An Experimental Study of Mixed Convection in Vertical, Open-Ended, Concentric and Eccentric Annular Channels

Abstract

An Experimental Study of Mixed Convection in Vertical, Open-Ended, Concentric and Eccentric Annular ChannelsThe effect of eccentricity on heat transfer in upward flow in a vertical, open-ended, annuiar channel with a diameter ratio of 0.61, an aspect ratio of 18:1, and both internal surfaces heated uniformly has been investigated experimentally. Results have been reported for eccentricities ranging from the concentric case to the near-contact case and three inlet bulk Reynolds numbers, equal approximately to 1500, 2800, and 5700. This work complements our recently reported experimental results on natural convection in the same facility. The present results are deemed to be largely in the mixed convection regime with some overlap with the forced convection regime and likely to include cases with laminar, transitional, and turbulent flows in at least a part of the test section. Small eccentricity had an essentially negligible effect on the overall heat transfer rate, but high eccentricity reduced the average heat transfer rate by up to 60%. High eccentricity also resulted in wall temperatures in the narrow gap region that were much higher than those in the open channel. The concentric-case Nusselt number was higher than the Dittus-Boelter prediction, whereas the highly eccentric-case Nusselt number was signiflcantly lower than that.

Aiding buoyancy driven flow and heat transfer features of converging and diverging trapezoidal cylinders

“…Flow field was examined (forced to mixed convection) over the range of conditions: flow velocity = 0.13, 0.23, 0.27 m/s with Re = 53, 94, 118, respectively. Investigation by [7] reported that Strouhal number increased slowly with Ri. Flow and heat transfer characteristics were also explored experimentally.…”

Numerical investigation of turbulent mixed convection flow and heat transfer characteristics of 2 × 2 subchannels with spacer grids

“…1 In a reactor core, during the accident conditions, the passive decay heat removal system in the reactor becomes active, throughout the long-term cooling phase, circulation of the coolant in fuel assembly is driven by buoyancy, and a mixed convection regime may occur under such conditions with a low flow rate. 2 In the early studies of convection, heat transfer, natural convection, and forced convection were usually studied separately, while the interaction between them was ignored. Since mixed convection is a combination of forced convection and natural convection and may occur in many technological and industrial applications, with the development of science and technology, more and more experimental and theoretical studies on mixed convection have been carried out in open literature.…”

“…Mixed convection flows, which are also known as combined free and forced convection flows, occur in many technological and industrial applications and are driven by both external force and density difference 1 . In a reactor core, during the accident conditions, the passive decay heat removal system in the reactor becomes active, throughout the long‐term cooling phase, circulation of the coolant in fuel assembly is driven by buoyancy, and a mixed convection regime may occur under such conditions with a low flow rate 2 . In the early studies of convection, heat transfer, natural convection, and forced convection were usually studied separately, while the interaction between them was ignored.…”