Laminar flowmeter for mechanical ventilator: Manufacturing challenge of Covid-19 pandemic.

The rapid and sudden attack of the covid-19 pandemic has emerged the urgent need for pulmonary resuscitation devices (ventilators). The airflow sensor is a main element in the ventilator. Sensing very low airflow rates is an essential requirement to meet the least significant bit of the analogue to digital converter included in the ventilator. This short communication describes the fabrication and test of five flow sensors using basic and the 3D printing techniques to overcome the severe challenge arising from the pandemic under strict quarantine. The principle of these five flow sensors is based on Fleisch pneumotachograph technology, which creates a pseudo-laminar flow within a bundle of capillary tubes. Amongst the five tested sensors, those fabricated by 3D printing technique were the most accurate and reliable. Results show that the 3D printed sensor of 33 trapezoidal capillary tubes and displaced pressure taps meet the requirement of sensing flowrates with less resistance to patient at exhalation and more linearity figure. The experimental data were correlated using a sophisticated MMF correlation with an R-squared factor of 0.9999 and a percentage error of 1.68%.

Numerical Investigation of Mixed Convection and Entropy Generation in a Wavy-Walled Cavity Filled with Nanofluid and Involving a Rotating Cylinder.

This numerical study considers the mixed convection and the inherent entropy generated in Al 2 O 3 -water nanofluid filling a cavity containing a rotating conductive cylinder. The vertical walls of the cavity are wavy and are cooled isothermally. The horizontal walls are thermally insulated, except for a heat source segment located at the bottom wall. The dimensionless governing equations subject to the selected boundary conditions are solved numerically using the Galerkin finite-element method. The study is accomplished by inspecting different ranges of the physical and geometrical parameters, namely, the Rayleigh number ( 10 3 ≤ R a ≤ 10 6 ), angular rotational velocity ( 0 ≤ Ω ≤ 750 ), number of undulations ( 0 ≤ N ≤ 4 ), volume fraction of Al 2 O 3 nanoparticles ( 0 ≤ ϕ ≤ 0.04 ), and the length of the heat source ( 0.2 ≤ H ≤ 0.8 ) . The results show that the rotation of the cylinder boosts the rate of heat exchange when the Rayleigh number is less than 5 × 10 5 . The number of undulations affects the average Nusselt number for a still cylinder. The rate of heat exchange increases with the volume fraction of the Al 2 O 3 nanoparticles and the length of the heater segment.