The scheme of carbon dioxide cogeneration and trigeneration plant with the use of secondary energy resources in the form of combustion products or flue gases that enables to produce electricity, thermal energy and cold for centralized and decentralized supply of consumers simultaneously, is presented. In addition, the plant can produce liquid and gaseous carbon dioxide. The main elements of the plant are a heating unit, a turbodetander unit and a carbon dioxide unit for the production of cold, liquid and gaseous carbon dioxide. A thermodynamic calculation and a brief exergy analysis of the plant were carried out. In the proposed plant, off-gases from glassmelting, metallurgical furnaces, heat power facility and other energy facilities with a secondary energy temperature of 250–400 °C and above can be used as secondary energy resources. The heating unit of the installation has been designed to produce thermal energy for heating and hot water supply systems. The carbon dioxide unit has been designed for the production of cold, electric energy and carbon dioxide in liquid and gaseous form in order to ensure the operation of the plant and the use for commercial purposes. The cold in the plant can be obtained in two evaporators operating at different boiling temperatures. At a higher boiling point of carbon dioxide, cold is used in air conditioning systems and in centralized cooling and storage systems, while at a lower boiling point of carbon dioxide – in freezing and storage systems. For the implementation of the reverse carbon dioxide cycle, a three-stage carbon dioxide compressor with a receiver after the third stage is used. To reduce compression performance of the compressor, complete intermediate cooling of carbon dioxide between stages should be provided.

The article considers 46 low-boiling working media (LBWM) with zero potential for ozone layer destruction. Out of them, 14 ones are single-component hydrofluorocarbon refrigerants, 28 ones are multi-component mixtures of hydrofluorocarbon refrigerants, and the four ones are native refrigerants. Thermodynamic analysis of working media based on the classical turbo-expander scheme with a heat exchanger designed to cool the superheated LBWM that has left the turbo-expander has been performed. For this scheme, a cycle is constructed in T–s-coordinates. The LBWM was compared using the exergetic coefficient of efficiency (KE). In the course of the study, it was found that for some LBWM, the sequence of location of the exergetic efficiencydependences on temperature at thermodynamically optimal working medium pressures is preserved over the entire temperature range under study (from 100 to 300 оC). In other words,if the working medium has the highest exergetic efficiency coefficient, then this property is inherent in it at any temperature in a given interval. It is proposed to perform the analysis of the LBWM for exergetic efficiency at an arbitrarily selected temperature (250 оC). The study demonstrated that the highest exergetic efficiency of natural refrigerants is R600A (50.25 %), among single component hydrofluorocarbon refrigerants – R245FA (50.00 %), R1233ZD(E) (49.91 %), R236EA (49.59 %), among multi-component mixtures of hydrofluorocarbon refrigerants – R429A (47.92 %), R430A (47.49 %) and R423A (47.47 %). Out of the all examined refrigerants, the following ones have the highest exergetic efficiency of all the considered LBWM: R600A, R245FA, R1233ZD(E), R236EA, R1234ZE(Z), R236FA. They belong to both natural refrigerants (hydrocarbons) and single-component hydrofluorocarbons. It should be noted that each of these working media has its drawbacks: some have a high potential for global warming, others are explosive, and others have a high cost.

The results of experimental research of heat exchange under the nucleate boiling of refrigerants R404a, R407c and R410a on the tubes with capillary-porous coating are presented. Experimental studies were carried out with the aid of an experimental installation in conditions of a large volume at pressures of saturation pн = 0.9–1.4 MPa and densities of the heat flux q = 5–35 kW/m2. For the first time the criterion equation for the calculation of the intensity of heat transfer during evaporation of ozone safe refrigerants on surfaces with high thermal conductivity sintered capillary-porous coating was obtained. Experimental data are summarized satisfactorily in a wide range of parameters of the porous layer, i.e. the pressure (pн = 0.9–1.4 MPa) and heat loads (q = 5–35 kW/m2). The ratio makes us possible to calculate the heat transfer coefficients within ±20 %. The dependence can be used in engineering calculations of the characteristics of the heat exchangers of the evaporative type. The coefficient of heat transfer during boiling of refrigerants on the investigated surfaces with the sintered capillary-porous coating, 4 times higher than on a smooth one and 1.5 times higher than on the finned surface, that allows us to come to a conclusion about the advantage of porous coatings. Boiling in capillary-porous coating leads to a decrease in weight and size of the installations due to the heat exchange intensification and the size of the tubes smaller as compared to the size of the finned ones.

Представлены результаты экспериментальных исследований теплообмена при кипении хладагентов R404а, R407с и R410a на гладкой технически шероховатой поверхности в условиях свободного движения в большом объеме. Установлены зависимости между количественными характеристиками процесса теплообмена при кипении, режимными параметрами и другими факторами, влияющими на интенсивность теплообмена. Ключевые слова: Теплообмен при кипении-Озонобезопасные хладагенты-Интенсивность теплообмена-Коэффициент теплоотдачи-Испаритель-Теплообменный аппарат.