The Role of Pin Fin Array Configurations and Bubble Characteristics on the Pool Boiling Heat Transfer Enhancement
Abstract
:1. Introduction
2. Experimental Methodology
2.1. Experimental Facility
2.2. Test Samples
2.3. Experimental Procedures and Uncertainty Analysis
3. Results and Discussion
3.1. Boiling Curve and Regime
3.2. Heat Transfer and Bubble Characteristics
4. Conclusions
- The boiling phenomenon was observed to be in the three regimes: natural convection (Ts < Tsat), isolated bubble (0 K < Tsat < ~10 K), and merged bubble (Tsat > 10 K). Natural convection showed no bubble generation due to a lack of surface temperature. Both isolated and merged bubble regimes were within the category of nucleate boiling, but demonstrated a discrepancy in the bubble interaction before lift-off. Whilst the isolated bubble did not have any interaction among the bubbles, the merged bubble regime showed the merging process occurring on the hot surface.
- The boiling heat transfer coefficient increased as the fin gap rose. The enhancement was observed at 63.4% for the circular pin fin array, whilst the rectangular pin fin array demonstrated lower enhancement at around 17.8%. This indicates that the enhancement was more impactful in the circular pin fin, particularly at the gap between 1 mm and 1.5 mm. This discrepancy is due to the different active nucleation site densities between both shapes.
- Overall, the isolated bubble regime demonstrated better cooling performance than the merged bubble at around 56.31% and 62.31% for circular and rectangular pin fin arrays, respectively. This is due to the blanket of vapor built on the hot surface due to bubble merging. This blanket increased the thermal resistance, undermining the bubble dynamics enhancement observed in the isolated bubble regime.
- Visualization and dimensionless number demonstrated enhanced bubble dynamics as the pin fin gap rose. By increasing the gap between the fins, the buoyancy force increased whilst the flow resistance reduced. This allows the bubble to depart easier and, hence, increases the heat transfer coefficient.
- From the dimensionless number plots, it was found that the buoyancy force was more dominant than the viscous force (Gr > 1), while the Bo plot showed that the buoyancy force was more influential than the surface tension (Bo > 1). Both results indicated the priority in enhancement, whereby the buoyancy force had a strong correlation with the pin fin gap which constitutes the magnitude of characteristic length.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Nomenclature
A | Insulation layer surface area (m2) |
Af | Fin total area (mm2) |
Fin width (mm) | |
Bo | Bond number (dimensionless) |
Fin height (mm) | |
Fin gap (mm) | |
Ca | Capillary number (dimensionless) |
Specific heat of the liquid (kJ/kg∙K) | |
DB | Bubble departure diameter (m) |
Dh | Hydraulic diameter (mm) |
Bubble departure frequency (Hz) | |
Gr | Grashof number (dimensionless) |
g | Gravity (m/s2) |
Boiling heat transfer coefficient (kW/m2∙K) | |
Average boiling heat transfer coefficient (kW/m2∙K) | |
Enthalpy of vaporization (kJ/kg) | |
Thermal conductivity of the fluid (W/m∙K) | |
L | Wall thickness (m) |
Characteristic length (mm) | |
NA | Active nucleation site density (sites/m2) |
Wetted perimeter (m) | |
Net heat flux = (W/m2) | |
Convection heat flux (W/m2) | |
Evaporation heat flux (W/m2) | |
Heat input of cartridge heater (W/m2) | |
Heat loss through the heating base wall (W/m2) | |
Rewetting heat flux (W/m2) | |
Surface temperature (K) | |
Saturation temperature (K) | |
Thermal expansion coefficient (1/K) | |
Superheat temperature = (K) | |
σ | Surface tension (mN/m) |
Kinematic viscosity (m2/s) | |
Density of the liquid (kg/m3) | |
Density of the vapor (kg/m3) |
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Test Sample | Pin Fin Shape | Number of Fins | Fin Width (a), mm | Fin Height (b), mm | Fin Gap (c), mm | Dh, mm | Af, mm2 |
---|---|---|---|---|---|---|---|
C1 | Circular | 196 | 1 | 1 | 1 | 4.09 | 1516 |
C2 | Circular | 169 | 1 | 1.16 | 1.25 | 5.45 | 1516 |
C3 | Circular | 144 | 1 | 1.36 | 1.5 | 6.96 | 1516 |
R1 | Rectangular | 196 | 1 | 1 | 1 | 3 | 1684 |
R2 | Rectangular | 169 | 1 | 1.16 | 1.25 | 4.06 | 1684 |
R3 | Rectangular | 144 | 1 | 1.36 | 1.5 | 5.25 | 1684 |
Properties | Values |
---|---|
Boiling point (K) | 334.15 |
Vapor pressure (kPa) | 27 |
Specific heat (J/kg∙K) | 1170 |
Latent heat vaporization (kJ/kg) | 112 |
Thermal conductivity (W/m∙K) | 0.068 |
Liquid density (kg/m3) | 1418.64 |
Vapour density (kg/m3) | 0.98 |
Kinematic viscosity (m2/s) | 3.008 × 10−7 |
Surface tension (mN/m) | 13.6 |
Thermal expansion coefficient (1/K) | 1.8 × 10−3 |
Dielectric strength 0.1″ gap (kV) | 40 |
Pin Fin Shape | Fin Gap (c), mm | Maximum Gr, ×105 | Maximum Bo | Average kW/m2·K | Average | hb Enhancement |
---|---|---|---|---|---|---|
Circular | 1 | 2.83 | 17.08 | 13.76 | 1408.55 | - |
Circular | 1.25 | 6.16 | 30.24 | 15.18 | 1954.74 | 10.3% |
Circular | 1.5 | 8.56 | 49.39 | 22.50 | 2819.55 | 63.4% |
Rectangular | 1 | 0.70 | 9.18 | 23.40 | 607.26 | - |
Rectangular | 1.25 | 1.34 | 16.84 | 24.41 | 906.71 | 4.3% |
Rectangular | 1.5 | 2.95 | 28.12 | 27.56 | 1736.86 | 17.8% |
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Pranoto, I.; Rahman, M.A.; Waluyo, J. The Role of Pin Fin Array Configurations and Bubble Characteristics on the Pool Boiling Heat Transfer Enhancement. Fluids 2022, 7, 232. https://doi.org/10.3390/fluids7070232
Pranoto I, Rahman MA, Waluyo J. The Role of Pin Fin Array Configurations and Bubble Characteristics on the Pool Boiling Heat Transfer Enhancement. Fluids. 2022; 7(7):232. https://doi.org/10.3390/fluids7070232
Chicago/Turabian StylePranoto, Indro, Muhammad Aulia Rahman, and Joko Waluyo. 2022. "The Role of Pin Fin Array Configurations and Bubble Characteristics on the Pool Boiling Heat Transfer Enhancement" Fluids 7, no. 7: 232. https://doi.org/10.3390/fluids7070232