Sponsored by BinMasterReviewed by Olivia FrostJul 2 2024
In simple terms, bulk density refers to the mass per unit volume of powder granules in a bulk state. When solids or powders are being handled, a bulk material’s weight is typically stated as lb./ft3 or g/cm3.
Experienced processors often know the weights of their materials by heart. Although the graphics and straightforward reports on BinCloud appear simple to produce, the bulk inventory data is derived from multiple calculations involving vessel size, headspace, and the bulk density of the measured material.
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High-Tech Measurements Rely on Bulk Density
A food production company uses level sensors to routinely monitor a silo of flour to ensure timely refills. However, when they switch brands of flour, the measurements are thrown off as the new flour holds higher bulk density. This delays the refill process and puts a halt to production.
In a liquid feed operation, a level sensor measures the mix in a storage tank. Due to temperature fluctuations, the density of the liquid changes. However, the sensor was not calibrated to account for these variations. As a result, the sensor underestimated the supply, leading to a production halt.
“There’s a lot of promises about bulk level sensors out there, but getting the right system, configured correctly, takes some know-how,” says Mike Mossage, a BinMaster vice president for eastern US.
“We’ve built our software to account for things like bulk density of material, and we always encourage operators to give us a call when material changes or level readings seem off,” he added.
When level sensors are used in applications where bins, tanks, and silos are used, they are not able to account for bulk density directly. Instead, they predict the levels based on a constant or known bulk density during calibration.
Image Credit: Plant & Soil Science eLibrary
Level sensors on bins, tanks, and silos do not directly measure bulk density. Instead, they are calibrated with the assumption of a constant or known bulk density. These sensors typically measure the headspace (the distance between the material and the top of the vessel) as well as vessel geometry, pressure, weight, and distance to generate a level reading. From this data, volume and weight are derived.
BinMaster engineers are advancing technology to enhance accuracy. Modern systems now feature multiple sensors, 3D and continuous level monitoring, and sophisticated software solutions like BinCloud.
“The density of a products can be different inside one silo. In some cases, material packs at the bottom, and not so much at the top. We’ll look at that. We’ll ask about how often that materials loads and unloads and we’ll come up with workable averages,” Explains Nathan Grube, BinMaster vice president for central US.
Image Credit: Binmaster
What Can Change Bulk Density Within My Vessel?
Particle Setting
Powders and granular particles settle over time due to gravity, filling pockets of space within a vessel. This can result in denser packing and higher bulk density at the bottom compared to the top.
Compression
The weight of bulk material, especially powders, can cause compression. The more material in the vessel, the greater the pressure on the lower layers, leading to compaction and increased bulk density in those lower portions.
Air
Powders often contain entrapped air or voids within their particles. During filling or discharge, these voids can compress or release, altering the bulk density. Higher air content results in lower bulk density, while lower air content leads to higher bulk density.
Flow
Powders exhibit different flow characteristics, sometimes clumping and causing uneven distribution and density throughout the vessel.
Bulk Density - Just for Fun
Corn
Corn density varies from region to region because of genetic variations, growing conditions, and agricultural practices. In fact, agricultural scientists often consider density when developing new varieties.
Packing Peanuts
Bulk density is worth considering when using packing peanuts, also known as foam popcorn. This material provides cushioning and protection during shipping, yet due to its low density, packing peanuts can occupy more space than the material they are protecting.
Pumice
Pumice's bulk density is relatively low due to its abundance of air cavities, which allow it to float on water.
References and Further Reading
- Schulze, D. (2021). Powders and bulk solids. Springer International Publishing.
- Kansas State University. Powder Flowability Testing and Material Properties Test Lab. (n.d.). https://bulk-solids.k-state.edu/powder-flow-test/index.html
This information has been sourced, reviewed and adapted from materials provided by BinMaster.
For more information on this source, please visit BinMaster.