Design of experiments to observe liquid-to-vapor expansions exploiting molecularly complex organic fluids

The rising interest in novel two-phase organic Rankine cycles, promising higher efficiency in exploiting low-enthalpy heat sources compared to current single-phase cycles, faces challenges in modeling the flashing process due to insufficient experimental data. To tackle this, the TROVA blowdown wind tunnel will be modified to enable the characterization of flashing processes of molecularly complex fluids. A lumped parameter model is developed to simulate the discharge process of a representative organic fluid, namely hexamethyldisiloxane (MM), and obtain insights into the characteristic times and dimensions compatible with the facility constraints. A preliminary design for a planar converging-diverging nozzle is simulated using computational fluid dynamics, employing a homogeneous equilibrium model. Calculations demonstrate achievable complete vaporization without flow detachment for a useful test duration, corroborating the feasibility of the proposed experimental campaign.