Calculating Pressure Drops in Piping Systems

摘要

Calculating pressure drops in piping systems using the Darcy-Weisbach Equation requires the friction factor to be calculated. The traditional approach used the Moody Diagram to solve the Colebrook Equation. Using the Moody Diagram directly has been left mainly to those generating tables or graphs that are published in various references. One example is in the 2007 ASHRAE Handbook-Fundamentals where pressure losses in steam piping is shown on Pages 35.12 to 35.14. Such tables or graphs are based on specific conditions that may not match exactly with the conditions that an engineer is designing to meet and are often difficult to interpret. This results in some level of inaccuracy. An alternative has been developed using a PC spreadsheet and an iteration function within the spreadsheet that may be unfamiliar to some engineers. In Microsoft~(~R) Excel, the iteration function is found under TOOLS/GOAL SEEK. In Lotus 1-2-3, the function is found under RANGE/ANALYZE/BACK SOLVE. The advantages of using the spreadsheet include exactly matching the conditions of the fluid, gas or vapor and eliminating difficult to read graphs and tables. Engineers often find the spreadsheet approach is more user friendly than tables or graphs.