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Boiling point of water increased with sugar, should steam temp increase?

  • 04-05-2011 1:40pm
    #1
    MarcoB
    Closed Accounts Posts: 34 ✭


    I am calibrating digital thermometers and can adjust the offset on one of them. I get todays atmospheric pressure and calculate the boiling point of water from this, then adjust for my altitude (I have to take off 0.3C from sea level boiling point).

    I wanted to use standard water rather than distilled, so I figured if I had a enclosed boiler with my probe in the steam then it would be exposed to distilled water -in the form of steam.

    I found this page about boiling points varying due to containers, I already knew this after heating and measuring water past 102C from a microwave. So I wanted to make sure my water was absolutely boiling and I was figuring the steam coming off it would be definitely at boiling point and no higher.

    So I added sugar to my water to get it past 100C, however now my probe which is only exposed to the steam is reading over 100C, up to 102C. I regularly calibrate it and know the offset should not be this high (i.e. I do believe the 102C reading). So I am wondering if the steam temp can be increased by the sugar, or is something else going on -e.g. could the air above the sugar water get so hot that it is heating the probe in addition to the steam.


Comments

  • #2
    Professor_Fink
    Registered Users, Registered Users 2 Posts: 861 ✭✭✭Professor_Fink


    MarcoB wrote: »
    So I added sugar to my water to get it past 100C, however now my probe which is only exposed to the steam is reading over 100C, up to 102C. I regularly calibrate it and know the offset should not be this high (i.e. I do believe the 102C reading). So I am wondering if the steam temp can be increased by the sugar, or is something else going on -e.g. could the air above the sugar water get so hot that it is heating the probe in addition to the steam.

    Are you suggesting that the steam should be at exactly the boiling water of distilled water? If so, this is entirely incorrect. The steam will be at or below whatever temperature it was produced at. If you have raised the boiling temperature of the water, you have also raised the temperature of the steam (or at least its initial temperature).


  • #3
    MarcoB
    Closed Accounts Posts: 34 ✭MarcoB


    Professor_Fink wrote: »
    Are you suggesting that the steam should be at exactly the boiling water of distilled water?
    That is what I had thought, since the steam is in effect pure water I thought it would immediately drop in temp.
    Professor_Fink wrote: »
    The steam will be at or below whatever temperature it was produced at.
    This is why I wanted to increase the boiling point, I did not want any heat losses to the surrounds. My original boiler took a while to reach equilibrium with the steam in it. It was losing heat to the surroundings and the probes took a while to get up to temp. I have since put loosely covered shroud inside the boiler to further insulate it, the probes go in this shroud and stabilise far quicker.

    Professor_Fink wrote: »
    If you have raised the boiling temperature of the water, you have also raised the temperature of the steam (or at least its initial temperature).
    So is there anyway to determine how quickly it will drop? or have you other suggestions I could try?

    My pot has boiling chips in it and reading the page I linked these could reduce the boiling temp, therefore the steam given off might not be the same as my theoretical value. If it drops in temp quickly enough I might just need a little added sugar.

    Before I read your post I was thinking it was similar to what would happen in an oven at 200C, if I had a probe inside exposed to steam the probe would be over 100C, the steam would be cooling it down but not totally.


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