Question

A mercury manometer (rho = 13,600 kg/m3) is connected to an air duct to measure the pressure inside. The difference in the manometer levels is 30 mm, and the atmospheric pressure is 100 kPa. (a) Judging from Fig. P1–65, determine if the pres- sure in the duct is above or below the atmospheric pressure. (b) Determine the absolute pressure in the duct

Answer 1

Answer:

P = 104 kPa

Explanation:

a) To know if the pressure is higher or lower than the atmospheric, we only have to see the tubes if the right side is higher the pressure is higher than the atmospheric, otherwise it is lower.

b) The pressure in a system is

          P = $P_{atm}$ + ρ g (Y2-y1)

Where $P_{atm}$ is the atmospheric pressure in the open part of the tuno,ρ is the liquid density and (y2-y1) is the difference height between the two sides of the tube.

Let's reduce to SI units

         (y2-Y1) = 30 mm (1m / 1000 mm) = 30 10-3 m

        $P_{atm}$ = 100 KPa = 100 10 3 Pa

Let's calculate the pressure

       P =  $P_{atm}$  + 13.6 9.8 30 10⁻³

       P = 100 10³ + 3,998

       P = 103,998 Pa

      P = 104 kPa