Flow of water in a venturimeter

[Karol]

Homework Statement

Water flows in a horizontal venturimeter. the diameter is 100 mm, and the throat is 50 mm.
The pressure at the entrance is 0.65[bar].
What is the maximum throughput that is allowed so that the absolute pressure in the throat will not drop under 0.3[bar]

Homework Equations

Bernoully equation:
$$H_1+\frac{V_1^2}{2g}+\frac{P_1}{\gamma}+H_P=H_2+ \frac{V_2^2}{2g} +\frac{P_2}{\gamma}$$

The Attempt at a Solution

The velocity V₂ in the throat:
$$V_2=V_1 \frac{0.1^2}{0.005^2}=4V_1$$
Bernoully equation:
$$\frac{0.65E5}{1E5}+\frac{V_1^2}{20}=\frac{0.3E5}{1E5}+\frac{16V_1^2}{20}$$
Which produces negative velocity.
Even if i use absolute pressures, the same. i use 1.65 instead of 0.65.

 

[TSny]

$$\frac{0.65E5}{1E5}+\frac{V_1^2}{20}=\frac{0.3E5}{1E5}+\frac{16V_1^2}{20}$$
Which produces negative velocity.

Hi, Karol.

I don't see how you're getting a negative velocity here.

Also, are you sure that your value of $\gamma$ is correct?

 

[Karol]

you are right!
Thanks...