Imperial College London
Portrait Picture

Dr Giovanni Giustini

Faculty of Engineering, Department of Mechanical Engineering

Honorary Lecturer
 
 
 
//

Contact

 

+44 (0)20 7594 9681g.giustini12 Website

 
 
//

Location

 

City and Guilds BuildingSouth Kensington Campus

//

Summary

 

Publications

Citation

BibTex format

@article{Ardron:2021:10.1063/5.0069686,
author = {Ardron, K and Giustini, G},
doi = {10.1063/5.0069686},
journal = {Physics of Fluids},
pages = {1--10},
title = {On the wetting behavior of surfaces in boiling},
url = {http://dx.doi.org/10.1063/5.0069686},
volume = {33},
year = {2021}
}
Download

RIS format (EndNote, RefMan)

TY  - JOUR
AB  - Nucleate boiling heat transfer is strongly influenced by surface wettability as characterized by the Young's contact angle, . The contact angle is usually obtained from measurements on sessile droplets on horizontal test surfaces, but in the case of water at high temperatures and pressures,  values from droplet experiments appear to be typically 30°–50° higher than values needed to explain bubble departure sizes for similar surfaces and temperatures. We explain the differences between  values for droplets and vapor bubbles by using the surface adsorption theory of Adamson. This theory suggests that in the case of bubble formation in high pressure boiling, as the non-wetted surface inside the bubble is in contact with a saturated vapor, it will be covered by an adsorbed liquid layer of nanoscale thickness. Droplet experiments, on the other hand, generally use autoclaves pressurized by permanent gases in which the vapor pressure is far below saturation: in these relatively dry gases, the adsorbed liquid nanolayer is expected to be absent. We suggest that the presence of the adsorbed layer in the case of vapor bubbles will increase the work of formation of a new wetted surface by an amount comparable to the liquid surface tension, resulting in a significant reduction in . We show that by applying Adamson's model with plausible choices for unknown parameters, it is possible to explain the magnitude of the differences in  in bubble and droplet experiments and to explain why  appears much less sensitive to surface material conditions in the case of departing vapor bubbles than in the case of sessile droplets. We conclude that  measurements for sessile droplets on heated surfaces in pressurized gas rather than saturated vapor environments may not be relevant to vapor bubbles and values should not be used directly in models of nucleate boiling.
AU  - Ardron,K
AU  - Giustini,G
DO  - 10.1063/5.0069686
EP  - 10
PY  - 2021///
SN  - 1070-6631
SP  - 1
TI  - On the wetting behavior of surfaces in boiling
T2  - Physics of Fluids
UR  - http://dx.doi.org/10.1063/5.0069686
UR  - https://doi.org/10.1063/5.0069686
UR  - http://hdl.handle.net/10044/1/92764
VL  - 33
ER  -
Download