with water filled troughs, it will dry slowly, leaving dirty spots of dissolved lime.

The air flow only makes sense if the air is dry and on properly sponged parts does not need to be important, but depends on the surface to be dried, 10cm2, 1m2 or 1000m2 !!! ..
In rain, drizzle and fog, nothing will dry, even at high air speed !!
So you have to heat the air and the rooms a bit too, i at least 30 to 40 ° C, having preheated the rooms for a few minutes to hours depending on the size of the rooms (from cm to meter !!) !!

So do not see that the air flow, but the whole, surface to be dried, amount of water per cm2, humidity,
The links given give you everything you need to calculate.
Vacuuming or blowing will not change much, except that by blowing, after the fan, the air is more turbulent, and therefore dries a little faster.

[phil53]

I am not of your opinion elephant, in a house it is better to blow healthy outside air than to suck in polluted air.
The opposite of what CMVs do

And dedeleco rightly before drying you have to drain well shake, blow with a blow gun, after that will dry quickly.