🇺🇸 🇮🇱 Greg Mehos & Associates LLC 🇺🇦 🇺🇸
Greg Mehos, Ph.D., P.E.
Greg Mehos & Associates LLC
Engineering • Consulting
Hopper, Bin, and Silo Design
Powder Flow Property Testing
Training
Services
Consulting
- Process development
- Functional design recommendations
- Solutions to powder flow problems
Testing
- Cohesive strength
- Internal friction
- Compressibility
- Wall friction
- Permeability
- DEM (discrete element method) calibration
Buy my book!
Storage and Flow of Bulk Solids
When I became an adjunct professor at the University of Rhode Island, I realized that most books on the subject of bulk solids testing and hopper design were either very terse or rather intense for readers who did not have a mechanical engineering background. My students encouraged me to convert my course material into a text book. Yes, some of the text may have been taken from my prior publications, but I figure that it isn’t plagiarism when you copy your own material. I only disclose analyses and design methods that are available in the open literature.
A few of the formulas I derived on my own, but they were all based on fundamental engineering principles. Consequently, some of the analyses that I present may be slightly different than what you might find published elsewhere, but I use them when I consult.
The paperback is 200 pages long and includes sections on analysis of stress, stresses in hoppers, flow property testing, bin design, feeders and flow aids, chute design, and design of process vessels.
The publisher charged me $5.00 per book, but the catch was I had to purchase one hundred of them! So I'm offering them on my website for $20.00, which includes USPS media rate snail mail shipping. For every book I sell, I either give a free book to a University of Rhode Island Student or make a donation to https://unitedhelpukraine.org 🇺🇦. I figure that if I'm charitable, I won't get into too much trouble for helping myself to some images from the web without permission.
You can pay me by credit card or PayPal. Please send an email to greg@mehos.net when you place an order if you have questions about international delivery options.
You can always download an abridged version from my downloads page. The unabridged version can also be downloaded but it requires a password. If you ask me nicely, I'll share it with you.
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My Blog
Shear cell testers
25 January 2020
I've used most of the common shear cell testers that are used to measure fundamental bulk solids flow properties, which can be used to predict powder flow behavior and design reliable hoppers, bins, silos, and feeders. Shown in the accompanying figure from left to right are the Jenike direct tester, Schulze RST-XS.s, Brookfield Engineering PFT, and Freeman Technology FT4.
The original Jenike direct tester is no longer available, but you might be able to find a used one. If you are considering a Jenike direct tester, I recommend that you have good health insurance that includes mental health coverage. You will go crazy trying to learn how to use it. Jenike & Johanson still uses it, and its lab technicians are talented.
I prefer the Schulze RST-XS.s. The -XS.s version can measure properties at very low stresses, which is important for mass flow hoppers or small-volume equipment.
The PFT is a bargain for the money. Its software is not very flexible, and it cannot measure properties at high stresses, which is important for designing funnel flow hoppers. It also measures wall friction by sliding the powder beneath a wall coupon, which can result in friction measurements lower than reality. A PFT is to a Kindle as an RST is to an iPad. I bought a Kindle when they first came out because I was too cheap to buy an iPad. Eventually I bought an iPad because it could do much more,
If an RST is a thoroughbred race horse, then a Freeman FT4 is a unicorn. In addition to shear cell properties, it measures magical properties. It is a torsional tester, which can result in unsatisfactory results and the wall coupon is above the powder. Many investigators state that the FT4 "rheometer" can pick up differences in powders that shear cell testers cannot.
Other than the Jenike tester, shear cell testers are easy to use. It takes some training to know what inputs to use and how to interpret the data. That's where I come in. The concepts are straightforward, but the analysis can be tedious because the equations are serpentine and the calculations are iterative. That's why I provide software that does all the work to my clients when I provide training.
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