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Temperature change with altitude 
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#1
Apr1112, 09:20 AM

P: 2

Alright guys, just looking for a point in the right direction for a tutorial question.
GIVEN VALUES: Temperature change with increasing altitude: 0.0065 K/m Temp at sea level: 15ºC Pressure at sea level: 101.5 kPa FIND: Atmospheric pressure at 7500m. So what I've done is found the temperature decrease between sea level and 7500m, so that temperature is 239.4K. And then tried (P1/T1)=(P2/T2), was a bit sceptical over this working.. it didn't. After that tried: ∫(1/P) dP = ∫(g/RT) dz Integrated that, giving: ln(P2/P1) = (g/RT)(z2z1) Placed in the values given/calculated, leading to: P = 101500*e^[(9.81*7500)/(287*288.15)] P = 41.7 kPa ... which is a wee bit off the stated answer of 38.3 kPa. Any ideas? 


#2
Apr1112, 10:38 AM

PF Gold
P: 961

Welcome to PF!
In your second integral you should integrate T as a function of z (you have treated it as a constant). Usually one makes the substitution dz = (1/(dT/dz)) dT, where dT/dz is the constant lapse rate so that you get pressure as a function of temperature. Edit: I see now that you have posted outside the homework section of this forum. Please post future homework questions in the homework section to get better responses . 


#3
Apr2212, 03:06 AM

P: 2

Fantastic, thanks Filip.



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