Understanding the Moody Chart Parameters
The Moody chart is a fundamental graphical tool used in fluid dynamics, particularly for analyzing pressure drop in pipe flow. It plots the Darcy friction factor ($f$) against the Reynolds number ($Re$) for different flow regimes.
Key Parameter on Moody Chart Curves
While the primary axes represent the friction factor ($f$) and the Reynolds number ($Re$), the chart displays a family of curves. Each curve corresponds to a specific value of another crucial parameter that significantly influences the friction factor, especially in turbulent flow. This parameter is the Relative Roughness.
Definition of Relative Roughness
- Relative Roughness is defined as the ratio of the average height of the surface imperfections (absolute roughness, $\epsilon$) of the pipe wall to the internal diameter of the pipe ($D$).
- Mathematically, it is expressed as:
- Different curves on the Moody chart represent distinct values of .
Significance in Fluid Flow Analysis
The relative roughness dictates how much the pipe's internal surface texture affects the fluid flow. In the laminar flow regime, the friction factor depends only on the Reynolds number. However, in the turbulent regime, both the Reynolds number and the relative roughness become important determinants of the friction factor, influencing energy losses and pressure drop.
Important Questions from Dimensionless Number
Match the following and select the correct answer from the codes given below the lists
List I
List II
A.
Steam Nozzle
1.
Mach number
B.
Compressible flow
2.
Reaction turbine
C.
Surface Tension
3.
Biot number
D.
Heat conduction
4.
Nusselt number
5.
Supersaturation
6.
Weber number
The Reynold’s number, used for critical velocity for turbulent flow of fluids, is given by the relation
Reynolds number for non - circular cross-section is:
[V = mean velocity, ν = kinematic viscosity, P = ratio of cross-sectional area to the wetted perimeter]
A) \(V.\frac{{4P}}{v}\)
B) \(\frac{{V.P}}{v}\)
C) \(\frac{{V.2P}}{{4v}}\)
D) \(\frac{{V.P}}{{4v}}\)
When the Mach number is less than unity, the flow is
The only possible dimensionless group that combines velocity ‘V’, body size ‘L’, fluid density ‘ρ’ & surface tension ‘σ’
