Mass Flow of Air

[ragga_muffin]

Hi,
I am trying to figure out the mass of air I will need to evaporate 310 kg of water.
The air properties are:
T= 80degree C
Relative Humidity=5.7%
specific Humidity = 0.017kg/kg
specific volume= 1.02 m^3/kg
enthalpy= 140.72kj/kg

The water removal rate is 44.28kg/hr

I am not sure how to approach this so any help will be appreciated.

 

[Latexman]

Get a air water psychometric chart. Most big A/C companies have them on their web site. Determine how humid you want the exit air, and find the exit specific humidity. Then it’s just a mass balance.

Maybe someone more knowledgeable in this could tell them about what outlet humidity to shoot for.

Good luck,
Latexman

Engineers helping Engineers

 

[LittleInch]

The other issue is how is the air picking up the water?

Bubbling it through or running the water through a counter flow contacting tower would get you very humid air. Blowing it across the surface won't.

Also what is the water temperature?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ragga_muffin]

So it is a dryer situation. The product is wet and I am trying to use hot air to evaporate 310 kgs of water.

I am not sure if that helps or not.

 

[Latexman]

Are you designing a dryer or is/did someone else? Whoever is designing the dryer is responsible for specifying how much hot air is required. What kind of dryer is it? There are many.

Good luck,
Latexman

Engineers helping Engineers

 

[ragga_muffin]

I am designing it. it is just a convective air dryer. I have got an element heating up the air to 80 degrees and that air is then being used to dry the product.

 

[Latexman]

Do you have a “go-by”!? Have you done drying studies/lab work? Have you brushed up on dryer technology? How many dryers have you designed?

Good luck,
Latexman

Engineers helping Engineers

 

[IRstuff]

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[dvd]

My opinion for one reason that Eng-Tips is a ghost town is that there are too many reasons to exclude people. Don't give students the answers, but don't run them off.

 

[dvd]

Mass Tranafer Operations by Robert Treybal is a great reference. Buy it used for a few bucks.

 

[Latexman]

You should team up with a ChE that has mastered Unit Operations. Probably a rising senior.

Good luck,
Latexman

Engineers helping Engineers

 

[LittleInch]

We looked at something similar some time ago

https://www.eng-tips.com/viewthread.cfm?qid=420946

So the basics - You can find out quite easily your maximum water content at 100% humidity leaving the dryer.

Your water leaving the product rate looks far too precise to me....

However the efficiency of your dryer is the experimental part here to determine how effective your dryer is (10%, 30%, 70%??) and also how this varies with the temperature of the mysterious "product" and whether the efficiency changes as the product dries out. So this gives you your range of possible volumes.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chicopee]

I am assuming that you had a course in thermodynamics, so if you did look up thread 403-433588. My reply related to a ventilation requirement for an indoor swimming pool and consisted of two pages. I could solve your problem but I have no inclination to work with Metric units however the units I used in my reply are in British units. Nonetheless the principles on solving the type of problem in your OP are the same as the ones I used in my reply. Conservation of mass and the first law of Themo.; I did not bother with the second law of Themo. as it would not apply.