This article was aimed to solve an urgent problem of ensuring quality for prilling processes in vibrational prilling equipment. During the research, the need for the application of vibrational prilling to create a controlled impact on the process of jet decay on droplets with the proper characteristics was substantiated. Based on the experimental and theoretical studies of the process of decay of a liquid jet into drops, axisymmetric droplet oscillation modes for the different frequencies were observed. Frequency ranges of transition between modes of decay of a jet into drops were obtained. As a result, the mathematical model of the droplet deformation was refined. The experimental research data substantiated this model, and its implementation allowed determining the analytical dependencies for the components of the droplet deformation velocity. The proposed model explains the existence of different droplet oscillation modes depending on the frequency characteristics of the superimposed vibrational impact. Based on an analytical study of the droplet deformation velocity components, the limit values of the characteristics defining the transition between the different droplet oscillation modes were discovered. Analytical dependencies were also obtained to determine the diameter of the satellites and their total number.

Effect of Superimposed Vibrations on Droplet Oscillation Modes in Prilling Process

With the wide application of anchored structures in various engineering, their durability and service life have become an important issue in the development of anchoring technique. The cement mortar is an important constituent of anchored structures, and the durability of the cement mortar is one of the main factors influencing anchored structures. In this paper, the method of indoor accelerated test is adopted, various unfavourable factors in the actual environment are simulated, the test data of cement mortar corrosion are obtained in a relatively short time. The research results of this thesis can provide scientific basis for the corrosion resistance of anchor cement mortar.

Experiment Study on the Corrosion Mechanism of Mortar Anchor Solid

In the present investigation, boiling heat transfer coefficients are measured for an electrically heated 390-μm-dia, platinum wire immersed in saturated water, and in water mixed with three different concentrations of sodium dodecyl sulfate (an anionic surfactant). The addition of a surfactant to water is known to enhance boiling heat transfer. A recently developed photographic/laser-Doppler anemometry measurement technique is used to quantify the vapor volumetric flow rate departing from the wire during the boiling process. The volumetric flow rate data are used to calculate the latent heat and, indirectly, the convection heat transfer mechanisms that constitute the nucleate boiling heat flux. Comparisons are made to determine how the heat transfer mechanisms are affected by the surfactant addition, and thus, which mechanism promotes boiling enhancement. The present data are also compared with similar data taken for a 75-μm-dia wire immersed in saturated FC-72 (a highly wetting liquid) to provide increased insight into the nature of the boiling heat transfer mechanisms.

Determination of the boiling enhancement mechanism caused by surfactant addition to water

The forces acting on the elementary volume of liquid in the pipeline in the laminar boundary layer are considered. A new dimensionless complex the surface number and the concept of the turbulence coefficient laminar boundary layer is proposed. The calculation of Froude, Euler numbers, the inverse Reynolds number and the surface number in laminar boundary layer for water under normal conditions is given. It is shown that the Froude number and the inverse Reynolds number are 4-5 orders of magnitude smaller than the surface number and Euler number in laminar boundary layer, which allows neglecting the forces of gravitation and friction in these conditions. Equations are proposed for calculating the average thickness of laminar boundary layer. The dependence of the surface number on the coefficient of surface tension of the refrigerant is obtained. It is shown that a decrease in the surface tension coefficient minimizes the average thickness of the laminar boundary layers in the wall system of the pipeline and liquid and increases the average velocities of the coolant flows in these layers, as a result of which such a system is capable of more efficient transfer of heat. It is substantiated and experimentally confirmed that at optimum concentrations of surfactants, the values of the surface number are minimal.

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Modeling the interaction of coolant flows at the liquid-solid boundary with allowance for the laminar boundary layer

1 Faculty of Food Technologies and Biotechnology, Stepan Gzytsky Natoinal University of Veterinary Medicine and Biotechnologies Lviv, 50 Pekarska, Lviv 79010, Ukraine 2 Department of Industrial Engineering, Alma Mater Studiorum-University of Bologna, viale Risorgimento 2, Bologna 40136, Italy 3 Faculty of Veterinary Medicine, Stepan Gzytsky Natoinal University of Veterinary Medicine and Biotechnologies Lviv, 50 Pekarska, Lviv 79010, Ukraine 4 Lviv Institute of Economy and Tourism Lviv, Menzinsky 8, Lviv 79007, Ukraine

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Changes in the Hydro-mechanical and Thermo-physical Characteristics of Liquid Food Products (for Example, Milk) under the Influence of Natural Surfactants

Received: 13 December 2017 Accepted: 5 March 2018 The sources of the literature are analyzed in the article on the influence of the average thickness of the laminar boundary layer (LBL) on the heat transfer coefficient of the various heat-conducting systems. Different authors at different times established the explicit correlation dependence of the increase in heat transfer coefficients with a decrease in the average thickness of the LBL. The average thickness of the LBL according to the literature data was reduced in the various ways (using electric or magnetic field for the flow of the liquid, using the nanoparticles in the flow and various of the metallic spiral inserts, etc.). Applying the similarity theory and using dimensionless Euler, Froude and Reynolds numbers in the LBL, and also applying a new surface number, we previously derived the formula for the calculation of the average thickness of the LBL, which in this paper is used to the calculation the overall heat transfer coefficient of the shell-and-tube heat exchanger. We brought out new number of the turbulent thermal conductivity in the LBL transitional zone by the dimensional analysis method. The relations have also been obtained for the calculating of the transitional viscosity and of the transitional thermal conductivity in the transitional zone of the LBL. The article provides the examples the calculation of the shell-and-tube heat exchanger using the classical method and the proposed formulas. The calculation of the resistance of the LBL and the turbulent zones of the refrigerant flows is carried out the taking into account the coefficients of the turbulent thermal conductivity, as well as the coefficients of the surface tension of the liquids. We proposed the calculation of the shell-and-tube heat exchanger using of the refrigerant with an optimum concentration of the propylene glycol in the water (47%). The increase of the overall heat transfer coefficient of the heat exchanger is about 10%.

http://www.iieta.org/sites/default/files/Journals/IJHT/36.01_02.pdf

Specific features of heat exchangers calculation considering the laminar boundary layer, the transitional and turbulent thermal conductivity of heat carriers

Received: 3 November 2019 Accepted: 16 Feburary 2020 This article analyzes the vast material of works devoted to the use of nanofluids in heat exchange equipment. It is proved that the use of the classical theories and equations for calculating the viscosities and thermal conductivities of nanofluids is not correct, since it does not coincide with the experimental results of most independent authors. A model of the chaotic motion of a nanoparticle is presented taking into account surface tension forces in a liquid coolant. The experimental results of the work of Malaysian and Iran authors on the effect of TiO2 nanoparticles with a concentration of 0.5%; 1.0% and 1.5% in the main liquid solution of ethylene glycol (EG) in water in a volume ratio of 40:60% in terms of heat transfer coefficient are compared with our theoretical studies. The results of the experiments presented in: an increase in heat transfer coefficients by 9.72%, 22.75%, 28.92% for 1.5% volume concentration of TiO2 nanoparticles at a coolant temperature of 30°C, 50°C, 70°C, respectively. Our theoretical result: increase in the obtained heat transfer coefficients by 9.79%, 22.22%, 29.09% according to our formulas (9, 10, 15) for calculating turbulent viscosities and thermal conductivities, which takes into account the effect of surface tension forces on the total flow of nanofluids in the channels of heat exchange equipment. A new method for calculating heat exchange equipment using nanofluids is presented, taking into account the action of surface tension forces, as well as predetermining the calculation of turbulent viscosities and thermal conductivity of nanofluids. A theoretical calculations a plate heat exchangers for a technological task performed by classical and new method is presented. Similar results were obtained, which differ by about 0.5 of a percent. The plate heat exchanger was calculated using a new method using TiO2 nanoparticles in water and in a mixture of EG in water in a ratio of 40:60%, as well as when pumpkin vegetable oil was added to milk with the optimal concentration.

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A New Universal Numerical Equation and a New Method for Calculating Heat-Exchange Equipment Using Nanofluids

Received: 3 June 2018 Accepted: 23 December 2018 The distribution of resistances values of individual thermal zones of coolants flows is analyzed for the example of milk and water in a shell-and-tube heat exchanger, which was calculated and selected by us in the work [11]. It is shown that thermal resistance of turbulent zones of coolants flows is about 37 % of the total thermal resistance of the heat exchange system in this heat exchanger. The specific thermals resistivity the laminar boundary layer (LBL) zones are much larger, but their total thermal resistance is about 1.5 % because of the very small average thickness of these zones. In this case, the method of analyzing the basic dimensions of physical quantities was used. At the same time, we deduced a new dimensionless number Blturb., which shows the ratio of turbulent viscosities or thermal conductivities to the transitional viscosities or thermal conductivities of the individual coolants zones. Formulas for the calculation of turbulent viscosities and thermal conductivities in coolants of are derived and the law of their distribution in the volume of coolant flows in the pipes and the annular space of the shell-andtube heat exchanger is established. It is shown that this law is an analog of the bell-shaped law of the distribution of Reichardt H. and Ludwig H., and the main difference is that the equation of this law derived by us contains the coefficients of surface tension and hydrophilicity of the wetting surfaces and also the values, reflecting the rates of thermal motion of the heat carriers molecules at a given temperature. A complete analysis of longitudinal sections of coolants flows is made using the example of milk and water in a shell-and-tube heat exchanger for their values of turbulent viscosities and thermal conductivities as well as the turbulent numbers Blturb.. It is shown that the most energy-efficient liquid refrigerants can be selected using a turbulent number Blturb..

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The Laws of Distribution of the Values of Turbulent Thermo-physical Characteristics in the Volume of the Flows of Heat Carriers Taking into Account the Surface Forces

Oksana Maksysko

Papers

Modeling the interaction of coolant flows at the liquid-solid boundary with allowance for the laminar boundary layer

Changes in the Hydro-mechanical and Thermo-physical Characteristics of Liquid Food Products (for Example, Milk) under the Influence of Natural Surfactants

Specific features of heat exchangers calculation considering the laminar boundary layer, the transitional and turbulent thermal conductivity of heat carriers

A New Universal Numerical Equation and a New Method for Calculating Heat-Exchange Equipment Using Nanofluids

The Laws of Distribution of the Values of Turbulent Thermo-physical Characteristics in the Volume of the Flows of Heat Carriers Taking into Account the Surface Forces