At the start of the project to develop the Hydro SV – the new small volume wet sample dispersion unit for the Mastersizer 3000 laser diffraction particle size analyzer – our product manager, Paul Kippax, presented the market requirements to the team and commented that “we just need a simple stirred cuvette…”
A simple product – what could be easier than that? I’ve since heard the following quote: “Any intelligent fool can make things bigger, more complex…. it takes a touch of genius – and a lot of courage – to move in the opposite direction”. Looking back, I can see that this makes complete sense now!
So off we set with our “keep it simple” mantra, to work out how we could get quality performance combined with simplicity.
Our first challenge was to get good sample mixing and suspension from a stirred cuvette. Initial prototypes showed that it was easy to suspend particles, but that it was equally easily to cause a bias between particles sizes due to recirculation and eddies in the cuvette. Using a combination of 3D printed prototypes, CFD (computational fluid dynamics) analysis and high speed camera observations, we were able to define a geometry that would provide great suspension performance, but without the need for complex flow paths.
In parallel with this, we found that the coupling between the magnetic stirrer bar and motor could sometimes be lost, especially when measuring in high viscosity liquids – this looked like being a show-stopper. We realized that this issue could not be solved through a design of experiments (DOE), as there were too many permutations that would need to be investigated. So, the modelling package Ansys Maxwell was used to test and optimize various configurations, with the results being corroborated using the Malvern Kinexus Rheometer. It wasn’t long before this was resolved too.
During practical tests of prototypes, it was then realized that cleaning the cuvette was more difficult than we’d hoped. We designed and tested cuvettes that could be disassembled for cleaning, but these we rejected due to complexity and difficulty of use. Instead, a novel wash-station solution was developed by our mechanical design team, after they observed the cleaning techniques our applications engineers were using. Here’s a clip from the Hydro SV launch event showing the wash station in action:
So, from the outside, the final design does look very simple. It’s just a motor, a magnetic stirrer and a sample cuvette. I like that people think that way! However, it took a lot of thought and effort in order to get it right. Perhaps “Simplicity is the ultimate sophistication.”