Experimental Analysis of Air Temperature Variation in Pneumatic Flexible Elements Connected by Multiple Flow Openings

Pneumatic flexible elements are widely used in mechanical systems for vibration damping, noise reduction, and improvement of dynamic properties. During cyclic loading, periodic compression and expansion of the enclosed air cause pressure fluctuations, airflow between interconnected chambers, pressure losses, and the conversion of mechanical energy into heat. This thermal loading may influence the stiffness, damping properties, durability, and operational reliability of elastomeric pneumatic elements. This study investigates the influence of the number of connecting openings on the thermal behaviour of two pneumatically coupled flexible elements under dynamic loading. Experimental measurements were carried out using a specially designed test rig at different charging pressures and with different numbers of active connecting openings. Three temperatures were monitored: the air temperature inside the pneumatic element Tair, the inner surface temperature Tin, and the outer surface temperature Tout. The results showed that increasing the number of connecting openings reduced all monitored temperatures and led to a more uniform temperature distribution within the pneumatic system. The thermal response also depended on the charging pressure, with a gradual transition from air-dominated heating at lower pressures to inner-surface-dominated heating at higher pressures. A simplified theoretical model was used to identify the main physical quantities influencing temperature development, including pressure, volume variation, airflow resistance, heat transfer, and energy dissipation. In addition, the interpretation of the observed temperature reduction was supported by a simplified analytical assessment based on the orifice–flow relationship, which showed that increasing the total flow area reduces the pressure difference required for cyclic airflow and consequently decreases pressure-loss-related heat generation. The findings demonstrate that the number of connecting openings is an important design parameter for controlling the thermal response of pneumatic flexible elements.