Experimental study on natural convection in the vertical enclosure of a double coaxial cylinder

Y. Zhang; T. Takeda; Y. Inaba

doi:10.1515/kern-2003-0093

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Experimental study on natural convection in the vertical enclosure of a double coaxial cylinder

Y. Zhang , T. Takeda and Y. Inaba

Published/Copyright: March 16, 2022

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From the journal Kerntechnik Volume 68 Issue 5-6

Abstract

This paper presents results of an experimental study on natural convection in the vertical enclosure of a double coaxial cylinder where the inner wall is at constant heat flux. It is the objective of this experiment to understand the basic characteristics of heat transfer under the condition of natural convection coupled with thermal radiation in a vertical enclosure. The range of Rayleigh numbers based on the width of the double coaxial cylinder is set to be 5.6 × 10₅ < Ra < 1.04 × 108, the radius ratio is 2.73, the aspect ratio is 3.43 (cylinder length divided by annular gap). The heat transfer coefficient of natural convection coupled with thermal radiation was obtained as function of the Rayleigh number, aspect ratio of the enclosure, and temperature of the hot and cold surfaces. The experimental results show that thermal radiation can’t be neglected in analyzing heat transfer of vertical annulus with natural convection. The results provide the basic data for the design and the performance assessment of the future passive cooling system used in a high-temperature engineering test reactor.

Abstract

In der vorliegenden Arbeit werden die Ergebnisse einer experimentellen Untersuchung zur natürlichen Konvektion im vertikalen Gehäuse eines doppelt-koaxialen Zylinders präsentiert. Ziel der Untersuchung war es, die grundlegenden Eigenschaften des Wärmetransfers unter Bedingungen der natürlichen Konvektion gekoppelt mit thermischer Strahlung in einem vertikalen Gehäuse zu verstehen. Der Bereich der Rayleigh-Nummern liegt bei 5.6 × 10⁵ < Ra < 1.04 × 108, das Verhältnis der Radien ist 2.73, das Längenverhältnis ist 3.43 (Zylinderlänge dividiert durch Ringschlitzlänge). Der Wärmetransferkoeffizient der natürlichen Konvektion gekoppelt mit thermischer Strahlung wurde als Funktion der Rayleigh-Nummer, des Längenverhältnisses des Gehäuses und der Temperatur der warmen und kalten Oberflächen bestimmt. Die experimentellen Ergebnisse zeigen, dass die thermische Strahlung bei der Analyse des Wärmetransfers nicht vernachlässigt werden kann. Die Ergebnisse liefern die Grundlagen für die Konstruktions- und Leistungsmerkmale des zukünftigen passiven Kühlsystems eines Hochtemperatur-Testreaktors.

Nomenclature

H =: Aspect ratio of the cylinder, l/d
l =: Height of the annulus, m
d =: Distance of the annulus, m
Pr =: Prandtl number
Nu =: Nusselt number
Nu_a =: Nusselt number based on the thermal radiation and the convection
Nu_c =: Nusselt number based on the convection
Ra(d) =: Rayleigh number based on the distance of the annulus, G_rPr
G_r =: Grashof number
T₀ =: Temperature on the outer surface of the heated rod, K
T₁ =: Temperature on the inner surface of the cylinder, K
g =: Constant of gravitational acceleration, m/s²
β =: Isobaric coefficient of thermal expansion, K^-1 Cinematic viscosity, m²/s
Rr =: Heat flux ratio, ρ_r /ρ_a
q_a: Heat flux based on the thermal radiation and the convection, W/m²
q_r =: Heat flux based on the thermal radiation, W/m²

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Received: 2003-05-04

Published Online: 2022-03-16

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https://doi.org/10.1515/kern-2003-0093