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Homework Help: Heat up water with low temperature steam

  1. Dec 18, 2008 #1
    1. The problem statement, all variables and given/known data

    - Is it possible to heat up water from 50 °C to 100 °C with saturated steam of 30 °C?
    - If my hand is at 37 °C, is this 30 °C steam hot or cold when I touch it?

    2. Relevant equations

    Steam tables.

    3. The attempt at a solution

    I'm a bit confused here because there are two ways to see it.

    Condensing of steam transfers heat. But temperature difference also transfers heat.
    But I'm guessing that the statement is not possible. I think the steam would just stay steam and not form condensate because it would have to release heat to my hand. That wouldn't be possible if my hand is hotter than the steam?

    Edit: oh wait, I just realized something. When my hand is at 37 °C, I would just superheat the steam to 37 °C... or my hand would cool off to 30 °C and suddenly when my hand would become 29 °C because of the surrounding cold air I would feel a surge of hot warmth to my hand and it will be kept at 30 °C.
    Last edited: Dec 18, 2008
  2. jcsd
  3. Dec 18, 2008 #2


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    Consider what pressure water is at when it is saturated at a temperature of 30 C. Can you find that pressure from the steam tables? It should be ~4.25 kPa (absolute pressure).

    Right. If the steam really is saturated at 30 C, the pressure is very low and your hand at 37 C would cool while the steam would superheat.
  4. Dec 19, 2008 #3
    I didn't search up this pressure.

    So it's 0.04 bara, I have a feeling that it's very low. At our plant we have vacuum at 0.2 bara. So basically we would strip out all energy of the water so there is less energy in that steam of 30 °C.

    BUT!: The condensing heat is still very high! So if my hand was at 10 degrees, we wouldn't need much steam to heat up my hand.
    Last edited: Dec 19, 2008
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