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Simple basic thermodynamics


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Hello everyone.

Simple condensation does not happen :


A bottle ¾ filled with water kept hot (~60°C).

On top of it, another bottle upside down kept at ambient temperature, coupled neck to neck with adhesive tape, forming a shape sort of an hourglass.


No condensation happens in the internal walls of the upside down top cool bottle, even after hours.


Why ? What is missing ? How can condensation be achieved ? :confused:


VERY easy to try and confirm by yourself !



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Given T1 = 333K, (RH)1 = 75%, and p1 = 1atm.


>From this information, at state 1:


(p)v = [(p)sat][(RH)1], where (p)sat corresponds to 333K.


With (p)v at state 1 and p1 = 1atm, the humidity


ratio w1 can readily be calculated. Verify that


w1 = 0.01095


If there is no condensation, then w2 = w1.

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the temperature diferential is only 35c to start with, then you have to factor in the appature through which the vapor molecules must pass, it would take days at that exchange rate to see a noticable effect. nice try though! :)

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Hello YT2095

Would had been a nice try if some results were obtained.

The aperture is narrow, yes. Solar stills with plain flat glass do produce a respectable amount of drinking water with the same temperature differential. No bottlenecks there.


The intention is to find a distilling application recycling the zero cost PET disposable beverage bottles, for the third or fourth world to get some drinking water using many of these contraptions.


The bottom sun exposed bottle is flat flack, the necks mating has a condensate collection ring and aquarium hose outlet. All that seems fine.


Ideas to make the vapors rise to the upper bottle are needed. Maybe venting the top bottle as in distilling colums would help by producing a tiny agitation of the water surface ¿? :-(



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  • 2 weeks later...

Here's my speculation:

In a closed environment such as this what you shall only witness is expansion/contraction within said environment. A tertiary factor must be introduced in order to achieve a third-degree reaction (water condensation).

Try a decent pin prick somewhere on the upper bottle.


You must've sealed the two necks beautifully with tape.

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It's more likely that the condensing vapour descended before settling on anything because its density changed, as you see between the panes of double-glazed windows that weren't properly evacuated before being sealed.


The hottest water vapour will always rise above the coolest.

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