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ABSTRACT
In this study, the effect of both hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) into the rectangular channel on heat transfer augmentation, Nusselt number and friction factor were experimentally investigated. In planning of the experiments, different Reynolds number, pin fin array, pin fin geometry and the ratio of the distance between pin fin spacing (s) to the pin fin hydraulic diameter (s/Dh) were chosen as the design parameters. Air was used as the fluid. The Reynolds number, based on the channel hydraulic diameter of the rectangular channel, was varied from 3188 to 19531. In the experiments, the heating plate was made of stainless steel foil. The foil was electrically heated by means of a high current DC power supply to provide a constantly heated flux surface. The heat transfer results were obtained using the infrared thermal imaging technique. The heat transfer results of the hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) are compared with those of a smooth plate. Best heat transfer performance was obtained with the hexagonal pin fins. The maximum thermal performance factor ((Ƞ), was obtained as Re = 3188, staggered array, s/Dh = 0, Ƞ = 2.28.
Nomenclature
| A | = | Total area, m2 |
| Dhe | = | Channel hydraulic diameter, m |
| Dh | = | Pin fin width, m |
| Df | = | Pin fin diameter, m |
| f | = | Friction factor (–) |
| h | = | Average heat transfer coefficient, W/m2K |
| h0 | = | Average heat transfer coefficient in smooth channel, W/m2K |
| H | = | Pin fin and channel height, m |
| I | = | Current, A |
| k | = | Thermal conductivity (W/m K) |
| L | = | Length of test section, m |
| Nu | = | Nusselt number, (-) |
| Nuavg. | = | Average Nusselt number, (-) |
| ΔP | = | Pressure drop (Pa) |
| Pr | = | Prandtl number (-) |
| T | = | Temperature (K) |
| Q | = | Heat transfer rate, W |
| qr | = | Radiation heat flux, W/m2 |
| Re | = | Reynolds number, (-) |
| Sx | = | Span-wise spacing (center to center) |
| Sz | = | Stream-wise spacing (center to center) |
| s | = | Distance between pin fin spacing, (m) |
| t | = | Thickness of the stainless steel foil, m |
| u | = | Mean velocity, m/s |
| V | = | Voltage, V |
| W | = | Channel width, m |
| x/Dh | = | Dimensionless distance along the stream-wise, (-) |
| y/Dh | = | Dimensionless distance along span-wise, (-) |
Greek symbols
| Ƞ | = | Thermal enhancement factor, (-) |
| v | = | Kinematic viscosity, m2/s |
| ϼ | = | Density, kg/m3 |
| ε | = | Emissivity |
| µ | = | Dynamic viscosity, kg/ms |
| f | = | Friction factor, (-) |
Abbreviations
| CPFs | = | Cylindrical pin fins |
| HPFs | = | Hexagonal pin fins |
| in | = | Inlet |
| out | = | Outlet |
| pp | = | Pumping power |
Acknowledgments
Financial support of this study by the research fund of the Hitit University under Grant No. MUH19003.14.001 is gratefully acknowledged.