Hardware | AFCM-Egypt

Capsule Chamber

The capsule chamber part - as shown above - has 2 inlets tangential to it’s inner diameter to prevent or reduce any possible chance to generate a flow separation or a recirculating flow region as much as possible. It is designed to get the optimum inlet volume flow rate and inlet velocity, in order to reduce impaction on the grid and the mouthpiece afterwards.

The capsule chamber is designed to host a HPMC capsule of size 3, so we created the whole assembly design according to that size. The HPMC capsule requires small puncture force relatively, compared to other capsule materials (e.g. Gelatine, …..etc).

Saleem et al., looked at the influence of pin number by using DPIs with a different number of punctures (2-pins vs. 8-pins). A significant difference was found, demonstrating that the 2-pin DPI device showed significantly lower MMAD. Another study conducted by Torrisi et al., comparing the puncture force needed in the case of (2 sets of 4-pins vs. 2 single pins DPI) with gelatine and HPMC capsules, showing – as expected – that 2 single pins need significantly less penetration force. So The capsule will be pierced by 2 piercing buttons with a 0.5 mm pierced aperture, which requires more E_dispersion, having a larger FPF less than 5 µm in diameter (FPF > 5 µm), while having a lower MMAD and ED.

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Part 2. Capsule Chamber

Piercing Buttons

The piercing buttons are designed to have 1 piercing pin each, with a 0.5 mm pierced aperture and travelling length of 3 mm to pierce the capsule with total number of 2 apertures. Each piercing button has 4 bias springs with length of 10 mm and diameter of 2 mm. The bias springs’ mission is to return the piercing buttons to their initial positions.

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Part 3, 4. Piercing Buttons (2 parts)

Cover

The cover is simply used to cover the mouthpiece to prevent any possible pollution to it, protecting the inhaler from dirt, dust and moisture, keeping it clean and dry when not in use.

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Part 5. Cover

Cap

The cap is responsible of covering the bottom of the capsule chamber to protect it from dust also, as the capsule chamber has lots of internal cuts to reduce it’s weight by removing the unneeded material from it, making it economical for production.

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Part 6. Cap

DPI Assembly

Then we assembled them:

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interactive DPI assembly or isometric view photo

DPI Assembly testing

Afterwards we tested the assembly for any possible errors or interferences between bodies and checked the clearances to make any modifications if needed.

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Fig 1. Checking for interferences using Interference Detection

After that we have made the engineering drawing of the assembly:

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Fig 2. Assembly Engineering Drawing

After creating the DPI assembly, which models the air flow from the inlets of the capsule chamber going through the mouthpiece to the outlet, we set the boundary conditions.

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Fig 3. Inlets Boundary Conditions

We set the thermodynamic parameters at the inlets to be atmospheric pressure (101325 Pa) and temperature of 20.05 °C. For turbulence parameters we used Turbulent Energy and Dissipation turbulence model (k-ε), we set them for 1 J/kg and 1 W/kg, respectively.

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Fig 4. Outlet Boundary Conditions

We set the volume flow rate at the outlet to be 100 L/min = 0.001667 m^3/s. this number is carefully chosen according to a specific age and severity, adult with type 2 severe asthma (uncontrolled). The mean peak inspiratory flow rate = 106 L/min with standard deviation of 16 L/min.

The volume flow rate though a DPI (Q) is proportional to the square root of the pressure drop (ΔP) the patient develops across it, namely:

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Equation

The constant of proportionality is termed: the device resistance (R).

Figure 5 presents volume flow rate resistance curves for a variety of inhalers, covering a range of pressure drops that are typically achievable by patients (2-6 Kpa).

Patients inhale faster throw low-resistance devices and slower through high-resistance devices because the pressure drops they generate tend to be similar.

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Fig 5. Volume Flow Rate vs. Device Resistance for several commercial DPIs

The wall conditions set is adiabatic wall with 0.0 µm wall roughness (smooth wall)

After specifying of the boundary conditions and air flow region, we will conduct the mesh, getting ready to run setup.

The mesh below models the DPI and the air flow region:

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Fig 6. Mesh of the DPI

To start the stage of mesh and simulation afterwards, we removed the unneeded parts (cover, cap, piercing buttons), external fillets and chamfers, …etc, in order to reduce the number of mesh cells by removing unnecessary parts, making it faster to run simulation and reducing the unneeded load on the CPU cores and then we have the ability to increase the number of mesh cells in the flow domain, and then to make the results more accurate, in addition to make the results more visualizable when removing these parts.

For the mesh settings we set the level of initial mesh to be 7 out of 7 which is the most accurate level, with a minimum gap size of 1e-06 m, giving a very accurate simulation of air flow and results. We also activated the advanced channel refinement.

After boundary conditions were specified, and the whole volume was meshed. We are ready to run the simulation’s setup.

Setup

We specified some goal plots to get sufficient information in order to see the quality of our design.

The inlets

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Fig 7. Goal Plot at the Inlets

The outlets

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Fig 8. Goal Plot at the Outlet

We did the simulation for 2 cases:

1. DPI device without a capsule

2. DPI device with a capsule

And we will discuss them in details below:

1. DPI device without a capsule

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These are the average values of pressure, velocity and volume flow rate at the both inlets and the outlet, showing a pressure drop of 4.8236 KPa. Having the volume flow rate, we got the resistance of the DPI device of about 0.02196269565〖 KPa〗^(1⁄2)/L/min, which is less than ~86% of the commercial DPI devices worldwide while not exhibiting the capsule.

We can clearly see that the flow is a turbulent flow, as Reynolds number at the inlet and the outlet, respectively:

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The following are the contours and plots we got as a result of the simulation:

Velocity Magnitude Plots

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Velocity Magnitude Flow Trajectories

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Velocity Magnitude Flow Trajectories

Showing the air trajectories from the inlet through the DPI device to the outlet. The variety of the velocity magnitude is presented as a variety of colors using contour palette.

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Plan Cut Isometric View Velocity Magnitude Contours

Showing an XZ plane cut plot from the internal base of the capsule chamber through the DPI device’s flow domain to the outlet. The variety of the velocity magnitude is presented as a variety of colors using contour palette.

Pressure Magnitude Plots

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Pressure Magnitude Flow Trajectories

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Pressure Magnitude Flow Trajectories

Showing the air trajectories from the inlet through the DPI device to the outlet. The variety of the pressure magnitude is presented as a variety of colors using contour palette.

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Plan Cut Isometric View Pressure Magnitude Contours

Showing an XZ plane cut plot from the internal base of the capsule chamber through the DPI device’s flow domain to the outlet. The variety of the pressure magnitude is presented as a variety of colors using contour palette.

Air Density Magnitude Plots

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Air Density Magnitude Flow Trajectories

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Air Density Magnitude Flow Trajectories

Showing the air trajectories from the inlet through the DPI device to the outlet. The variety of the air density magnitude is presented as a variety of colors using contour palette.

Temperature Magnitude Plots

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Temperature Magnitude Flow Trajectories

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Temperature Magnitude Flow Trajectories

Showing the air trajectories from the inlet through the DPI device to the outlet. The variety of the temperature magnitude is presented as a variety of colors using contour palette.

At the outlet, there are some parameters that vary according to the position on the outlet perimeter. Hereafter, we mentioned some of them:

Vorticity

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Vorticity variation based on position on the outlet perimeter

Pressure

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Pressure variation based on position on the outlet perimeter

Relative Pressure

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Relative pressure variation based on position on the outlet perimeter

Air Density

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Air density variation based on position on the outlet perimeter

Goal plots

Here are some of the goal plots mentioned before in the setup section:

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Average Static Pressure

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Average Dynamic Pressure

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Average Total Pressure

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Average Inlet Velocity

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Average Outlet Velocity

2. DPI device with a capsule

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These are the average values of pressure, velocity and volume flow rate at the both inlets and the outlet, showing a pressure difference of 4.90896 KPa while exhibiting the capsule. Having the volume flow rate, we got the resistance of the DPI device of about 0.02215617295〖 KPa〗^(1⁄2)/L/min, which is less than ~78% of commercial DPI devices worldwide and somewhat close to the least resistance commercial DPI devices in the world, whose resistance = 0.0125 〖 KPa〗^(1⁄2)/L/min, such as Rotahaler.

We can clearly see that the flow is a turbulent flow here also, as Reynolds number at the inlet and the outlet, respectively:

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