Abo Bibliothek: Guest
TSFP DL Home Archive Vorstand

INFLUENCE OF BUOYANCY ON MEAN FLOW AND TURBULENCE UNDER CONDITIONS OF MIXED CONVECTION IN AN ANNULUS

Tian-Hua Wu
School of Engineering, University of Manchester Manchester, M13 9PL, UK

Zeyuan Xu
Department of Mechanical Aerospace and Manufacturing Engineering UMIST POB 88, Manchester M60 1QD, UK

Shuisheng He
School of Engineering The Robert Gordon University Schoolhill, Aberdeen, AB10 1FR, UK; Department of Mechanical Engineering University of Sheffield Sheffield, UK, S1 3JD

John Derek Jackson
School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M1 3 9PL, UK

Abstrakt

LDA measurements are reported of mean flow and turbulence in water as it flows downwards through a long vertical passage of annular cross-section having an inner surface which can be uniformly heated and an outer one which is adiabatic. Under buoyancy-opposed conditions, which were achieved by heating the core and operating at reduced mass flow rate, the flow near the inner surface was retarded, turbulent velocity fluctuations and turbulent shear stress were increased and the effectiveness of heat transfer was enhanced. When the influence of buoyancy was very strong, flow reversal occurred near the inner surface. Under such conditions, turbulence was produced very readily and the heat transfer process remained very effective, even when the Reynolds was reduced to values at which the flow was laminar in the absence of heating. The measurements of turbulence in buoyancy-opposed flow made in this study provide direct confirmation of the validity of the ideas currently used to explain the influences of buoyancy on mixed convection in vertical passages.