I'm doing an experiment and want to boil down a liter of room temp water in a vacuum chamber. I bought a 5 gallon vacuum chamber with a 1/3HP Single Stage 4CFM Pump.The room temp water starts boiling rapidly after about 1 minute and keeps boiling for 5 or so minutes if I leave the pump on. However, I'm scared of leaving the pump on for an extended period of time and if I turn the pump off the pressure stays at around -29.2 Hg. Will the water eventually start boiling again once the temperature rises?

Does anyone else have a suggested on how to boil down water effectively at room temperature if this doesn't work?

Do I need a more powerful vacuum pump?

  • $\begingroup$ There's no such thing as "-29.2 Hg". Please clarify. $\endgroup$ – Gert Aug 24 '16 at 2:19
  • $\begingroup$ I think he is quoting gauge pressure in terms height of mercury column. @Tobias Mention the length units. $\endgroup$ – Deep Aug 24 '16 at 5:02
  • $\begingroup$ Water chills when it boils off; your sample evaporates slower when it gets too cold. A heater would be required to keep it at room temperature, and some nucleation sites for bubble formation would speed the process. Stirring would help, too (stratification makes a chilled surface layer). $\endgroup$ – Whit3rd Aug 24 '16 at 6:22
  • $\begingroup$ Yes I mean the gauge pressure. Apologies for the mix up. What type of heater would you suggest? I currently leave the water in a separate plastic container in the vacuum chamber. Could I just leave the water in the chamber or does it have to be in a separate bucket to allow for the evaporation? $\endgroup$ – Tobias Tomas Lindvall Aug 24 '16 at 13:16

Consult steam tables for water, and see what is the saturation pressure for water at room temperature. If you are able to maintain pressure in your chamber lower than this you will get boiling. Remember: what is given in steam tables is usually absolute pressure, but what a pressure sensor usually shows is gauge pressure. Learn the relation between them and interconvert.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.