# Homework Help: Flow of air in a pipe

1. Aug 25, 2012

### Karol

1. The problem statement, all variables and given/known data
air flows in a 4" pipe. at point A a 2[bar] pressure was measured and the temperature was 22°C. the velocity V1was 5[m/sec].
At point B, down the stream, a 1.2[bar] pressure was measured and the temperature was 32°C.
What is the velocity V2at point B.

2. Relevant equations
The continuity equation:
$\gamma$1A1V1=$\gamma$2A2V2
Where $\gamma$=specific gravity, A=section area.

The gas law:
pv=RT
Where: p=absolute pressure
$v=\frac{1}{\rho}$, $\rho$=specific mass

3. The attempt at a solution
The specific gravity at point A:
$$\gamma_1=10\frac{2E5}{287\cdot 295}=23.6[N/m^3]$$

The specific gravity at point B:
$$\gamma_2=10\frac{1.2E5}{287\cdot 305}=13.7[N/m^3]$$

The continuity equation, without the area, since it's the same on both points:
$$23.6\cdot 5=13.7\cdot V_2 \Rightarrow V_2=8.6$$

2. Aug 25, 2012

### TSny

Are the measured pressures "gauge pressures"?

3. Aug 25, 2012

### Karol

the problem statement is exactly as written in the book.
Maybe they should be, but that's the books mistake.

4. Aug 25, 2012

### TSny

Well, measurements of pressure are often gauge pressures. See what you get for the answer if you assume they are gauge pressures

5. Aug 26, 2012

### Karol

yes, thank you, it solved. bye