Nucleate pool boiling
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Nucleate Pool Boiling: Insights from Recent Research
Introduction to Nucleate Pool Boiling
Nucleate pool boiling is a heat transfer process where a heated surface is submerged in a liquid, causing the formation of vapor bubbles. This process is critical in various industrial applications, including power generation and cooling systems. Recent studies have explored different aspects of nucleate pool boiling, including surface structuring, fluid mixtures, and experimental conditions, to enhance heat transfer efficiency.
Surface Structuring and Heat Transfer Enhancement
Laser-Textured Surfaces
Research has shown that laser-textured surfaces significantly improve the heat transfer coefficient (HTC) in nucleate pool boiling. Experiments with saturated pure water and ethanol-water mixtures on laser-textured stainless-steel foils revealed that the HTC could be enhanced by up to 280% for pure water and 268% for pure ethanol, depending on the width of the laser patterns. The optimal enhancement for binary mixtures was achieved with 2.0-mm wide laser-textured regions, improving HTC by 235% and 279% for 0.4% and 4.2% ethanol-water mixtures, respectively.
Other Surface Structuring Methods
Other surface structuring methods, such as wire electrical discharge machining (WEDM) and etching, have also been investigated. These methods increase the nucleation site density (NSD) and modify the contact angle, leading to enhanced heat flux. For instance, surfaces structured by WEDM showed a 121% increase in HTC compared to plain surfaces, while etched surfaces showed a 37% increase. The highest performance was observed with a specific structured surface, which exhibited a 177% increase in HTC.
Copper-Diamond Textured Surfaces
Copper-diamond composite layers deposited by the Cold Spray technique have also been used to create textured surfaces. These surfaces support liquid wicking and exhibit mild hydrophobicity, resulting in a 300% increase in HTC and a 35% increase in critical heat flux (CHF). The capillary wicking effect at high heat fluxes plays a crucial role in these enhancements.
Fluid Mixtures and Boiling Behavior
Ethanol-Water Mixtures
The boiling behavior of ethanol-water mixtures has been extensively studied. The HTC enhancements for these mixtures depend on the concentration and the surface structuring. For example, laser-textured surfaces with specific pattern widths significantly improved the HTC for different ethanol-water mixtures.
Polymer Solutions
Aqueous solutions of hydroxyl ethyl cellulose (HEC) exhibit unique boiling characteristics due to their non-Newtonian, shear-thinning properties. At low heat fluxes, heat transfer is initially degraded but subsequently enhanced by up to 45% at higher heat fluxes. This behavior is influenced by changes in liquid-solid interface wetting, vapor-liquid interfacial tension, and the viscosity of the polymeric solutions.
Experimental Conditions and Boiling Dynamics
Pool Temperature Effects
Experiments with pure R113 under various pool conditions (subcooled, saturated, and superheated) have shown that bubble growth behavior and heat flow rates are significantly affected by the pool temperature. The bubble growth during different pool conditions can be characterized using dimensionless parameters and a modified Jakob number.
Microgravity Experiments
Nucleate pool boiling experiments conducted in microgravity on the International Space Station revealed that heat transfer coefficients and maximum heat fluxes are lower than those under normal gravity conditions. The presence of a large vapor bubble acting as a sink plays a crucial role in the boiling dynamics in microgravity.
Conclusion
Recent research on nucleate pool boiling has highlighted the importance of surface structuring and fluid properties in enhancing heat transfer efficiency. Laser-textured surfaces, WEDM, and etching methods have shown significant improvements in HTC and CHF. Additionally, the boiling behavior of fluid mixtures and the effects of experimental conditions, such as pool temperature and gravity, provide valuable insights for optimizing boiling processes in various applications.
Sources and full results
Most relevant research papers on this topic
Investigation of Nucleate Pool Boiling of Saturated Pure Liquids and Ethanol-Water Mixtures on Smooth and Laser-Textured Surfaces
Experimental and semi-analytical investigation of heat transfer in nucleate pool boiling by considering surface structuring methods
An experimental investigation of nucleate pool boiling in aqueous solutions of a polymer
Enhanced nucleate pool boiling on copper-diamond textured surfaces
A depletable micro-layer model for nucleate pool boiling
Pool boiling—binary liquid mixtures
Nucleate and transition boiling heat transfer under pool and external flow conditions
Experimental study of pool temperature effects on nucleate pool boiling
Stability of nucleation sites in pool boiling
Nucleate Pool Boiling eXperiment (NPBX) in microgravity: International Space Station
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