UNSTEADY HEAT TRANSFER IN A HORIZONTAL GROUND HEAT EXCHANGER

By the three-dimensional model of heat transfer in the system "ground - horizontal ground heat exchanger - heat transfer agent", an analysis of the efficiency of the horizontal multi-loop heat exchanger, which is an element of the heat pump system, was carried out. Based on the results of numerical simulation, the time dependence of the heat transfer agent temperature at the outlet from the ground heat exchanger and the amount of heat extracted from the ground is determined. The results of calculations by the presented model are satisfactorily agree with the experimental data.

INFLUENCE OF MALTODEXTRIN AS A STRUCTURAL ADDITIVE ON THE PROCESS OF DRYING DROPS OF PHOSPHOLIPID SUSPENSIONS

Emulsions with phospholipid nanostructures are heterogeneous disperse systems, which, when dried, show thermoplastic and adhesion properties. Improvement of their structure-forming and conducting properties in spray drying requires the use of structuring additives. The purpose of the work was to investigate the effect of maltodextrin on the process of heat transfer by drying single droplets of emulsions with phospholipid nanostructures in order to determine the rationale heat-engineering parameters of powder form production. Emulsions with phospholipid nanostructures and maltodextrin in different proportions of solids from 10% to 40% were investigated on the system of "drop-vapor-gas medium" in the stream of heated heat-carrier. The processes of forming, structuring and deformation changes of droplets during drying, the manifestation of thermoplastic and adhesion properties of dried particles under the influence of high temperatures and cooling were studied. It was established that with the content of dry matter of 20-30% and the ratio of lecithin and maltodextrin-trine as 1: 1, it is achieved by reducing the drying time of droplets of emulsions with phospholipid nanostructure-ram by 25-30%, and the strengthening of the structure of dried particles is provided by cooling them. References9, figures 3.

DETERMINATION OF LOAD DURATION CURVE (ROSSANDER GRAPH) FOR THE REGIONS OF UKRAINE

The purpose of this work is to determine the duration of the ambient air temperatures of different gradations during heating periods in different regions of Ukraine, based on the climatic data for 2005-2018 and the construction of load duration curves for the respective regions. The load duration curve (Rossander graph) is used to determine the number of maximum thermal load using hours, as well as in cases where the thermal load is provided by several sources - to determine their level of participation in the total annual heat energy production. It is important for a more accurate technical and economic evaluation of implementation results for some thermal energy sources. The climatic data of meteorological stations located in the regional centers of Ukraine and the capital of Autonomous Republic of Crimea, or as close as possible to them, were used for the study. The climatic data of heating periods from the autumn of 2005 to 2018 were considered. As the result of study, the duration of various degrees of ambient air temperature in the heating period was determined for all the regional centers of Ukraine. Taking into account the significant climatic differences in the regions of Ukraine, the results were analyzed separately for two groups of regions, for which, according to averaged data, load duration curves were determined. The examples of using of obtained results for calculations are given. On the basis of obtained data regarding duration of ambient temperatures higher than +8°C during the heating season, the energy saving potential of implementation of weather-dependent regulation of heat energy production for heating purposes in different regions was theoretically estimated, which is, on average, 8.4% for the first temperature zone (north, center) and 13% for the second zone (south).

WORLD AND DOMESTIC EXPERIENCE OF BIOETHANOL PRODUCTION

The paper presents an overview of bioetanol production technologies. It is noted that world fuel ethanol production in 2017 amounted to more than 27,000 million gallons (80 million tons). Eight countries, namely the USA, Brazil, the EU, China, Canada, Thailand, Argentina, India, together produce about 98% of bioethanol. In Ukraine, the volume of bioethanol production by alcoholic factories in recent years has been gradually increasing and amounted to 2,992.8 ths. dal in 2017. The production of ethanol as an additive to gasoline, with regard to the raw materials used, as well as the corresponding technologies, is historically divided into three generations. The first generation of biofuels produced from food crops rich in sugar or starch is currently dominant. Production of advanced biofuels from non-food crop feedstocks is limited. Output is anticipated to remain modest in the short term, as progress is needed to improve technology readiness. The main stages of bioethanol production from lignocellulosic raw materials are pre-treatment, enzymatic hydrolysis and fermentation. The pre-treatment process aims to reduce of sizes of raw material particles, provision of the components exposure (hemicellulose, cellulose, starch), provision of better access for the enzymes (in fermentative hydrolysis) to the surface of raw materials, and reduction of crystallinity degree of the cellulose matrix. The pre-treatment process is a major cost component of the overall process. The pre-treatment process is highly recommended as it gives subsequent or direct yield of the fermentable sugars, prevents premature degradation of the yielded sugars, prevents inhibitors formation prior hydrolysis and fermentation, lowers the processing cost, and lowers the demand of conventional energy in general. From the perspective of efficiency, promising methods of pre-treatment of lignocellulosic raw materials to hydrolysis are combined methods combining mechanical, chemical and physical mechanisms of influence on raw materials. One method that combines several physical effects on a treated substance is the discrete-pulsed energy input (DPIE) method. The DPIE method can be applied in the pre- treatment of lignocellulosic raw material in the technology bioethanol production for intensifying the process and reducing energy consumption. Ref. 15, Fig. 2.

ANALYSIS OF THE USE OF FUEL BY HOUSEHOLDS AND NON-INDUSTRIAL CONSUMERS

Purpose of the paper is to analyze the available statistical data on fuel consumption by population in every region of Ukraine. To identify similarities and differences in development trends the comparison of structure of final energy consumption in Ukraine and the world was done. The degree of distribution of individual heating systems in urban settlements and rural areas in 2015 is determined. Analysis of the use of the main types of fuel by households sector in regions of Ukraine is performed. The amount of fuel consumed by the population does not linearly depend on the share of individual heating systems in the region (this was shown by an example), therefore to develop strategy for extending the use of renewable energy sources (RES) in the households more factors will need to be considered. Ukrainian and world energy balance data for 2015 (item “Other” which includes residential sector, commerce and public services, agriculture, fishing, other consumers) on the consumption of four main types of fuel (coal and peat, oil products, natural gas, biofuels and waste) were compared. It was concluded that in Ukraine the proportion of basic fuels consumption corresponds to world trends. However, after analyzing the distribution of total final energy consumption certain differences were observed. Analysis of renewable energy sources use by sectors has demonstrated that the residential sector is the leader in renewable energy sources consumption both in the world and in Ukraine. In Ukraine statistical data on biofuel consumption is mainly based on information about firewood and wood biomass consumption. This explains the higher percentage of biofuel consumption in forested areas. It should also be noted that in Ukraine 32% of the wood used by population was sold to households by enterprises and 68% was obtained from self-preparation. Over the past decade consumption of biomass fuel for household needs in Ukraine has doubled, and it is increasingly replacing coal fuel, thus exerting a positive impact on the environment.

RESEARCH THERMAL CHARACTERISTICS OF THE PROCESS OF PYROLYSIS OF METHANE IN THE ELECTROTHERMAL FLUIDISED BED

The main products of high-temperature pyrolysis of methane are carbon and hydrogen. Due to their unique physical and chemical properties, pyrocarbon and pyrographite can be used in various industries and energy. Hydrogen is an energy-efficient and environmentally friendly energy carrier. Despite the large number of research works on methane pyrolysis, carrying out of this process in the electrothermal fluidized bed (ETFB) is not studied enough. The purpose of the study is to determine the thermophysical characteristics of the process of methane pyrolysis (the main products of the reaction are hydrogen and pyrocarbon) in reactors with different types of ETFB. The temperature of the complete disposition of methane to carbon and hydrogen is 800 K. This value is based on the thermodynamic calculations. A laboratory and a pilot plant with a different type of ETFB have been created for this process. Experimental studies of the process of methane pyrolysis had been carried out on these plants and experimental data were compared with the calculations. The method which allows to determine the amount of precipitated carbon has been developed. It is based on the gas analysis data. Nusselt's criterion for different types of reactors with ETFB has been calculated. It was showed that electrothermal heating of a fluidized bed of conductive particles is much more efficient than the external electric heating of a fluidized bed. This result is based on previous researches. It is explained by the direct influence of the plasma of microcircuits and by advantages of heat generation directly in the middle of the fluidized bed. Taking into account the obtained results and the specifics of the application of the pyrocarbon coating on dielectric materials, a scheme of a reactor with ETFB, which allows to use both external heating and classical ETFB at the same time, has been developed.

ANALYSIS OF POSSIBILITIES FOR THE PRODUCTION AND CONSUMPTION OF AGROBIOMASS BRIQUETTES IN UKRAINE. PART 1

The purpose of the work is to analyze existing preconditions, driving forces, and barriers for the widespread introduction of the production and use of fuel briquettes from biomass in Ukraine. The task of the work is to determine the advantages and prospects of the process, first of all, for domestic consumers, as well as to develop recommendations for creating a positive environment for the development of this segment of bioenergy in Ukraine. This part of the paper presents the current state of the market for solid biofuels in Ukraine. It is shown that in the biofuel market, the largest segment is solid biofuel in the form of firewood, wood chips, pellets and biomass briquettes, baled straw. Currently, a large amount of pellets and briquettes are exported from Ukraine to Europe due to the insufficient demand in the domestic market. The main features of the solid biofuels production in Ukraine are regional unevenness and relative non-uniformity of production as well as a large number of small-scale enterprises that work with traders. The advantages of the use of biomass briquettes as fuel were analyzed. The main advantages are the conformity of characteristics of briquettes with the requirements of boiler equipment for fuel, better ecological indicators in comparison with the burning of low-quality wood, no needs for specialized energy equipment in contrast with the use of pellets, availability of a significant amount of feedstock especially for briquettes from the biomass of agricultural origin. The current volume of the Ukrainian market for fuel briquettes from biomass for individual heating of the population can be estimated at the level of 500 th. t/year with its growth to over 3 million t/year until 2035. This part of the paper considers possible types of feedstock for the production of fuel briquettes and requirements for it. It is noted that the feedstock for the production of fuel briquettes can be soft and hard wood, straw, reed, sunflower husk, rice and buckwheat husk, flax sheave, and other vegetable residues. Typical requirements for the feedstock: water content – 6...12%, fraction composition – 2...10 mm.

COMPREHENSIVE METHODS OF EVALUATION OF EFFICIENCY AND OPTIMIZATION OF HEAT-UTILIZATION SYSTEMS

At present, Ukraine has the necessary potential for the implementation of effective energy-saving technologies for heat recovery, and therefore the problem of their development and implementation is relevant for the country's energy sector. The solution of this problem is related to the need for systematic studies of the efficiency of optimization of heat recovery facilities from the standpoint of modern methodological approaches. The paper outlines the main stages in the development of integrated methods for assessing the efficiency and optimization of heat recovery systems based on the principles of exergic analysis, statistical methods for planning the experiment, structured variational methods, multilevel optimization methods, the theory of linear systems and the thermodynamics of irreversible processes. Examples and illustrations illustrate some of the stages in the development of complex methods. The necessary general step in the development of methodologies is the development of new performance criteria. Such criteria are highly sensitive to changes in the regime and design parameters of heat recovery systems due to the inclusion of some exergic characteristics in them. The developed criteria also serve as target optimization functions. For individual elements of heat recovery systems, efficiency and optimization methods usually include the definition of the functional dependencies of the selected efficiency criteria on the main parameters. For this, balance methods of exergic analysis and statistical methods of experiment planning are used. If such dependencies are established, optimization is carried out using known mathematical methods. For complex heat recovery systems involving a large number of elements, it is not possible to establish general analytical dependencies of the optimization objective functions on the parameters of the system when constructing mathematical models necessary for their optimization. Complex methods based on the basic principles of structural-variant methods, methods of multilevel optimization, the theory of linear systems, and the thermodynamics of irreversible processes have been developed for such cases. For this purpose, structural diagrams of plants, block diagrams of multi-level optimization have been developed, complete input matrices have been constructed, mathematical models for the processes under investigation have been developed, formulas have been derived for calculating the loss of exergy power in heat conduction processes and formulas for calculating dissipators of exergy. A well-founded choice of the methodology for evaluating efficiency and optimization raises the effectiveness of optimization, since it allows the use of parameters maximally close to optimal when developing the heat recovery system design, which in turn increases the efficiency of the system. References 14, figures 5.

ANALYSIS AND PREDICTION OF RADIOACTIVE DUST TRANSFER AT THE NEW SAFE CONFINEMENT OF CHNPP OPERATION

The results of analysis and forecasting of the radioactive aerosols (RA) spread in the New Safe Confinement (NSC) under various conditions are presented. The conditions for the commissioning NSC, operation, dismantling of the OS (early dismantling) and removal of radioactive waste from the central hall of the OS are considered. Such analysis and forecasting was performed using computer CFD (computational fluid dynamics) model of the OS and NSC. The model takes into account sedimentation, accumulation and secondary dust emissions on the surfaces under the NSC, which allows obtaining distributions of surface contamination and determine the places of the highest contamination. References 5, tables 1, figures 5.

METHOD OF PROFILING OF VORTEX VALVE CHAMBER

The basics of designing a vortex chamber of an internal combustion engine are given. The described method allows to design the surface of the vortex chamber of the inlet channel that meets modern technological requirements.