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ABSTRACT
Numerical simulations were conducted on nine U-tube electric heater models of 45 U-tubes with a unique tube layout of one-plus-two units, including eight helical baffle schemes of different baffle shapes and assembly configurations and a segmental one. Secondary flow and leakage flow are presented on eccentric longitudinal slices and unfolded concentric hexagonal slices, respectively. The tube surface temperature contours are also demonstrated. The results indicate that the average values of heat transfer coefficient and comprehensive index of h·Δp−1/3 of the folded helical baffle scheme with axial separation FH20(10)° are, respectively, 15.93 and 30.28% higher than those of segment scheme S200.
Nomenclature
| G | = | mass flow rate (kg/s) |
| h | = | heat transfer coefficient (W/m2 · K) |
| k | = | turbulence kinetic energy (m2/s2) |
| p | = | pressure (kPa) |
| q | = | heat flux (J/m2 · s) |
| SΦ | = | generalized source term |
| T | = | temperature (K) |
| U | = | velocity vector (m/s) |
| u | = | velocity component in the x-direction (m/s) |
| v | = | velocity component in the y-direction (m/s) |
| w | = | velocity component in the z-direction (m/s) |
| ΓΦ | = | generalized diffusion coefficient |
| Δp | = | pressure drop (kPa) |
| Δtm | = | logarithmic mean temperature difference (K) |
| ε | = | turbulence kinetic energy dissipation rate (m2/s3) |
| ρ | = | fluid density (kg/m3) |
| Φ | = | universal variables |
| Subscripts | = | |
| f | = | fluid |
| in | = | inlet |
| m | = | mean value |
| out | = | outlet |
| w | = | wall of tube |
Nomenclature
| G | = | mass flow rate (kg/s) |
| h | = | heat transfer coefficient (W/m2 · K) |
| k | = | turbulence kinetic energy (m2/s2) |
| p | = | pressure (kPa) |
| q | = | heat flux (J/m2 · s) |
| SΦ | = | generalized source term |
| T | = | temperature (K) |
| U | = | velocity vector (m/s) |
| u | = | velocity component in the x-direction (m/s) |
| v | = | velocity component in the y-direction (m/s) |
| w | = | velocity component in the z-direction (m/s) |
| ΓΦ | = | generalized diffusion coefficient |
| Δp | = | pressure drop (kPa) |
| Δtm | = | logarithmic mean temperature difference (K) |
| ε | = | turbulence kinetic energy dissipation rate (m2/s3) |
| ρ | = | fluid density (kg/m3) |
| Φ | = | universal variables |
| Subscripts | = | |
| f | = | fluid |
| in | = | inlet |
| m | = | mean value |
| out | = | outlet |
| w | = | wall of tube |