Refrigeration engineering and technology

4-10

Authors: L. I. Morosuk, B. G. Grudka

Exergy analysis is a part of thermodynamic analysis. It became very popular in scientific research in the field of refrigeration and heap pumps. Information obtained from the exergy analysis is deeper than information obtained from any other methods, for example energe- tic analysis. It can also be applied to the absorption machines that are most complex among all refrigeration machines. In the paper, the algorithm of the exergy analysis for the absorption-resorption refrigeration machine (as a particular case of an absorption refrigeration machine) has been developed. The main difference between absorption-resorption and absorption refrigeration machines is that four phase change processes with the working fluid (mixture) occur at variable temperature: heat transfer to the generator, cold generation in degasator, heat rejection in resorber and absorber. In analysis, this particular case is taking into account through considering the sum of physical and chemical exergy for each material stream. Using an example, the methodology for determination of the reference state for calculating the physical exergy for the mixture with different concentrations has been demonstrated. Such an approach for analysis of components of absorption machines leads to an increase in the accuracy of the obtained results and understanding the thermodynamic inefficiencies. As the results it will help to develop the ideas for improvement of the overall system. The algorithm of the exergy analysis for the components and the overall resorption machine can be used for evaluation of any of absorption machines independent of the used working fluid (mixture) and schematics.

20-26

Authors: O. B. Vasyliv, A. S. Titlov, A. O. Kholodkov

Currently, developers of modern refrigeration equipment, in accordance with the plans of the UN, are moving to natural refrigerants (hydrocarbons, carbon dioxide and ammonia) that do not have an adverse technological impact on the ecosystem of the planet. In domestic refrigeration technology, one of the options is absorption refrigerator, the working body of which is water-ammonia mixture with addition of hydrogen. Having a number of unique advantages over compression analogs, absorption systems are characterized by lower energy characteristics. Since the absorption apparatus is designed initially to "hard" operating conditions, then with a decrease in the ambient temperature, and, consequently, heat flows into the chamber, all the basic elements of the ARU, with the exception of the reflux condenser, are able to operate under more favorable conditions. A reflux condenser, which is also designed to operate under "hard" conditions, in this case, in addition to its direct function of cleaning ammonia vapors from water vapor, also detains part of the ammonia entering the condenser. At the same time, it is obvious that the lower the ambient temperature, the greater this part will be. Ultimately, a decrease in the ambient temperature results in a decrease in the cooling capacity with a constant thermal load on the thermosyphon, COP of the refrigeration unit. As the analysis showed, the maximum thermodynamic losses in absorption refrigeration aggregates are concentrated in the generator unit during evaporation of ammonia, its purification from water vapor and transport to the evaporator. In this connection, the mathematical modeling of the thermal modes of the reflux condenser was performed, which is responsible for the purification and transportation of ammonia vapor. Modeling was carried out on standard designs of absorption cooling units taking into account reasonable assumptions and results of own experimental researches. At the heart of model representations lie the laws of conservation of heat and mass. Due to the high thermal inertia of the processes in the rectifier, stationary operating modes were modeled. In the simulation, the flow mode of the vapor mixture in the rectifier was considered turbulent, and the radial diffusion processes were neglected. As a result, the method for calculating the thermal modes of a reflux condenser, which is applicable for typical design of household absorption refrigeration unit has been developed.

35-39

Authors: V. V. Aftaniuk, S. K. Bandurkin, S. E. Zholud

The technique and results of numerical simulation of the stress-strain state of the blades of the vortex burner swirler developed for the modernization of heating boilers are outlined. For the modernization of water-tube boilers, the design of the vortex burner was proposed. A feature of the proposed burner is the design of a swirl device (), which is a body with inwardly mounted two rows of opposing guide blades. This permits to increase the turbulence and twisting of the flow and, as a result, improves the combustion process, and also considerably extends the range of geometry regulation and flame parameters. The purpose of swirlers numerical simulation is to check the structure reliability under the influence of hydrodynamic forces during operation. The study of the oscillations of the vortex burner blades makes it possible to determine the places with the greatest equivalent stresses, and, consequently, the most probable foci of failure, the place of change in the operating conditions of safe operation. The mathematical formulation of the problem is formulated; the method of modeling with the help of the finite element method is described. To carry out the simulation, specialized computer programs were used. A solid model of a vortex burner was developed. The solid model is divided into two modeling elements, external and internal. The surfaces on which the loads and surfaces are in relative rest were determined. The loads on the vortex blades were determined from the empirical relationships given in the specialized literature. The analysis of the mechanisms and regularities of damage to the blades, residual stress fields was carried out. The quantitative estimates of the reliability parameters of vortex blades obtained as a result of modeling are presented. Analysis of the diagrams made it possible to determine the zones (on the surfaces of the blades) in which maximum forces and displacements are observed. The results of the design check showed sufficient design reliability for accident-free operation, for all faces of the model, the safety factor is greater than 1.

44-53

Authors: Y. V. Baidak, M. Masaryk, V. A. Matukhno

During operation of electrical equipment and its design there is always a need to solve the problem of its heating and cooling, and especially the heating and cooling problem of the windings insulation as the most sensitive construction element The successful solution of the problem promote creation economically reliable equipment and the formation of a reasonable usage. The result of the study is the expediency substantiation of heat balance equations drawn up for the active part of the voltage distribution transformer simulation results implementation, at the final and qualifying design stage. The active part is in the transformer oil environment, and emission of heat is carried out by convection and heat transfer. The heat balance mathematical model corresponds to the equivalent thermal circuit, consisting of two adjacent units with heat outlet – generalized winding and ferromagnetic core and the third unit which is adjacent to them - moving substance from the oil which additionally contacts with the environment of infinite heat capacity. The solutions of equations are obtained for the winding mean temperatures, magnetic circuit core and oil in function of time that allows to determine their expected values during the transformer operation, and especially with the uneven schedule of its load as well as to make the justified choice of magnetic induction in the magnetic circuit core and current density in the windings in terms of permissible heating temperatures in them.

63-70

Authors: S. A. Moroz, N. N. Lukianov, V. P. Zhelezny

The results of an experimental study for the temperature and concentration dependencies of the density and viscosity of solutions of R600a / mineral oil HF16-12 / C60 fullerenes are presented in the paper. The density measurements were performed by a pycnometric method in the temperature range 258-353 K. The viscosity was measured by the rolling ball method in the temperature range 253-283 K. Based on obtained experimental data, the effect of admixtures of compressor oil and additives C60 fullerenes on the density and viscosity of R600a was analyzed. It was shown that the additives of fullerenes contribute to lowering the viscosity of the working fluid (refrigerant R600a / mineral oil HF16-12) in entire range of experimental parameters. The working fluid R600a / mineral oil HF16-12 / fullerenes C60 is recommended for application in domestic refrigeration.

76-83

Authors: L. F. Smirnov

The freezing technology for producing heavy water is proposed. The technology is based on a significant coefficient of hydrogen isotopes separation in the process of freezing. The principle of column crystallization and melting of ice along the height of the distillation column is used, which makes it possible to obtain a high concentration of deuterium at a still not very high column height. The physical and mathematical models of the column crystallization are considered with the determination of the method for calculating the deuterium concentration along the height of the column. The technology is particularly promising in combining the production of heavy water with desalination-separation of salt water by freezing, when already obtained pure ice desalination is used in the heavy water concentrator even before its melting. This significantly reduces the energy and capital costs of its production.