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ABSTRACT
In numerical computations, axial fans are typically abstracted as two-dimensional surfaces, and this forms the basis for the “Lumped Fan” (LF) model. The LF-model relies on experimentally derived P–Q (fan) curves which should conform to the published test codes. Despite its simplicity, the LF-model’s accuracy depends on the application and acceptable error margin. Therefore, with decreasing error margins in thermal engineering, there has been an interest in accurate fan modeling techniques such as “Multiple Reference Frame” (MRF) model. The current effort provides a two-part validation of the MRF model results for an axial fan against the relevant experiments: comparison of the (i) P–Q curves, and (ii) temperature distribution in an electronic enclosure. In the former, both fan models exhibit good agreement with the experiments, however the flow structures determined by the two models exhibit substantial differences. Given these flow structures’ strong influence on the temperature field, the MRF model demonstrates good correlation and significantly better agreement with the measured temperature distribution, compared to those of the LF-model. In light of these findings, benefits, limitations, and possible applications of both models are also discussed.
Nomenclature
| A | = | area (m2) |
| cp | = | nondimensional pressure, |
| D | = | diameter (m) |
| eΔ | = | error |
| E | = | specific internal energy (m2/s2) |
| FAR | = | free flow area ratio (%) |
| h | = | enthalpy (J/kg·K) |
| I | = | unit tensor |
| k | = | turbulent kinetic energy (m2/s2) |
| LF | = | Lumped Fan |
| LFS | = | Lumped Fan with Swirl |
| MRF | = | Multiple Reference Frame |
| P | = | static pressure (Pa) |
| Q | = | volumetric flow rate (m3/s) |
| r | = | radial coordinate (m) |
| R | = | electric resistance (Ω) |
| S | = | source term in Equations 3 and 7 (W/m3) |
| T | = | temperature (K) |
| TI | = | turbulence intensity, |
| u, v | = | velocity (m/s) |
| um | = | mean velocity, Q/A (m/s) |
| U | = | nondimensional velocity, u/um |
| x, y | = | planar coordinates (m) |
| z | = | axial coordinate (m) |
| κ | = | thermal conductivity (W/m·K) |
| λ | = | electric current (A) |
| μ | = | absolute viscosity (Pa·s) |
| ω | = | angular velocity (rad/s) |
| ρ | = | density (kg/m3) |
| σ | = | standard deviation of errors |
| Θ | = | power dissipation (W) |
| Subscripts | = | |
| amb | = | ambient |
| f | = | fan |
| r | = | rotating reference frame |
Nomenclature
| A | = | area (m2) |
| cp | = | nondimensional pressure, |
| D | = | diameter (m) |
| eΔ | = | error |
| E | = | specific internal energy (m2/s2) |
| FAR | = | free flow area ratio (%) |
| h | = | enthalpy (J/kg·K) |
| I | = | unit tensor |
| k | = | turbulent kinetic energy (m2/s2) |
| LF | = | Lumped Fan |
| LFS | = | Lumped Fan with Swirl |
| MRF | = | Multiple Reference Frame |
| P | = | static pressure (Pa) |
| Q | = | volumetric flow rate (m3/s) |
| r | = | radial coordinate (m) |
| R | = | electric resistance (Ω) |
| S | = | source term in Equations 3 and 7 (W/m3) |
| T | = | temperature (K) |
| TI | = | turbulence intensity, |
| u, v | = | velocity (m/s) |
| um | = | mean velocity, Q/A (m/s) |
| U | = | nondimensional velocity, u/um |
| x, y | = | planar coordinates (m) |
| z | = | axial coordinate (m) |
| κ | = | thermal conductivity (W/m·K) |
| λ | = | electric current (A) |
| μ | = | absolute viscosity (Pa·s) |
| ω | = | angular velocity (rad/s) |
| ρ | = | density (kg/m3) |
| σ | = | standard deviation of errors |
| Θ | = | power dissipation (W) |
| Subscripts | = | |
| amb | = | ambient |
| f | = | fan |
| r | = | rotating reference frame |