Modelling of natural convective heat transfer at an internal surface

In this study, convective heat transfer phenomena were investigated by means of a Guarded Hot Box (GHB) apparatus. An experimental setup characterized by air and surface temperature probes, and a hot-wire anemometer was used. Five small fans were installed in the metering chamber to generate a forced air flow characterized by different velocity values. So, the GHB was used for investigating the influence of different air speed values on internal convective coefficients. Considering horizontal heat fluxes, an internal convective coefficient values of 2.5 W/m2K is reported in the Standard ISO 6946. However, no exhaustive description about this value is provided. The aim of this work is to experimentally determine the internal thermal surface resistance, quantifying how the convective heat transfer coefficient varies as air velocity changes.

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On Convective Heat Transfer and Flow Dynamics Through a Straight T-Bifurcating Channel

Journal of Heat Transfer ◽

10.1115/1.4037208 ◽

2017 ◽

Vol 140 (3) ◽

Author(s):

Lakehal Abdelhak ◽

Nait-Bouda Nora ◽

Pelle Julien ◽

Harmand Souad

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Convective Heat Transfer ◽

Convective Heat ◽

Stokes Equations ◽

Dynamical Behavior ◽

Symmetry Plane ◽

Internal Surface ◽

Local Heat Transfer ◽

Flow Dynamics

Both experimental and numerical studies of a turbulent flow in a bifurcating channel are performed to characterize the dynamical behavior of the flow and its impact on the convective heat transfer on the sides of the branch. This configuration corresponds to the radial vents placed in the stator vertically to the rotor–stator air gap in the electrical machines. Indeed, our analysis focuses on the local convective heat transfer on the vents internal surface under a turbulent mass flow rate. The flow field measurements were carried out with two components particle image velocimetry (PIV) system, and the local heat transfer on the sides of the bifurcation branch was measured using an infrared thermography device. The convective heat transfer and the flow dynamics through the geometry are investigated numerically considering a three-dimensional (3D) flow. The closure system of the Navier–Stokes equations for steady and incompressible flow is based on the low-Reynolds numbers Reynolds stress model (RSM) (RSM-stress-ω). The comparison of the 3D computed results with the measurements in the xy symmetry plane is satisfactory in the vertical and horizontal channels. The numerical prediction of the secondary flow in the vertical branch was analyzed and complements the experimental results. It was particularly noticed that the accelerated flow observed at the right side of the branch's inlet allows more pronounced heat transfer comparatively to the left side. Beyond approximately 7 hydraulic diameters from the entrance of the branch, the Nusselt number curves on the two sides of the branch tend to be the same developed Nusselt number, Nud.

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