THE INVESTIGATION OF THE PRANDTL NUMBER EFFECT ON MIXED CONVECTION IN THERMAL DEVELOPMENT IN A CYLINDRICAL DUCT

Abstract

This study concernsanumerical simulationofthree-dimensionalconjugateheat transferin ahorizontal pipe heatedby Joulean effectthroughits entire thickness.The mixed convection in the fluid domain is combined with heat conduction in the thickness of the solid duct.The physical propertiesof the fluidare heatdependent andthermal losses,the outer surfaceofthe conduit tothe environment, aretaken into consideration. At the entranceof the pipe,the fluidispresentedwitha constant temperatureequal to 15C°andaparabolicvelocity profile. The numerical methodoffinite volumeis used forsolving the equationsofconservation ofmass,momentum and energy. The resultsof this study areperformedfor fourdifferent fluids (water, Butanol, Syltherm800, Ethylene Glycol)whichcorrespond to thePrandtl, ReynoldsandGrashof numberswhich arecalculatedfrom thetemperature entrance(Pr= 8.0820, 80.5, 140, 305), (Re=143.2836, 39, 128.6, 20 ), (Gr=257534, 102336, 47802, 9300) respectively.Theelectric intensityisconsidered I = 40 Amperes, and thegeometricaspect ratiois equal to 104.17. The results producedwere conductedsoas to showthe influenceof the Prandtl numberonthe dynamic fieldsandtheNusselt numberinforced convectionmodes(Gr =0)andmixed convection. An empirical correlationexpressing theNusselt numberdepending onthenumber ofthePrandtl and thenumber of theRichardson Numoy = f (Pr, Ri),Numoy=19.543 * Ri 0.1598* Pr - 0.0539