Droplet Evaporation Research Articles

Physics-based reduced-order modeling of flash-boiling sprays in the context of internal combustion engines

Flash-boiling injection is one of the most effective ways to accomplish improved atomization compared to the high-pressure injection strategy. The tiny droplets formed via flash-boiling lead to fast fuel–air mixing and can subsequently improve combustion performance in engines. While most of the previous studies related to the topic focused on modeling flash-boiling sprays using three-dimensional (3D) computational fluid dynamics (CFD) techniques such as direct numerical simulations (DNS), large-eddy simulations (LES), and Reynolds-averaged Navier–Stokes (RANS) simulations, the present work introduces a reduced-order cross-sectionally averaged spray (CAS) model with significantly reduced computational cost. The proposed CAS model incorporates several physical submodels in flash-boiling sprays such as those for air entrainment, drag, superheated droplet evaporation, flash-boiling induced breakup, and aerodynamic breakup models. The CAS model is then applied to different fuels to investigate macroscopic spray characteristics such as liquid and vapor penetration lengths under flash-boiling conditions. It is found that the newly developed CAS model captures the trends in global flash-boiling spray characteristics reasonably well for different operating conditions and fuels. Moreover, the CAS model is shown to be faster by up to four orders of magnitude compared with simulations of 3D flash-boiling sprays. The novelty of the present work lies in providing a reduced-order flash-boiling spray model that offers cost-effective computational representations of complex phenomena. The proposed model can be very valuable for applications, such as experimental design, fuel screening, and creating digital twins, thus playing a crucial role in the advancement of research and development in the field of spray combustion.

Enhanced controllability of droplet evaporation via DC electric field

To enhance the controllability of droplet evaporation, this study introduces a system that integrates an electric field with a temperature field. In addition, lattice Boltzmann method (LBM) simulations were performed to examine the flow field and heat transfer within the droplet, confirming the mechanism of evaporation rate transition. The impacts of the electric field on droplet evaporation and the characteristics of heat and mass transfer were thoroughly investigated through experimental, theoretical and numerical approaches. The findings indicate that elevating the substrate temperature and intensifying the electric field can modify the evaporation rate of droplets via distinct mechanisms: the temperature field governs droplet evaporation by increasing the heat flux and changing droplet surface tension, whereas the electric field predominantly enhances or inhibits droplet evaporation by affecting the droplet’s surface tension and deformation. According to the Rayleigh limit, charge accumulation reduces the droplet’s surface tension, thereby accelerating evaporation. Conversely, greater deformation resulting from a stronger electric field increases the thermal resistance of the droplet, which dampens heat transfer and inhibits droplet evaporation. Furthermore, an excessive electric field may induce oscillation or droplet breakup. Simulations of droplet evaporation under an electric field further revealed that an increased electric field significantly influences the internal flow of the droplet. A low Peclet (Pe) number suggests that internal flow has a negligible effect on the temperature distribution compared to the impact of heat conduction. This research provides critical insights into the precise manipulation of droplet evaporation.

Numerical investigation on heat transfer and vapour layer geometry of a droplet impacting on a spherical particle in Leidenfrost regime

Understanding the heat transfer mechanism and dynamic behaviors of droplet-particle collision in Leidenfrost regime is essential for the pyrohydrolysis process of pickling liquor, which is sprayed into a fluidized bed and then decomposes to oxides and acid vapour. In this study, the droplet deformation, heat transfer characteristics and vapour layer geometry of Leidenfrost droplet impacting spherical particle are investigated by constructing a microscale phase change model in VOF framework. The applicability of the computational model in capturing droplet dynamics and thermodynamics is verified by comparing it with experimental outcomes. The results indicate that the vapour layer geometry is relatively uniform in spreading but shows instability in recoiling. The vapour layer thickness increases rapidly in both spreading and early recoiling, while decreases in the late recoiling phase. Furthermore, the heat transfer and droplet evaporation depend on the vapour layer thickness strongly. Specifically, the thinner the vapour layer, the lower the heat transfer resistance. The increasing surface temperature, We and Re can effectively enhance heat transfer and raise droplet temperature. In addition, the maximum spreading factor and liquid–solid contact time play an important role in heat transfer and they both show a clear power-law dependency on We and Re for viscous droplets. The effect of droplet size on contact time is consistent with first-order vibration theory but the contact time is independent of surface temperature and impact velocity.

Deconstructing plasma fog collection technology: an experimental study on factors impacting collection efficiency

Water scarcity is a global challenge that hinders human development. In recent years, electrostatic fog collection technology has emerged as a promising technology to alleviate this issue. Although electrostatic fog collectors based on a variety of electrode structures have been developed previously, there has been less research into other factors affecting the efficiency of electrostatic fog collection (e.g. electrical factors, environmental factors, etc), which has delayed the commercial application of the technology. In this paper, we experimentally investigate the effects of power supply polarity, voltage, airflow direction, airflow velocity, fog concentration and temperature on collection efficiency using a typical wire-mesh electrode fog collector as an example. The results show that both electrical and environmental factors influence the collection efficiency by changing the charge and the electric field force of the droplets. Negative polarity corona and high voltage are more favorable for fog collection. High velocity airflow and high fog concentration increase the amount of water collected due to the ability to bring more droplets into the electric field. However, the collection efficiency is reduced by the weakening of the corona discharge. High temperature accelerates the evaporation of fog droplets, which is not favorable for fog collection. In conclusion, this work will not only contribute to revealing the underlying mechanisms of the electrostatic fog collection but also will guide the development of highly efficient fog collectors.

Multi-component precursor droplet evaporation in spray synthesis of cathode materials

Spray synthesis methods are highly attractive for manufacturing materials for energy storage and conversion owing to their scalability and controllability. The key to achieving high controllability in spray synthesis is understanding the complex relationship between the precursor spray droplet evaporation process and the final product structure. Although several studies on precursor droplet evaporation have been reported, very few consider multi-component droplets, which are relevant in practical applications. In this study, we analysed the evaporation of multi-component single precursor droplets used in flame-assisted spray pyrolysis (FASP) of Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode materials. The product particles of FASP were characterized using SEM, EDS and EELS to determine the structure and morphology of particles obtained from precursors with and without urea additives. The qualitative and quantitative changes during evaporation were analysed using high-speed visualization of suspended single droplets on cross-wires. An in-house developed numerical model was used to track the trajectory of the solutes within the evaporating droplet and elucidate the connection between the evaporation process and the final product structure. It was found that evaporating droplets with multiple precursor solutes (Li, Ni, Co, and Mn) formed product particles with gradient element distribution in the radial direction. However, the addition of a small amount of urea (2.5 wt%) caused significant disturbances in the droplet evaporation process triggered by the urea decomposition reaction leading to uniformly distributed elements in the final product particle. The study contributes towards enhancing fundamental knowledge on multi-component droplet evaporation leading to improved design of spray drying and synthesis processes.

Influence of the Droplet Diameter on Compressor Rotor Performance under Constant Humidification

Aiming at the near-clogging boundary condition of a certain type of transonic compressor rotor, a numerical simulation method is used to systematically study the influence of different droplet diameters on its performance under the condition of moisture content of 3%. The results show that humidifying the intake air of the transonic compressor near the blockage boundary can reduce the exhaust temperature, the mass flow rate, and the total pressure ratio. In the axial direction, the mass fraction of water vapor increases slowly and linearly under the large droplet condition, while the mass fraction of water vapor under the medium and the small droplet conditions presents a two-stage parabolic growth. The mass fraction of water vapor under the three conditions increases by 0.002, 0.0055, and 0.0072 from inlet to outlet, respectively. On the radial section with the axial span = 0.7, the difference in water vapor mass fraction between the shroud and the hub under the small droplet condition is 0.00329, and that under the medium and the large droplet condition are 46.81% and 27.96% of the small droplet condition. The research results can provide theoretical guidance for the analysis of droplet evaporation at different positions in compressor near-plugging conditions.

A new experimental set-up for aerosol stability investigations in microgravity conditions

The temporal and spatial evolution of dispersed media is a fundamental problem in a wide range of physicochemical systems, such as emulsions, suspensions and aerosols. These systems are multiphasic and involve compounds of different densities. They are therefore subject to the influence of gravity which determines the sedimentation rate of their dispersed phase. This effect can be dominant and prevent a detailed study of the phenomena occurring between the constituents themselves, such as the coalescence of drops in emulsions, the evaporation of droplets or the flocculation in suspensions. In this context, the Centre National d’Etudes Spatiales (CNES) has recently supported the development of a new instrument to produce populations of droplets, a few micrometers in radius, under controlled conditions with the objective of allowing a detailed study of their properties in microgravity conditions. The principle of this instrument is to generate, by a fast compression/expansion of air, populations of water droplets and to track their evolution by optical scanning tomography in transmission mode within a volume of approximately 2 mm 3 . Parabolic flight experiments have shown the possibility to generate and accurately follow the evolution of populations of several hundred droplets for more than 20 s. The first experimental results show that it is possible to study their evaporation kinetics or their motion when imposing von Karman swirling flows. This work is part of the AEROSOL project of DECLIC-EVO supported by CNES and aims to help the understanding of cloud microphysics which remains a critical open problem in the context of global warming.

Droplet-based assembly of magnetic superballs

The self-assembly of materials driven by the inherent directionality of the constituent particles is of both practical and fundamental interest because it enables the fabrication of complex and hierarchical structures with tailored functionalities. By employing evaporation assisted self-assembly, we form opal-like structures with micro-sized magnetic superball particles. We study the structure formation of different superball shapes during evaporation of a dispersion droplet with in-situ small angle x-ray scattering with microradian resolution in the absence and presence of an external magnetic field. In the absence of a magnetic field, strong shape-dependent structures form as the water evaporates from the system. Applying a magnetic field to the droplet has a unique effect on the system; strong magnetic fields inhibit the growth of well-ordered assemblies due to the formation of out-of-equilibrium dipolar structures while lower magnetic fields allow particles to rearrange and orient without inhibition. In this work, we show how the superball assembly inside a droplet can be controlled by the magnetic field strength and the superball shape. The tunability of these parameters not only enables the controllable formation of macroscopic colloidal assemblies but also opens up possibilities for the development of functional materials with tailored properties on a macro-scale.

Heat and Mass Transfer Processes and Evaporation of a Liquid Droplet on a Structured Surface

The characteristics of water droplet heating and evaporation on structured hydrophobic and hydrophilic surfaces in the range of static contact angles from 73° to 155° were studied experimentally using high-speed video recording. Two fundamentally different technologies for applying coatings on a metal surface were used in comparison with the results on a polished surface. Microscopic studies were conducted to identify the features of the formed coatings. The wetting properties were characterized by means of the static contact angle and the contact angle hysteresis: on polished surface No. 1 (contact angle—73°, hysteresis—11°), on structured surface No. 2 (contact angle—125°, hysteresis—9°), and on structured surface No 3 (contact angle—155°, hysteresis—7°). The experimental dependences of the droplet evaporation rate on the different surfaces under normal conditions (ambient air temperature—293 K, atmospheric pressure, humidity—35%) were obtained. The evaporation regimes of droplets on the surfaces under study were identified. Water droplets evaporated in the pinning mode on surfaces No. 1 and No. 2. When a water droplet evaporated on surface No 3, the droplet was in the constant contact angle regime for ≈90% of its lifetime. Based on the experimental data obtained, a two-dimensional model of conjugate heat and mass transfer was developed, which describes the heating and evaporation of a liquid droplet on structured hydrophobic and hydrophilic surfaces at a wide range of contact angles. Satisfactory agreement was obtained between the numerical simulation results and experimental data. Using the model, the fields of temperature, concentration and other key characteristics were established at different points in time. Recommendations for its application in the development of gas–vapor–droplet applications were formulated.

Evaporation of Leidenfrost droplets on microtextured substrates

A thin thermally insulating vapor layer beneath a levitating Leidenfrost droplet adversely affects the heat transfer from the underlying hot substrate during cooling applications. In this work, we present a theoretical model to determine the total heat transfer to a Leidenfrost droplet on microtextured substrates, taking into account the curved shape of the liquid-vapor interface. The profile of the vapor gap and vapor flow field beneath a Leidenfrost droplet on a microtextured surface is shown to be dependent on the substrate morphology. The shape of the liquid-vapor interface beneath the Leidenfrost droplet, in turn, influences the rate of evaporation on a microtextured substrate. We determine the variation of the minimum and maximum vapor gap over micro-pillared surfaces with different substrate permeability for various droplet volumes and wall superheat. The heat transferred to the droplet is via conduction across the vapor gap beneath the droplet and convection from the ambient air around the droplet. We determine the total evaporation time of a Leidenfrost droplet over a micro-textured substrate using the curved interface model and the conventional flat vapor gap interface model and compare with that obtained from experiments. The overprediction of the average rate of evaporation of a Leidenfrost droplet by the flat interface model ranges from ∼59 % for tall and sparse pillars (marked by high substrate permeability) to ∼ 29 % for short pillars (with low substrate permeability). We show that the average rate of evaporation of the LF droplet obtained using the curved interface model agrees reasonably (within 9%–23 %) with that observed in the experiments.

Novel cellulose nanocrystal/metal-organic framework composites: Transforming ASA-sized cellulose paper for innovative food packaging solutions

In this study, a novel cellulose nanocrystal/metal-organic framework composite (MC) was developed as a stabilizer for alkenyl succinic anhydride (ASA) Pickering emulsions, demonstrating remarkable sizing performance and antimicrobial properties for advanced food packaging applications. The MCs exhibited superior emulsion stabilization capabilities compared to pure metal-organic frameworks, with the optimum MC concentration identified as 1.0 wt% CNC. The hydrophobicity of the sizing paper was found to be enhanced with increasing CNC content. The MC-ASA sized paper demonstrated commendable storage stability, robust gas adsorption, and resistance to water vapor or water droplets. The MCs-ASA sized paper showed excellent food preservation efficacy, maintaining the freshness of strawberries for up to seven days, compared to ASA-sized paper without MCs. The antimicrobial assays targeting Escherichia coli and Staphylococcus aureus highlighted the intrinsic antimicrobial properties of the MCs, contributing to the extended freshness of the encased strawberries. The water vapor barrier efficacy and water retention capabilities of MCs-ASA sized paper were found to be superior to those of the paper without MCs, emphasizing the potential of the developed composite as an innovative and effective food packaging solution. This study offers valuable insights into the synthesis and implementation of CNC/MOF composite particles for versatile applications in food packaging, water-resistant materials, and environmental protection.

The effects of aerosol concentration on the evolution, transport, and deposition of hygroscopic droplets in the highly idealized MT model: A numerical study

Inhalation therapy is widely used to treat various respiratory diseases. Nebulizers have been widely adopted due to their ease of operation, high drug delivery efficiency, and low residual volume. Traditional studies on drug delivery in the respiratory tract typically use a one-way coupled method to track drug transport and deposition for non-hygroscopic drug particles. However, neglecting the concentration of nebulized hygroscopic droplet aerosols can lead to significant discrepancies in the deposition efficiency (DE) of nebulized drugs in the airways. To investigate the effect of different nebulization rates on the evolution, transport, and deposition of droplets, a highly idealized mouth-throat (MT) model was selected as a testbed for the in silico trials of drug delivery to the respiratory tract. The interaction between continuous and discrete phases was modeled using a two-way coupled model of highly concentrated droplet aerosol-water vapor interaction, innovated by the particle parcel method. The effects of different coupling methods and boundary conditions on the average droplet diameter and droplet deposition distribution pattern at the outlet of the MT model were compared using a computational fluid dynamics (CFD) method. Simulation results indicate that neglecting the effect of water vapor evaporated from the droplets on the relative humidity (RH) in the oral cavity could lead to a 2.2-fold prediction error of the average droplet diameter at the outlet of the MT model for a conventional nebulization rate of 0.386 g/min. As the nebulization rate increases, the difference in the predicted average droplet diameter at the outlet of the MT model between the one-way coupled method and the two-way coupled method also increases. Increasing the nebulization rate during inhalation therapy could lead to incomplete evaporation of drug droplets, resulting in deposition of larger diameter drug droplets in the oral cavity. In contrast, a lower nebulization rate can reduce the droplet diameter at the outlet of the MT model, allowing it to enter deeper airways.

Enhanced and spatially controllable neuronal activity induced by transcranial focused ultrasound stimulation combined with phase-change nanodroplets

Non-invasive ultrasound neuromodulation (USNM) is a powerful tool to explore neural circuits and treat neurological disorders. Due to the heterogeneity of the skull and regional variations in modulation and treatment objectives, it is necessary to develop an efficient and spatially controllable neuromodulation approach. Recently, transcranial focused ultrasound (tFUS) combined with external biomicro/nanomaterials for brain stimulation has garnered significant attention. This study focused on tFUS combined with perfluoropentane (PFP) nanodroplets (NDs) to improve the efficacy and spatial controllability of USNM. The developed two-stage variable pulse tFUS sequence that include the acoustic droplet vaporization (ADV) pulse for vaporizing PFP NDs into microbubbles (MBs) and the USNM sequence for inducing mechanical oscillations of the formed MBs to enhance neuronal activity. Further, adjusting the acoustic pressure of the ADV pulse generated the controllable vaporization regions, thereby achieving spatially controllable neuromodulation. The results showed that the mean densities of c-fos+ cells expression in the group of PFP NDs with ADV (109 ± 19 cells/mm2) were significantly higher compared to the group without ADV (37.34 ± 8.24 cells/mm2). The acoustic pressure of the ADV pulse with 1.98 MPa and 2.81 MPa in vitro generated the vaporization regions of 0.146 ± 0.032 cm2 and 0.349 ± 0.056 cm2, respectively. Under the same stimulation conditions, a larger vaporization region was also obtained with higher acoustic pressure in vivo, inducing a broader region of neuronal activation. Therefore, this study will serve as a valuable reference for developing the efficient and spatially controllable tFUS neuromodulation strategy.

A new solution to a weakly non-linear heat conduction equation in a spherical droplet: Basic idea and applications

A new analytical solution to a non-linear heat transfer equation in a spherically-symmetric droplet is suggested. All thermophysical properties inside the droplet are considered to be close to their average values. This allows us to consider the non-linearity of this equation as weak. The solution is presented as T=T0+T1, where T0 is the solution to a linear heat conduction equation, and T1≪T0. The equation for T1 is presented as a linear heat conduction equation with a source term depending on the distribution of T0 and its spatial derivatives inside the droplet. The latter equation is solved analytically alongside the linear equation for T0, and the final solution is presented as T=T0+T1. The predictions of the numerical code in which this solution was implemented are verified based on a comparison of those predictions with the predictions of COMSOL Multiphysics code using input parameter values that are typical for nanofluid (water and SiO2 nanoparticles) droplet evaporation in atmospheric conditions. It is demonstrated that for these experiments T1≪T0 which justifies the applicability of the linear heat conduction equation used for the analysis of this process. Small differences in the temperatures predicted by both non-linear and linear models lead to a much more noticeable difference in integral characteristics such as time before the start of the formation of the cenosphere when the mass fraction of nanoparticles at the droplet surface reaches about 40%.

Influence of spray parameters and thermal environments under convection heat transfer on the application of spray cooling technology in deep-buried high-temperature building tunnel

Spray cooling technology is an effective and sustainable cooling method that is frequently used in hot environments, both indoors and outdoors. This paper studied the theory of droplet evaporation under convection heat transfer and established a model of tunnel construction under high-temperature. The results of the field measurements were used to determine the boundary conditions for the model. After that, the cooling effect under various spray conditions (spray pressure Pn and water temperature Tw) was explored. Next, it was discussed how the tunnel's thermal environment affected the droplet evaporation, and a suitable layout of nozzles was chosen. The results showed that, firstly, the droplet group produced by spraying was in an irregularly cone-shaped distribution, with most droplets falling within the particle size range of 30–40 μm. Secondly, when the spray pressure (Pn) was increased, the break-up of droplets was better, which would improve the evaporation flow of droplets. However, the evaporative ratio of the droplets exhibited a peak value. When Pn = 4 MPa, the droplet evaporation ratio reached its maximum at 82.7 %. Thirdly, in a high-humidity environment, the evaporation ratio of droplets would decrease, and the average evaporation time of a single droplet would increase, leading to the reduction of the spray cooling effect. When D increased from 5 g/kg to 25 g/kg, the average evaporation time rose at 5.7 s. Fourthly, when constructing in the tunnel's high-temperature zone, the number of nozzles (N) could be raised to achieve the cooling effect; and the cooling effect was optimal when the spacing between nozzles (Δx) was 20–30 m. The research results enriched the study of spray parameters and thermal environments on the cooling effect of droplet evaporation, which could provide a reference for applying spray cooling technology in the tunnel.

Self-similar behavior of successive Coulombic fissions of evaporating charged water droplets

Charged droplets suspended in an electrodynamic balance experience a form of instability known as Coulombic fission when electric forces (resulting from the electrical charges on the droplet surface) surpass surface tension forces. For a pure-fluid droplet with a given diameter, a charge limit (known as Rayleigh limit, qR) exists at which Coulombic Fission occurs. In an evaporating droplet with a certain initial amount of charge (q), the Rayleigh limit is reached when the droplet decreases to a certain smaller diameter due to evaporation. During Coulombic fission, the droplet releases some of the charges and returns to a stable state. Further evaporation will lead to the next Rayleigh limit. As a result, several successive Coulombic fissions may occur during the evaporative lifetime of a droplet. In this study, charged, sub-millimeter droplets of deionized water were suspended using an electrodynamic balance and left to evaporate into their surroundings. As many as 15 Coulombic fissions were observed during the evaporation of a single droplet. The time of evaporation and droplet diameter at Coulombic fissions were recorded using high-speed imagery and digital image processing. The amount of charge at the time of each fission was calculated based on droplet size and Rayleigh limit. It was found that during each fission, the droplet releases about 14 % of its charge. Results indicated that droplets with similar initial relative charge (q/qR) sustained Coulombic fissions at similar normalized diameters independently of initial droplet size and evaporation rate. As a consequence of this, and in accordance with the d2-law of pure-fluid droplet evaporation, the times at which Coulombic fissions occur during the droplet's lifetime can be predicted for a given initial droplet size and evaporation rate.

A Numerical Study on Droplet Evaporation using Mass and Heat Transfer Approach

Liquid fuel is injected into many combustion devices like engines, boilers, and gas turbines where it evaporates, mixes with air, and finally burns. The combustion process influences by evaporation and corresponding air-fuel mixing. Hence, the evaporation study of the fuel droplets is important in different thermodynamic conditions. In the present paper, fuel droplet evaporation has been numerically studied by two different approaches i.e., mass transfer and heat transfer. Multiple case studies have been conducted by varying the droplet surface temperature, its initial diameter, and the temperature of ambiance to understand the influence of each parameter on the evaporation process by the two different concepts. Transfer numbers (B), evaporation constants (K), and droplet lifetime are obtained through both heat and mass transfer models. These observations are highly helpful to understand the droplet evaporation process and comparing the two different approaches to droplet evaporation modeling.

Experimental and numerical investigations on flash evaporation of a sessile droplet under reduced pressure

Flash evaporation of droplets under reduced pressures is versatile in industrial applications for its low energy consumption. More vigorous flash explosions may occur by the subsecond expansion of internal bubbles, leading to inefficient heat transfer and facility damage. In this work, we propose using the aerosol with an inherent low thermal conductivity as the substrate to study the flash evaporation of sessile droplets, which reduces the number of nucleate sites and suppresses the flash explosion, in contrast to the pendant one. We experimentally reveal the effect of ambient pressure, initial droplet temperature, and size on droplet temperature evolution and evaporation rate. A revised diffusion coefficient is proposed based on the experimental droplet lifetime with the aid of D2-law, which is utilized in axisymmetric simulations for acquiring the flow field, temperature, and vapor concentration distribution. The analogy between experimental and numerical results has demonstrated the validity of this revision. The interplay of two convection flows aroused by the Marangoni effect and thermal convection is displayed at the early stage of flash evaporation, and the latter is predominant for the rest of evaporation.

Experimental Study of Evaporation of Nanofluid Droplets on Substrates under Solar Radiation

This work is devoted to the experimental study of evaporating droplets of titania-, silica-, and diamond-based nanofluids on a substrate under solar radiation. The influence of various factors, including the type of a material, concentration of nanocomponents, irradiation direction, droplet volume, and substrate material, on the droplet evaporation has been investigated. As a result, the critical concentrations of nanoparticles, at which the evaporation rate reaches a stable level, have been determined for droplets of the studied nanofluids. The regimes and stages of the droplet evaporation process have been analyzed for the cases of the subcritical and critical nanoparticle concentrations. The efficiency of droplet evaporation under solar radiation has been shown to strongly depend on radiation direction. The effects of droplet volume and substrate material on the evaporation rate have been studied. In addition to the evaporation efficiency, the morphology of the structures deposited from the droplets has been analyzed. It has been shown that these structures depend on the concentration and material of nanoparticles, as well as on the regime of droplet evaporation. The results of this study enable one to gain a deeper insight into the behavior of the droplets during evaporation under irradiation especially in the IR region and confirm the promise of application of nanofluids in the solar thermal energy systems.

Improvement of the Technology of Aapplication of Biological Preparations for Plant Protection

The issues of improving the quality of application of fungal and bacterial biological products when applying the flow rates of working fluid up to 20 l/ha are considered. Along with the traditional methodology for assessing the quality of applying the working fluid of biological products to the treated surface, a new method for evaluating the effectiveness of applying biological products was also used, which consisted in selecting a certain area of the potato leaf surface by plant tiers 1 day after processing to determine the viability of fungal and bacterial preparations with low-volume (LV) and ultra-low-volume (ULV) technologies spraying. It is shown that when applying the technology of spraying up to 10 l/ha, despite the high coating density, the cells of microorganisms fall on the leaf surface with an insufficient amount of liquid for their active reproduction on the treated surface. In addition, at low humidity, due to the rapid evaporation of droplets from the surface of the treated leaves, microorganisms do not multiply and are carried away by the wind when drying. The conducted research tests of the use of the mushroom biological preparation Trichocin at a consumption rate of 20 l/ha on test objects (potato plants of the Galla and Riviera varieties) using especially pure glycerin and the moisture-retaining food additive sorbitol as antiparators showed that their use ensured the viability of the cells of the biological product and the high rate of their reproduction on the treated surface due to moisture retention.