# Design of a Mass Air Flow Sensor Employing Additive Manufacturing and Standard Airfoil Geometry
## 5 Conclusions  
A thermal air flow sensor for use as a Mass Air Flow (MAF) measuring device for small to medium size IC engines was designed and fabricated successfully, employing additive manufacturing technology combined with PCB technology; the proper functionality of the developed prototype was validated by performing a preliminary electrical characterization. The design of the sensor's housing was derived from an appropriate Computational Fluid Dynamic (CFD) study; three basic design concepts, which employ different approaches for the design of an internal air flow bypass pathway, were investigated. As a result, the optimum design determined is based on a \"Hatch and Orifice\" topology for the bypass air inlet, while well-established airfoil geometries in the automobile industry (NACA and Joukowski) are the basis for the challenging air flow profile shaping over the sensing element, minimizing the developed circulating air flow. An appropriate set of simulations were additionally performed in order to further optimize the selected concept's geometry, with regard to an assumed maximum engine air intake of 1000 kg/h (14,076 SLPM), which exceeds by over 50% the maximum air intake for a typical low power Industrial IC engine [14]. Subsequently, the final housing design features two bypass sections, each with a separate sensing element: one bypass (\"High Velocity Bypass\") with an optimized geometry for a moderate incoming flow range (0-350 kg/h) and a second bypass (\"Low Velocity Bypass\") for a considerably higher flow range (350-1000 kg/h). Additive manufacturing was successfully employed for the fabrication of the challenging housing design by employing a commercially available desktop 3D printer and standard building materials (PLA/PVA), while PCB technology was selected for the sensing element for increased robustness and limited process steps. The developed device was integrated into a typical four-cylinder low power engine on a DIESEL engine testbed, in series with the integrated Mass Air Flow (MAF) reference sensor. The air intake was varied from 0 to 485 kg/h (6944 SLPM) by running the testbed at appropriate operating points of speed and mechanical load applied, while the hot-wire principle of operation on constant current (CC) mode was selected. A significant variation in the sensor's output signal was recorded for both pathways, with respect to the incoming flow, validating the functionality of the fabricated sensor. Furthermore, a drastic extension of the measuring range was noticed when employing either bypass compared to mounting the sensing element directly on the main inflow pathway. Saturation in the sensor's signal manifested itself for flow rate values above 280 kg/h (4000 SLPM), approximately, when High Velocity Bypass topology was employed, while no saturation was present in the case of the Low Velocity Bypass, even for the maximum engine air intake of 485 kg/h (6944 SLPM). The sensing element's temperature was drastically reduced by 40 \({}^{\circ}\)C or 46 \({}^{\circ}\)C depending on the topology employed. Based on the findings of previous relative research work [12], but also on the current experimental findings, the adaptation of standard airfoil geometry to the housing design, in combination with the \"Hatch and Orifice\" topology for the bypass air inlet, lead undoubtedly to an extensive increase in the measurement range of the sensing device, mainly attributed to the drastic reduction of the circulating flow inside the bypass pathway. Furthermore, the experimental results strongly supported the CFD study performed with regard to the optimum design geometry of the housing. Key features of the developed device are low-cost, fast on-site manufacturing, robustness, and simple fabrication procedure, suggesting numerous potential applications in marine engineering and in industrial applications in general.