Cavitating flows of organic fluid with thermodynamic effect in a diaphragm pump for organic Rankine cycle systems.

Diaphragm pumps often experience cavitation and subsequent fluid flow oscillation when delivering an organic fluid in small/micro scale organic Rankine cycle (ORC). The cavitation behaviour of diaphragm pumps has rarely been investigated for organic fluids so far. Three-dimensional, unsteady cavitating flows of organic fluid R245fa in a diaphragm pump were simulated with ANSYS 2019R2 CFX in suction stroke in terms of the k - ω turbulence model, the ZGB cavitation model, rigid body motion model for one-dimensional motion of valve and moving mesh technique for the first time. The thermodynamic effect in cavitation of R245fa was considered. The vapour volume fraction threshold for cavitation inception was determined, and the cavitation inception and cavitation developed states were identified, and vortex production and entropy generation rate during cavitation were clarified. Cavitation inception emerges at the edge of the valve seat, then on the valve surface. With cavitating development, the pressure and force on the valve, valve opening, and velocity oscillate violently due to vapour bubble collapse cycles. Expansion cavitation and flow induced cavitation happen in sequence at different crank rotational angles. The maximum temperature depression is 0.549 K in the cases studied. The volume-integrated entropy generation rate in the valve chamber correlates to cavitation states. • Cavitating flows of organic fluid in diaphragm pump were simulated. • Cavitation inception emerges at edge of valve seat, then on valve surface. • Pressure and force on valve, valve opening, velocity oscillate in cavitation. • Expansion cavitation and flow induced cavitation happen in sequence. • Vortex production and entropy generation rate in cavitation were clarified. [ABSTRACT FROM AUTHOR]