Question

26. A 20$°$ C temperature in horizontal pipe pressure falls 60 kPa/100 m and water flow in pipe with rate 3 lit/min then what is approximate radius of pipe. (Coefficient of viscosity at 20$°$C = 10^-3 Pa)
(1) 2.52 cm
(2) 3.64 cm
(3) 1.23 cm
(4) 4.63 cm

Answer 1

Dear Student
Using Poiseuille’s law we can write
$$\begin{gathered} Q=\frac{∆P\pi r^4}{8\eta l} \\ Where,Qisrateofflow \\ \frac{8\eta lQ}{∆P\pi }=r^4 \\ \frac{∆P}{l}=\frac{60kPa}{100}=\frac{60000}{100}=600Pa/m \\ Sustitutingvalues \\ {r}^4=\frac{8\times {10}^{-3}\times 3\times {10}^{-5}{m}^3/s}{3.14}\times \frac{1}{600} \\ r=0.033\times {10}^{-2}m=0.33cm \end{gathered}$$

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