Flow Field Characteristics in Vertical Channel with One Heated Surface
Author
Mikkelsen, Maria Bagge
Term
4. term
Publication year
2015
Submitted on
2015-10-23
Pages
195
Abstract
Denne afhandling undersøger turbulent naturlig konvektion (luftbevægelse drevet af temperaturforskelle) i en lodret kanal dannet af to parallelle plader, hvor den ene væg er opvarmet. Et litteraturstudie viser, at der ud over den normale gennemstrømning kan opstå to typer recirkulation: (1) en stærk, kanalomfattende recirkulation, hvor luften bevæger sig i én retning tæt ved den opvarmede væg og i modsat retning ved den kolde væg, og (2) recirkulation, der kun optræder i begrænsede områder. Om recirkulation opstår afhænger af dimensionsløse tal som Rayleigh- og Reynolds-tal samt forholdet Gr/Re^2, der afspejler balancen mellem opdrift, viskositet og inerti. Vi udførte forsøg i en lodret parallelpladekanal med én opvarmet flade for at finde de betingelser, hvor recirkulation optræder, og for at sammenligne med resultater fra litteraturen. Temperaturen blev målt langs kanalens højde og bredde. Målingerne gav flere indikationer på strømningsvending, set som dynamisk adfærd og deformationer i både vertikale og horisontale temperaturprofiler. Temperaturvariationerne forventedes at være små, men stor usikkerhed i opsætning og målinger betød, at indikationerne ikke kunne bekræftes endeligt. Endelig blev en numerisk model undersøgt og stemte overens med forsøgene inden for mindre end 10 % afvigelse.
This thesis examines turbulent natural convection (air movement driven by temperature differences) in a vertical channel formed by two parallel plates, where one wall is heated. A review of prior studies shows that, beyond the standard through-channel flow, two recirculation patterns can occur: (1) a strong, channel-wide recirculation in which air moves in one direction near the heated wall and in the opposite direction near the colder wall, and (2) recirculation that appears only in limited regions. The onset of these patterns depends on dimensionless parameters such as the Rayleigh and Reynolds numbers and the ratio Gr/Re^2, which reflect the balance between buoyancy, viscosity, and inertia. We conducted experiments in a vertical parallel-plate channel with one heated surface to identify the conditions under which recirculation occurs and to compare with the literature. Temperatures were measured along the height and width of the channel. The measurements showed several indications of flow reversal, seen as dynamic behavior and distortions in both vertical and horizontal temperature profiles. The temperature variations were expected to be small, but high uncertainty in the setup and measurements meant these indications could not be confirmed. Finally, a numerical model was studied and agreed with the experiments within a difference of less than 10%.
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