Thread: Thein baffle vs Dust Deputy

Originally Posted by jack620

Sure. I don't have a current clamp for my multimeter, but I do have a power meter. My setup wasn't very scientific. I just measured the motor power as I added components to the system. See the attached table. Hopefully it makes sense. I'm assuming a direct correlation between power and CFM as I have no way to accurately measure CFM. According to my readings the cyclone has twice as much effect on airflow as the 4m of 5" flexi. Which is an interesting finding as Onieda told me the cyclone is equivalent to 10ft of 5" ducting. That's not what I measured.

The flexi was laying on the garage floor. It was fairly straight, but not stretched tight.

The problem with comparing the Oneida and your results is that we don't know their actual setups (eg naked or hooded air intakes, testing using a proper test duct or just waving an air flow meter in the vicinity of a duct opening), or at what pressures the flows were measured. If low staring flows / pressures are used this usually will result in low flow rate losses and VV. That's why on some systems folks don't see any noticeable change in flows using separators. Even the power figures are only rough estimates. The only way to really compare is with all parameters as equal as possible and then using a flow meter.

The ultimate comparision is done via fan curves (P loss V flow rates) so we know what the %losses are at all flow rates.

Originally Posted by jack620

Sure. I don't have a current clamp for my multimeter, but I do have a power meter. My setup wasn't very scientific. I just measured the motor power as I added components to the system. See the attached table. Hopefully it makes sense. I'm assuming a direct correlation between power and CFM as I have no way to accurately measure CFM. According to my readings the cyclone has twice as much effect on airflow as the 4m of 5" flexi. Which is an interesting finding as Onieda told me the cyclone is equivalent to 10ft of 5" ducting. That's not what I measured.

The flexi was laying on the garage floor. It was fairly straight, but not stretched tight.

Thank you. I did see that and forgot about it. Sorry.

One thing about comparing the makeup of the loss is that pressure drop varies with the square of the flow. Adjusting for that the loss of the cyclone is actually equivalent to about 3.6m of your flex. Note that when I say "loss" I mean the ratio of pressure drop to velocity pressure, not a flow ratio. The flow ratio, as Bob has pointed out, varies with just about everything. The pressure loss coefficient changes only slightly with flow.

Originally Posted by dmorse

One thing about comparing the makeup of the loss is that pressure drop varies with the square of the flow.

Yes, I know. A better setup would have been if I had tested the power change with each component separately. However, I don't have that much patience!

Originally Posted by dmorse

Adjusting for that the loss of the cyclone is actually equivalent to about 3.6m of your flex.

I'd love to see how you calculated that. My crude power figures suggest the cyclone is almost twice as lossy as the 4m of flex, but you're suggesting it is actually less lossy.

Originally Posted by jack620

...I'd love to see how you calculated that. My crude power figures suggest the cyclone is almost twice as lossy as the 4m of flex, but you're suggesting it is actually less lossy.

Well, we might both get some abuse for violating the tacit "no math" forum rule, but here goes.

First step is to model the fan curve in the range of interest as P =P0 - R0 x Q^2 where P0 and R0 are the modeling constants. P is the fan pressure and Q is the flow. With the inlet open the the system pressure is P = R1 x Q^2 where R1 is the entrance loss expressed as a resistance. I that case we have P1 = R1 x Q1^2 = P0 - R0 x Q1^2. Or, P0 = (R0 + R1) x Q1^2. We can follow the same logic to get P0 = (R0 + R1 + R2) x Q2^2 = (R0 + R1 + R2 + R3) x Q3^2 = etc.... where R2 etc are the resistances of the added components.

So with R2 the resistance of the cyclone we can solve R2/(R0 + R1) = ((Q1/Q2)^2 - 1) and R3/(R0 + R1) = ((Q1/Q3)^2 -1) -R2/(R0 + R1) etc

The other assumption is that power is proportional to flow. So for your example Q1/Q2 = (1125-430)/(978-430) = 1.268 giving R2/(R0 + R1) = .608 and
R3/(R0 + R1) = .638 - .608 = .03
R4/(R0 + R1) = 1.187 - .638 = .548

So the ratio of the cyclone resistance to the hose resistance is R2/R4 = .608/.548 = 1.109

At this point I realize that in my previous post I divided instead of multiplying so the actual equivalent hose length is 4.4 not 3.6. (1.109 x 4m)

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Well, after rereading this I'm afraid it's not very coherent. Let me know if you can make any sense of it. I can try again tomorrow morning if necessary.

Originally Posted by dmorse

Let me know if you can make any sense of it.

Not really, but thanks anyway. My maths is pretty good, but I'm not clear on the meanings of some of the variables. I'll have another look later. No need to address this any further as it's fairly academic.

Originally Posted by dmorse

The other assumption is that power is proportional to flow.

OK. Are you saying that is a good assumption? If so, would that mean power consumption would be a good indicator of filter clogging?

Originally Posted by jack620

Not really, but thanks anyway. My maths is pretty good, but I'm not clear on the meanings of some of the variables. I'll have another look later. No need to address this any further as it's fairly academic.

Ah, too late. I already drew a picture. Need it or not, here it is:



The Blue line is the fan curve with entrance loss and velocity pressure baked in. That is, P = P0 - (Ro + R1) x Q^2. I've set P0 to 1 since its actual value is irrelevant here and power substitutes for flow. Again, no need for actual values, relative is all we need.

The other three parabolas represent the system curves of the three configurations you tested. Where they cross the fan curve is the values you measured. Fitting those curves is equivalent to solving for R2, R2+R3, and R2+R3+R4 as in my previous post.

To compare the individual parts we calculate the difference in pressure between adjacent curves at the same flow rate, in this case 695.

OK. Are you saying that is a good assumption? If so, would that mean power consumption would be a good indicator of filter clogging?

It's an indicator. Keep in mind that the relationship between flow and fan power depends upon air density, which can vary quite a bit. I just checked mine and it's about 5% higher than it was when I was doing some testing last October. It would be a lot more than that if I had done the testing in thunderstorm weather in July. Since your span is less than half the total that 5% would more than double if you didn't make two power measurements to get only the difference. That still gives you a 5% or more error. That limits the the flow reduction you can accurately resolve.

The usual method checks static pressure across the filter. Pressure is also affected by air density but since flow varies with the square root of pressure the error is reduce by half. So, a 5% density variation causes a 2.5% flow measurement error.

Hi all, does anyone have dimensions for a 6" inlet /outlet Thien baffle? I need inside diameter, height and the size of the slot in the baffle. I have seen n+1 videos of builds, but dimensions are about as plentiful as rocking horse droppings. I'm going with the FM-400 and 6" reticulation.

Originally Posted by jon542

Hi all, does anyone have dimensions for a 6" inlet /outlet Thien baffle? I need inside diameter, height and the size of the slot in the baffle. I have seen n+1 videos of builds, but dimensions are about as plentiful as rocking horse droppings. I'm going with the FM-400 and 6" reticulation.

Are you considering adding a Thein separator to the FM-400 or replacing the two separators it already has?

Also, what are you trying to accomplish with the baffle? What, to you, is the relative importance of separation efficiency versus flow reduction?

Originally Posted by dmorse

Are you considering adding a Thein separator to the FM-400 or replacing the two separators it already has?

I imagine Jon is considering adding a Thein. I also assume you are referring to the cylindrical metal objects between the plastic bags and the filter bags as separators? I guess technically that is correct, but I don't think it's what most of us consider to be a separator. I may be wrong, but I reckon most people would consider a separator to be a cyclone or Thein baffle installed before the blower.

You raise an interesting point though. That is, why bother paying for all that extra hardware if you don't need it? However, at $549 I think the FM-400 is cheap enough that it doesn't matter. If Jon's Thein is good enough, those plastic bags will almost never need emptying. Later, if he wants to upgrade to better filters or move the DE outside, it would be a very simple job to modify it. I reckon it's a good DE for tweaking.

https://www.timbecon.com.au/3hp-dust-extractor

Originally Posted by jon542

Hi all, does anyone have dimensions for a 6" inlet /outlet Thien baffle? I need inside diameter, height and the size of the slot in the baffle.

Hi Jon,
I think as a start you could simply find a 4" design you like and scale it up to 6". I would just scale it up by 50%. Although the cross-sectional area of the ducting increases with the square of the diameter, so does the area of the slot and the collector bin. They look fairly simple to make, so be prepared to experiment. Don't be blinded by science!

Originally Posted by jack620

I imagine Jon is considering adding a Thein. I also assume you are referring to the cylindrical metal objects between the plastic bags and the filter bags as separators? I guess technically that is correct, but I don't think it's what most of us consider to be a separator. I may be wrong, but I reckon most people would consider a separator to be a cyclone or Thein baffle installed before the blower.

Correct on both points. The "bag holder" is indeed a centrifugal separator, in the same family as a Thein separator or a cyclonic separator. And, yes, common language often mislabels technology.

You raise an interesting point though. That is, why bother paying for all that extra hardware if you don't need it? However, at $549 I think the FM-400 is cheap enough that it doesn't matter.

It's not about the monetary cost. It's the performance cost that's significant. Those "bag holders" have a surprising amount of pressure loss. Static pressure is a limited resource and it's a shame to waste it when nearly all of the separation will occur in the Thein, which will have plenty of pressure loss on it's own.

If Jon's Thein is good enough...

Hence the question about the goal of the project. There's a strong trade off between pressure loss (resulting in reduced flowrate) and separation performance. The question really comes down to "Which is more important to you, maximizing fine dust collection or minimising filter cleanings?" That affects the size of the Thein (and, actually, any other) separator.

Originally Posted by dmorse

It's not about the monetary cost. It's the performance cost that's significant. Those "bag holders" have a surprising amount of pressure loss. Static pressure is a limited resource and it's a shame to waste it when nearly all of the separation will occur in the Thein, which will have plenty of pressure loss on it's own.

Everything you say makes sense, but what's your end game? Are you suggesting Jon just buys a blower if he intends to add a Thein? These aren't readily available which is why a lot of us buy a complete DE and modify it. We've talked about how a pre-separator saves the hassle of emptying bags and how the bags are prone to developing pinholes from the circulating wood chips.

BTW, Jon has already stated money is an issue.

Originally Posted by dmorse

The question really comes down to "Which is more important to you, maximizing fine dust collection or minimising filter cleanings?" .
That affects the size of the Thein (and, actually, any other) separator.

Do you have any suggested sizes for the Thein in a 3HP/6" system that might achieve a good compromise for both criteria? Or even sizes that will optimise each criteria? Then Jon could choose one or the other or a hybrid of both.

Originally Posted by dmorse

Are you considering adding a Thein separator to the FM-400 or replacing the two separators it already has?

Also, what are you trying to accomplish with the baffle? What, to you, is the relative importance of separation efficiency versus flow reduction?

Hi Dave,
I'm adding it to the FM-400, or that's the intention. The reason being that I want to separate out the chips, shavings and most of the dust before the DC to save me having to be emptying those blasted plastic bags with monotonous regularity when I'm working. As has been pointed out, I'm no spring chicken and the body isn't as flexible as it was. What flexibility was left took a hit with the L3-L4-L5 fusion. If I can get the frequency of emptying down to once or twice a year, that'll suit me fine. Remounting the damned things is the killer. If I wasn't on a minuscule budget I'd look seriously at building a mini electrostatic precipitator and have that empty into a bucket like the Thien, or cyclone.

I already have an idea or two about modifying the bags to make them easier to remount by fixing an elastic band to the top of the bag to hold it in position while I wrestle the clamp back into position. Reducing the overall length of the bags won't matter, seeing that the amount they collect should be small.

Mine is in a large drum.
These are the photos of mine. I cant remember the exact measurements but they came off the WEB. I can dismantle it if you like and measure the parts.
The only thing is that mine has 4" pipes, not 6"

IMG_0882.jpgIMG_0881.jpgIMG_0880.jpgIMG_0879.jpg