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ABSTRACT
An experimental study on heat transfer characteristics of steam and air flows in a V-shaped ribbed channels was conducted. The effects of Reynolds numbers and rib angles on heat transfer of steam and air were obtained. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were 13.9%, 20.6%, 27.1%, and 27.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively. The correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air in V-shaped ribbed channels were developed.
Highlights
The heat transfer distributions of V-shaped rib-roughness channel cooled by superheated steam and air flows were experimentally investigated.
Influences of rib angle on heat transfer enhancement of V-shaped ribbed channel under steam and air cooling were both studied.
Advantage of steam cooling to air cooling in V-shaped ribbed channel with different rib angle was compared and analyzed.
Correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air cooling in V-shaped ribbed channels were developed.
Nomenclature
| A | = | area of the heat plate, m2 |
| AR | = | Aspect ratio of channel |
| Cp | = | specific heat at constant pressure |
| Dh | = | hydraulic diameter of the channel, mm |
| e | = | rib width and rib height, mm |
| e/Dh | = | relative rib height, |
| H | = | channel height, mm |
| h | = | heat transfer coefficient, W/m2/K |
| I | = | current provided by DC, A |
| L | = | length of the heat transfer surface, mm |
| Nu | = | Nusselt number |
| Nulocal | = | local Nusselt number |
| Nuave | = | area-averaged Nusselt number |
| P | = | rib pitch, mm |
| P/e | = | rib pitch-to-height ratio |
| Pr | = | Prandtl number |
| Qloss | = | heat loss dissipating to the environment, W |
| Qnet | = | heat flux provided by heat plate, W |
| QT | = | total heating power, W |
| Re | = | Reynolds number, based on hydraulic diameter of the channel |
| Tw | = | temperature on target plate, °K |
| Ts | = | temperature of the coolant in the channel, °K |
| Tin | = | temperature of the coolant at the inlet, °K |
| Tout | = | temperature of the coolant at the outlet, °K |
| U | = | voltage provided by DC, V |
| V | = | the flow velocity in the channel, m/s |
| W | = | channel width, mm |
Greek symbols
| α | = | rib angle, ° |
| λ | = | thermal conductivity, W/(m.K) |
| μ | = | dynamic viscocity, kg/(m.s) |
| ρ | = | density, kg/m3 |