61 research outputs found
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
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
A Review of the Criteria and Methods of Reverse Logistics Supplier Selection
This article presents a literature review on reverse logistics (RL) supplier selection in terms of criteria and methods. A systematic view of past work published between 2008 and 2020 on Web of Science (WOS) databases is provided by reviewing, categorizing, and analyzing relevant papers. Based on the analyses of 41 articles, we propose a three-stage typology of decision-making frameworks to understanding RL supplier selection, including (a) establishment of the selection criteria; (b) calculation of the relative weights and ranking of the selection criteria; (c) ranking of alternatives (suppliers). The main discoveries of this review are as follows. (1) Attention to the field of RL supplier selection is increasing, as evidenced by the increasing number of papers in the field. With the adaption of circular economy legislation and the need resource and business resilience, it is expected that RL and RL supplier selection will be a hot topic in the near future. (2) A large number of papers take “sustainability” as the theoretical approach to carry out research and use it as the basis for determining the criteria. (3) Multi-criteria decision making (MCDM) methods have been widely used in RL supplier selection and have been constantly innovated. (4) Artificial intelligence methods are also gradually being applied. Finally, gaps in the literature are identified to provide directions for future research. (5) Value-added service is underrepresented in the current study and needs further attention
GENerator of reduced Organic Aerosol mechanism (GENOA v1.0): An automatic generation tool of semi-explicit mechanisms
This paper describes the GENerator of Reduced Organic Aerosol Mechanisms (GENOA) that produces semi-explicit mechanisms for simulating the formation and evolution of secondary organic aerosol (SOA) in air-quality models. Using a series of predefined reduction strategies and evaluation criteria, GENOA trains and reduces SOA mechanisms from explicit chemical mechanisms (e.g., the master chemical mechanism (MCM)) under representative atmospheric conditions. As a consequence, these trained SOA mechanisms can preserve the accuracy of explicit VOC mechanisms on SOA formation (e.g., molecular structures of crucial compounds, the effect of non-ideality and hydrophilic/hydrophobic partitioning of aerosols), with a size (in terms of reaction and species numbers) that is manageable for three-dimensional aerosol modeling (e.g., regional chemical transport models). Applied to the degradation of a sesquiterpene (β-caryophyllene) from MCM, GENOA builds a concise SOA mechanism (2 % of the MCM size), consisting of 23 reactions and 15 species, six of them being condensable. The generated SOA mechanism has been evaluated for its ability to reproduce SOA concentrations under varying atmospheric conditions encountered over Europe, with an average error lower than 3 %.</p
Coalescence of immiscible sessile droplets on a partial wetting surface
Droplet coalescence is a common phenomenon and plays an important role in
multi-disciplinary applications. Previous studies mainly consider the
coalescence of miscible liquid, even though the coalescence of immiscible
droplets on a solid surface is a common process. In this study, we explore the
coalescence of two immiscible droplets on a partial wetting surface
experimentally and theoretically. We find that the coalescence process can be
divided into three stages based on the timescales and force interactions
involved, namely (I) the growth of the liquid bridge, (II) the oscillation of
the coalescing sessile droplet, and (III) the formation of a partially-engulfed
compound sessile droplet and the subsequent retraction. In stage I, the
immiscible interface is found not to affect the scaling of the temporal
evolution of the liquid bridge, which follows the same 2/3 power law as that of
miscible droplets. In Stage II, by developing a new capillary timescale
considering both surface and interfacial tensions, we show that the interfacial
tension between the two immiscible liquids functions as a nonnegligible
resistance to the oscillation which decreases the oscillation periods. In Stage
III, a modified Ohnesorge number is developed to characterize the
visco-capillary and inertia-capillary timescales involved during the
displacement of water by oil; a new model based on energy balance is proposed
to analyze the maximum retraction velocity, highlighting that the viscous
resistance is concentrated in a region close to the contact line.Comment: 20 pages, 9 figure
An Integrated Multicriteria Decision-Making Approach for Collection Modes Selection in Remanufacturing Reverse Logistics
Reverse logistics (RL) is closely related to remanufacturing and could have a profound impact on the remanufacturing industry. Different from sustainable development which is focused on economy, environment and society, circular economy (CE) puts forward more requirements on the circularity and resource efficiency of manufacturing industry. In order to select the best reverse logistics provider for remanufacturing, a multicriteria decision-making (MCDM) method considering the circular economy is proposed. In this article, a circularity dimension is included in the evaluation criteria. Then, analytic hierarchy process (AHP) is used to calculate the global weights of each criterion, which are used as the parameters in selecting RL providers. Finally, technique for order of preference by similarity to ideal solution (TOPSIS) is applied to rank reverse logistics providers with three different modes. A medium-sized engine manufacturer in China is taken as a case study to validate the applicability and effectiveness of the proposed framework
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