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# How to heat a metallic bowl containing a liquid, which must be evaporated, using peltier element? Answered

Hello everyone,
I'm Georgios and thank you for your time

My goal is to create a mechanism which will be able, using peltier element, to heat a metallic bowl (metallic because of its heat conductivity). In the bowl I will put acetone and I want to evaporate this liquid. Also I want to control the temperature of the bowl. The evaporated acetone will be kept in a closed box. Then, using second peltier element I want to cool the acetone, to liquidity it?

Do you know if this is possible? And in general do you think that it is a good idea to use peltier element for heating and cooling, only with electricity, acetone? My goal is also to heat in a fast way.

The temperature must be 80 C for evaporation.

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## Discussions

You said this was a closed box, yes?

The boiling point of a liquid, is the temperature at which its vapor pressure

https://en.wikipedia.org/wiki/Vapor_pressure

is equal to the pressure of the gas above it.

Let me say this another way: the boiling point of a liquid depends on the pressure of the surrounding gases. If I increase the gas pressure above a liquid, its boiling point increases. If I decrease the gas pressure above a liquid, its boiling point decreases.

This is likely a story you have heard before. The usual practical example is the influence of altitude on boiling water. At sea level water boils at 100 C. In Denver, which is about 1600 m above sea level, water boils at about 95 C.

https://en.wikipedia.org/wiki/Boiling#In_cooking

The reason this is relevant to your plans to boil a liquid in a closed container, is because when you do that, the pressure of the gas in your closed container can be very different from the pressure outside the closed container, and as a consequence, boiling points will be very different from the sea level boiling points.

For example you could probably make the boiling point of your acetone much lower, if you pump all the air out of your closed container, so that the only gas in the container is acetone vapor.

In contrast, if you do not pump atmospheric air out first, I expect the boiling point of the acetone, in this sealed container, will be higher than its sea level value, because of higher pressure, from the trapped air plus acetone vapor.

By the way, there is an existing, practical device, based on a closed length of pipe containing a volatile liquid, and no air, just that liquid in equilibrium with its own vapor. It is called a, "heat pipe",

https://en.wikipedia.org/wiki/Heat_pipe

Basically the way it works is, liquid inside the pipe naturally boils on the hot side of the pipe. Then the vapor quickly moves to the cold side, or actually any side that is colder than the hot side, and then the vapor condenses in the colder place.

By the way, if you plan on heating liquids inside a closed container, there is possibility of creating very high pressure, and I would feel bad for you if you accidentally killed yourself due to exploding plumbing. So you should take some steps to keep your pipes from exploding, like including a pressure gauge, to tell you about internal pressure, and maybe also a pressure relief valve,

https://en.wikipedia.org/wiki/Relief_valve

or some component designed to fail in a predictable way,

https://en.wikipedia.org/wiki/Rupture_disc

and vent gas and pipe fragments in a predictable direction.

By the way, the usual application for heat pipes is moving heat, like for to cool hot things like engines, and microprocessors, and that sort of thing.

However there are a few applications I have noticed that take advantage of the actual mass flow inside a heat pipe, to do some mechanical work when the center of mass of the heat pipe changes, due to the fluid moving around inside it.

One of these is a contrivance that uses freon to keep a PV array pointed at the sun.
http://www.zomeworks.com/photovoltaic-tracking-rac...

Another is the classic novelty toy, dippy drinking bird.
https://en.wikipedia.org/wiki/Drinking_bird

Vapor degreaser cleaners are 4 foot deep metal trunks with electric heater boiling acetone or trichloroethylene at the bottom and a cooling coil at 3 feet around the trunk wall..

You place a metal basket with a dirty oily machine at 2 3/4 feet and the vapor condenses on the metal dissolving dirty oil products and drip to the bottom heater leaving a clean machine.. Any vapor rising above 3 feet is condensed to liquid by the cool coils and continuously returns back to the bottom of the metal tank...

There is no fast way with peltier elements and they are not really what you call efficient either.
Similar trouble for the acetone.
You need a condensation point and with just the peltier you won't have real control.
Pressure is the next issue as the vapor will increase it quite a bit.
Sure you could use one side of the element for heating and the other for cooling at the same time but if that works out in the long run, no clue.