Posted Wed Jul 22, 2009, 2:50am Subject: Re: Using a Siphon Coffee Maker
al_bongo Said:
In short the increase in pressure in the lower chamber is a result of the increasing amounts of water vapour from heating the water to higher temperatures until eventually the water boils.
I don't think anyone is denying that water is going up the tube, they're saying that gas is what's pushing water up the tube. Even the full quotation that you snipped from Mark's article says that. He says:
"Once the siphon coffee maker is assembled, heat is applied to the lower container. As it heats up, some of the water is converted to a gas - water vapour. A gas occupies a lot more space than its liquid or solid variant, and it can expand as more heat is applied. Gas can be compressed, but only to a point, whereas liquids do not compress. The water vapour continues to expand and it seeks some relief from all the compression it's starting to have. The only escape route out of the bottom vessel is the siphon tube traveling up to the top, but the problem is, there's a lot of liquid blocking its way. So what does the gas vapour do? It pushes the water up the siphon tube!"
It is not your opionion this is a fact (at least at the start of the process). No one is disputing this point. Where you seem to be going awry is in the understanding of what makes this happen (see philosogeek's post for the most recent explanation).
Philosopher Senior Member Joined: 13 Feb 2007 Posts: 189 Location: Australia Expertise: I like coffee
Espresso: Silvia Grinder: Rocky
Posted Wed Jul 22, 2009, 3:53pm Subject: Re: Using a Siphon Coffee Maker
al_bongo Said:
You would be wrong. The higher the temperature the faster the vapourisation reaching a max at boiling point.
Perhaps a better word is evaporation rather than vapourisation. It rains a lot is Scotland, but the puddles do eventually evaporate even with our current temp of 19*C.
You will also note that when you heat water or take a bath or shower steam rises from the water at a temperature well below 100*C.
Evaporation: The process by which kinetic energy within a liquid causes molecules on the SURFACE of a vessel to change state into vapour. Boiling poinst: the temperature at which vapour pressure exceeds atmospheric pressure. Gas can form and escape from WITHIN the vessel (boiling)
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