Abstract
Influence of variable thermophysical properties is investigated in airflows established by natural convection inside vertical tubes. Systematic numerical results are obtained for covering the entire range laminar to turbulent (modified Rayleigh number ranging 10−3–109), for both isothermal and isoflux heating conditions. Particular attention is devoted to the effects of variable properties of air. Own functions are used to take into account the variation of thermophysical properties as a function of temperature. Results are compared to those computed assuming the Boussinesq approach. For isoflux heating, it is proven that the disruptive effect consisting of the emerging of a critical heat flux and the consequent thermal crisis phenomenon, appear in the regarded cylindrical geometry. An analytical estimation of the critical heat flux is developed for vertical tubes, valid for the laminar regime, and an overall correlation is proposed for the laminar-turbulent range. The impact of the height and the widening of a funnel-shaped adiabatic extension is explored for selected values of the modified Rayleigh number, and the conditions under which its inclusion is beneficial to postpone the appearance of the crisis phenomenon, are determined.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
