Development of a Thermal Mass Airflow Sensor for Low Velocity Ducted Flow Applications

Abstract

This study was conducted to develop a flat plate, calorimetric based, mass airflow sensor capable of measuring low-speed flow typically found in heating, ventilation, and air conditioning (HVAC) systems. Moreover, to develop a numerical model that accurately predicts the fluidic and thermal behaviour of the sensor design. Current findings indicate that the numerical and experimental results were in close agreement, with the predicted leading-edge temperatures within 1-2% of those recorded experimentally. However, this error increased in the trailing edge to a maximum of 8%; inclusion of the trailing edge flap within the numerical model reduced this to less than 3%, suggesting that the flap generates enhanced cooling within the trailing region. The temperature deltas predicted by the numerical model were on average twice that of the experimental values, however, the average temperature change was still less than 0.03°C per 1 m/s increase in velocity. It was concluded that the copper sensor design was unsuitable for mass flow measurement. The numerical findings for the stainless-steel sensor indicate a 600% increase in the maximum temperature delta measured from 0.069°C to 0.49°C. Which suggests the subsequent increase in accuracy is a result of the decreased thermal diffusivity of stainless-steel, which is 96% lower than that of copper. Other findings include, a further increase in temperature delta values when the heater size is decreased, resulting in a maximum temperature delta value of 0.58°C and an average change of 0.49°C for a 1 m/s change in flow velocity. Thus, it can be implied that the modified calorimetric airflow sensor would accurately predict the mass flow rates within HVAC ducting systems.