![]() Note that the DC fan operates at 12V but shares a ground with the Arduino for PWM purposes. The wiring between the BME280, MPXV7002DP, DC motor, and Arduino board is given diagrammatically in the figure above and by component pins in the table. Fortunately, the sensors used to measure differential pressure, barometric pressure, and temperature have simple libraries that make the data acquisition easy and straightforward. The open-source Arduino platform has been widely recognized as a useful educational tool for undergraduate engineering due to its simplified approach to electronics software and hardware integration. Arduino is particularly specialized for this application due to the platform’s integration of on-board analog-to-digital converters, complex digital protocol libraries, and the ability to use pulse-width modulation to control motors (a DC fan in our case). The Arduino board serves as the DC fan controller and data acquisition device for the ensuing experimentation. A drawing of an example venturi tube is given below: ![]() The wiring of the sensors, fan, and Arduino board is also introduced in the next section. The first sensor measures barometric pressure and ambient temperature, while the second measures the pressure differential across the venturi tube. An Arduino board is used to both control the fan rotation speed and record data measured by a pair of sensors. The fluid dynamics theory is introduced as it relates to ideal gas flow through the venturi tube. The complete background of compressible and incompressible flow through a venturi tube is not given here, but can be found in the full PDF version of the analysis. Luckily, the perfect combination of fan size and geometry for the venturi tube were found for the 3D printing domain. The fan diameter will dictate the size of both the inlet and the tapered section of the venturi tube. ![]() Another design constraint is the size of the fan being used at the inlet. The venturi tube introduced here is designed to fit within the limits of many common desktop 3D printers that often have vertical printing capabilities limited to 300mm or less (see popular printers by Creality, Ultimaker, Monoprice, Makerbot, Prusa). Commonly, steel or other hardened metals are used in the design of venturi tubes however, for the low velocity conditions of our experiments, pressures are expected to be far below the stress limits observed for 3D printed materials. The ASME venturi design specification is applied to the current application using fused deposition modeling-a common form of 3D printing. One particular measurement device, the ASME venturi tube, has been widely tested and calibrated under strict laboratory conditions, where errors can be less than 0.5% under optimal design conditions. The ASME performance test code standard on flow measurement, PTC 19.5-2004, outlines specifications for measuring fluid flow with a variety of differential pressure meters.
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