Effects of a flow mode transition on natural convection heat transfer in a heat tracing enclosure

Abstract

This paper presents a numerical study of transient buoyancy-induced fluid flow and heat transfer between two horizontal, differentially heated pipelines inside a circular, air-filled enclosure. Numerical simulations based on the finite difference method were conducted to investigate the flow mode transition of the buoyant airflow and its effects on the heat transfer characteristics of the pipelines. The results indicate that the fluid flow complexity and the heat transfer of air between the pipelines are strongly affected by the Rayleigh number. When Ra = 6 × 105 and 1.2 × 106, both the flow field and the temperature distribution exhibit periodic variations with different patterns. The former ( Ra = 6 × 105) is a complete alteration of the flow direction from clockwise to counterclockwise, whereas the latter is a variation in the flow field strength that varies between strong and weak. The latter has a lower variation frequency than that of the former.

Transient Heat Transfer Between Two Horizontal Pipelines in a Heat Tracing Enclosure

“…To verify the formulation and numerical method, the simulation results for the selected steady state cases of the same configuration and parameters were compared with the results obtained in our previous study [8,13]. The comparison revealed that the calculated streamline patterns and flow visualization photographs were highly consistent, thus confirming the reliability of the simulation results.…”

“…A grid independence test was performed for each subgrid domain to test the accuracy of the calculations, employing a (15 × 41, 5 × 89, 45 × 57) composite grid system and ∆Fo = 5 × 10 -5 and 10 -5 (for 10 5 ≤ Ra <10 6 and Ra ≥ 10 6 , respectively) [13].…”

“…The typical composite overlapping grid system used in this study. [13] Using this composite grid system, the dimensionless governing differential equations were obtained in cylindrical polar coordinates around the two horizontal cylinders and the circular enclosure and in general curvilinear coordinates for the interior among the three cylindrical grids. In cylindrical polar coordinates:…”

“…The aim of this research was to build on insights gained in previous studies [8,13] regarding the nature of transient buoyancy-driven fluid flow and heat transfer using a similar geometric configuration (shown in Figure 1); however, in this study, a cold cylinder was placed above a hot cylinder to study transient behavior. Using numerical simulations via the finite difference method, the transient two-dimensional natural convection phenomenon induced in a heat tracing system consisting of differentially heated horizontal cylinders inside a circular enclosure was investigated.…”