Abstract
In this paper, we present experimental results for a non-isothermal vertical confined backward facing step conducted with a low-Prandtl number fluid. The eutectic alloy gallium–indium–tin is used as the working fluid. We conducted experiments for different Reynolds and Richardson numbers covering both forced and mixed convection regimes. Time-averaged velocity profiles were measured at six streamwise positions along the test section center-plane with so-called permanent magnet probes. The local Nusselt number was measured in streamwise and spanwise directions along the heating plate mounted right after the step. We further ran RANS simulations of the experiment to study the qualitative influence of assuming a constant specific heat flux thermal boundary condition for the experiment heating plate. The measured velocity profiles show the expected behavior for both studied convection regimes, while the measured streamwise local Nusselt number profiles do not. This is explained by how the heating plate thermal boundary condition is defined. We performed an order of magnitude estimate to estimate the forced- to mixed convection transition onset. The estimate shows good agreement with the experimental data, although further measurements are needed to further validate the estimated transition threshold. The measurement of fluctuating quantities remains an open task to be addressed in future experiments, since the permanent magnet probe measurement equation needs further adjustments.Graphical
Highlights
The numerical solution of the Reynolds-averaged Navier–Stokes equations (RANS) is the preferred method in industry for the numerical calculation of heat transfer related problems
The present paper shows the results for an experiment that presents results for a Pr ≪ 1 ( Pr = O 10−2 ) confined backward facing step for both forced and mixed convection regimes
The measured dimensionless velocity profiles for probes P1 to P6 (Fig. 1) and the local Nusselt number along the heating plate for this parameter set are shown in Fig. 6 and Fig. 7, 1 3
Summary
The numerical solution of the Reynolds-averaged Navier–Stokes equations (RANS) is the preferred method in industry for the numerical calculation of heat transfer related problems In order for these models to properly predict heat transfer rates and wall temperatures, turbulent heat folfuxaevsaiul′iaTb′lemvuastlibdeataicocnudraattealyfocraulc′iuTl′a-mtedo.dTelhsecvoavsetrmParjaonrdittyl numbers ( Pr ) of the order of unity, while experimental data for very low Pr ( Pr ≪ 1 ) fluids are rare. The main reason is due to intrinsic complications and challenges related to the design and operation of liquid metal facilities and the respective instrumentation, for the local and simultaneous measurement of the temperature and velocity of the flow Within this context, the preferred turbulent heat flux model validation methodology for Pr ≪ 1 flows is to validate the models against DNS data.
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