Day to Day horsepower differences?
03-29-2005, 04:23 PM
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Just like to follow up on the discussion of yesterday. Let me work out three examples (I neglect non ideal situations and forget that we have also some other stuff in air besides oxygen and nitrogen and I assume all the gasses will be well mixed at each altitude):
1. Pressure (P) = 1 atmosphere (atm), Temperature (T) = 60 F, Humidity = 0% (this is hardly possible, but just a reference case): on a molar basis we have 21% O2 and 79% N2, which give a partial pressure for O2 (pO2) of 0.21 atm and 0.79 atm for N2 (pN2).
2. Pressure = 1 atmosphere, Temperature = 60 F, Humidity = 99% (very close or at the dew point): at this conditions we can have a little more than 1% of water vapor in air. Resulting in the following partial pressures: pO2 = 0.205, pN2 = 0.785, pH2O = 0.01.
So, the at the same pressure the oxygen goes down a little tiny bit.
3. Mountain: P = 0.9 atm, T = 60 F, Humidity = 0%. pO2 = 0.189 atm, pN2 =.711 atm.
So available O2 is significant less.
4. Hot Houston day: P = 1 atm, T = 110 F, Humidity = 99%. Now up to 6% of the total pressure can be water vapor, so about 18 to 18.5% is O2.
If people are interested we can go in more detail and look at the influence of pressure and temperature on each of those cases as the density is changing when changing the temperature and/or pressure, which have all kind of good and bad influences.
1. Pressure (P) = 1 atmosphere (atm), Temperature (T) = 60 F, Humidity = 0% (this is hardly possible, but just a reference case): on a molar basis we have 21% O2 and 79% N2, which give a partial pressure for O2 (pO2) of 0.21 atm and 0.79 atm for N2 (pN2).
2. Pressure = 1 atmosphere, Temperature = 60 F, Humidity = 99% (very close or at the dew point): at this conditions we can have a little more than 1% of water vapor in air. Resulting in the following partial pressures: pO2 = 0.205, pN2 = 0.785, pH2O = 0.01.
So, the at the same pressure the oxygen goes down a little tiny bit.
3. Mountain: P = 0.9 atm, T = 60 F, Humidity = 0%. pO2 = 0.189 atm, pN2 =.711 atm.
So available O2 is significant less.
4. Hot Houston day: P = 1 atm, T = 110 F, Humidity = 99%. Now up to 6% of the total pressure can be water vapor, so about 18 to 18.5% is O2.
If people are interested we can go in more detail and look at the influence of pressure and temperature on each of those cases as the density is changing when changing the temperature and/or pressure, which have all kind of good and bad influences.
