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..

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%.

INTRODUKTIONIn the current energy crisis, the issue of energy efficiency of heat exchange processes and equipment for their provision in food, chemical, pharmaceutical, processing and other technologies becomes decisive. To increase the heat transfer coefficients in heat exchangers, various methods are used, in particular, the modification of the structural elements of boilers and other equipment [1], the increase in the turbulence of the refrigerant flows [2], the use of liquids with the optimal concentration of surfactants (SAS). For example, the maximum rate of heat exchange was observed when a nonionic surfactant was added to water [3]. The authors of [3] believed that the maximum rate of heat exchange in the first place may be due to the fact that this additive has a minimum capacity for the formation of foam. In addition, it is known that surfaceactive substances significantly, approximately 2 times, reduce the coefficients of surface tension of water and other liquids. PROBLEM FORMULATIONAfter analyzing the literature sources, we came to the conclusion that the rate of heat exchange in liquid refrigerants through the laminar boundary layer (LBL) depends on the following main factors: -laminar flow is responsible for the turbulent flow, but is less energy-efficient [2,4]; -LBL, namely its average thickness is responsible for the total thermal resistance of the system [5,6]; -the thermal resistance depends on the coefficient of surface tension of the refrigerant [7]; -the intensity of heat exchange depends on the hydrophilicity or hydrophobicity of the wetting surface [8];Based on the foregoing, the purpose of this article was to offer a model for the interaction of refrigerants with a separating solid wall, which will cover all the above factors as much as possible. : 0392-8764 Vol. 35, No. 3, September 2017, pp. 678-682 DOI: 10.18280 INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY ISSN ABSTRACTThe 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 s...

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℃, 50℃, 70℃, 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.

The surface properties of vegetable oils are investigated. It is shown that the investigated vegetable oils at the interface between the liquid-gas, liquid-solid surfaces, liquid-liquid behave as surface-active substances for milk. It is shown that the hydromechanical characteristics of milk are changing, which moves in the pipeline or apparatus, namely in the boundary layer under the influence of plant surface-active substances (surfactants). It is shown that the reduction of the surface tension coefficient minimizes the thickness of the boundary layer A in the system wall of the pipeline-milk, which means that it increases the average flow velocity in it and as a consequence, such a system is capable of effectively transmitting the amount of heat. A numerical range of the surface criterion for milk was found for adding surfactants.