||Conductive sublayer of turbulent heat transfer for heating of water in a circular tube
Hata, Koichi ,
Fukuda, KatsuyaMasuzaki, Suguru
2576 , 2017-08 , Springer Verlag
The steady-state and transient turbulent heat transfer coefficients in circular platinum (Pt) test tubes (inner diameters: 3 and 6 mm; heated lengths: 66.5 and 100 mm and 69.6 mm, respectively) were systematically measured using an experimental water loop for a wide range of flow velocities, inlet liquid temperatures, Prandtl numbers, inlet pressures, and exponentially increasing heat inputs (Q (0) exp(t/τ), τ: exponential period). The Reynolds-averaged Navier–Stokes equations and the k–ε turbulence model for unsteady turbulent heat transfer in circular test sections were numerically solved for heating of water with heated sections of diameter 3 and 6 mm and length 67 and 100 mm and 70 mm, respectively, by using computational fluid dynamics code under the same conditions as those in the experiment and with temperature-dependent thermophysical fluid properties. The thickness of the conductive sublayer, δCSL,st and δCSL [=(Δr)out/2], and the nondimensional thickness of the conductive sublayer, (yCSL,st+)TEM[=(fF/2)0.5ρlu δCSL,st/μl] and (yCSL+) (TEM) [=(fF/2)0.5 ρluδ CSL /μ l ], for steady-state and transient turbulent heat transfer at various heated length-to-inner diameter ratios, inlet liquid temperatures, and exponential periods were measured on the basis of the numerical solutions. The correlations of the thickness of the conductive sublayer, δCSL,st, and nondimensional thickness of the conductive sublayer, (yCSL,st+)TEM, for steady-state turbulent heat transfer and those of the thickness of the conductive sublayer, δCSL,st, and nondimensional thickness of the conductive sublayer, (y CSL+)TEM , for transient turbulent heat transfer in a circular tube were derived.