Kettle Evaporation -

[Wolfy]

Anymore holes you can pick?

No more holes, just that both my comments were related to real life (non experimental) observations:

I know that when I cook if I put the lid fully on the saucepan it will not (usually) boil dry, however if I don't put the lid on (and still cook/boil for the same time/intensity) then most often things will boil dry on me (I even managed to boil dry some soup the other day - go figure!). So from that perspective, I'd have thought that having the lid 'fully on' would make a huge difference to any losses, not just minor, minimal or perhaps no change as your experiment showed.

When I 'boil' my wort, with my kettle/setup/ideal boil, I do not see masses of bubbles on the surface as per your beaker experiment, what I see instead is a large 'convection bump' from the hot wort rising from above the (electric) heating element and breaking the surface - kindof like one big continuous bubble. So I was interested/concerned as to how putting a lid partly on would impact the convection currents within the wort, since in my case that is where most of the mixing comes from not from the 'bubbles'. But as you pointed out for your experiment most of the 'mixing' of the water is due to the bubbles rising from the bottom rather than any 'convection currents'.

 

[Thirsty Boy]

I see what you mean, I seem exactly the same thing in my kettle... But that convection bump is full of bubbles and I don't think it's just, or even mostly from convection, I think its a stream of bubbles combined with convection thats causing am pretty fast wort flow.

I don't know if this is true, but it seems to me that if it was purely, or even mostly convection - that bump would be there before the wort boils. Does 99 degree water convect at so much slower a rate than 100 degree water? Yet the major disturbance to the surface only happens after the bubbles start. Convection currents of course happen - But for instance in my HLT... 2400W at the bottom doesn't even produce enough mixing by convection currents to give an even temperature through the vessel... The top can be at 90+.... While under the element it's only 75 or 80, yet let it start to actually boil, with bubbles reaching the surface... And then it becomes uniform mighty fast as the rising bubbles mix things up.

Might not be the case, but that's the way it seems to me.

I'm surprised by the lid results too.... I thought that pretty much no matter what the circumstance, a lid would reduce liquid lost.... Seems it's not that cut and dried. I suspect a full lid in a large pot would make for a much more distinct result. But I also suspect that that might have a lot to do with reflux, and has been mentioned before, too much reflux could be a bad thing. I don't think it's anything like a problem if you are talking about a lid partially, even most of the way on, that you are using to cut back on excessive liquid loss - but if a lid can be an issue, one that's all the way on, and cutting down liquid loss by a significant margin.... That'd be where the issue's gonna be found. I'd certainly never put a lid all the way on the brew pot and leave it there, I don't think I've ever suggested it... Lid all the way on testing for me has just been a way of demonstrating the most extreme end of the "Lid on vs Lid off" comparison. I'm not sure that I have managed to test it though. The light lid and the always there gap at the spout might have rendered those tests more of a "Lid really really nearly all the way on" test instead. Which is less valid from a point of trying to illustrate the extremes... But perhaps more relevant?? Maybe.

Thanks heaps for your input

 

[Thirsty Boy]

I see what you mean, I seem exactly the same thing in my kettle... But that convection bump is full of bubbles and I don't think it's just, or even mostly from convection, I think its a stream of bubbles combined with convection thats causing am pretty fast wort flow.

I don't know if this is true, but it seems to me that if it was purely, or even mostly convection - that bump would be there before the wort boils. Does 99 degree water convect at so much slower a rate than 100 degree water? Yet the major disturbance to the surface only happens after the bubbles start. Convection currents of course happen - But for instance in my HLT... 2400W at the bottom doesn't even produce enough mixing by convection currents to give an even temperature through the vessel... The top can be at 90+.... While under the element it's only 75 or 80, yet let it start to actually boil, with bubbles reaching the surface... And then it becomes uniform mighty fast as the rising bubbles mix things up.

Might not be the case, but that's the way it seems to me.

I'm surprised by the lid results too.... I thought that pretty much no matter what the circumstance, a lid would reduce liquid lost.... Seems it's not that cut and dried. I suspect a full lid in a large pot would make for a much more distinct result. But I also suspect that that might have a lot to do with reflux, and has been mentioned before, too much reflux could be a bad thing. I don't think it's anything like a problem if you are talking about a lid partially, even most of the way on, that you are using to cut back on excessive liquid loss - but if a lid can be an issue, one that's all the way on, and cutting down liquid loss by a significant margin.... That'd be where the issue's gonna be found. I'd certainly never put a lid all the way on the brew pot and leave it there, I don't think I've ever suggested it... Lid all the way on testing for me has just been a way of demonstrating the most extreme end of the "Lid on vs Lid off" comparison. I'm not sure that I have managed to test it though. The light lid and the always there gap at the spout might have rendered those tests more of a "Lid really really nearly all the way on" test instead. Which is less valid from a point of trying to illustrate the extremes... But perhaps more relevant?? Maybe.

Thanks heaps for your input