Water enters the constant 130-mm inside-diameter tubes of a boiler at 7 MPa and 65°C and leaves the tubes at 6 MPa and 450°C with a velocity of 80 m/s. Calculate the velocity of the water at the tube inlet and the inlet volume flow rate.

Respuesta :

Answer:

The velocity of water at the tube inlet [tex]V_{1}[/tex] = 32 [tex]\frac{m}{s}[/tex]

The value of flow rate at inlet  Q = 0.4415 [tex]\frac{m^{3} }{sec}[/tex]

Explanation:

Given data

[tex]P_{1}[/tex] = 7 M pa  

[tex]P_{2}[/tex] = 6 M pa  

[tex]T_{1}[/tex] = 65 °c = 337 K

[tex]T_{2}[/tex] = 450°c = 723 K

[tex]V_{2}[/tex] = 80 [tex]\frac{m}{s}[/tex]

Where 1 & 2 represents inlet & outlet conditions.

We know that mass flow rate through the boiler is constant so

Mass flow rate at inlet = mass flow rate at outlet

[tex]\rho_{1} A_{1} V_{1} = \rho_{2} A_{2} V_{2}[/tex]

Since area of the tube if the boiler is constant so

[tex]A_{1} = A_{2}[/tex]

⇒ [tex]\rho_{1} V_{1} = \rho_{2} V_{2}[/tex]

⇒ [tex]\frac{P_{1}V_{1} }{RT_{1} } = \frac{P_{2}V_{2} }{RT_{2} }[/tex]

⇒ [tex]\frac{P_{1}V_{1} }{T_{1} } = \frac{P_{2}V_{2} }{T_{2} }[/tex]

Put all the values in above equation

⇒ [tex]V_{1} = \frac{162240}{5061}[/tex]

[tex]V_{1}[/tex] = 32 [tex]\frac{m}{s}[/tex]

This is the velocity of water at the tube inlet.

Now volume flow rate at inlet [tex]Q = A_{1} V_{1}[/tex]

Area of the boiler tube is given by

⇒ [tex]A_{1} = A_{2} = 2\pi r^{3}t[/tex]

⇒ [tex]A_{1} =[/tex] 2 × 3.14 × [tex]0.13^{3}[/tex] × 1

[tex]A_{1} =[/tex] 0.0138 [tex]m^{3}[/tex]

Now flow rate at inlet Q = 0.0138 × 32

⇒ Q = 0.4415 [tex]\frac{m^{3} }{sec}[/tex]

This is the value of flow rate at inlet.