GCI TECH NOTES ©

Volume 4, Number 12

A Gossman Consulting, Inc. Publication

December 1998

by

David L. Constans

One of the major considerations when designing liquid waste fuel storage and burner supply systems is trying to maintain turbulent flow. The need to maintain turbulent flow is usually associated with the need to keep solids suspended in the fluid, so that the solids do not settle and plug the piping. However, maintaining turbulent flow may not be necessary if the fluid viscosity is sufficiently high enough to impede the settling of the solids. Indeed if the viscosity is too high it may not be possible to achieve turbulent flow without special pumps and high pressure rated piping. In most cases it is worthwhile to try to achieve turbulent flow since it reduces the flow resistance of the fluid and consequently the pressure losses in the piping system due to this flow resistance. As an example a 5 to 10% flow rate increase, going from laminar to turbulent flow, can result in a 30+% decrease in flow resistance for a 100 centipoise viscosity fluid being pumped through a 1-1/2 inch pipe. This may mean the difference between using schedule 40 pipe versus schedule 80 pipe and a centrifugal pump versus a positive displacement pump.

This all assumes that the fluid is Newtonian. Most fluids in hazardous waste fuel facilities are Newtonian. Non-Newtonian fluids such as greases and oil well drilling muds show high flow resistance when at rest and until a certain shear stress value has been exceeded, at which point they exhibit much less flow resistance. So even for non-Newtonian fluids it is still preferable to achieve and maintain turbulent flow if the required initial shear stress can be achieved with the desired equipment.

Calculating the Reynolds number that determines whether the fluid is in the turbulent or laminar flow range is relatively simple. The formula is in numerous engineering texts and there are several software packages that will do the calculation as well. For those of you who do not want to shell-out several hundred dollars for the software or have forgotten more of your or college engineering than you care to admit to, GCI has added a webpage to our site that will calculate the Reynolds number. You can insert values for all four system characteristics (pipe size, velocity, viscosity, density) and it calculates the Reynolds number and tells if it is in the turbulent or laminar flow range or you can leave out one of the values and it will tell you what the value must be to achieve turbulent flow. Go to this page and try out our Reynolds number calculator. GCI is also setting up a web page to calculate dioxin TEQ values, look for this in the near future.