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Evaporator Two Stage - Working Of Vacuum Pump


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#1 Orzelgorskiego


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Posted 02 September 2019 - 12:58 PM



I was wondering how one vacuum pump which is connected to the second stage of the evaporator can decrease the boiling point in the first stage?


I understand that in the second stage pump can suck the vapour through the separator, but how it can suck from the first stage? 


The liquid is distributed in the pipes from the top in the first stage and the vapour is in the separate chamber in which tubes are placed. 


Maybe somebody can explain me how the temperature is decreased in the first stage of falling film evaporator and how the vacuum pump is sucking the vapour from the first stage?


Thank you in advance


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  • Evaporator 2 stage falling film.png

#2 Pilesar


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Posted 02 September 2019 - 04:06 PM

Think of it this way: As the vapor condenses, there are fewer vapor molecules in the same volume and the pressure is reduced. Condensing is the key. The vacuum pump is for removing the remaining vapor molecules that are not condensed. If the condenser could condense all the vapor molecules, the vacuum pump would have no purpose. If there were no vacuum pump, any vapor molecules that do not condense would have no way of leaving the system. You could not vent the non-condensed vapor directly to the atmosphere since the atmosphere is at higher pressure. So the vacuum pump provides a means to vent the uncondensed vapor molecules while keeping the system at a low pressure.

#3 breizh


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Posted 02 September 2019 - 08:05 PM

Hi Tomasz,

Your drawing is confusing , the aim of the condenser is condense the condensable vapor , this means you need an outlet for the liquid including a barometric guard ,a second outlet is for the non condensable vapor connected to your vacuum system .

Consider the link underneath to support your work.



hope this is helping you .


Edited by breizh, 02 September 2019 - 08:07 PM.

#4 Orzelgorskiego


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Posted 15 September 2019 - 06:13 AM

Thank you very much for help.

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