An Observation, and Conundrum

[Graham MeekParticipant @grahammeek88282]

By way of a bit of mental stimulation, an Observation, and a Conundrum.

I have been noticing the following for sometime. I have a clear plastic water bottle that I use. It is placed on the counter top by the sink to be washed up. The sink is in front of a double glazed window which the water bottle is also in front of.

When it comes to washing up the bottle there is always a film of water condensed on the side of the bottle nearest the window. Even when the bottle is in direct sunlight.

We are taught that a water vapour will always condense, or form on the coldest surface. At first glance this would not seem to be the case. As one would assume the side nearest the Sun would be the warmest.

I don't know if this conundrum has ever been looked into scientifically or not, but I do have a theory as to why this might be happening.

Does the forum have any constructive thoughts, or theories?

Regards

Gray,

[Graham MeekParticipant @grahammeek88282]

[Ady1Participant @ady1]

Air around a window always cools and drops towards the floor because windows are a weak point

Having slept on the floor for various reasons over the years I know this 100%

sooo… the sun heats the bottle and the cooler air on the window side condenses on the window side of the bottle

[Jeff DaymanParticipant @jeffdayman43397]

Hi Gray! I think the issue is where the sunlight's energy is absorbed on the bottle rather than where it shines. If there is a cool draught from the window cooling the bottle on that side, condensing will happen there. If there is a label or surface topography on the bottle on the side of the bottle away from the window, that is likely where the majority of the sunlight's energy will be absorbed, warming that side. Just my thoughts.

[Graham MeekParticipant @grahammeek88282]

Hi Ady1,

While I thank you for your response and I concur with your observation, I feel it is not the whole picture.

The water bottle if observed from above would have the window at twelve o'clock. Thus the side nearest the window should be the coolest. The vapour always tends to form at two to three o'clock. Which coincides with the position of the Sun's rays coming through the window.

The down wash from the window flowing over the edge of the sill onto the counter top. Rather like the Dry Ice special effects mist used on stage performances, flowing off the stage into the audience.

Would I feel tend to make the vapour form nearer the base of the bottle and all the way around the base of the bottle.

This does not happen, the vapour always forms a near perfect vertical band up the entire length of the water bottle. The height of the bottle has no effect, as a taller version of the bottle exhibits the same vertical vapour band.

Placing the water bottle in the window on the cold tiled window sill, yields the same result.

Regards

Gray,

Hi Jeff,

I think your views are on the right track and you may well be right. I was of the opinion that the Sun's rays were being reflected around the curvature of the bottle internally. Thus heating the sides and rear of the bottle more than the side nearest the Sun. Which due to it's shiny surface would tend to reflect some sunlight.

As an aside, and a further observation. On the mornings when the Sun is not out, and the Bread Maker is in use and sits next to the sink. The water bottles still exhibit the same vertical vapour pattern and at about the same two o'clock position. The Bread Maker being at the nine o'clock position.

Which would tend to blow my theory out of the water.

Regards

Gray,

 

Edited By Graham Meek on 18/11/2022 11:12:55

[Martin KyteParticipant @martinkyte99762]

How about this then. The sun warms the gas in the bottle most on the side in line with the window. A temperature gradient is established within the bottle and convection currents set up a slow circular motion up the wall of the bootle on the window side and down the opposite side. Moisture is picked up from the liquid surface and the moist gas traveling up the window side wall of the bottle causes some of the liquid to condense out making the gas stream dryer. The gas stream encounters the opposite side of the bottle but as it is less humid does not condense as much if at all. I suspect there is very little difference in the wall temperatre of the bottle between sides being very transparent and in intemate contact with the ambient air. Comments regarding cool window drafts will make that side cooler if anything.

regards Martin

[Martin KyteParticipant @martinkyte99762]

It would be interesting to fit small baffles in the bottle to see if the effect could be made to deflect or spiral up the wall of the bottle.

Martin

[SillyOldDufferModerator @sillyoldduffer]

Posted by Martin Kyte on 18/11/2022 12:04:35:

How about this then. The sun warms the gas in the bottle most on the side in line with the window. A temperature gradient is established within the bottle …

regards Martin

I thought similar, the point being heat is trapped inside the bottle like a greenhouse and circulates, cooling as it expands.

However, I suggest the far side of the bottle is hotter because energy reflected off the inside wall of the bottle is trapped inside, causing air at the far wall to be counter-intuitively warmer than air on the sunny side. Maybe!

Not that I don't trust Graham, but the experiment needs to be repeated to see if others get the same result before we rush to explain it. The exact conditions need to be noted: air temperature in the room, humidity, is there any water in the bottle, and is the bottle sealed or not. I'm looking for empty plastic bottles, hard because it was recycling day here and they've all been taken away!

Dave

[John HinkleyParticipant @johnhinkley26699]

Sounds to me like you have basis for a PhD thesis there. You could probably get a grant from an obscure ministry to investigate the phenomenon. Without looking into it too deeply, is it possible that the bottle is acting as a lens and thus warming a part of the structure such that there is a difference in surface temperature, somehow encouraging the condensation?

Or, move the bottle out of the sunlight.

John

[Jouke van der VeenParticipant @joukevanderveen72935]

This invites for experiments!

[Graham MeekParticipant @grahammeek88282]

Hi All,

I did think this might stimulate the grey matter.

I will be honest I don't have an answer for this conundrum. I was hoping someone might come up with a link to research, (the PhD), on the subject. Not that I want to read at great length what is going on, but just a simple explanation would be good.

The bottle is indeed closed, or sealed and it contains the last few drops of the water I took to bed with me for a drink during the night before. Humidity in the kitchen first thing is about 75%, according to the de-humidifier. Air temperature would be about 20 C. The window is A rated double glazing with no airflow from outside, ie trickle vent closed.

The closed micro climate put forward by Martin is indeed happening as when the top is taken off and the bottle left, the vapour disappears. Indicating the convection currents go straight out to atmosphere.

One thing I definitely don't get is why the vapour is in the same two o'clock position, with, or without the Sun being out. As clearly the heating of the bottles contents is taken care of by the radiated heat from the Bread Maker. Which would be 180 degrees from the Sun's position.

As regards experiments I have no wish to go down this route, I like to do things by observation and logic whenever possible, but if others wish to go down this route, then by all means feel free to do so, but do let us know how you get on.

Regards

Gray,

[Kiwi BlokeParticipant @kiwibloke62605]

Look up 'solar still' on Wikipedia.

[Graham MeekParticipant @grahammeek88282]

Posted by Kiwi Bloke on 19/11/2022 02:07:09:

Look up 'solar still' on Wikipedia.

I understand fully the process involved in evaporation and condensation. It is what is happening with regards to this particular bottle set-up. The vapour does not form on what would logically be the coldest surface next to the down wash from the window. Instead it is skewed around the bottle by 70 or so degrees. Nor does it form at the rear of the bottle furthest away from the sunlight. Instead it forms on the side nearest the sunlight.

I am sure the cylindrical body of the bottle is acting like a Lens and this is why the vapour outline is so parallel down the length of the bottle.

Regards

Gray,

[Kiwi BlokeParticipant @kiwibloke62605]

Gray, I didn't mean to imply that evaporation and condensation were a mystery to you. Perhaps I should have written "If you want further examples of counter-intuitive, somewhat similar phenomena, look up 'solar still' on Wikipedia". I, at least, find the fact that the water condenses on the sun-facing, transparent surface of some of these stills, rather surprising. It seems that cooling by radiation has a lot to do with it, probably also in your case. No doubt the interior of your kitchen is rather warmer than deep space… (yes, I know that cloudy UK skies are 'warmer' than deep space, but the principle still stands…). I'm not suggesting that is the whole story; the previously-mentioned optical and convection effects, draughts and who knows what else will have their part to play. It's complicated…

I'll try to remember to see whether similar effects happen with beer bottles. Hopefully, it will take a lot of experiments.

Edited By Kiwi Bloke on 19/11/2022 21:58:49

[Graham MeekParticipant @grahammeek88282]

Hi Kiwi Bloke,

My apologies if my reply came across a little terse, it was never intended. I should have read your reply, gone to Wikipedia and not gone with my rather doubtful memory on Solar Stills.

There is indeed a lot more going on in the bottle than at first appears. To add further confusion the water bottle was left on the Landing window this morning which is South facing, as opposed to the Kitchen window which faces due East. I add this was not done intentionally, just that I had forgot to take it to the kitchen.

The vapour was again from top to bottom of the bottle, but it was on the side furthest from the Sun. Which is where I would expect it to be. The Sun at this time would not be full on this window, but neither was it full on Kitchen window with the prior example.

The Conundrum continues,

Regards

Gray,

 

Edited By Graham Meek on 20/11/2022 11:23:44

[Author]

Posts