The Moody Chart, which provides values for friction factors for flows through pipes and ducts, has been one of the more useful charts in fluid mechanics since its introduction by L.F. Moody in 1944. This online calculator provides a simple way to determine Moody Friction Factors for turbulent and laminar flows that would be using in calculating headloss in flow conduits of circular and noncircular cross section areas.
Type of Material:
An online calculator.
For students solving problems in pipe or duct flow.
A JAVA-enabled browser. It works well using both Netscape Navigator 7.1 and Internet Explorer 6.0. Other browsers were not tested.
Identify Major Learning Goals:
To provide students of fluid mechanics with a convenient means of calculating the friction factor for liquid or gas flows in pipes or ducts.
Target Student Population:
College level civil,chemical or mechanical engineering students taking classes in fluid mechanics.
Prerequisite Knowledge or Skills:
Knowlege of fluid friction losses and some familiarity with the traditional Moody chart.
Evaluation and Observation
The calculator is reasonably accurate over most of its stated range of validity and employs accepted relations for calculating the friction factor in the laminar (Re < 2100)and fully turbulent (Re > 5000)flow regimes. It wisely makes no attempt to calculate friction factors in the transition range (2100 <5000).
The calculator uses an explicit equation for determining the friction factor in the turbulent flow regime instead of the implicit Colebrook equation on which the Moody diagram is actually based. Over most of the range of validity, this results in errors on the order of 1% or less. However, at a Reynolds number of 5000 and a relative roughness (e/D) of 0.01, an error of 2.8% occurs.
Potential Effectiveness as a Teaching Tool
The calculator is based on one of the explicit relations for the friction factor often used in fluid mechanics classes. It also includes tables for fluid properties and typical surface roughness values for commonly used pipes and ducts. Hence, it maybe used as a demonstration tool for lecture purposes.
Although useful as a calculator, this object would be more useful as a teaching tool if it included more background material, such as a discussion of the Colebrook Equation on which the Moody diagram is based. It does, however, provide a link to another page where the Colebrook Equation is at least given.
Ease of Use for Both Students and Faculty
The calculator is both easy and intuitive to use, with little effort required to begin using the calculator. Values may be entered in either English or SI units as long as the units are employed consistently. It permits six different combinations of user input data. Displaying the output values in blue and the input values in black is a nice feature.
A useful addition to the calculator is a set of online tables for pertinent fluid properties and pipe roughness values in both English and SI units.
Users should be instructed to enter values for the kinematic viscosity and surface roughness to replace the default values provided. Beginning students may not be aware of this. For non-circular duct input, the user prompt ("Non-circular Duct: Enter A, P, and" ) is incomplete. Presumably it should read: "Non-circular Duct: Enter A, P, and Q".
Other Issues and Comments:
Overall, this calculator is quite useful and reasonably accurate for determining friction factors for flows in pipes. However,its accuracy could be improved by either using the implicit Colebrook equation with an iterative approach or by using a more accurate explicit method.