Flow nature inside vertical asymmetrically heated channel

Todorova, Nikol Venelinova ; Dimitrov, Radi Dimitrov

4. term

Indoor Environmental and Energy Engineering, Master

2016

2016-06-09

159

Denne afhandling undersøger, hvordan luft bevæger sig og opvarmes i en lodret kanal med parallelle vægge, der opvarmes asymmetrisk—den ene varm, den anden kold. Formålet er at forbedre forståelsen af strømningsmønstre i lukkede kanaler og særligt i dobbeltskindsfacader med ind- og udsugningsåbninger i de lodrette flader. Vi målte temperaturer og lufthastigheder inde i kaviteten. En litteraturgennemgang bruges til at udlede dimensionsløse kriterier til at karakterisere strømningen; med disse kriterier bekræftes, at alle forsøg ligger i området for turbulent naturlig konvektion, det vil sige bevægelse drevet af opdrift fra temperaturforskelle uden brug af ventilatorer. Gennemgangen underbygger også antagelsen om en todimensionel strømning i kaviteten (ændringerne foregår hovedsageligt i et lodret plan), hvilket forenkler forsøgene. Inden de egentlige målinger blev der lavet videooptagelser for at få overblik over processen og for at identificere uventede strømningsmønstre. De efterfølgende undersøgelser fokuserer på et lodret 2D-plan, særligt på udviklingen af randlag langs den varme og den kolde overflade samt på strømningen i den øverste del af kaviteten. Ifølge litteraturen er casen en bred kavitet, hvor randlagene langs overfladerne udvikler sig hver for sig, mens det overordnede strømningsmønster forbinder dem i et samlet recirkulerende flow. Resultaterne samles i en generel beskrivelse, der sammenfatter de observerede bevægelser i kaviteten.

This thesis investigates how air moves and heats up inside a vertical channel with parallel walls that are heated unevenly—one warm, the other cool. The goal is to improve understanding of flow patterns in enclosed channels and, in particular, in double-skin facades with supply and exhaust openings on the vertical surfaces. We measured temperatures and air velocities inside the cavity. A literature review was used to derive dimensionless criteria to characterize the flow; using these criteria, we confirm that all experiments fall within turbulent natural convection, meaning motion driven by buoyancy from temperature differences rather than by fans. The review also supports treating the flow as two-dimensional in the cavity (changes occur mainly in a vertical plane), which simplifies the experiments. Before conducting measurements, we recorded videos to gain an overview and identify unexpected flow patterns. Subsequent analyses focus on a vertical 2D plane, examining the development of boundary layers along the hot and cold surfaces and the flow in the upper part of the cavity. Consistent with the literature for wide cavities, the boundary layers along the two walls develop largely independently, while the overall circulation links them into a single recirculating flow. The results are distilled into a general description that summarizes the observed flow behavior within the cavity.

[This abstract was generated with the help of AI]

DSF ; Double Skin Facade ; flow nature ; asymmetrically heated ; vertical ; channel ; turbulent ; free convection ; recirculation ; temperature ; velocity ; LDA ; non-convergent

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