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The venturi mask, also known as an air-entrainment mask, is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy. [ 1 ] [ 2 ] The mask was invented by Moran Campbell at McMaster University Medical School as a replacement for intermittent oxygen treatment.
The upstream volumetric flow rate is lower than the downstream condition because of the higher upstream density. The choked velocity is a function of the upstream pressure but not the downstream. Although the velocity is constant, the mass flow rate is dependent on the density of the upstream gas, which is a function of the upstream pressure.
Flow rate is determined by the diameter of the venturi, which was cast into the float chamber side as a number within a circle representing the venturi size in inches: 0.98 - 190 cfm, 1.01 - 240 cfm, 1.02 - 245 cfm, 1.08 - 287 cfm, 1.14 - 300 cfm, 1.21 - 351 cfm, 1.23 - 356 cfm, 1.33 - 424 cfm [2]
A flow of air through a pitot tube Venturi meter, showing the columns connected in a manometer and partially filled with water. The meter is "read" as a differential pressure head in cm or inches of water. Video of a Venturi meter used in a lab experiment Idealized flow in a Venturi tube
Both types of mask masks use a reservoir bag which can economise on oxygen consumption when the flow rate is set correctly for the current breathing rate by ensuring that the reservoir bag fully deflates at the end of inhalation and fully inflates by the end of exhalation. Some field user maintenance is possible using the spare parts kit.
It describes the relationship between the pressure drop across an orifice valve or other assembly and the corresponding flow rate. Mathematically the flow coefficient C v (or flow-capacity rating of valve) can be expressed as =, where, Q is the rate of flow (expressed in US gallons per minute), SG is the specific gravity of the fluid (for water ...
The simple face mask can deliver higher flow rates than nasal cannula (6–10 liters per minute) for an FiO2 of 30- 60% oxygen. [1] Nasal cannula and simple face masks are described as low flow delivery systems. [2] [3] Unlike the non-rebreather and partial rebreather masks, the simple face mask lacks a reservoir bag.
In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge or efflux coefficient) is the ratio of the actual discharge to the ideal discharge, [1] i.e., the ratio of the mass flow rate at the discharge end of the nozzle to that of an ideal nozzle which expands an identical working fluid from the same initial conditions to the same exit pressures.