Pneumatic System for Pressure Probe Measurements in Transient Flows of Non-Ideal Vapors Subject to Line Condensation

This paper presents the design, construction and commissioning of a pneumatic system for pressure probe measurements in flows of organic vapors in non-ideal conditions, close to the liquid-vapor saturation curve and the critical point where the ideal gas law is not applicable. Experiments were performed with fluid siloxane MM, employed in medium/high temperature Organic Rankine Cycles, in the TROVA blow-down wind tunnel at Politecnico Milano. Challenges linked to condensation in pneumatic lines (vapor-liquid menisci, hydrostatic head, mass-sink), were evaluated with theoretical calculation and experiments, and were avoided with a nitrogen flushing procedure. Commissioning tests were performed with a Pitot tube in non-ideal subsonic flows at Mach numbers of 0.2 and 0.5. Measurement delay issues were identified and solved through a dynamic testing procedure. The correct performance of the complete system was verified for probe measurements of total, static and dynamic pressure in non-ideal flows of organic vapors.