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Homework Help: Human body Physics 2020 question

  1. Sep 16, 2010 #1
    1. The problem statement, all variables and given/known data

    If a person breathes 10 liters per minute or air at 68 deg(F) and 50% relative humidity, how much water per day must the internal membranes supply to saturate the air at 98.6 Deg(F) (Assume all moisture is exhaled) If each gram of water extracts 580 calories as it is vaporized, how much daily heat loss in kilo-calories (Food calories) does the represent? (Saturation vapor pressure at 20 degrees(C) is 17g/m^3 and at 37 deg(C) 44g/m^3.

    Water Per Day:
    Energy per day lost:

    2. Relevant equations

    3. The attempt at a solution
    I am clueless where to start
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 17, 2010 #2
    Thats a good one.
    For the first part: you need to find how much water is in a liter of air at 50% humidity at 68F, figure out what that corresponds to at 98F, and see how much more water is needed to get to 100% humidity (saturated).
    % humidity is the percentage of saturated vapor pressure for a given temperature.
    Once you have that, the second part is easy.

    Does that make sense?
  4. Sep 19, 2010 #3
    Yes it does what formula am I going to use now that I have figured them out?
  5. Sep 19, 2010 #4
    I assume you mean for the second part ('how much daily heat loss....').

    Well, its essentially just a really big conversion problem:
    It says we breath 10L per minute, so we need to figure out how many liters that is per day. Then we have to convert liters/day to grams/day (so you need to the density of water). Finally, it says one loses 580 cals/gram of water, so we need to convert grams/day to cal/day---> and thats the answer!
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