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ABSTRACT
The present paper reports the thermal behavior of flat and curved surfaces with impinging jets employing circular and elliptical nozzle for identical equivalent diameter (de). Tests are performed with the Reynolds number varying from 11,250–22,500, varied range of plate to nozzle distance (z/d = 1–6), various nozzle aspect ratios (AR = 1–4). A comparison of thermal behavior between flat and concave surfaces (d/D = 0.05) is discussed in this study. The maximum enhancement in the stagnation Nusselt number found to be 27.4% and 24.8% with the increase in AR = 1 to 4 for flat surface, curved surface, respectively.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
| a | = | Major axis length of nozzle, mm |
| As | = | Surface area of test foil, m2 |
| b | = | Minor axis length of nozzle, mm |
| de | = | Equivalent diameter of the nozzle, mm |
| D | = | Test surface diameter, mm |
| I | = | Current passing through test foil, A |
| k | = | Thermal conductivity of cooling fluid (air), W m−1 K−1 |
| m | = | Mass flow rate of air, kg s−1 |
| Nu | = | Nusselt number |
| P | = | The pressure in airline, kg m−1 s−2 |
| Q | = | Flow rate of air, m3 s−1 |
| q”conv | = | Heat flux taken by the impinging jet, W m−2 |
| q”gen | = | Heat generated by the joule heating, W m−2 |
| q”loss | = | Heat loss from the surface, W m−2 |
| s | = | Distance in the circumferential direction, mm |
| t | = | Thickness of test surface, mm |
| Tamb | = | Ambient temperature, K |
| Taw | = | Adiabatic wall temperature, K |
| V | = | Voltage drops across the test foil, V |
| x | = | Distance in the longitudinal direction, mm |
| z | = | Nozzle to plate distance, mm |
| z/d | = | Non-dimensionless nozzle to plate distance |
| Greek Symbols | = | |
| ε | = | Emissivity of a test surface |
| μ | = | Dynamic viscosity of cooling fluid (air), Kg m−1 s−1 |
| ρ | = | Density of cooling fluid (air), kg m3 |
| Subscripts | = | |
| gen | = | Heat generation |
| loss | = | Heat loss |
| stag | = | Stagnation |
| sur | = | Surface |