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## Main Question or Discussion Point

Hi, I am an undergraduate, doing an experiment regarding of minor losses due to sudden contraction. However, I found that my theoretical loss is higher than the experimental loss.

The flow rate = 3.28*10^-4 (m^3/s)

(Inner diameter) D1= 3.652*10^-2 m

(Inner diameter) D2= 1.539*10^-2 m

by using the energy equation

[tex]\frac{P_1}{\gamma}+\frac{V_1^2}{2g}=\frac{P_2}{\gamma}+\frac{V_2^2}{2g}+h_L[/tex]

rearranged

[tex]\frac{P_1}{\gamma}-\frac{P_2}{\gamma}=\frac{V_2^2}{2g}-\frac{V_1^2}{2g}+h_L[/tex]

I assumed that major head loss/friction head loss negligible since the length between to the two points is only 50mm.

SO [tex]h_L[/tex]= minor loss

[tex]h_L=K_L\frac{V^2}{2g}[/tex]

Based on the charts given in the book, Fluid Mechanics by McGrall Hill. I found that [tex]K_L[/tex] roughly equals to 0.45 and V=the velocity of the smaller pipe.

By using all these, I calculated the pressure difference = 0.22m

But my experimental result = 0.159m

Could anyone help me with this, I expected my experimental results would yield bigger pressure difference, yet it gave me less.

I built a simple piezometer to measure the pressure difference between the two points.

The flow rate = 3.28*10^-4 (m^3/s)

(Inner diameter) D1= 3.652*10^-2 m

(Inner diameter) D2= 1.539*10^-2 m

by using the energy equation

[tex]\frac{P_1}{\gamma}+\frac{V_1^2}{2g}=\frac{P_2}{\gamma}+\frac{V_2^2}{2g}+h_L[/tex]

rearranged

[tex]\frac{P_1}{\gamma}-\frac{P_2}{\gamma}=\frac{V_2^2}{2g}-\frac{V_1^2}{2g}+h_L[/tex]

I assumed that major head loss/friction head loss negligible since the length between to the two points is only 50mm.

SO [tex]h_L[/tex]= minor loss

[tex]h_L=K_L\frac{V^2}{2g}[/tex]

Based on the charts given in the book, Fluid Mechanics by McGrall Hill. I found that [tex]K_L[/tex] roughly equals to 0.45 and V=the velocity of the smaller pipe.

By using all these, I calculated the pressure difference = 0.22m

But my experimental result = 0.159m

Could anyone help me with this, I expected my experimental results would yield bigger pressure difference, yet it gave me less.

I built a simple piezometer to measure the pressure difference between the two points.

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