Imaging method for the determination of the minimum agitation speed, Njs, for solids suspension in stirred vessels and reactors

Baran Teoman, Shriarjun Shastry, Sara Abdelhamid, Piero M. Armenante

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Njs, the minimum agitation speed to just suspend dispersed solids in stirred liquids is commonly measured experimentally using the visual method, consisting of determining the agitation speed N at which the solids are observed to rest on the vessel bottom for 1–2 s (Njs–Visual). This method is observer dependent. Here a novel observer-independent method to experimentally obtain Njs was developed by capturing images of the vessel bottom at different agitation speeds and processing them with ImageJ software to quantify the area AS covered by the solids. Plots of AS vs. N, extrapolated for AS going to zero, yielded the value of Njs (Njs–Imaging). The values of Njs–Imaging and Njs–Visual were found to be in excellent agreement with each other for a large number of different impeller types and locations, vessel geometries, and solids size and fractions. The imaging method proposed here could find applications in many solid–liquid mixing processes.

Original languageEnglish (US)
Article number116263
JournalChemical Engineering Science
StatePublished - Feb 15 2021

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering


  • Agitation
  • ImageJ
  • Just-suspended Speed
  • Solid-Liquid Mixing
  • Solids Suspension


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