Disappointment with a recent purchase

[ShuShu]

The current update is that I spent a few hours filing through the lid, spout and spout holes and was able to lower the pour speed to about 8 seconds.

before/after pics?

I haven’t taken any before pics, but here are the after. I think it’s obvious it was filed. In the last pic you can see the simple set of tools I have used.

Btw - I have a strong feeling that it can even be faster if I put some more work on the lid - I have this intuition about all pots but hope an expert of the mechanics of air flow here can confirm that.

[Chadrinkincat]

Nice job!
I need to do this to a few of mine.

[.m.]

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

[Victoria]

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

Interesting I hadn’t noticed this before. I just checked my Yixing and out of 20 pots, 15 (shuiping + others) have a larger inside lid hole diameter and smaller outside diameter, like you said. With Kyusu on the other hand, only 2 have this feature; one from Emu, the other Jozan III.

[ShuShu]

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

I hear. Its just that this is the third pot that filing through the lid beyond 1mm (as you can see in pics) makes such a difference, this is why I’m puzzled about this. I’m having lunch this Saturday with a friend who is a senior engineer of AC systems. Perhaps he can shed some light

[Victoria]

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

I hear. Its just that this is the third pot that filing through the lid beyond 1mm (as you can see in pics) makes such a difference, this is why I’m puzzled about this. I’m having lunch this Saturday with a friend who is a senior engineer of AC systems. Perhaps he can shed some light

In architecture it is called ‘the Venturi effect’. Basically, a similar conical concept except larger scale; two windows on one wall and the opposite wall has one, this will increase air flow. Here is an example;

F5BF17B0-2C8F-4EC5-9365-9F1DD5372723.jpeg (237.73 KiB) Viewed 7166 times

[Kale]

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

I hear. Its just that this is the third pot that filing through the lid beyond 1mm (as you can see in pics) makes such a difference, this is why I’m puzzled about this. I’m having lunch this Saturday with a friend who is a senior engineer of AC systems. Perhaps he can shed some light

In architecture it is called ‘the Venturi effect’. Basically a similar conical concept except larger scale; two windows on one wall and the opposite wall has one, this will increase air flow. Here is an example;
F5BF17B0-2C8F-4EC5-9365-9F1DD5372723.jpeg

Interesting!
So that means that at a certain point - when the lid’ hole diameter becomes larger than or equal to the spout hole —the air flow may actually worsen when the lid opening is larger

[pedant]

something else though: a larger airhole (for sure more than 1mm) is needed if you care about it getting clogged with water. this doesn't matter during pouring since the pressure difference unclogs it, but it does matter on some pots when you put the lid on after filling with water. if the hole's clogged, water gets pushed out of the pot when you put it on.
some of my (modern) pots have a large lid airhole, and i appreciate this feature.

left: F1 pot | right: 'uncloggable' modern pot



however, on a shuiping (or similar) lid, you need a knob big enough to support such a hole.
i wouldn't go filing the lid on the left chasing after uncloggability. too big of a chance of breaking it or making it too fragile, and even if that didn't happen, i think it would be ugly because the proportions would be off.

also, my japanese lids have big holes and don't really clog either, but that doesn't really matter for them since they are designed to be flat and rest on a recessed shoulder (no volume inside the pot to displace).

I'm not an expert in airflow, but i can say from experience that you don't need more than 1mm airhole on the lid for a good flow. It seems that the shape is more crucial. It is good if it is conical, both the airhole and the spout with the inside opening larger than the outside. On a lot of shuiping pots the inside diameter tends to be about twice the outside one.

why do you think it's important that the lid hole be conical for good flow? never thought about that aside from aesthetics.

[pedant]

...
In architecture it is called ‘the Venturi effect’. Basically a similar conical concept except larger scale; two windows on one wall and the opposite wall has one, this will increase air flow. Here is an example;
F5BF17B0-2C8F-4EC5-9365-9F1DD5372723.jpeg

Interesting!
So that means that at a certain point - when the lid’ hole diameter becomes larger than or equal to the spout hole —the air flow may actually worsen when the lid opening is larger

that's not what's going on here.

it's true that liquid flowrate out of the pot is maximized at a certain lidhole size, but liquid flowrate is not reduced if you exceed it.

explanation will follow... i'm building up the energy needed to draw diagrams. more tea maybe?

[pedant]

obviously, the driving force behind tea pouring is gravity. gravity pulls the liquid, and part of the pot isn't supporting the liquid when tilted downwards: the spout opening.

since the teapot is rigid, the only things that can change how the liquid flows out are:

• swinging the teapot around
• the air pressure at the exposed surfaces

the exposed liquid surfaces are inside the teapot and at the spout opening.
call the pressures at these surfaces P_in and P_out, respectively.



liquid flowrate increases with increasing P_in and decreasing P_out.
P_out is clearly fixed -- it's atmospheric pressure.
also, P_in is only going to be at most atmospheric pressure unless you're blowing into the lid hole while pouring:

• P_in ≤ P_atm = 1atm

however, if the lid hole is small enough (resisting airflow), gravity can pull the liquid out of the pot faster than air rushing into the pot can equalize the pressure between the pot interior and exterior. in this case, a vacuum is created (P_in < P_atm).

increasing lid hole size is only going to help up to the point where the pressure can fully equalize to atmospheric pressure inside the pot while you pour.
making the hole smaller than that will always make it pour slower, and making it bigger will never make it pour faster (or slower for that matter).

[Victoria]

An engineering head to the rescue. Nice diagram and formula pedant. Still wrapping my head around your formula. Did you take condensation and heat into consideration? I guess you did since you speak of air pressure...

To clarify my comment regarding the Venturi effect. I was only speaking of the conical lid hole opening, not the relationship between the lid hole and the spout size. To try and explain my comment a little more;
Hot water condenses around the lid opening effectively sealing it, especially so if the lid has a tight fit. If no lid hole opening is present, heat will escape more slowly, a vacuum can form, and low pressure will be created inside the pot when pouring, eventually stopping the pour. To get a continuous stream low pressure needs to be replaced by air coming in from somewhere, in our case the lid hole opening. The lid opening let’s air pressure in and steam out. If the lid opening is conical it should suck air in more quickly, thus my reference to the Venturi effect.

[pedant]

venturi effect shows this kind of relationship between speeds at various points:


that's supposed to be a pot lid btw (with conical hole in knob)

pretending the fluid is incompressible (it's not), it's easy to say something like:

• v₂ > v₃ > v₄ > v₁

i.e. the air speed is probably fastest at point 2 (the narrowest point).

but i don't think a conical hole gives you more airflow, and it shouldn't make the pot pour faster.

Did you take condensation and heat into consideration?

well, i was wondering if the hole being conical is supposed to help fight clogging via condensation.
if that's why it's conical, i don't think it works well.

at this point, i don't think there is functional intent behind the conical holes.
i think they just happen to use a tapered hole poker.

[pedant]

after looking at the lids carefully, i think that the holes aren't even really conical anyways.

i think the holes are made in the knob and lid separately before assembly, and the knob poker is just narrower.

here's a 90s F1 pot:




this is viewed from the inside of the lid.
the two holes are not perfectly aligned, and you can see the clean edge of the lid hole (what was the exterior of the lid before the knob was attached).

[Victoria]

after looking at the lids carefully, i think that the holes aren't even really conical anyways.

i think the holes are made in the knob and lid separately before assembly, and the knob poker is just narrower.

here's a 90s F1 pot:




this is viewed from the inside of the lid.
you can see that the two holes are not perfectly aligned, and you can see the clean edge of the lid hole (what was the exterior of the lid before the knob was attached).

Could be a result of mass production post mid- 80s. Maybe your pot maker used two tools one for inside, another from outside of lid. Looks like pretty obvious misalignment before assembly. How is the pour?

[pedant]

pour is ok, but lid fit is not good which helps