Abstract:
The design, the construction and the commissioning of a seeding
system for Laser Doppler Velocimetry operating in non-ideal
conditions, namely in the close proximity of the liquid-vapor saturation
curve and critical point, is presented. The system is implemented
in the Test Rig for Organic VApors (TROVA), a facility
built at CREALab (Politecnico di Milano) with the aim of
characterizing non-ideal gas flows representative of those occurring
in Organic Rankine Cycle turbine passages. The tested fluid
is the siloxane MDM (Octamethyltrisiloxane – C8H24O2Si3), a
silicon oil of particular interest for high temperature ORC applications.
Depending on the test operating conditions, the fluid under
scrutiny expands in a convergent-divergent nozzle from total
pressure and total temperature ranging from 4 bar to 25 bar and
from 253:2 C to 310:3 C respectively, therefore the seeding has
to be injected in a high temperature and high pressure environment,
without altering the thermo-fluid dynamic behavior of the
fluid. A suspension of the tracer particles (titanium dioxide, TiO2
or silicon dioxide, SiO2) in the working fluid is atomized into the
flow, in a plenum ahead of the nozzle inlet. Since the surrounding
fluid is in superheated vapor (or supercritical) conditions, the
spray then evaporates leaving the solid particles free to follow
the flow. The designed system consists of a tank, pressurized
with nitrogen and containing the MDM-seeding suspension, of
a jet mixing system, to maintain the suspension stirred, and of a
drawing line ending with the atomizing nozzle. During normal
operation, the tank is pressurized at a pressure higher than the
plenum one and the fluid flows naturally through the atomizer.
The system has been commissioned and validated through the
verification of its operation. The system is suitable for all cases
where optical measurements (LDV, PIV, etc.) have to be applied
in high temperature, high pressure conditions similar to those
occurring in the TROVA and whenever the use of auxiliary fluids
different from the working one is not feasible. The reported test
proves the suitability of the system in properly seeding the flow.
Description:
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.
