Superheating in Autoclaves
Superheating in Autoclaves
(OP)
I am new to the industry and my thermo is a little rusty, but I have read that it is very important that all the air is removed from the autoclave chamber for the steam sterilization process to work correctly. In addition, I also have read that air leaks can cause superheating. Can someone explain this to me or point me to a link that might have additional info on Autoclave operations?
Thanks!
Thanks!





RE: Superheating in Autoclaves
As for superheating, I don't believe the air has anything to do with that. However, when the steam goes from a high pressure to the much lower pressure in the autoclave, superheating is possible. It is not usually a problem in autoclaves as the superheat level is low and there is usually enough risidual water in the autoclave to quickly desuperheat the steam. It is a problem in wood drying kilns where the residual superheat reduces the humidity level in the kiln that is important to prevent warping and cracking, but this is another application altogether.
RE: Superheating in Autoclaves
RE: Superheating in Autoclaves
RE: Superheating in Autoclaves
The next question is what are the actual temperatures you are measuring in this top portion (or the bottom). Is this temperature above that of saturation at 30 psig (274 deg F)? If it is not, there is little chance of superheat present.
What may be happening is that the steam is condensing on the top portion and subcooled condensate then drips down cooling the lower section a bit. Or a longshot is that there could be an air pocket at the outlet because the steam trap cannot handle air well.
RE: Superheating in Autoclaves
Thanks again!
RE: Superheating in Autoclaves
You are right that the temperature should reduce upon air ingress and it takes more time to get the sterilization temperature. However, HTM2010(the best guide on sterilization process) allows you a temp. difference of 30C from the cold point to the maximum temperature. Further, you should check for proper draining of condensate from the autoclave. One more thing is to check the accuracy of temperature probes. Calibrate the cold point probe and the top probe with same reference standard at the same time. You can get good information from www.fedegari.com
Joesteam,
With the advent of software, the things become very easy and Mollier Charts are passe
http://www.chemicalogic.com/steamtab/downloads.htm
Go to the saturated tab and get the properties at the required pressure. Entlapy of steam remains same during the expansion. Now go to the Superheated/Subcooled tab and choose the new pressure and enthalpy. This will give the actual temperature. Again calculate the saturation temperature and you will get the degree of superheat. For example, enthalpy at 45psig(or 59.7psia) pressure is 1177.71btu/lb. With 30psig(or 44.7psia) and 1177.71btu/lb enthalpy, the temperature is 284.616F. The saturation temperature at 44.7psia is 273.999F. Steam gets superheated by 10.617F.
Regards,
RE: Superheating in Autoclaves
Thanks again!
RE: Superheating in Autoclaves
RE: Superheating in Autoclaves
RE: Superheating in Autoclaves
RE: Superheating in Autoclaves