Hi everyone,

I just wanted to share with you some preliminary simulation results which I managed to obtain in my free time.

The LHS of the attached video gives the transient behavior of the temperature (degrees Celsius) both in the water and solid material, sampled using a plane. The RHS shows the behavior of the velocity within the water together with surface-streamlines.
I have performed a warm-up simulation of a greatly simplified E61 group head. The thermosyphon pipes are connected to the brew boiler. Inside the boiler is an 'invisible' heater with a power of 1.2kW. At the beginning of the simulations everything is cold, and over time the warm water starts to heat up the brass group.

There is a chamber (hollow cylinder) within the brass, which is filled with water and connected to the pipes. Circulating water within the chamber transfers the heat to the brass. This chamber represents the space between the mushroom and the group head - when the machine is not pulling a shot. The water circulation is driven by the water density difference, i.e., I have not put an invisible pump within the system.

The simulation captures the first three minutes, and as the videos suggests, the group is not heated up (the temperature of the brass is still low). I would need to program a custom heat-source to accurately simulate the heater behavior when the water reaches high-temperatures, e.g., when the temperature of water at certain point within the boiler (location of physical thermal probe) goes above (heater off) or below (heater on) a certain temperature. I just wanted to share some preliminary results.

I'm a proud owner of an ECM Classika PID, so the setup and geometry are relatively similar to my machine at home. However, for simplification reasons the internals are far from the real thing.

The results are obtained using CFD software (Computational Fluid Dynamics), or to be more precise using OpenFOAM.

Any comments and/or suggestions are more than welcome

Omg kudos to you!
I used to do simulation on wind turbine using OpenFOAM... 10 years ago lol
I am so glad to see someone taking on this...
I assume you are modelling this based on a dual boiler E61, instead of the HX right?
It would be really interesting to see how things would change with a HX tube in there for the thermosiphoning

Thanks!

Yep, this configuration resembles a dual-boiler E61 (or a single-boiler when the heater is not in steaming mode).

The HX simulation should be relatively straightforward if we neglect the complicated physics within the boiler (evaporation and multiphase flow), but I'm always open for a discussion regarding which phenomena should be considered and/or neglected...

If somebody has (and is allowed to share) a CAD model of the internals of a particular machine, I would be very grateful. I only have one machine at home, which is my daily driver, and I cannot afford to dismantle it for several days just to take measurements.

Check out E61 Group Espresso Machine: Detailed Interior Schematics

you may be able to contact lino and see if he can share his models

That being said, What's the point? Turn on wait 20 to 40 minutes, brew...

Nice, thanks for sharing!

Yes, I agree. This seems like overkill just to predict the heat-up time. I just wanted to show the capability and level of details which this kind of simulation can provide. We are not just limited to heat up simulations, we can also predict the thermal equilibrium state of the HX machine and investigate the influence of a flow-restrictor on the flowrate of the thermosyphon, etc.

I would like to think that such insight could help us develop even better machines, with better thermal stability and lower heat-up times.

But to be honest, I was just looking for an excuse to do some simulations of my machine