--- title: Scaling down the physics, not just the volume description: At the University of Stuttgart, a 3 L reactor with a p4b pDS insert was tested in a pH-shift mixing experiment followed by a CHO process. With the insert, mixing slowed from a few seconds to about 30 seconds, matching what is expected in a 2000 L XCellerex. image: https://www.p4b.io/hubfs/website/video/stuttgart-gassing.webp --- [![p4b](https://www.p4b.io/hubfs/raw_assets/public/p4b/images/p4b-logo-white.svg) ![p4b](https://www.p4b.io/hubfs/raw_assets/public/p4b/images/p4b-logo-navy.svg)](https://www.p4b.io/) Products [**pDS inserts**Large-scale conditions in your lab bioreactor](https://www.p4b.io/pds) [**Advanced CFD**Gradients, lifelines and cell experiences](https://www.p4b.io/cfd) [**DREAM-bio**Find the best geometry for your bioreactor](https://www.p4b.io/dream-bio) [**Ambr 250 vs. 2,000 L**Interactive CFD comparison of the mixing](https://www.p4b.io/compare) [Case studies](https://www.p4b.io/case-studies) [Insights](https://www.p4b.io/insights) [Events](https://www.p4b.io/events) [About](https://www.p4b.io/about) [Contact](https://www.p4b.io/contact) [Request a quote](https://www.p4b.io/contact#quote) [Home](https://www.p4b.io/) / [Insights](https://www.p4b.io/insights) Case study · 23 Oct 2026 # Scaling down the physics, not just the volume At the University of Stuttgart, a 3 L reactor with a p4b pDS insert was tested in a pH-shift mixing experiment followed by a CHO process. With the insert, mixing slowed from a few seconds to about 30 seconds, matching what is expected in a 2000 L XCellerex. The University of Stuttgart ran a mixing experiment (pH shift) followed by a CHO process with our downscale inserts. The 3 L reference reactor without an insert mixed in a few seconds. The same 3 L reactor with our insert took about 30 seconds, and a 2000 L XCellerex also takes about 30 seconds, based on CFD and tracer data. A standard 3 L system mixes far too quickly compared to large-scale conditions. With the insert, mixing slows down to what you would expect in a 2000 L reactor, which makes small-scale experiments much more representative. In the same collaboration, we compared four cases in the 3 L reactor with a pDS insert: CFD without bubbles, CFD with bubbles, an experiment without gassing (pH shift) and an experiment with gassing. Only the gassed CFD reproduced the experimental behavior. Gas holdup, bubble-induced turbulence and buoyancy fundamentally change the hydrodynamics, so mixing becomes significantly faster and qualitatively different. Liquid-only CFD can look elegant, but it systematically misses these effects. Large-scale data is hard to access, which makes this approach even more valuable. If you can't easily measure it at scale, you need to make sure your small-scale system behaves like it. That is what p4b is aiming for: scaling down not just the volume, but the physics. [← All insights](https://www.p4b.io/insights) Get in touch ## Let's find out how your process reacts to scale Tell us your system and target scale - we come back with a proposal for your insert set. 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