Phase Doppler Anemometry in Unsteady Two-Phase Flow: A Novel Post-Processing Data Algorithm

• This thesis presents a novel method to estimate particle fluctuations in unsteady two-phase flow using phase Doppler anemometry (PDA). A comprehensive derivation and asuccessful validation of a PDA data post-processing algorithm are given.Fluctuations in unsteady two-phase flow, such as in circulating fluidized-bed (CFB)boilers, are important to understand for prediction of combustion and generation and destruction of emissions. Thus, PDA measurements were performed in the upper dilutepart of a riser of a cold laboratory-scale CFB, operated to approximately represent CFB boiler conditions.The existing method of processing the sampled raw time series (based on ensembleaveraging) resulted in strongly biased moments of particle velocity and mass flux. On the contrary, in the new algorithm extensive properties of each validated particle are weighted with their inverse measurement volume to account for the procedure of particlesampling and fluctuations in the particle concentration, yielding unbiased time-moments.To compensate for the short characteristic length of the validation volume, the properties of particles are expressed by fields of particle groups, using a local averaging time. This allows for estimation of time fluctuations, which can be compared with results from numerical two-phase flow simulations, adopting an Eulerian/Eulerian approach.The novel algorithm was extensively tested and validated by applying it on: (i) artificial time series, which were generated based on a measured time series, (ii) a timeseries obtained by a numerical simulation of a gas/solid flow around a bluff-body, and (iii) measured time series covering a cross-section of the CFB riser, and comparison ofthe estimated vertical mass flux over the cross-section with its value in the cyclone leg.Particle clustering was investigated based on the PDA measurements in the CFB riser. A new cluster criterion was introduced to distinguish particle clusters from thesurrounding dilute flow. Profiles of time mean and time fluctuations in particle velocity,concentration, and mass flux were estimated in the riser.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Övrig annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Other Engineering and Technologies not elsewhere specified (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Nyckelord

Circulating fluidized bed

Particle groups

Phase Doppler anemometry

Eulerian/Lagrangian simulation

Particle flow measurements

Two-phase flow

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