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CFD ANALYSIS OF FLOW DISTRIBUTION AND PRESSURE DROP THROUGH HEPA FILTER

 

THE PROBLEM

IONEX Research Corporation produces high performance equipment used to protect the environment and personnel from hazardous airborne chemicals and contamintants (click here to visit the IONEX website). IONEX was requisitioned to deliver a HEPA filter for filtering the ambient air of a manufacturing facility.

The HEPA filter unit consisted of an inlet plenum, an outlet plenum, two banks of filters in a parallel configuration, and a clamping mechanism for holding the filters in place. As part of the requisition, their customer required that IONEX demonstrate that the air flowing through the filter unit would flow uniformly through both banks of filters and the overall pressure drop across the filter unit did not exceed a specified value. For this, IONEX turned to Endesin for a computational fluid dynamics analysis of the air flowing through the filter.

 

THE ANALYSIS

The steps used to perform the analysis were as follows:

  • A CAD model of the filter unit was created from drawings supplied by IONEX.
  • The CAD model was idealized removing any features or components that did not have a significant impact on the flow of air through the filter unit.
  • The filter banks were idealized by placing a series of screens perpendicular to the flow and a series of flow surfaces parallel to the flow. The screens were used to simulate the pressure drop experienced by the air as it flowed through the filters and the flow surfaces were used to simulate a straightening effect that the filters had on the air as it flowed through the filters. These elements can be seen in the first, second and third figures on the right.
  • Once the geometry had been idealized, the fluid domains were extracted and meshed. The mesh can be seen in the fourth figure on the right.
  • Boundary conditions were applied to the inlet nozzle, the outlet nozzle and the screens.
  • Once the analysis was complete, the overall pressure drop across the filter unit was recorded, and the velocity of the air passing through the filters was plotted relative to position moving across the filter faces. The velocity contour plot can be seen in the fifth figure on the right and the plot of velocity versus position can be seen in the sixth figure.

These steps were completed for three different configurations of the HEPA filter. The initial configuration is shown in the first figure on the right, the second configuration is shown in the second figure and the final configuration is shown in the third figure. After the first analysis, the inlet and outlet were nozzles were extended and baffles were placed in the inlet and outlet plenums. After the second analysis, the configuration of the inlet and outlet nozzles were modified as can be seen in the third figure.

 

THE TOOLS

This analysis was completed using NX Advanced Simulation for pre and post processing and the solver used was NX Flow.

 

THE SOLUTION

IONEX was required by their customer to demonstrate that the filter unit they delivered met certain requirements with regard to the distribution of the air flow through the filter. For this they turned to Endesin, and by collaborating on multiple design iterations, IONEX was able to demonstrate that their product performed as required before manufacturing had begun. This saved IONEX time and money and enabled them to deliver a product that met their customers’ expectations on time and within budget.