Dust Collection Pressure-Flow Calculation Program
ust collection sizing is one of those Goldilocks problem. Size the duct too big and the dust settles out in the big ducts. Size it too small and the pressure losses are too great and there is not enough flow at the tool to collect the dust. I wrote a Matlab program to calculate the intersection of the fan performance curve and the duct system pressure loss curve. This is a standard engineering problem for predicting the flow and flow velocity. . I just programmed it up. I used the most accepted pipe friction factor formula (an explicit version of Colebrook) and loss coefficients from ASHRAE for the fittings. It is a Matlab program. The user inputs are just the lengths of various diameters and types of pipe and the numbers of fittings. The list is not extensive but enough for almost any small shop. The list can be readily extended. The same sort of too much or too little applies to the dust collector itself. I intend the program as a design tool for my own use but the activity on this topic on the forum suggests others might be interested.
What is different about may program? Most duct calculators online only calculate the system loss for a given flow (given as input by the user). This is not what you really want to know. What you want is the system flow given the system design. To find the actual operating point for the flow you would have to iterate manually between the fan head curve and the loss calculation. My program has the iteration built in.
I have all the correlations and data built-in. You just input the configuration data and run the code. I have checked my calculations against other data sources and correlations so it is reasonably reliable.
I use form loss coefficients for fittings rather than equivalent length. This form loss method is the textbook recommended approach.
I also have a separate version that does a main duct with two active branches. I created this version for my Sawstop with the over arm guard. It be useful for any tool that has two collection points, like router tables with collection box below the table and connection on the fence above or a bandsaw with a small nozzle right at the blade and another connected to the housing for the lower wheel. It would also work for two tools operating simultaneously
I have provided a method for including special terms that are present in dust collection systems but are not readily available from handbooks. This includes a way to model the losses in the cyclone and filter and entrance loss coefficients specifically for woodworking tools. I have not fully populated this cability with data but I have bought a hot wire anemometer and a manometer (Testo brand) to measure them experimentally. I have just embarked on this part of the calculator. Oneida may have seen me coming with this idea. Since I bought my system, they discontinued publishing the data that I used to estimate the flow losses in the cyclone and filter.
If anyone is interested in acquiring the coding, I will polish up the comments and put it on the Mathworks File Exchange. It is free but with no warranty or guarantee. I would say using the coding requires basic Matlab skills because you enter your data in the Matlab script and have to edit the source file to do so. And gyou would benefit from a general undergraduate-level knowledge of flow in pipes. Not too much because the coding is all done. You just have to understand the meaning of the labeling on the results.
Or, if you just want to discuss this kind of stuff, I am always available to listen or to explain or both.
TW
