From 9b1346f8f04629a1e2770ecb11ebe5866f6f7d41 Mon Sep 17 00:00:00 2001 From: Alvie Rahman Date: Sun, 23 Apr 2023 19:13:58 +0100 Subject: [PATCH] add errata, fix typos --- .../pumps.md | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/uni/mmme/2047_thermodynamics_and_fluid_dynamics/pumps.md b/uni/mmme/2047_thermodynamics_and_fluid_dynamics/pumps.md index d412f2a..4062616 100755 --- a/uni/mmme/2047_thermodynamics_and_fluid_dynamics/pumps.md +++ b/uni/mmme/2047_thermodynamics_and_fluid_dynamics/pumps.md @@ -11,6 +11,16 @@ exercise_sheets: [ ./exercise_sheets/Turbomachinery-problems.pdf] Turbomachinery are rotating devices that add (pump for liquids; fan, blower, or compressor for gases at <0.02, <1 bar, and > 1 bar respectively) or extract (turbine) energy from a fluid. +# Errata + +## Worked Example 3 Diameter Incorrect (lecture slides 42, lecture notes p. 13) + +Question specifies 21" diameter, but should be 32" diameter I think?? +Solution provided in lecture slides continues to use 21" dia, but measures +from graph as if is 32". +Weird. + + # Positive Displacement (PD) Pumps - PD pumps force fluid along using volume changes (e.g. bike pumps, the heart) @@ -112,7 +122,7 @@ This is where cavitation occurs and causes wear on the blade. The following conditions must be satisfied to prevent cavitation: \begin{equation} -H_i - \frac{p_v}{\rho g} > \text{NSPSH} +H_i - \frac{p_v}{\rho g} > \text{NPSH} \end{equation} where $H_i = \frac{p_i}{\rho g} + \frac{v_i^2}{2g}$ is total head at inlet, $p_v$ is saturation @@ -146,8 +156,8 @@ Pi-theorem allows the following coefficients to be derived: Therefore it can be expressed that: \begin{align*} -C_H &= g_1(C_Q, \text{Re}, \frac{\epsilon}{D} \\ -C_P &= g_2(C_Q, \text{Re}, \frac{\epsilon}{D} +C_H &= g_1\left(C_Q, \text{Re}, \frac{\epsilon}{D}\right) \\ +C_P &= g_2\left(C_Q, \text{Re}, \frac{\epsilon}{D}\right) \end{align*} However for pumps it is assumed that Reynolds number and roughness parameter are constant