Design method for calculations of dense phase pneumatic conveying lines

Universal Conveying method

Excel Calculation files

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Section summary
1. introduction
2. Rhodes
3. Air only pressure drop method
4. Universal conveying method
5. Modified Zenz-Othmer method

Section summary

1. introduction

2. Rhodes

3. Air only pressure drop method

4. Universal conveying method

5. Modified Zenz-Othmer method

1. Introduction

There are not many design models for pressure dense phase published in the literature. If for dilute phase conveying some methods can be found, it is much harder to find anything for dense phase conveying where the knowledge remains almost exclusively with equipment suppliers. This page is referring to 1 method published which is actually valid for both dilute and dense phase provided the right abacus are used.

Some explanations on the model are given and an Excel Calculation Sheet is proposed for the pressure drop calculation method. The abacus can however not be reproduced here, thus the reader will have to refer to the source to know more.

These explanations and files are given without guarantee and the user should keep a critical eye on the results and revert to reputable companies for detail design.

Note some of the methods are iterative. It is necessary to make some assumptions perform iteration to confirm them by calculation.

Commercial companies and consulting firms have indeed their own models or have modified the methods presented in this page to make them more accurate. They also have large database of materials conveyed that are helpful to calibrate the models.

2. Methods from Rhodes

This method has been published in Principles of Powder Technology, M.J. Rhodes et al., Wiley, 1990. It is a rigorous method in its approach which is to breakdown the pressure drop in multiple components, allowing to calculate them one by one.

The following link gives access to an Excel file performing the calculations according to this method - no guarantee is given, one should use this file as a 1st approximation and consult a reputable company for detail design : Link

The file is showing an example given in the solutions to the problems of the books and that can be found in the site of the editor (Link). There are minor differences in the calculations results.

3. Air only pressure drop method (Mills)

Contrary to the method proposed by Rhodes, this method is mainly empirical and relies 1st on the calculation of the pressure drop of the conveying flowing alone (air ONLY). From this pressure drop, a correlation is applied to estimate the pressure drop when materials is transported. This calculation procedure for calculating the pressure drop in dilute phase conveying is given in Pneumatic Conveying Design Guide, Mills, 2004, Elsevier.

The file is showing the example used in the book of Mills, page 411 onwards.

4. Universal Conveying method (Mills)

This method is also empirical and relies on abacus built from experimental data on a 53 mm bore line. To be used, the characteristics of the industrial line foreseen must therefore be scaled down to define what is specific pressure drop foreseen as a function of the air flowrate and product flowrate. From the specific pressure drop, the calculation of equivalent length of the industrial line for horizontal, vertical and bends allow to calculate the expected pressure drop.

This design method is given in Pneumatic Conveying Design Guide, Mills, 2004, Elsevier. To be noted that this method is also valid for dense phase conveying.

The method is not given here but the reader can refer to the book mentionned.

5. Modified Zenz-Othmer method (Agarwal)

This method is similar to the one presented by Rhodes (see above) as it breaks down the pressure drop in several components that are representing the physical phenomena experienced by the fluid and the solids and which are leading to pressure drop. It is modified from the original method of Zenz-Othmer as the friction due to the solid has been simplified and represented by a single coefficient K called friction multiplier. This factor must be calculated from experimental data for every product transported.

This makes the method very interesting in order to adjust the model to a particular component thanks to the K friction multiplier. However, it means that the method cannot be used a priori, while the methods presented above can.

The file shows the example given in the article from Agarwal, the reader will not there is a slight difference in the results of the article and the calculation file probably due to slightly different inputs. The note can be found on internet. Please refer to the article for more details on the inputs required.

Shortcut calculation method

When almost no data are available on the product to transport, a shortcut calculation method can be used to have an idea of the pressure drop of a line. Note that it is not at all an accurate methodology and should therefore not be used for the design of industrial installation.