Natural convection heat transfer from a vertical single cylinder with helical wire spacer in liquid sodium

Abstract

Abstract Natural convection heat transfer from a vertical single cylinder with helical wire spacer in liquid sodium was numerically analyzed on the following four effects, the influences of surface heat flux, gap between helical wire and heated cylinder surface, pitch of helical wire and helical wire diameter on heat transfer. The unsteady laminar three dimensional basic equations for natural convection heat transfer caused by a step heat flux were numerically solved until the numerical solution reaches a steady-state. The PHOENICS code was used for the calculation considering the temperature dependence of thermo-physical properties concerned. The heated cylinder for diameter (D = 7.6 mm), heated length (L = 200 mm) and L/d (= 26.32), and the helical wire spacers for gaps (0–1 mm), pitches (100–200 mm), helical wire diameters (d = 1–2 mm) and height (H = 470 mm) were used in this work. The surface heat fluxes for each cylinder with helical wire spacer were equally given for a modified Rayleigh number, (Raf,L)w-s, ranging from 3.059 × 104 to 3.147 × 107 (q = 1 × 104 to 7 × 106 W/m2) in liquid temperature (TL = 673.15 K). The values of gap were given from 0 to 1 mm at d = 1.2 mm and a pitch of 165 mm, those of pitch were given from 100 to 200 mm at d = 1.2 mm and a gap of 0.2 mm and those of wire diameter were given from 1 to 2 mm at a gap of 0.2 mm and a pitch of 165 mm on each cylinder with helical wire spacer. The spatial distributions of local and average Nusselt numbers, (Nuθ,z)w-s and (Nuav)w-s, on each cylinder with helical wire spacer were clarified. The values of average Nusselt number, (Nuav)w-s, for a vertical cylinder with helical wire spacer were calculated to examine the effects of (Raf,L)w-s, gap, pitch and helical wire diameter on heat transfer. The correlation for (Nuav)w-s for a vertical cylinder with helical wire spacer above mentioned including the effects of (Raf,L)w-s, gap, pitch and helical wire diameter was developed. The correlation can describe the theoretical values of (Nuav)w-s for a vertical cylinder with helical wire spacer within −2.74 to 1.63% differences.