Diskontinualni granični sloj i analogije prenosa u pakovanim, fluidizovanim i transportnim sistemima tečnost-čestice

Abstract

U ovom radu eksperimentalno je ispitivan diskontinualni granični sloj ianalogije prenosa količine kretanja, toplote i mase u fluidizovanim i pakovanimslojevima i pri hidrauličkom transportu sistema tečnost-čestice. Cilj ovog rada je upravopovezivanje karakteristika graničnog sloja sa prenosom količine kretanja, toplote imase, sa akcentom na analogije između ovih prenosa. Fenomenološkim pristupom ovojproblematici, daje se doprinos koji bi olakšao teorijsko razmatranje višefaznih sistematečnost-čestice (pakovani sloj, fluidizovani sloj, vertikalni transport), koji su izuzetnosloženi.Za izvođenje eksperimentalnog dela istraživanja u ovoj doktorskoj disertacijikorišćeni su različiti sistemi: standardne kolone različitih prečnika sa omotačem ili bezomotača, sa pakovanim, fluidizovanim i transportnim sistemima u cilju dobijanjaparametara za koeficijente prenosa količine kretanja, mase i toplote i segmentiranekolone sa fluidizovanim česticama u cilju dobijanja parametara na koje utiče debljinagraničnog sloja. Sva eksperimentalna merenja su izvršena u širokom opseguhidrodinamičkih uslova: brzina strujanja fluida, veličina čestica čvrste faze i poroznostislojeva.Kao rezultat istraživanja razvijen je novi teorijski model za prenos mase i toplotezasnovan na analizi graničnog sloja koji se u disperznom sistemu formira od sudara dosudara čestica. Na osnovu modela dobijena je debljina difuzionog i termičkog graničnogsloja, izvedene su jednačine za korelisanje koeficijenata prelaza, Sherwood-ovog iNusselt-ovog broja i faktora prenosa mase i toplote. Na osnovu uspostavljenog modelaizvedena je jednačina za određivanje maksimalne vrednosti koeficijenata prelaza toplotei poroznosti sloja pri kojoj do nje dolazi.U ovom radu je uspostavljena analogija prenosa količine kretanja, mase i toploteu partikulativno fluidizovanim slojevima zasnovana na modelu graničnog sloja.Postojeća analogija u fluidizovanom sloju, data na osnovu normalizovanih vrednostikoeficijenta trenja čestice-fluid i faktora prenosa mase proširena je na analogiju sva triprenosa. Dobijeni model je upotrebljen za definisanje faktora prenosa mase i toplote priminimalnoj fluidizaciji i transportu čestica...

In this thesis the discontinued boundary layer and the analogues amongmomentum, heat and mass transfer were examined experimentally for fluidized andpacked beds and for hydraulic transport in liquid-particles systems. The aim of thispaper is to connect the characteristics of the boundary layer with the momentum, heatand mass transfer, with an emphasis on analogies between these phenomena. Transportphenomena approach to this problem provides a contribution that facilitates theoreticaldescription of multiphase liquid-particles systems (packed beds, fluidized beds, verticaltransport), which are extremely complex.Different experimental systems have been used to perform the research in thisdissertation: standard columns of different diameters with or without heating jacket,with packed and fluidized beds and transport systems in order to obtain parameters forthe momentum, heat and mass transfer coefficients, and segmented fluidized bedscolumns in order to obtain parameters influenced by the thickness of the boundary layer.All experimental measurements were performed in a wide range of hydrodynamicconditions: fluid velocities, solid particles sizes and bed voidages.As a result of this research, a new theoretical model for mass and heat transfer sdeveloped. Model is based on the analysis of the boundary layer, which in dispersesystems forms between the two adjacent particles collisions. Based on the model, thethickness of the concentration and thermal boundary layer was obtained and theequations for correlating the transfer coefficients with Sherwood and Nusselt numbersand the mass and heat transfer factors were derived. On the basis of the establishedmodel, the equation for determining the maximum value of the heat transfer coefficientand the bed voidage for this value is derived. In this thesis, the analogue based on the boundary layer model for themomentum, mass and heat transfer in particulate fluidized beds is established. Theexisting analogy for the fluidized beds, based on the normalized values of the frictioncoefficient fluid-particles and the mass transfer factor, has been extended to analogy forall three phenomena. The obtained model was used to define the mass and heat transferfactors at the minimum fluidization and transport of particles...