The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.

The growth of vapor bubbles in superheated liquids. report no. 26-6

Review of pool boiling enhancement by surface modification

Pool boiling and flow boiling on micro- and nanostructured surfaces

Effect of surface roughness on pool boiling heat transfer at a heated surface having moderate wettability

https://dr.ntu.edu.sg/bitstream/10356/146092/2/Manuscript%20-%20Saturated%20pool%20boiling%20of%20FC-72%20from%20enhanced%20surfaces%20produced%20by%20selective%20laser%20melting.pdf

Saturated pool boiling of FC-72 from enhanced surfaces produced by Selective Laser Melting

Pool boiling has been proven as a very effective process for heat transfer in cooling applications. Surface wettability plays a vital role in pool boiling heat transfer.

/pdf/bubble-dynamics-and-heat-transfer-on-biphilic-surfaces-4hw9hh1jdb.pdf

Bubble dynamics and heat transfer on biphilic surfaces

On the process of bubble growing and departure on hydrophilic, superhydrophobic and biphilic surfaces

The present work introduces an alternative approach which combines heat transfer measurements, high speed visualization and PIV to infer on the effect of surface micro-structuring in the various heat transfer parcels. The PIV provides particularly interesting information on the bubbles vertical velocity, allowing to infer how the microstructures affect the bulk induced flow. The micro-patterns are composed by arrays of cavities with fixed shape and depth, only varying the distance between cavities, S. The results confirm the importance of enhancing the pool boiling performance, by promoting the increase of the bubble frequency and active nucleation sites density with micro-patterned surfaces. The role of the patterns is different, depending on the properties of the fluids. Hence, for liquids with very high latent heat of evaporation and surface tension, the parcel of heat transfer related to the phase change is very important. Based on the force balance on the departing bubbles, it is evident that in this case the micro-patterns will mainly affect the bubble coalescence, which may lead to steep deterioration of the heat transfer coefficient. On the other hand, for liquids with lower thermal properties (and lower surface tension) the micro-patterns play an important role in increasing and stabilizing the vertical velocity of the bubbles, thus favoring a very efficient boiling performance, with high boiling frequencies and large active nucleation sites density. This role of the micro-patterned surfaces is well captured by the representation proposed here, which relates the heat transfer coefficient with the distance between micro-patterns S, made dimensionless by the characteristic dimension (Lc=(?lv/(?l-?v))1/2). This representation actually shows the best performance of the HFE7000 in comparison to that of ethanol, when the micro-patterned surfaces are used, despite the lower thermal properties of HFE7000. This trend was confirmed experimentally in our measurements.

/pdf/evaluation-of-pool-boiling-heat-transfer-over-micro-1krjsrdsew.pdf

Evaluation of pool boiling heat transfer over micro-structured surfaces by combining high-speed visualization and PIV measurements

Effect of wettability on nucleate boiling

The present paper addresses the quantification of the various terms of the pool boiling heat transfer over microstructured surfaces. The micro-structures are composed by regular patterns of quadrangular cavities, with fixed sizes, where only the distance between the center of the cavities, S is varied. The surfaces are made from silicon wafers. The wettability of the surfaces, quantified by the contact angles is not dramatically changed during the structuring process. The independent data required for bubble nucleation and heat transfer characterization are collected coupling high speed camera visualization, PIV (Particle Image Velocimetry) and heat flux/surface temperature measurements. The results confirm the relative importance of the induced bulk convection, particularly in the boiling of liquids with smaller values of the latent heat of evaporation (e.g. refrigerants). In this context, a more detailed characterization of the flow and of the bubble dynamics is presented. Based on this characterization, an alternative approach is suggested to correlate the experimental data with a modified Rohsenow formulation, using a characteristic bubbles’ velocity to compute the Reynolds and the Stanton number, both associated to the bubble detachment and motion in bulk induced convection. Despite the devised relations still have an empirical nature, the work is in progress towards a more mechanistic and objective approach.

/pdf/study-of-the-combined-effects-of-liquid-properties-and-goccc6gw4q.pdf

E. Teodori

Papers

Bubble dynamics and heat transfer on biphilic surfaces

On the process of bubble growing and departure on hydrophilic, superhydrophobic and biphilic surfaces

Evaluation of pool boiling heat transfer over micro-structured surfaces by combining high-speed visualization and PIV measurements

Effect of wettability on nucleate boiling

Study of the Combined Effects of Liquid Properties and Surface Micro-Patterning on Pool Boiling Heat Transfer