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ABSTRACT
This paper presents a numerical analysis on flow configurations and heat transfer characteristics of turbulent forced convection in spirally corrugated tubes. The influences of corrugation depth (DR = 0.02–0.16), pitch ratio (PR = 0.10–1.00), and Reynolds number (Re = 5,000–20,000) on flow structure and heat transfer characteristics are described. Comparisons between the full length and periodic domains are also reported. The results show that spirally corrugated tubes induced vortex flows which helped to increase heat transfer due to enhanced fluid mixing. The maximum thermal enhancement factor of 1.16 was obtained by using the spirally corrugated tube with DR = 0.06, PR = 0.25 at Re = 5,000.
NOMENCLATURE
| A | = | cross-sectional area, m2 |
| D | = | characteristic diameter of spirally corrugated tube |
| DR | = | corrugation depth ratio, (e/D) |
| PR | = | corrugation pitch ratio, (p/D) |
| e | = | corrugation depth, m |
| f | = | friction factor |
| h | = | convective heat transfer coefficient, W m−2 K−1 |
| k | = | turbulent kinetic energy, ( |
| ka | = | thermal conductivity of air, W m−1 K−1 |
| Nu | = | Nusselt number |
| p | = | corrugation pitch, m |
| P | = | static pressure, Pa |
| Pr | = | Prandtl number |
| PR | = | pitch spacing ratio, p/D |
| Re | = | Reynolds number, (ρu0D/μ) |
| T | = | temperature, K |
| TEF | = | thermal performance enhancement factor, (Nu/Nu0)/(f/f0)1/3 |
| ui | = | velocity component in xi-direction, m s−1 |
| ui' | = | fluctuation velocity in xi-direction, m s−1 |
| u0 | = | mean or uniform velocity in smooth tube, m s−1 |
| x | = | coordinate direction |
| μ | = | dynamic viscosity, kg s−1 m−1 |
| Γ | = | thermal diffusivity |
| ε | = | dissipation rate |
| ρ | = | density, kg m−3 |
| Subscripts | = | |
| 0 | = | smooth tube |
| pp | = | pumping power |
NOMENCLATURE
| A | = | cross-sectional area, m2 |
| D | = | characteristic diameter of spirally corrugated tube |
| DR | = | corrugation depth ratio, (e/D) |
| PR | = | corrugation pitch ratio, (p/D) |
| e | = | corrugation depth, m |
| f | = | friction factor |
| h | = | convective heat transfer coefficient, W m−2 K−1 |
| k | = | turbulent kinetic energy, ( |
| ka | = | thermal conductivity of air, W m−1 K−1 |
| Nu | = | Nusselt number |
| p | = | corrugation pitch, m |
| P | = | static pressure, Pa |
| Pr | = | Prandtl number |
| PR | = | pitch spacing ratio, p/D |
| Re | = | Reynolds number, (ρu0D/μ) |
| T | = | temperature, K |
| TEF | = | thermal performance enhancement factor, (Nu/Nu0)/(f/f0)1/3 |
| ui | = | velocity component in xi-direction, m s−1 |
| ui' | = | fluctuation velocity in xi-direction, m s−1 |
| u0 | = | mean or uniform velocity in smooth tube, m s−1 |
| x | = | coordinate direction |
| μ | = | dynamic viscosity, kg s−1 m−1 |
| Γ | = | thermal diffusivity |
| ε | = | dissipation rate |
| ρ | = | density, kg m−3 |
| Subscripts | = | |
| 0 | = | smooth tube |
| pp | = | pumping power |