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ABSTRACT
An experimental and numerical investigation is performed in order to determine the outcome of dimple geometries on the heat transfer and friction factor in a dimple cooling channel subjected to turbulent flow. Two geometries taken into consideration are spherical and inclined teardrop. In order to have a better comparison between the two different dimple channel, the dimple depth, total wetted area of dimple, and dimple pitch have been kept constant. In case of spherical and inclined teardrop dimple channels, heat transfer augmentation, friction losses, and flow pattern have been obtained for a Reynolds Number range from 14,000 to 65,000. The investigation shows that the dimple geometry has a significant contribution to increasing the heat transfer augmentation and determining the flow pattern. The inclined teardrop dimple arrangement shows the maximum heat transfer that is 17% higher than the spherical dimple channel, whereas inclined teardrop dimple results in the rise of friction factor of about 5.93–16.14% times as compared to the spherical dimple within the specified Reynolds number. The inclined teardrop and spherical dimple channel show the heat transfer enhancement of 2.74 to 3.20 times and 2.38 to 2.68 times than that of smooth channels provided thermal boundary conditions and flow conditions are kept same. The numerical study has been performed, which provided a detailed insight into the flow structures and vortex formations in spherical and inclined teardrop dimple channel.
Nomenclature
| d | = | Dimple print diameter |
| h | = | Dimple depth |
| Qair | = | Net Heating Power (W) |
| QTotal | = | Total Power |
| AW | = | Total Wetted area of dimple plate (m2) |
| h | = | Average Heat Transfer Coefficient(W/m2K) |
| Qloss | = | Heat loss (W) |
| Ts | = | Mean surface temperature |
| T∞ | = | Bulk mean temperature |
| VH | = | Voltage (V) |
| IH | = | Current drawn by the heater (A) |
| T∞,i | = | Inlet Air Temperature (K) |
| T∞,o | = | Outlet Air Temperature (K) |
| Nu | = | Average Nusselt Number of dimple channel |
| Dh | = | Channel Hydraulic Diameter (m) |
| k | = | Thermal Conductivity (W/mK) |
| f | = | Friction factor of dimple channel |
| f0 | = | Friction Factor for smooth channel |
| ΔP | = | Pressure drop across dimple test channel |
| ρ | = | Density of air (kg/m3) |
| = | Mean velocity (m/s) | |
| l | = | Length of test channel (m) |
| Re | = | Reynolds Number |
| Pr | = | Prandtl Number |
| Nu0 | = | Nusselt number in case of smooth channel |
| TP | = | Thermal Performance |
| e | = | Eccentricity of teardrop dimple |
| IT | = | Turbulence Intensity |