Inscrição na biblioteca: Guest

ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

IMPACT OF EXTERNAL TEMPERATURE DISTRIBUTION ON THE TURBULENT AND THERMAL FIELDS IN A VERTICAL UNIFORMLY HEATED CHANNEL

Get access (open in a dialog) DOI: 10.1615/IHTC16.cov.023383
pages 3113-3120

Resumo

This work presents an experimental and numerical study of the impact of the external temperature stratification on the velocity and the thermal fields in a vertical open-ended air channel of finite height, with one side uniformly heated. A stable and non-controlled external temperature stratification occurs naturally in the laboratory as the result of the heat flux injection in the channel and other heat sources. A heat flux, corresponding to a Rayleigh number, based on the distance between the wide walls, of 3.0×107was imposed on the heated wall for different external temperature gradients. The temperature and velocity fields were obtained with thermocouples and Particle Image Velocimetry measurements. It is observed that as the thermal stratification of the atmosphere outside the channel increases, the mass flow rate decreases in the channel. Moreover the temperature measurements, at the heated wall surface, suggest that the transition of the flow, related to a local maximum of temperature, is occurring lower in the channel. A three-dimensional Large-Eddy-Simulation numerical investigation is then performed showing good qualitative agreement with the experimental results. From the whole numerical field it is possible to confirm that as the external thermal stratification increases, the transition to turbulence occurs lower in the channel. Moreover the increase of the shear stresses in the channel and of the intensity of the backflow entering from the top of the channel are concomitant with the increase in the external thermal stratification and have been identified as potential factors that could trigger an early transition.