Air enters a nozzle steadily at 2.21 kg/m3 and 40 m/s and leaves at 0.752 kg/m3 and 180 m/s. If the inlet area of the nozzle is 90 cm2, determine (a) the mass flow rate through the nozzle, and (b) the exit area of the nozzle.


(a) 0.796 kg/s,
(b) 58 cm2

Respuesta :

Answer

Given,

Air enter density, ρ₁ = 2.21 kg/m³

speed of entry, v₁ = 40 m/s

Air exit density , ρ₂ = 0.752 kg/m³

speed of exit, v₂ = 180 m/s

Inlet area = 90 cm²

a) mass flow rate through nozzle.

   [tex]m = \rho_1 A_1 v_1[/tex]

   [tex]m = 2.21\times 90\times 10^{-4}\times 40[/tex]

            m = 0.796 kg/s

b) exit area

  Using continuity equation

  [tex]\rho_1 A_1 v_1=\rho_2A_2 v_2[/tex]

  [tex]A_2 = \dfrac{\rho_1 A_1 v_1}{\rho_2 v_2}[/tex]

  [tex]A_2 = \dfrac{2.21\times 90\times 40}{0.752\times 180}[/tex]

  [tex] A_2 = 58\ cm^2[/tex]

Exit area of nozzle is equal to [tex]58\ cm^2[/tex]

(a) The mass flow rate through the nozzle is 0.796 kg/s.

(b) The exit area of the nozzle is 58 cm².

(a)

Using the formula of flow rate,

M' = DvA..................... Equation 1

Where M' = mass flow rate through the Nozzle, D = Density of air as it enters the nozzle, A = inlet area of the nozzle, v = entering velocity of the air

From the question,

Given: D = 2.21 kg/m³, v = 40 m/s, A = 90 cm³ = 9.0×10⁻³ m²

Substitute these values into equation 1

M' = 2.21(40)(9.0×10⁻³)

M' = 0.7956

M' ≈ 0.796 kg/s

Hence, The mass flow rate through the nozzle is 0.796 kg/s

(b)

Also,

making A the subject of the equation in equation 1

A' = M'/D'v'................. Equation 2

where A' = exit area of the nozzle, D' = exit density of air, v' = exit velocity

From the question,

Given: M' = 0.796 kg/s, D' = 0.752 kg/m³, v = 180 m/s

Substitute these values into equation 2

A' = 0.796/(0.752×180)

A' = 0.00588 m²

A' ≈ 58 cm²

Hence, The exit area of the nozzle is 58 cm²

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