>> The Investigation of Application of 90° Elbow Pressure Difference on the Air Volume Measurement of Rectangular Ducting System

We already introduced 90° elbow pressure difference on the air volume measurement of circular ducting system in the section of other information of our e-News volume 004 on June 2007.

Here we would like to extend that concept to the application of rectangular ducting system for your further reference.

 

>> Preface

Preface

A normal standard air volume measurement of ducting system is to locate a suitable cross section of duct, to measure many points of velocity on the cross section, and to find out the air volume by multiplication of averaged velocity and area of that cross section.  This traditional method is time-consuming and required to pre-drill many holes on the duct surface, especially for large dimension of ducting system.  

In this issue, we would like to introduce another concept for air volume measurement of ducting system to just simply use pressure difference of 90° elbow and validate/compare with the results of CFD(Computational Fluid Dynamics).

>> Fundamental Concept

Fundamental Concept

The so called pressure difference of 90° Elbow means as following figure shown,

 

What we talk about the pressure difference △p of 90° Elbow is the pressure difference of point a and b.  The air volume could be easily calculated from the following equation if the △p could be identified.

 

>> Experimental Measurement

Experimental Measurement

We set up a rectangular ducting system as shown below and got the air volume (parameter A) via traditional air volume measurement and also found out the parameter B from the value of pressure difference △P.  The result is as shown in the following,

 

>> CFD Simulation

CFD Simulation

We also set up numerical model based on our experimental system via Star-CD software. Following the similar concept of experimental measurement, we could get the parameters A and B and make the curve as shown below,

 

>> Comparison of Experimental Measurement and CFD Simulation

  Comparison of Experimental Measurement and CFD Simulation

A comparison is made as shown below,

It could be found the results of experimental measurement and CFD simulation are similar and they match the requirement of engineering tolerance.

>> Conclusions

Conclusions

The concept of pressure difference of 90° Elbow could be used not only for circular ducting system but also for rectangular system.

And this will largely simplify the air volume measurement of ducting system and then a better engineering service could be provided.