Design and simulation of mechanical ventilators

Abstract

During this period of COVID-19 pandemic, the lack of medical equipment (like ventilators) leads to complications arising in the medical field. A low-cost ventilator seems to be an alternative substitute to fill the lacking. This paper presents a numerical analysis for predicting the delivered parameters of a low-cost mechanical ventilator. Based on several manufactured mechanical ventilators, two proposed designs are investigated in this study. Fluid-structure interaction (FSI) analysis is used for solving any problems with the first design, and computational fluid dynamic (CFD) analysis with moving boundary is used for solving any issues with the second design. For this purpose, ANSYS Workbench platform is used to solve the set of equations. The results showed that the Ambu-bag-based mechanical ventilator exhibited difficulties in controlling ventilation variables, which certainly will cause serious health problems such as barotrauma. The mechanical ventilator based on piston-cylinder is more satisfactory with regards to delivered parameters to the patient. The ways to obtain pressure control mode (PCM) and volume control mode (VCM) are identified. Finally, the ventilator output is highly affected by inlet flow, length of the cylinder, and piston diameter.

Keywords: CFD, COVID-19; Fluid-structure interaction; Mechanical ventilator.

Fig. 1

The physiology of the breathing system .

Fig. 2

The operating principle scheme of mechanical ventilation .

Fig. 3

Typical curves of flow, pressure, and volume in the case of VCM .

Fig. 4

Design of the Ambu-bag based on a low-cost mechanical ventilator . .

Fig. 5

Stress-strain curves for the silicon rubber material.

Fig. 6

Flowchart of the FSI solution procedure .

Fig. 7

Boundary conditions and generated mesh for the structural domain.

Fig. 8

Boundary conditions and generated mesh for fluid domain.

Fig. 9

The second mechanical ventilator design. .

Fig. 10

The mesh and boundary conditions of the fluid domain of the piston-cylinder-based design.

Fig. 11

Total displacement of the ventilator with silicon-rubber Ambu-bag, at 1 s. (PVC material, 100% O2, inlet flow = 12 l/min, UAZ = 0.09 m).

Fig. 12

Mesh history of fluid domain during one cycle of breathing. (PVC material, 100% O2, inlet flow = 12 l/min, UAZ = 0.09 m).

Fig. 13

Surface streamlines history on the vertical plane for the first design. (PVC material, 100% O2, inlet flow = 12 l/min, UAZ = 0.09 m).

Fig. 14

Displacement uz of point1 and point 2 (PVC material, 100% O2, inlet flow = 12 l/min, UAZ = 0.09 cm).

Fig. 15

Outlet flow rate history (100% O2, inlet flow = 12 l/min, UAZ = 0.09 cm).

Fig. 16

Outlet flow rate history for different compression displacements (UAZ) (Silicon rubber material, 100% O2, inlet flow = 12 l/min).

Fig. 17

Mesh displacement at different moments of the piston-cylinder system. (100% O2, inlet flow = 12 l/min, uniformly rectilinear, Lc = 150 × 10−3 m, Dp = 37 × 10−3 m).

Fig. 18

Flow rate at the outlet and the inlet of Piston-cylinder ventilator for cases A and B. (100% O2, inlet flow = 12 l/min, Lc = 150 × 10−3 m, Dp = 37 × 10−3 m).

Fig. 19

Volume history of Piston-cylinder ventilator for cases A and B. (100% O2, inlet flow = 12 l/min, Lc = 150 × 10−3 m, Dp = 37 × 10−3 m).

Fig. 20

PCM and VCM modes of mechanical ventilation .

Fig. 21

Surface streamlines on the vertical plane of the piston-cylinder ventilator. (100% O2, inlet flow = 12 l/min, uniformly rectilinear, Lc = 150 × 10−3 m, Dp = 37 × 10−3 m).

Fig. 22

Surface streamlines on the horizontal plane of the piston-cylinder ventilator. (100% O2, inlet flow = 12 l/min, uniformly rectilinear, Lc = 150 × 10−3 m, Dp = 37 × 10−3 m).

Fig. 23

Effects of different parameters on the outlet flow. (100% O2, uniformly rectilinear Upx).