Preventing entrainment of fluid droplets in ethanol condenser

[bendhoward]

I would just like to preface this by saying that heat and mass transfer is far from my area of expertise, so I apologize if this post is too elementary. That being said, any suggestions regarding design or even just potentially useful reading material would be greatly appreciated.

What I have is a mist of 100% ethanol droplets (around 1 - 4 microns diameter) in a relatively slow moving air stream (less than 10 LPM at STP in a 1" tube). My goal is to remove a large potion of the ethanol from the stream using a system of a heater and cooler.

The heater brings the stream temperature to 150 C, successfully evaporating the droplets, and then the cooler brings it down to 4 C. The issue I'm having is that instead of condensing on the side of the copper pipe in the cooler, the vapor re-forms droplets entrained in the air stream that exit as mist, thus preventing the capture of the ethanol.

Aspects of the system I can change easily are the ratio of ethanol droplets to air volume, air flow rate, and temperatures of the heater and cooler. A bit more difficult but still possible are copper tube diameter and length.

Thanks in advance for your help.

-Ben

 

[TD2K]

Doesn't sound very efficient to first heat and cool the stream, why not cool it and run the air/ethanold droplets through say a coalescing filter?

 

[gr2vessels]

bendhoward,
there is an issue with your goal, it doesn't seem realistic and the first advice for you is not waste energy on a simple separation process. The end piece of equipment is a condenser which will change the vapor in liquid, so all what you need is a method of removing the non-condensables (air in this case) from the process flow. If you are unable to accomplish the separation in the condenser, then you cool the air methanol mixture below the saturation and/or use a dedicated 2 phase separator, just upstream of your useless condenser (remember, you have already condensed the methanol). As far as the re-mixing of droplets in the flow, just read your own words, the air flow is very slow moving, hence no chance in the world to entrain the droplets. Also, try to change (as you said) the air flow down to zero, that will help.
Cheers,
gr2vessels

 

[bendhoward]

I'm sorry; I think I may have oversimplified the problem a bit in my original post.

The use of pure ethanol has really only been a test of whether the system is working. My actual goal for the final system is to take in an aerosol of ethanol/oil droplets suspended in air (each droplet contains a mixture of ethanol and low vapor pressure oil), evaporate the ethanol in the heater leaving oil droplets suspended in ethanol vapor and air, and then remove the ethanol vapor leaving just an oil aerosol. It is important that I not remove the oil droplets in the process.