Refrigeration engineering and technology

12-20

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

Absorption refrigerators (AR) with absorption cooling units (ACU) have an increased energy consumption during operation due to the thermodynamic imperfection of the absorption refrigeration cycle, the presence of low-intensity diffusion processes of mass transfer in the evaporator and absorber and the losses associated with evaporation and Subsequent transportation of ammonia from the generator unit to the condenser and then the evaporator. The greatest effect in energy saving during the operation of ACU with minimal changes in design can be achieved by improving the operation modes of generating units. The main direction of modern research of AR is aimed at qualitative obtaining of experimental data. The objects of experimental research were modernized models of household absorption single-chamber refrigerators "Kyiv- 410" and "Kristall-408". The modernization consisted in the installation of an additional heat-insulating casing on the generating set in such a way that the entire lifting section of the reflux condenser was closed. The parameters of the heatinsulating casing were chosen taking into account the known recommendations, in particular, the thickness of the thermal insulation made of glass fiber was 4 mm. To estimate the rate of displacement of the inert gas during the starting period, the amount of generated steam was calculated by calculation. For the analysis, the results of known studies and own experience were used. It was shown the expediency of forcing the heat load on the generator - the reduction of energy costs during the start-up period can be from 25 to 35%. Taking into account the calculation results, the original three-position control methods of AXA with the thermal load input to the generator "110 - 70 - 0" and "130 - 70 - 0" were proposed. It is shown that the method of controlling the AR with a constant two-stage supply of heat load and controlling the flow temperature at the outlet of the reflux condenser allows to reduce energy consumption by up to 20 %, in comparison with traditional position control. Despite the constant in time supply of heat load to the generator, the advantage was achieved due to: A) maintaining the elements of the generating set in the "warmed up" state, which makes it possible to minimize the transition time to the mode with the rated refrigerating capacity of the evaporator; B) maintaining the minimum refrigerating capacity of the evaporator in the "waiting" mode. The energy-saving effect of the new control method is largely related to the installation of the heat-insulating casing on the dephlegmator. This allows not only to use the minimum refrigerating capacity of the evaporator (at Q = 40 W), but also to switch to a lower level of rated thermal load (Q = 70 W) compared to the serial version (Q = 110 W). The duration of the working period for absorption refrigerators is related to the inertia of the startup processes, when all the energy input is spent only on the heating of the elements of the generator assembly. In this regard, measures aimed at maintaining energy-efficient operation modes of the generating set, despite the additional energy costs, provide advantages in energy saving. It is possible to achieve a sufficiently significant increase in the efficiency of the ACU operation, taking into account the peculiarities of their operation over a wide range of ambient air temperatures. One of the effective and low-budget methods for increasing the energy efficiency of ACU is the technology to reduce losses when transporting ammonia to the artificial cold zone (evaporator). A key role in this process is performed by the AR reflux condenser, which purifies ammonia vapor by removing the heat of a phase transition into the environment in the temperature range from 10 to 32°C. To reduce losses during the transportation of ammonia through the AR dephlegmator, it is necessary to install a thermal insulation that would efficiently purify ammonia vapor (at high ambient temperatures) within the working temperature range and promote its minimum condensation of ammonia (at low ambient temperatures). An original design of the mobile heat insulation of the dephlegmator transport zone is proposed, which regulates the air supply to the dephlegmator by moving the bellows walls filled with a low-boiling liquid.

29-33

Authors: N. A. Prusenkov

The systems of temperatures regulation on the surfaces of multi-layered enclosing structures (MES), providing the achievement of different and even opposite aims: а) maintenance of the predetermined temperature of MES internal surface, which is bounded by the normalization of losses at constant resistances to the heat transfer through the layers (closed); б) intensification of exchange by heat with space through MES surfaces, by the change of temperature of coolant-moderator during exploitation (movable) are well-known and used in the different processes. At the same time, the acting DBN recommends a replacement in calculating of heat transfer through the MOS for heat exchange in thermal envelope of buildings, that contradicts the postulates of the constancy and exclusivity of enclosed enclosure designs requiring the modernization of the regulatory and theoretical basis for their creation. The regulation of the characteristics of closed (a) and mobile (b) systems components, combined into a single evolutionary one based on the principles of superposition and distribution of their interaction results, ensures the manifestation of the exergic properties of the interaction of heat exchange and heat supplied during the transition, which are absent in systems for the interaction of which conditions are created. This ensures the formation of a new goal that is not achievable at a local operation of each of the interacting systems. The energy balance of the unification of these systems stimulates the evolution of the operational mode, creating an exergic system of closed and mobile flows interaction, achieving the goal of publication. The presented result proves the expediency of supplementing the current standards with instructions governing the elimination of energy release through the outer surfaces of enclosures.

39-44

Authors: K. Smirnova, А. Smirnov, O. Olshevska

The issue of critical importance objects safety, namely in the electric power engineering, is always acute both for the owners of enterprises and for the state. The article considers the features of providing information protection for the electric power engineering. The concept of organization of technological processes automated control systems information security is proposed. The concept touches upon both electric power enterprises and industrial enterprises as a whole.

49-52

Authors: Yu. Zhuravlov

The possibility of rational design of thermoelectric device in systems for providing thermal modes for radioelectronic equipment during operation in various climatic conditions is considered. The aim of the work was to find solutions that allow choosing a variant of thermoelectric device design at a changing temperature of the environment, which ensures a reduction in energy costs and an increase in reliability indicators. The calculations of the basic energy and reliability parameters of thermoelectric devices for various operating modes have been carried out. The influence of the ambient temperature is analyzed and it is shown that the heat load, operating current, power consumption and intensity of failures increase with temperature. The expediency of thermoelectric devices functioning in the mode of minimum failure rate is substantiated, which allows reducing the failure rate by 1.5 times in comparison with the maximum cooling capacity mode.

14-17

Authors: V. V. Trandafilov, M. G. Khmelniuk

Plate-fin heat exchangers are widely used in refrigeration technique. They are popular because of their compactness and excellent heat transfer performance. Here we present a numerical model for the development, research and optimi-zation of a plate-fin heat exchanger for a rotary-vane gas refrigeration machine. The method of analysis by graphic method of plate - fin heat exchanger is proposed. The model describes the effects of secondary parameters such as axial thermal conductivity through a metal matrix of the heat exchanger. The influence of geometric parameters and heat transfer coefficient is studied. Graphs of dependences of length, efficiency of a fin and pressure drop in a heat exchanger on the thickness of the fin and the number of fins per meter are obtained. To analyze the results of numerical simulation, the heat exchanger was designed in the Aspen HYSYS program. The simulation results show that the total deviation from the proposed numerical model is not more than 15%.

21-30

Authors: A. S. Titlov, I. N. Ishchenko, O. A. Titlova, A. O. Kholodkov, Yu. A. Ocheretyany

To ensure the safety of food products, many technologies are used. However, no processing technology, except for cooling, is able to extend the shelf life of products and at the same time preserve their original properties. An important role in ensuring the proper quality of food products has a continuous refrigeration chain (CRC). The CRC is a collection of refrigeration equipment and technologies, as well as organizational arrangements that provide the necessary regimes for refrigeration and storage of agricultural raw materials and products along the entire path from producer to consumer. As the long experience shows, the greatest deviation from the recommended and optimal regimes in terms of storage and energy consumption takes place in domestic refrigerators. At present, the most popular refrigerators in the household refrigeration industry are refrigerators based on compression refrigerators. Absorption refrigerators are an alternative to compression refrigerators in domestic refrigeration technology. The composition of the absorption refrigerators includes absorption refrigerating apparatus (ARA), which realize a pump-free absorption-diffusion refrigeration cycle. The working substance of ARA consists of natural components and does not adversely affect the atmosphere of the planet. However, ARA have a significant drawback - more, in comparison with compression analogues, the consumption of electrical energy during operation. Thus, the current task is to reduce the consumption of electricity during the operation of household ARA. The solution of the problem will allow ARA to compete successfully with compression analogues and take a worthy place in the market of household refrigeration equipment. It is shown that significant progress in reducing energy costs during the operation of ARA can be achieved by taking into account changes in the temperature of the outside air, in particular, the air environment of the room. As the analysis shows, the increase in pressure in the system adversely affects the diffusion processes that take place in the evaporator and absorber ARA, since the diffusion coefficient is inversely proportional to the absolute pressure in the system. At the same time, the simultaneous increase in temperature and pressure in the absorber shifts the equilibrium of the water-ammonia solution (WAS) toward large amounts of ammonia in the WAS and, as a result, the intensity of the absorption process increases, despite a certain deterioration in the diffusion processes. The increase in pressure in the system causes a corresponding increase in the temperatures in the generator and the specific energy consumption for evaporation of the WAS. By the positive moment of ARA operation in conditions of high ambient air temperature, it is possible to include minimal losses from the surface of the thermal insulation casing of the ARA generator assembly. The first and the main - the lift section of the reflux condenser works as an ammonia condenser, and the condensate flows into the generator. The second factor is that most of the heat supplied is dissipated into the environment. As a result, a small amount of ammonia enters the condenser and further into the evaporator, which even under favorable operating conditions cannot provide the required cooling conditions in the cooled chambers. To assess the energy efficiency of the operating modes of the ARA generator at various pressure levels in the system, an appropriate analysis was conducted, taking into account the results of ex-perimental studies of serial ARA produced by the Vasilkovsky Refrigeration Plant. The pressure in the system varied from 12 to 20 bar. The analysis of the obtained results allows to draw a conclusion about the favorable effect of the reduction of the pressure level on the energy efficiency of the ARA generator. Thus, with a pressure drop of 20 bar to 12 bar, the specific heat consumption for evaporation of 1 kg of ammonia is reduced by 7.8%. There are proposals to reduce the working pressure in the ARA system associated with changes in the composition of the working fluid, in particular, the amount of inert gas (hydrogen) when the temperature of the surrounding air changes. Their disadvantage is the complexity of the design of the control system and the need for sources of electrical energy. To increase the autonomy of ARA, the external impact on the system is promising. Promising is the possibility of forced blowing of heat dissipating elements (absorber, condenser, dephlegmator) both by using fans with electric drive (when driving a vehicle) and driven by a flow of hot gases (in the parking lot). In view of the cooling effects found, the original design of a transport absorption refrigerator with forced external air cooling the heat dissipating elements of the ARA (absorber and condenser) was proposed, while the temperature potential of the combustion products (220 ... 260 °C) flowing through the ventilation duct was suggested as a circulation stimulator.

39-43

Authors: A. V. Solodkaya, I. L. Boshkova

Heat exchangers of contact type have a number of undoubted benefits in comparison with heat exchangers of surface type. Features of contact heat exchangers is the transfer of heat through direct contact of working bodies. The main advantages are the high intensity of heat transfer processes due to the developed heat exchange surface, the absence of the separation wall, the simplicity of design. The subject of the study is a heat recovery exchanger, in which heat exchange is carried out between gas flow and dispersed material. The importance of knowledge about the influence of individual factors and conditions on the temperatures distribution and heat exchange efficiency determine the need to construct the appropriate mathematical models. A two-component model describing heat exchange between gas and particle flows in a differential form is presented. As a result of its solution, analytical dependencies for calculating the temperatures of gas and solid components in the conditions of the steady-state regime for a direct-flow and countercurrent motion scheme were obtained. The results of calculations of component temperatures for two types of dispersed materials, gravel and expanded clay are presented. The obtained dependencies make it possible to study the processes of heat exchange analytically and can be proposed to assess the effect of geometric and physical characteristics on the efficiency of heat recovery exchangers, in which flows of gas and dispersible material interact.

49-59

Authors: T. V. Diachenko, V. N. Artiukh, A. S. Titlov

Natural gas is an important energy source in the overall energy system. Liquefied natural gas is one of the options for delivery to hard-to-reach regions. This article reviews the world natural gas market: reserves, production, consump-tion. More specifically, attention was paid to Europe, the issue of its infrastructure and market was touched. Examples of successful use of liquefied natural gas in some European countries and new potential liquefied natural gas consum-ers are given.

66-73

Authors: N. A. Kniazieva

In this paper the method for determining the functional survivability of intelligent superstructure, that performs decentralized control of the process of providing intelligent services is proposed and also are obtained formulae for estimation functional survivability for providing intelligent services the performance a subset of functions that realize the purpose of the functioning of the system (the provision of intelligent services of a certain class), and also performance of at least of one of the functions from a subset (providing at least one kind of certain class intelligent service). The received formulae can be objectively used at the design of the control system over the intelligent service, at the choice of a control principle, at the decision of the problems of control system functional survivability increasing over intelligent service

80-87

Authors: I. N. Nikolenko, V. A. Masur, D. G. Pascu

The single-channel line driver of average and major time intervals of high accuracy (FTI) on the basis of the known method of summation of single temporal increments is developed. Increase in time interval accuracy is provided due to value reduction of the instrument dynamic error which always arises at the time of front (end, edge) time interval formation. Reduction of an instrumental dynamic uncertainty is provided by simplification of the canal of program time codes conversion of the known FTI structure to fronts of time intervals. Formation of the high accuracy time interval front is executed in two stages. At the first stage, the program code of time В from the RAM outputs proceeds to the canal of preliminary conversion where its value decreases on 1. Then comparison of the received B-1 code with a real code of time A, proceeded from outputs of the real time counter is executed in the unit of the codes comparison circuit (CCC). In case of equality of the B-1 and A codes, the received result of comparison from an output of the unit CCC is recorded in the T-trigger. At the second stage the next program pulse of the generator proceeds simultaneously on the preliminary conversion canal input and to a time intervals fronts formation path on a dynamic input of D-trigger synchronization. At this moment copying of the kept result of comparison from the T-trigger to the D-trigger with simultaneous D-trigger state change is executed, i.e. formation of the real time interval program front on an FVI output corresponding to a B=A+1 program time code. Pulse "Start-up" of FVI marks the beginning of formation of time intervals.

11-19

Authors: E. A. Osadchuk, V. Kh. Kirilov

The mathematical model of film flow modes with an upward flow of a steam mixture with a highly efficient heat removal in the forced convection mode has been developed. The parameters of the liquid film flow and the vapor flow (velocity and Reynolds number) were estimated for typical values of rectifier tubes diameters in 20, 32 and 40 mm. It was shown that the mode of film flow is laminar; of the steam flow – developed turbulent, and the thickness of the film is practically unchanged for the rectifier tubes dimensions under consideration.

27-34

Authors: A. E. Denysova, G. V. Luzhanska, I. O. Bodnar, A. S. Denysova

The problem of energy saving becomes one of the most important in power engineering. It is caused by exhaustion of world reserves in hydrocarbon fuel, such as gas, oil and coal representing sources of traditional heat supply. Conventional sources have essential shortcomings: low power, ecological and economic efficiencies that can be eliminated by using alternative methods of power supply, like the considered one: low-temperature natural heat of ground waters on the basis of heat pump installations application. The considered heat supply system provides an effective use of two stages heat pump installation operating as heat source at ground waters during the lowest ambient temperature period. The calculation method of heat pump installations on the basis of groundwater energy is proposed. The values of electric energy consumption by the compressors’ drive, and the heat supply system transformation coefficient µ for a low-potential source of heat from ground waters allowing to estimate high efficiency of two stages heat pump installations are calculated.

40-43

Authors: I. L. Boshkova, N. V. Volgusheva, N. A. Kolesnychenko

Heating in the microwave field opens the possibility of developing fundamentally new technologies for creating materials that are significantly higher in comparison with existing operational and functional properties. High heating rates in the microwave field result in significant power savings and reduction in sintering time, which is important when creating high-quality materials. This method allows obtaining products with a finely dispersed and defect-free microstructure and, as a result, improved functional properties. The paper deals with the features of heating of dense materials used in the technical ceramics production, under the action of a microwave field. Silica carbide powders and alumina powders were used as the test material. The estimation of power efficiency of microwave sintering technology is presented on the example of ceramic substrates production. For evaluation, data on the technological parameters of sintering of silicon carbide in an oven by MARUWA and the values of the speed and duration of microwave heating were used. It is established that the intensity of sintering during the transition to microwave technology is significantly increased, while the power costs are significantly reduced.

54-62

Authors: A. A. Petrik, I. G. Yakovleva

One of the most important problem in the development of power-saving steelmaking technologies is the problem of blowing a bath of a steelmaking unit with the organization of an efficient oxygen modes of reburning CO oxygen in steel-smelting furnaces with the purpose of smelting heat balance improvement. In conditions of shortage and high cost of power sources, this technology allows to bring the expense of steel smelting process. In order to analyze and intensify the thermal and oxygen modes of melting and determine the influence of the purge intensity on the thermophysical and gas-dynamic processes in the bath, the heat exchange in the volume of the steelmaking unit during bubbling of the melt was performed. The results of studies aimed to the study of the effect of thermophysical parameters of the feeding gas on the intensification of heat transfer processes during bubbling of the melt in the bath of the steelmaking unit are given. The influence of the blower nozzles inclination angles and the position of the tuyeres over the melt on the heat transfer process was determined. The dependence of the heat flux value during the interaction of the oxygen jet with the surface of the slag melt on the oxygen consumption and the heat transfer coefficient was found. It is established that with the increase of the nozzles inclination angle, the values of the heat transfer coefficient and the heat flux reduce. This is due to the increase in the length of the jet, the decrease in the depth of the hole. This leads to a decrease in the intensity of bath mixing and less heat transfer to the slag and to the metal. When the blowing device approaches to the melt, an increase in the heat transfer coefficient and heat flux is noted. It is connected with the intensification of the bath mixing.

71-75

Authors: HuiYu Zhou, O. V. Korolov

The paper presents a mathematical model of cap-damper of pressure oscillations in piston pumps and its approbation on practical calculations. The aim of the study is the theoretical justification of the rationale for the cap- damper of pressure fluctuations calculation in the given conditions. It is shown that two previously known methods of cap- dampers calculation do not satisfy the conditions of the practice. By analyzing the transfer function of the cap as the converter (attenuator) of signal, the ratio was obtained, which allows to calculate the structural characteristics of the cap- damper on the desired degree of pressure reduction. Calculations under the terms of industrial and power pumps were carried out. The resulting expression allows you to evaluate the size of the cap-damper taking into consideration the properties of gas and structural conditions at the outlet of the absorber. It is shown that the effectiveness of the cap-damper does not depend on the pump operation mode. The design of the cap-damper calculated on the proposed method has a lower metal content than the conventional constructions.

84-88

Authors: M. M. Al-Dhabi, O. V. Drozd, M. O. Drozd, I. M. Nikolenko

Features of operation diagnosing of digital components in the information controlling systems of critical application ensuring the functional safety of objects of the increased risk including cryogenic technique are considered. Feasibility of development of operation diagnosing for digit-by-digit pipeline nodes of digital components which allow solving successfully a problem of the hidden failure reducing fail safety of digital circuits in the most responsible emergency operation of operation is shown. Within model of approximate data, control methods on inequalities gained further development for working diagnosing of digit-by-digit pipelines. Result models were proposed as the lower and upper boundaries within which the result is defined by authentic. For three types of digit-by-digit pipeline multipliers models of data access in monitoring are defined. The program estimating probabilities of detection of an error depending on error amount for monitoring on inequalities with use of different boundaries of result is developed. Increase in probability of error detection in the conditions of growth of error size is shown.