A Consideration on Volcanic Ash Ingress into the Horizontal Air Intake of Air Conditioning

Abstract

A preliminary consideration is conducted on the amount of vertically falling volcanic ash sucked into the horizontal air intakes of the exterior device for air conditioning (AC) using a numerical calculation code consisting of transport equations of airborne ash concentration, equations of motion of ash particles, and a simplified airflow model. This study focuses on the effect of the inertia force acting on the ash particle on the process of ash ingress into the horizontal air intake of AC. The results with the ash particle of sphericity 0.8 indicate that the inertia force reduces the amount of the ash ingress into the air intake by 22, 31, and 51% for the diameters of 67.5, 125, and 250 μm, respectively, as compared to the case neglecting the inertia force. The ashfall depths (thickness of deposited ash) derived as the ones leading to reduction of the performances of AC from our previous laboratory experiment on an open-type cooling tower are re-evaluated with the code. The results suggest that the ashfall depth affecting AC performances can be larger by a factor of 1.6 to 2.1, depending on the particle sphericity, than that obtained in the experiment where the inertia force was neglected in the conversion from the ash amount provided to the test piece to the “actual” ashfall depth. Simulations on the effect of installing a hood over the air intake are also made, indicating limited but substantial reduction of the expected ash ingress. The importance of mitigating ashfall impacts is stressed.