Abstract
Wall-to-bed momentum, heat and mass transfer in vertical liquid-solids flow, as well as in single phase flow, were studied. The aim of this investigation was to establish the analogy among those phenomena. Also, effect of particles concentration on momentum, heat and mass transfer was studied. The experiments in hydraulic transport were performed in a 25.4 mm I.D. cooper tube equipped with a steam jacket, using spherical glass particles of 1.94 mm in diameter and water as a transport fluid. The segment of the transport tube used for mass transfer measurements was inside coated with benzoic acid. In the hydraulic transport two characteristic flow regimes were observed: turbulent and parallel particle flow regime. The transition between two characteristic regimes (?*=0), occurs at a critical voidage ??0.85. The vertical two-phase flow was considered as the pseudofluid, and modified mixture-wall friction coefficient (fw) and modified mixture Reynolds number (Rem) were introduced for explanation of this system. Experimental data show that the wall-to-bed momentum, heat and mass transfer coefficients, in vertical flow of pseudofluid, for the turbulent regime are significantly higher than in parallel regime. Wall-to-bed, mass and heat transfer coefficients in hydraulic transport of particles were much higher then in single-phase flow for lower Reynolds numbers (Re<15000), while for high Reynolds numbers (Re>15000), there was not significant difference. The experimental data for wall-to-bed momentum, heat and mass transfer in vertical flow of pseudofluid in parallel particle flow regime, show existing analogy among these three phenomena.
Highlights
Eksperimentalna aparatura za ispitivanje prenosa količine kretanja, toplote i mase: a- mlaznica, b - raspodeljivač, c - transportna cev, d1 - omotač za paru, d2 - prsten ispunjen benzoevom kiselinom, e- preliv čestica i vode, f - preliv vode, g - kutija za merenje protoka čestica, h - dozer čvrstih čestica, i - piezometri, j - merači protoka, k - ventili, L - rastojanje transportne cevi od mlaznice, m - generator pare 30 kW, n - termopar, o - bakarna cev 8/6 mm, p - omotač oko transportne cevi, q - zid transportne cevi, r - izolacija, s - rastop benzoeve kiseline, u - prsten
Modifikovani Reynoldsov broj za smešu fluid–čestice je: Reynolds number (Rem)
The experimental data for wall-to-bed momentum, heat and mass transfer in vertical flow of pseudofluid in parallel particle flow regime, verify analogy among these three phenomena
Summary
Potpuno definisanje vertikalnog dvofaznog toka fluid–čestice podrazumeva poznavanje fluido-dinamike i prenosnih karakteristika ovih sistema. Koeficijent trenja fluid–zid transportne cevi određuje se iz korelacija za strujanje fluida bez prisustva čestica za glatku cev [11]: 0,0791 Re0.25. Korelacija za koeficijent trenja čestice-zid transportne cevi, koja se najčešće koristi u transportnim sistemima tečnost–čestice je [5]: fp = 7,33×10−3v−2. U vertikalnom toku fluida i čestica, prisustvo druge faze posebno utiče na prenos količine kretanja odnosno ukupni koeficijent trenja, pa samim tim i na uspostavljanje analogije [13,18,20]. Koja je koncipirana u formi Chilton–Colburnove analogije [21], data je za fw, koeficijent trenja smeše „fluid–čestice“–zid transportne cevi u paralelnom režimu dvofaznog toka kao [6,18]: fw 2. Prvi put u ovom radu, svi potrebni parametari za definisanje navedenih prenosa, mereni su istovremeno u cilju uspostavljanja analogije prenosa pri vertikalnom hidrauličkom transportu
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