Variables in sieve plates

[flyingdutchman]

Hey,
I see alot of people interested in variables in perforated plates. here is a really cool paper on exactly what happens to sieve plates and overall column performance when we change stuff. Read the paper and then it would be cool to discuss what we each take away from this.

FD

variables in perforated plate column efficiency and pressure drop.pdf

(114.98 KiB) Downloaded 748 times

PS
Table 1 lists the two types of columns used and the specifications (notice thay are in the range of amatuer distillers!!!)
Figure 4 is where I think it gets interesting because they talk about what % effect free area on a plate

PSPS Bushman this is the paper I wanted to send you before but couldnt so here it is

[flyingdutchman]

OK maybe someone has had the time to read it so I will take a shot at getting this started. In the introduction on page 226 they say..

The mechanical design features studied were : hole diameter, per cent free area, weir height,downcomer cross-sectional area, and pitch-diameter (ratio of the distance between hole centers to the hole diameter in a triangular pattern).

Right beneath that it defines percent free area as

Per cent free area is defined as the actual hole area available for bubbling contact divided by the superficial cross-sectional area of the column and multiplied by 100.

Now on page 228 there is a graph with the X axis labeled Mass Vapor Velocity and the Y axis labed Plate Efficiency There is an key in the lower right hand corner that shows that they are looking at different percent free areas on the plates that range from 2.7 % free area to 16.2 % free area.
Now to me it looks like they are asking..
What happens when i drill more or less holes in a my sieve plate and how does my column perform as I turn the heat up in my boiler (more heat = more boiling = faster vapor velocity).
They completely discuss what the found from the graph on page 229 and 230.
SO.. look at the graph, read what they said and then post what you are thinking after reading this!
That way we can all see what we take away fromm reading it.

FD

[flyingdutchman]

Ok I will try putting up the graph to get some discussion going here (mind you can see it better in the PDF)...

The first thing big thing I see is that.....
1) Changing the percent free area does not appear change the plate efficiency.
In other words a plate with 2.7% free area is just as efficient as a plate with 16.2 percent free area. i would not have thought that!!
Then I see...
2) The second thing is that the lower the % free area the less the mass vapor velocity can be before it reaches the dump point (thats where all the liquid just falls back through the holes).
Now this makes sense to me! If it is the vapor velocity keeps the liquid from dumping through your seive holes and you have VERY FEW holes it seems to me that you need less vapor velocity to hold the liquid back.What this means to me is with a very low percent free area you could turn the heat way down on the boiler and not have the plates dump. The opposite case would be where your plate is like a spagetti stainer and then its gonna take a whole lot of vapor velocity to hold that liquid back.
3) Now the flip side of that, is that as you increase the percent free area you can have a much greater mass vapor velocity and still not flood the plates! Remember it is mass vapor velocity so that vapor is not just air rushing by, it is water and ethanol so more vapor is more mass and more mass translates to more and more liquid in the system as it gets turned up (remeber your refluxing). This says to me you can turn your burner way up and still not flood those plates. (ofcourse now you cant turn the heat as low so its a trade off)
Lastly (and this is pretty cool)
4) The greatest efficiency for all plates is really close to the dumping point! Now this caught me by surprise but thinking about it it makes sense! Once your past the point where it dumps plus a little more that should probably be the sweet spot. Beyond that your starting to push the system harder and harder the more you turn up the heat.

So here is what I take home from this with respect to percent hole area. How much you want to have is a trade off between bieng able to turn it down without dumping or turn it up without flooding. Turning up the heat is like stepping on the gas pedal in your truck. Sure you will get there faster but the engine probably wont run as effieciently so its gonna cost you. Again its a trade off no one wants to spend 16 hours watching this thing go drip drip drip but remember that the more you turn it up the less efficeient your separation will be (as in lower ABV and maybe smearing of flavors)!

So what do you think interesting, boring, couldnt care less??

[drinkingdog]

Definitely a lot of good information there. I looked at it yesterday on my phone at work and was having trouble understanding everything. Of course the graphs were harder to read because of the smaller screen size of my phone. Thanks for your interpretation of the info. It will help when I look at it again on the computer. The information should really help me when I build the plates for a flute. Thanks

[flyingdutchman]

Hi Justapup,
Thanks its great to see people reading the paper. I thouhgt it had some great information in it but wasnt sure if others thought the same . When you get a chance open the PDF on your laptop or PC the graph is awhole lot easier to see.

Now they also look at the effect of the hole diameter on plate efficiency. That is figure 9 on page 231 , and they discuss the results on page 231-232. This graph is laid out with the X axis labeled Vapor Velocity and the Y axis labed Plate Efficiency There is an key in the lower right hand corner that shows that they are looking at different sieve hole diameters from 1/16 to 3/16. You can see the graph a whole lot better in the paper but I will add it here also..

Regarding this their interpetation was

The results of the 1/16-inch-diameter hole test indicates a much longer throughput range of operation than those obtained from the larger hole sizes tested. The effect of surface tension in preventing the dumping of liquid through the holes would be more pronounced on the hole plates of smaller diameter.

I should have liked to have seen a 3/32 hole graphed also. However what I seem to see here is that the 1/16 gives a MUCH longer operating range. You could turn the heat way down (or way up) and the plate still performs like a champ. The 1/8, 5/32, and 3/16" diameter holes appear to me to operate in a similiar manner above their minimum vapor velocity. That said if I were building plates where ANY sort of fouling was an Issue, I would be tempted to use a larger diameter hole for safety reasons. Because if you completely clog a plate (or block off the vapor path in any "still") you have a bomb

Since the efficiency of all the plates are roughly about the same within their specific operating pressures/ranges (or at least very closely parallel) this sort of implies they do an equally good job of separation. So the final product should be about the same ABV IF you run them within their designated range and at the same pressure.
FD

[demodenny]

Really interesting information, makes me want to experiment with some ideas of my own,
Anyone have an extra 3" perforated plate sitting around they want to donate to that cause? I will post results and pay shipping.. PM me

[Stainless dude]

Great stuff Dutchman, thank you for all of your efforts. I am currently starting another build and drilled my plates to 5/64ths inch. Am still debating if I should redrill larger holes. It would have been interesting to see 3/32 hole size in the chart like you said.
SD

[flyingdutchman]

Hey glad you all like it.
Its really an old paper but still applies to what we do today.
Ya I am also curious about 3/32 holes but I would hate to see you change your design just to find out that 3/32 doesnt have the same effect with the surface tension, I know I would always wonder then if the 5/64th would have worked. Maybe just goofing with a plastic sieve plate made from a drink cup in a funnel with some air pressure and water might go a long way towards answering that b-4 building it.
PLUS this is Toluene and n-Octane I would be willing to guess that Water and Ethanol have a higher surface tension (think about hydrogen bonding between the the atoms I posted about this somewhere here) so perhaps the effect is extended to larger holes sizes because of this!
I also wonder if hole size might effect entrainment but there is nothing I saw in this paper covering that. What is also interesting is the effect of weir height on efficiency...

[flyingdutchman]

So here is another part of the paper where they examine the effect of weir hieght vs efficieny of the plates. Again the X axis is Mass Vapor Velocity and the Y axis is Plate Effieciency. There is an key in the lower right hand corner that shows that they are looking at different weir heights from 0" to 1". Now what they are really looking at I believe is the clear liquid height above the plate since weir height is approx equal to the height the downcomer is extended above the plate.

Now the operating range is the range between dumping (too low vapor flow) and flooding (too much mass vapor flow). T
1) This changes with weir height and 0" has the biggest operating range and 1" has the least (of all the sizes shown). This makes sense, as we gett taller and taller liquid heights, it takes more vapor velocity to hold all that liquid up.
2) Then there is a BIG jump in efficiency from the 0" to 1/4". Again not too big of a surpise with almost 0" of liquid on the plate there cant bee too much interaction between the vapor an dthe liquid and that is exactly what causes the whole separation to occur. So way less separation way less efficiency.
3) As weir height increases so does effieciency BUT at the same time operating range decreases
4) finally as seen before the best possible efficiency for any given plate is again near the dumping point.

I find the greatly increased range of the 0" weir height interesting (makes me think of dual flow plates and the ease of not having to make any downcomers at all) but truth be told I would never want to take that kind of hit on plate effeciency. Then from 1/4" to 1" is somewhere around 10% difference which isnt too bad at all.

[Flyer Tuck]

I am a new member and just tried to download the PDF in the first post and it only comes in at 115kB instead of 1.37MB, is only has the first page and that is unreadable.

How do I get the whole paper?

Thanks in advance,

Flyer

[manu de hanoi]

me too

I am a new member and just tried to download the PDF in the first post and it only comes in at 115kB instead of 1.37MB, is only has the first page and that is unreadable.

How do I get the whole paper?

Thanks in advance,

Flyer

[drinkingdog]

Try this.

[DAD300]

Nice find...thank you...

[Halfbaked]

TONS better. I am glad you reposted a better reading link.

[rumbuff]

I have read through the posts, but I'm at work and can't download the pdf. From what i can tell it seems that it's hard to build a system for speed and efficiency, as the two generally conflict. Seems like making an auto adjusting plate would be the way around this. I'm thinking of larger, deeper holes. If there was a ball bearing in there, it would allow higher volumes of vapour at higher presser, and automatically lower as the vapour pressure dropped, thereby allowing maximum efficiency as it would maintain just above dumping, would it not?

[wv_cooker]

Thanks for the link DD.

[drinkingdog]

I don't know what happened to the original pdf link. Good thing I downloaded it when it was first posted.

[Flyer Tuck]

I'm thinking of larger, deeper holes. If there was a ball bearing in there, it would allow higher volumes of vapour at higher presser, and automatically lower as the vapour pressure dropped, thereby allowing maximum efficiency as it would maintain just above dumping, would it not?

You are describing a "Valve Plate" and they exist, but are expensive in time and treasure to build!

http://homedistiller.org/forum/viewtopi ... 39&start=0

[Flyer Tuck]

From what i can tell it seems that it's hard to build a system for speed and efficiency, as the two generally conflict.

When you are doing tradeoffs, something always has to give.

I work in the Semiconductor Capital Equipment business and we describe it as:

Fast - Accurate - Cheap -- Pick any two!

Fast and Cheap -- Easy.
Accurate and Cheap -- Easy.
Fast and Accurate -- Ain't Cheap.

Flyer

[acfixer69]

Posting only to defend valved plates. They are easier then sieve plates to make and only slightly more costly. They cut down operating cost so you get your money back is a short time. Check out sungy's build I posted on my valve build on another site and this a forum about sieve plates.

AC

[rumbuff]

You are describing a "Valve Plate" and they exist, but are expensive in time and treasure to build!

http://homedistiller.org/forum/viewtopi ... 39&start=0

I don't mean just the valve, which seems like it would be more of an on, off type deal, but the variability of using the ball bearing. If you were to set up a punch press, you could form a shaped channel for the bearing to sit in, with a fairly small hole, and then just put stainless balls in it. Seems easier than making a valve plate, but having better performance.

*edit* Maybe even having one larger ball bearing, and more of a bubble cap arrangement