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The influence of mean-free path in vapour, temperature and composition of liquid upon evaporation at nano and microscale
Principal Investigator: Daniel Jakubczyk, Ph.D., D.Sc., Eng.
Research project objectives
Mass and energy transport phenomena at the liquid–gas interface (e.g. evaporation) has been be-yond correct analytical description for more than 100 years (journal paper published together by IPC PAS and IP PAS [Rep. Prog. Phys., 76, 034601 (2013)] IF=14.937). Our collaborators from IPC PAS discovered that under low pressure, transport of heat to evaporating droplets is limited and additionally, a temperature drop appears on the phase boundary [Phys. Rev. Lett, 100, 055701 (2008)]. In IP PAS we have built unique scientific instruments to measure evaporation of freely suspended droplets of micrometric sizes [J. Phys. Chem. A, 112, 5152 (2008)]. Collaboration be-tween our research groups has already resulted in important publications, e.g. [Rep. Prog. Phys., 76, 034601 (2013)]. In our work [Soft Matter, 9, 7766 (2013)], we merged molecular dynamic (MD) computer simulations of the research group from IPC PAS with experimental results obtained from levitating microdroplets of water, glycols and glycerine performed at IP PAS, and we proposed an analytical equation describing evaporation of droplets. We tested it for 11 orders of magnitude in the time scale and 4 orders of magnitude in radius. Our description requires only two parame-ters: the first is related to temperature drop during evaporation, while the second is responsible for description of particles mean free path in vapour surrounding droplet. Given equation has been veri-fied experimentally for standard (room) temperature at atmospheric pressure. On the other hand, our partners from IPC PAS in their work [J. Chem. Phys., 130, 074707 (2009)] also investigated nu-merically the rules governing evaporation of liquids in vacuum. The goal of the current project is to describe quantitatively evaporation in the middle range of pressures, i.e. between atmospheric pres-sure and vacuum, and in large range of temperatures. We plan to change particles mean free path in vapour at least by 3 orders of magnitude (from ~70 nm at normal conditions up to ~100 μm) by decreasing the ambient pressure. We will also test the proposed description as a function of tem-perature from ~230 K to ~330 K (also in the vicinity of the triple point) and chemical composition of droplets. Necessary computer simulations will be carried out at IPC PAS as the complement to physical experiments of IP PAS.
In the physical experiment we will measure evolution of freely suspended, evaporating droplets with various volatility, molecular weight (glycerine, glycols, water) and composition under different temperature conditions, pressure and composition of ambient atmosphere. We will use the experimental setup presented in Figure beside. Droplet evolution will be precisely measured with methods based on the light scattering and electrostatic weighting developed at IP PAS. Scientific equipment built at IP PAS (see Figure) will be modified to conduct measurements under lower pressure and in vacuum. Additionally, surfaces of liquid will be analysed with dielectric and metallic inclusions. In that case, measurements will be performed for droplets of suspensions.
Research Project impact
Numerous physical phenomena at macroscale are governed by evaporation of liquids in gases at micro and nanoscales. For instance, evaporation of oceans is mainly caused by evaporation of droplets atomised by wind from water surface. 80-90% of water vapour (main contributor of the greenhouse effect) in atmosphere comes from the oceans. Therefore, understanding of evaporation processes is needed to develop multiscale models of weather and climate. Currently, several re-search groups are working on cooling of electronic microcircuits by spraying out droplets of liquids. Similarly, fuels are transported to combustion chamber of engines as microdroplets. Their evapora-tion absorbs significant part of heat released by fuel burning and ultimately this process is govern-ing engines’ efficiency.
Bibliography. Rep. Prog. Phys., vol. 76 (3), pp. 034601, 2013.
. Phys. Rev. Lett, 100, 055701 (2008).
. J. Phys. Chem. A, 112, 5152 (2008).
. Soft Matter, vol. 9, pp. 7766, 2013.
. J. Chem. Phys., 130, 074707 (2009).
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