Refrigeration engineering and technology

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.