Refrigeration engineering and technology

12-17

Authors: L. I. Morosuk

The cascade refrigeration machines are used for producing the cold at temperature level –110…-50℃. The thermodynamic cycle of the cascade refrigeration machine consists of one-stage refrigeration cycles in series. In earlier time, R12 or R22 were used as the working fluid for the high-temperature cascade as well as R13 or R14 as the working fluid for the low-temperature cascade. In modern refrigeration engineering these working fluids are forbidden. This fact requires to select another working fluids taking into account energy saving and ecological issues. R744, R717 and R290 (different combinations between high-temperature and low-temperature cascades) are the working fluids that can be used for generating the cold at temperature level -30…-60℃. They have the following advantages: the ODP values are equal to zero as well as GWP values tend to zero. In the paper, the thermodynamic analysis of the cascade refrigeration machines with R744/R744, R744/R717, R744/R290 has been conducted with R744 transcritical cycle for the high-temperature cascade. The thermodynamic analysis is based on the method of the comparison of the thermodynamic cycles proposed by R. Plank. For each cascade machine the operation parameters have been optimized to solve the “energetic problem”. For the R744/R744 cascade refrigeration machine the “transport” and the “unification” problems are also solved. The parametric study of effect of the temperature within the condenser-evaporator on effectiveness of the thermodynamic cycles has been reported. The influence of the thermodynamic properties of the working fluids to the energetic and volumetric characteristics of the cascade refrigeration machines has also been evaluated.

23-34

Authors: A. V. Doroshenko, V. A. Goncharenko, A. N. Tsapushel, Yu. I. Demianenko

The schematics of heat and mass transfer apparatus are worked out with the fluidized beds attachment "gas - liquid - solid body" for the evaporated cooling of environments (evaporative coolers of water (cooling towers CTW) and evaporative coolers of air (direct and indirect type coolers). The multifunction solar refrigeration systems and air conditioning system are worked out on the based on absorbing open-cycle with the indirect regeneration of absorbent. In the basic contours of drainage of air and cooling of environments of the solar systems heat and mass transfer apparatus are used with fluidized beds. Decisions for heat and mass transfer apparatus with the fluidized beds "gas - liquid - solid body" have been worked out in a few basic variants, in particular, with possibility of heat-exchanger placing directly in the volume of the fluidized beds. It is the evaporated air coolers of indirect type (IECg) and evaporated liquid coolers of indirect type (IECw) of cool contour of the solar systems; absorber on the air flow and desorber-regenerator of absorbent of contour of drainage of outward air of the solar systems. The cycle of experimental researches of fluidizing bed "gas - liquid - solid body" features was executed both for a variant with the free fluidized bed of attachment and in a variant with placing of heat-exchanger directly in the volume of the fluidized bed of attachment. Influence of height of stationary layer of elements, geometrical parameters of distributive grate was studied, initial parameters of current of air, entering in the heat and mass transfer apparatus. On the basis of cycle of theoretical and experimental researches practical recommendations were proposed on determination of optimal geometrical parameters of basic elements and regime parameters of heat and mass transfer apparatus operation in autonomous regime and in composition with multifunction solar absorbing systems.

42-47

Authors: A. Pavlenko, B. Usenko, H. Koshlak

The article presents the results of research of energy-resource-saving technologies of massive amorphous structures formation. This technology differs mainly the realization internal heat removal by means of local heat sink (inoculator). The peculiarities of processes of heat and mass transfer during the formation of in the melt additional active cooling centers, local heat sink to generate internal heat removal. A mathematical model of melting inoculator in melts for optimizing the process of obtaining massive amorphous structures, which allows to reduce time of experimental research and material resources to create massive amorphous structures. Mathematical modeling of processes heat and mass transfer inoculator in melts allows you to identify peculiarities of the technological process, and establish influence inoculator on the degree of amorphization melt. The results of physical experiments are compared with the results of the calculation. The results can be used to analyze the physical regularities and informed choice of technological modes of formation of massive amorphous structures in different metals and alloys. The melt metal with the cooled particles (inoculator) is characterized by supercooling condition throughout the volume of the solid ingot. Inoculators not only remove overheating and supercooling melt. The results provide an effective assessment of the intensity of heat transfer during the casting process, which makes it possible to estimate and predict the ability of alloys to the amorphization of the structure.

53-61

Authors: O. Yu. Rozina, V. B.Rogankov

The present paper concerns the generation of the sonic-capillary heat flux. Its conceptual model was presented in paper [1] and based on the experimental investigation of the sonic-capillary effect. The main statements of this model are: if the capillary was immersed into liquid, where an ultrasonic field was formed, the cavitations arise near the capillary cannel and due to the sonic-capillary force are translating into the capillary. Thus, all thermodynamic processes, connected with extension of cavities need some quality of heat should be located near the capillary cannel; the decreasing of cavities and reverse of heat to liquid are located in the capillary cannel; that’s why the heat flux is form throw the open capillary section. In this paper the results of numerical investigation of the optimal conditions for the generation of the sonic-capillary heat flux are presented. Using the original program product, the influence of the cavity parameters on the heat flux is investigated. It is shown, that an ultrasonic frequency ν determines the acceptable range of the internal diameters of the capillary, and, as consequence, the permissible range of cavities radius Rmax can be also defined. The calculations cover the range ν = (20÷100) kHc, and corresponding range of cavities radius Rmax= (0,025÷0,100) mm. Also, the results of numerical investigation for the wide range of equilibrium temperature of liquid are presented. It is shown, that due to the arising of the equilibrium temperature the kinetics of vaporization changes its parameters: the vapor in cavity remains unsaturated, thus the quality of heat, transferred throw the open end of capillary, decreases. The boundary temperature for two regimes of the evaporating is caused by the ultrasonic frequency too.

66-69

Authors: N. I. Lapardin, V. Z. Geller

The present work is dedicated to the development of the model for calculating the viscosity of the oil-refrigerant solutions based on experimental data. The results of experimental studies of density and viscosity of the mixture of compressor lubricant ISO 10 with the refrigerant R134a over a temperature range from 273 to 353 K and oil mass concentration from 0.7 to 1 are presented. Description of liquid viscosity at various temperatures and pressures based on the rough hard sphere (RHS) model, in recent years successfully in use for hydrocarbons, including pure refrigerants – derivatives of ethane and methane. Parameters of the modified RHS model were derived from experimental data for many polar liquids, including refrigerant R134a. The same model was used to describe the viscosity of binary and ternary refrigerant mixtures with the help of combination rules of molecular parameters for pure substances. We have modified the RHS model in order to apply it to the oil-refrigerant solutions. The obtained experimental viscosity data were introduced in the form of reduced viscosity, and the correlations of the reduced viscosity and density in the hard spheres model were determined with the empirical and universal for different fluids function of molar volume. Changes in the RHS model related to one of the combination rules of the molecular parameters and using an additional nonlinear term in the specified empirical polynomial function. As a result, the use of the hard spheres model for the viscosity of the oil-refrigerant mixtures was successful in spite of the task complexity (the viscosity of the lubricant is higher than the viscosity of the refrigerant by two to three orders of magnitude). The standard deviation for all compositions and temperatures was less than 6 %. Density and viscosity of the mixtures of synthetic polyolester lubricant oil ISO 10 with the refrigerant R134а have been measured over a temperature range from 273 до 353 K and a range of oil mass fraction from 0,7 to 1. The viscosity of liquid mixtures of lubricant oil-refrigerant is modeled with the modified rough hard-sphere method. The results are compared with the experimental data.

80-85

Authors: L. N. Yakub, O. S. Bodiul

The theoretical equation of state for solid methane, developed within the framework of perturbation theory, with the crystal consisting of spherical molecules as zero-order approximation, and octupole-octupole interaction of methane molecules as a perturbation, is proposed. Thermodynamic functions are computed on the sublimation line up to the triple point. The contribution of the octupole-octupole interaction to the thermodynamic properties of solid methane is estimated.