Abstract
Direct velocity measurements in a non-ideal expanding flow of a high temperature organic vapor were performed for the first time using the laser Doppler velocimetry technique. To this purpose, a novel seeding system for insemination of high-temperature vapors was specifically conceived, designed, and implemented. Comparisons with indirectly measured velocity, namely inferred from pressure and temperature measurements, are also provided. Nozzle flows of hexamethyldisiloxane (MM, C_6H_{18}OSi_2) at temperature up to 220,^circ mathrm {C} and pressure up to 10 bar were taken as representative of non-ideal compressible-fluid flows. The relative high temperature, high pressure and the need of avoiding contamination pose strong constraints on the choice of both seeding system design and tracer particle, which is solid. A liquid suspension of tracer particles in hexamethyldisiloxane is injected through an atomizing nozzle in a high-temperature settling chamber ahead of the test section. The spray droplets evaporate, while the particles are entrained in the flow to be traced. Three different test cases are presented: a subsonic compressible nozzle flow with a large uniform region at Mach number 0.7, a high velocity gradient supersonic flow at Mach number 1.4 and a near-zero velocity gradient flow at Mach number 1.7. Temperature, pressure and direct velocity measurements are performed to characterize the flow. Measured velocity is compared with both computational fluid dynamics (CFD) calculations and velocity computed from pressure and temperature measurements. In both cases, the thermodynamic model applied was a state-of-the-art Helmoltz energy equation of state. A maximum velocity deviation of 6.6% was found for both CFD simulations and computed velocity.Graphical abstract
Highlights
Compressible flows of fluids operating at thermodynamic conditions close to the vapor saturation line and the critical point are of interest in various applications in the oil and gas sector, in the chemical process industry, and in the energy field, including power systems as organic Rankine cycles (ORCs), supercritical carbon dioxide cycles, steam Rankine cycles and high temperature heat pumps
High-fidelity computational fluid dynamics (CFD) tools conceived for highly non-ideal flows (Guardone and Vigevano 2002; Colonna and Rebay 2004; Cinnella and Congedo 2005; Vitale et al 2015), and implementing state-of-the-art thermodynamic models (Span and Wagner 2003; van der Stelt et al 2012; Thol et al 2016), were developed and largely applied to perform fundamental studies and to design and analyze performances of the above described components
Temperature and pressure measurement were complemented with the first-ever direct velocity measurements in such flows, carried out by means of laser Doppler velocimetry
Summary
Compressible flows of fluids operating at thermodynamic conditions close to the vapor saturation line and the critical point are of interest in various applications in the oil and gas sector, in the chemical process industry, and in the energy field, including power systems as organic Rankine cycles (ORCs), supercritical carbon dioxide cycles (sCO2 ), steam Rankine cycles and high temperature heat pumps. These are vapor or supercritical fluid flows, occurring at moderate to high temperature, including supercritical states, in components which are typically unconventional turbomachines, valves, heat exchangers, and pipelines.
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