380 research outputs found
Melting process of frozen sessile droplets on superhydrophobic surfaces
Superhydrophobic surfaces can exhibit icephobicity in many ways due to their
large contact angles and small rolling angles. The melting process of frozen
droplets on superhydrophobic surfaces is still unclear, hindering the
understanding of surface icephobicity. In this experimental study of the
melting process of frozen sessile droplets on superhydrophobic surfaces, we
find two types of melting morphologies with opposite vortex directions on a
single-scale nano-structured (SN) superhydrophobic substrate and a
hierarchical-scale micro-nano-structured (HMN) superhydrophobic substrate.
Melting pattern visualizations and flow field measurements showwed Marangoni
convection and natural convection occuring in the melting sessile droplets. For
the HMN superhydrophobic substrate, the internal flow was found to be dominated
by Marangoni convection due to the temperature gradient along the surface of
the droplet. For the SN superhydrophobic substrate, Marangoni convection was
inhibited by the superhydrophobic particles at the surface of the droplet,
which were shed from the fragile superhydrophobic substrate during the
freezing--melting process, as confirmed by surface characterizations of the
substrate and flow measurements of a water pool. These results will help
researchers better understand the melting process of frozen droplets and in
designing novel icephobic surfaces for numerous applications.Comment: 31 pages, 12 figure
Breakup of particle-laden droplets in airflow
The atomisation of suspension containing liquid and dispersed particles is
prevalent in many applications. Previous studies of droplet breakup mainly
focused on homogeneous fluids, and the heterogeneous effect of particles on the
breakup progress is unclear. In this study, the breakup of particle-laden
droplets in airflow is investigated experimentally. Combining synchronised
high-speed images from the side view and the 45 view, we compare the
morphology of particle-laden droplets with that of homogeneous fluids in
different breakup modes. The results show that the higher effective viscosity
of particle-laden droplets affects the initial deformation, and the
heterogeneous effect of particles appears in the later breakup stage. To
evaluate the heterogeneous effect of particles quantitatively, we eliminate the
effect of the higher effective viscosity of particle-laden droplets by
comparing cases corresponding to the same inviscid Weber number. The
quantitative comparison reveals that the heterogeneous effect of particles
accelerates the fragmentation of liquid film and promotes localised rapid
piercing. A correlation length that depends on the particle diameter and the
volume fraction is proposed to characterise the length scale of the
concentration fluctuation under the combined effect of the initial flattening
and later stretching during the droplet breakup process. Based on this
correlation length, the fragment size distributions are analysed, and the
scaling results agree well with the experimental data.Comment: 29 pages, 19 figure
Benefits and Cost-effectiveness Analysis of Exhaust Energy Recovery System Using Low and High Boiling Temperature Working Fluids in Rankine Cycle
AbstractIn this paper, six attactive working fluids, including low boiling refrigerants such as R123, R141b and R245fa (Group L) and high boiling substances such as cyclohexane, ethanal and water (Group H), are applied on Rankine cycle, in order to examine the potential of these two categories of working fluids in high temperature exhaust energy recovery system (EERs) from a gasoline engine. The influences of engine speed at full load and evaporating pressure on the EERs performances are analyzed. The results reveal that water in Group H and R141b in Group L contribute the peak improvement in system benefits, while fluids in Group H show better cost-effectiveness. The EERs performances would be influenced strongly by evaporating pressure at high engine speed, while it also requires high pressure to enhance the performances at low speed. Besides, when the evaporating pressure is low, selection of working fluid should be emphasized
- β¦