add notes on extended bernoulli eqn
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@ -147,7 +147,7 @@ Examples of this are line dye or a smoke stream which is produced from a continu
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### Viscosity
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### Viscosity
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A fluid offers resisistance to motion due to its viscosity or internal friction.
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A fluid offers resistance to motion due to its viscosity or internal friction.
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The greater the resistance to flow, the greater the viscosity.
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The greater the resistance to flow, the greater the viscosity.
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Higher viscosity also reduces the rate of shear deformation between layers for a given shear stress.
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Higher viscosity also reduces the rate of shear deformation between layers for a given shear stress.
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@ -184,10 +184,10 @@ to the velocity gradient when straight and parallel flow is involved:
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$$\tau = \mu\frac{\mathrm{d}v}{\mathrm{d}y}$$
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$$\tau = \mu\frac{\mathrm{d}v}{\mathrm{d}y}$$
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Where $\mu$ is the constant of proportinality and known as the dynamic viscosity, or simply the
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Where $\mu$ is the constant of proportionality and known as the dynamic viscosity, or simply the
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viscosity of the fluid.
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viscosity of the fluid.
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This is Newton's Law of Viscosity and fluids that ovey it are known as Newtonian fluids.
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This is Newton's Law of Viscosity and fluids that obey it are known as Newtonian fluids.
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### Viscosity and Lubrication
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### Viscosity and Lubrication
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@ -393,7 +393,7 @@ Head form:
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\frac{p_s}{\rho g} + z &= \text{piezometric head}
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\frac{p_s}{\rho g} + z &= \text{piezometric head}
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\end{align*}
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\end{align*}
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# Steady Flow Energy Equation (SFEE)
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# Steady Flow Energy Equation (SFEE) and the Extended Bernoulli Equation (EBE)
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SFEE is a more general equation that can be applied to **any fluid** and also is also takes
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SFEE is a more general equation that can be applied to **any fluid** and also is also takes
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**heat energy** into account.
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**heat energy** into account.
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@ -486,7 +486,7 @@ Dividing everything by $\delta m$ and with a bit of rearranging we get:
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$$q + w_s = e_2-e_1 + \frac{p_2}{\rho_2} - \frac{p_1}{\rho_1}$$
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$$q + w_s = e_2-e_1 + \frac{p_2}{\rho_2} - \frac{p_1}{\rho_1}$$
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#### Substiute Back for $e$
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#### Substitute Back for $e$
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$$e = u + \frac{v^2}{2} + gz$$
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$$e = u + \frac{v^2}{2} + gz$$
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@ -534,7 +534,7 @@ $$\dot W = \dot m (h_2-h_1) = \dot m c_p(T_2-T_1)$$
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#### Mixing Devices
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#### Mixing Devices
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e.g. hot and cold water in a shower
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e.g. Hot and cold water in a shower
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In these processes, work and heat transfers are not important and you can often
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In these processes, work and heat transfers are not important and you can often
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neglect potential and kinetic energy terms, giving us the same equation as for the throttle valve
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neglect potential and kinetic energy terms, giving us the same equation as for the throttle valve
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@ -546,3 +546,109 @@ which you may want to write more usefully as:
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$$\sum \dot m h_{out} = \sum \dot m h_{in}$$
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$$\sum \dot m h_{out} = \sum \dot m h_{in}$$
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## SFEE for Incompressible Fluids and Extended Bernoulli Equation
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$$\frac{w_s}{g} = H_{T2} - H_{T1} + \left[ \frac{(u_2-u_1)-1}{g}\ \right]$$
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or
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$$w_s = g(H_{T2}-H_{T1}+H_f$$
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If we assume shaft work, $w_s$, is 0, then we can get this equation:
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$$H_{T1}-H_{T2} = H_f$$
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This is very similar to the Bernoulli equation.
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The difference is that it considers friction so it can be applied to real fluids, not just ideal
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ones.
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It is called the *Extended Bernoulli Equation*.
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The assumptions remain:
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- Steady flow
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- No shaft work
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- Incompressible
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### $H_f$ for Straight Pipes
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$$H_f = \frac{4fL}{D} \frac{v^2}{2g}$$
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$$\Delta p = \rho g H_f \text{ (pressure form)}$$
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This equation applies to long, round and straight pipes.
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It applies to both laminar and turbulent flow.
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However be aware that in North America the equation is:
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$$H_f = f \frac{L}{D} \frac{v^2}{2g}$$
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Their $f$ (the Darcy Friction Factor) is four times our $f$ (Fanning Friction Factor).
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In mainland Europe, they use $\lambda = 4f_{Fanning}$, which is probably the least confusing version to use.
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### Finding $f$
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#### $f$ for Laminar Flow
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$$f = \frac{16}{\Rey}$$
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#### $f$ for Turbulent Flow
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For turbulent flow, the value defends on relative pipe roughness ($k' = \frac k d$) and Reynolds
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number.
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Note when calculating $k'$ that **both $k$ and $d$ are measured in mm** for some reason.
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A *Moody Chart* is used to find $f$:
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![A Moody Chart](./images/vimscrot-2022-03-08T09:28:38,519555620+00:00.png)
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### Hydraulic Diameter
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$$D_h = \frac{4 \times \text{duct area}}{\text{perimeter}}$$
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### Loss Factor $K$
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There are many parts of the pipe where losses can occur.
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It is convenient to represent these losses in terms of loss factor, $K$, times the velocity head:
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$$H_f = K \frac{v^2}{g}$$
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Most manufacturers include loss factors in their data sheets.
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#### Loss Factor of Entry
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![](./images/vimscrot-2022-03-08T10:01:31,557158164+00:00.png)
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#### Loss Factor of Expansion
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$$K = \left( \frac{A_2}{A_1} - 1\right)^2$$
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This also tells us the loss factor on exit is basically 1.
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For conical expansions, $K ~ 0.08$ (15 degrees cone angle),
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$K ~ 0.25$ (30 degrees).
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For cones you use the inlet velocity.
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#### Loss Factor of Contraction
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$\frac{d_2}{d_1}$ | K
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----------------- | ----
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0 | 0.5
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0.2 | 0.45
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0.4 | 0.38
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0.6 | 0.28
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0.8 | 0.14
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1.0 | 0
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#### Loss Factor of Pipe Bends
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On a sharp bend, $K ~ 0.9$.
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On a bend with a radius, $K ~ 0.16-0.35$.
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#### Loss Factor of Nozzle
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$$K ~ 0.05$$
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But you use the outlet velocity, increasing losses.
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