Flow Field Characteristics in Vertical Channel with One Heated Surface

Mikkelsen, Maria Bagge

4. term

Indoor Environmental and Energy Engineering, Master

2015

2015-10-23

195 pages

Turbulent naturlig konvektion i en vertikal parallel kanal var studeret i den foreliggende projekt. En litteratur analyse viste, at to mulige typer strømnings tilstande kan forekomme udover det fra teorien kendte standard strømnings forhold. Det er, et tilfælde med ekstrem recirculation strømning, som foregår i hele kanalen, hvor luften er varmet op og strømmer langs den varme flade mens den ændrer retning langs den kolde flade. Et andet muligt type flow er også recirculation, men kun i et begrænset området. Det var bevist i den analyserede litteratur, at tilsynekomsten af recirculerende strømninger var afhængig af de dimensionsløse parametre Rayleigh og Reynolds tal samt Gr /Re2-forhold. Eksperimentalt arbejde var udført på et forsøgs anlæg konstrueret af to vertikale plader, hvoraf en kunne opvarmes, og et forsøg er gjort på at finde det interval, hvor recirculation forekommer sammenligned med litteraturen. Temperature var målt i højden of bredden af den vertikale kanal. Målingerne visten flere tegn på recirculation som fx. dynamiske forhold and deformationer på vertikale og horisontale temperatur profiler. Temperaturene i boksen var forventet at variere med meget lille afvigelse, men på grund af usikkerheder forbundet med målingerne og selve setuppet, kunne indikationerne angående recirculation ikke bevises. Til sidst var en numerisk løsning studeret, som var antaget, at være valideret i forhold til de eksperimentelle resultater, da afvigelsen var mindre en 10 %.

The turbulent natural convection in a vertical parallel-plate channel has been studied in the present work. A literature study revealed that two types of flow conditions may occur besides from the standard channel flow. That is, a case of extreme recirculation flow occuring in the entire channel with air moving downtstream near the heated surface and reversed direction at the colder surface, and another case where the recirculation flow was appearing in limited regions. In the studied literature it was proved that the appearance of recirculation flow was dependent on dimensioless parameters such as Rayleigh and Reynolds number and Gr /Re2-ratio. Experiments was conducted on a test facility of a vertical parallel-plate channel with one heated surface, and an effort was being done to find the range of appearance of recirculation flow compared to the literature. Temperatures were measured along the height and the width of the channel. They revealed several indiations of occurence of flow reversal by dynamic behavior and deformations in both vertical and horizontal temperature profiles. The temperature variations were expected to vary within a small deviation, but due to high uncertainty regarding the set up and measurements the implications were not proved. At last, a numerical solution was studied that was validated according to the experiment within a limit less than 10 %.

Turbulent naturlig konvektion

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