Calibration of a novel airflow transducer for use in pneumotachography

Abstract

Wave energy research at Coventry University (formerly Coventry Lanchester Polytechnic) led to the development of the Clam wave energy converter. In operation the Clam allows wave motion to produce air displacement and, through the use of a Wells turbine, electricity may be generated. The need to test the Clam at model scale led to the development of an airflow transducer which mimics the linear pressure–flow characteristics of the Wells turbine in bi-directional airflow. Medical instrumentation research leading on from this at Coventry University has identified a pneumotachograph, novel in the sense that it employs such a transducer, which offers a highly sensitive method of monitoring lung function parameters. The core of the transducer is formed by a sectored disk with unprofiled blades driven by a small dc motor at a constant speed, which creates a constant resistance to airflow irrespective of the flow direction. A series of damper disks with different solidities have been designed and extensively calibrated to confirm the existence of a linear pressure–flow relationship for each disk, and to establish this relationship as a function of parameters such as solidity and disk rotational speed. The linear pressure–flow relationship exists for disk speeds of equal to or greater than approximately 5500 rpm. Increasing the disk speed alters the transducer sensitivity making it extremely suitable for the wide range of flow-rates encountered in human breathing. Whilst the application area concentrated on was pneumotachography, the transducer offers the potential for the flow measurement of any gas at almost any flow-rate.