Piano World Home Page Forums Our Most Popular Forums Piano Forum Investigating humidity in piano via numerical simulation

Hi all,

In fulfilling one of my assignment in my uni studies, I am glad to say that I want to do something related to piano. I am doing computational fluid dynamics (CFD) where I learn to use computer software to solve fluid related problem. I am given freedom to choose any topics of interest for my assignment and I chose to simulate the humidity within an upright piano. I am simulating for a piano subject to a tropical climate, where RH is assumed to be at 90-100%. (In controlling humidity in tropical countries, we usually use only a heater bar to heat the interior of piano, chasing away the humidity.)

However, I need some further input from piano experts to ensure my model is correct. Here is my question.

Which part of piano is actually allowing air to passing in and out. On my Hailun, I find that there is this small gap between the right-angle meeting of the front panel with the upper lid. is there any other places where air is entering? From the bottom or from the behind of soundboard?

Thanks in advance for all the help and will surely keep you all informed about the result once I have run the case successfully.

... all the little spaces between the keys.

Thanks. Indeed those are the parts where it does affect, but it's difficult to actually model such small spaces implicitly. Might not consider that in my first few runs. What I am looking for is those that are big enough that are actually exchanging air from the inside with the outside.

Well, put it another way. What I am looking for are gaps/holes that will change the humidity significantly if left open/close. I am sure the humidity will not change too much even if the keys are sealed.

And also, in simplifying the case, any absorption of water of the wooden parts within it, the soundboard, action etc. will not be considered.

Hi Tanjinjack,

I’m also interested in fluid dynamics engineering; in engineering calculations, air is always treated as a fluid; but, I'm sure you knew that already.

In regards to where the air/atmosphere gets inside a piano, I would say lots of places. Between the keys, as has been mentioned, underneath the panels and covers around the back frame, kick-board (foot-board) between the pedals and else ware. I don’t think any part of the piano is actually hermitically sealed from the surrounding atmosphere.

Also, there is always humidity in the air; there is no such thing as 0% relative humidity on earth, even though it might be very low… 10% etc… We live on a wet planet.

You can use the psycrometric chart to determine the known properties of air for any given situation. If you know any two variables, wet-bulb temp and dry-bulb temp, etc... you can calculate BTU’s per pound of air (enthalpy), grains of moisture per pound of air, RH, due-point, and a host of other variables. However, I’m sure you knew this already.

Good luck with your assignment!

Rick

Thanks Rickster.

Yeah, I know those (hopefully I still do). But I am taking a different approach now. In CFD, the fundamentals may not be that important. What's important is if you understand the problem and constrain it correctly for the software to find the solution for you.

I am trying to model air that comes with water vapour (and I am in command to decide how much I want it to be to start with). So, it's about building a box (which is a piano) and poke some holes (where air really escapes) around it, put in the air-water vapour mixture, and leave it to compute over the day, and that's it. (Oh well, it's still hard actually as to build the model and mesh it could be hard, since it's a 3D model)

The difficulty here is about poking some holes around the box (piano). Poking so many gaps for the keyboard (i.e., doing it explicitly) will invoke very high computational effort. Thus, simplifying is important. So, I will be looking at making some bigger holes that will really affect the humidity in it rather than just smaller holes like those in between the keys (not to mention they will make even lesser impacts if the fallboard remains close).

And yes, the pedal gap is quite big and that is something I must be aware of (how could I overlook this). But in some parts of the piano where I can't just observe it, I don't know if that's such a big hole that is crucial in driving the humidity away.

Wait, are we having a same theory of how heater bar drives away humidity?
For me, what I think is that, as the heater bar heats up the air around it, the hotter air moves up and colder air comes down. The colder air is then heated up near the heater bar where the upper hotter air gets a bit cold already.
So, after it reaches equilibrium, we get an overall hotter air inside, which also contains less water vapour per unit volume already (hotter, more energy, more spaces between particles in air). So, we see an increase of volume. But the volume within the piano is limited, how do we accommodate the increase of volume. This is achieved as we push them out of the holes.

Do we have the same theory?