Volume 51 Issue 3
Section 1. Refrigeration engineering
V. A. Smyk, Yu. V. Baidak
CONVECTIVE HEAT EXCHANGE FROM THE REFRIGERATING CONTAINER PROBLEM SIMULATION
Materials of the study are directed on the solving the problem of air velocity calculating in a confined volume of refrigerating chamber of 20 foot refrigerated container with forced air convection from Carrier Transicold producer firm and on this basis –of convective heat transfer. Problem simulation has been performed in a two-dimensional coordinate system using COMSOL Multiphysics, Femlab 3.0, Fluid Dynamics - Incompressible Navier-Stokes - Convection and Conduction software. As an object of research differential equations of air movement impulse and transfer of energy with it were applied. As a subject of research was selected thermal physical phenomena inside and around the net volume of empty and loaded refrigerated container at air movement. Significant impact of the air movement on the temperature distribution inside the refrigerating container chamber has been established. The obtained results allow to get closer to the theoretical evaluation of the refrigerating machine efficiency in an ordered mode during changes of thermophysical parameters of cargo volume and the environment during perishable products transportation. Tested method is useful for application by scientists and post-graduate students engaged in theoretical simulation of heat transfer problems in the field of refrigeration engineering.
Key words: Simulation; Refrigerating container; Refrigerating machine; Refrigerating chamber; Forced convection; Velocities field; Temperatures field.
А. V. Zimin
AIR-DISTRIBUTION SYSTEMS FOR FRUIT AND VEGETABLE PRODUCTS STORAGE ROOMS
At refrigeration storage of fruit and vegetables it is necessary to support the optimal technological mode in stores. Deviations of the mode result in the considerable losses of mass and product quality. Basic influence on evenness of the temperature-humidity field is rendered by the systems of storage room air-distribution. The systems of air-distribution are a channel, channel-less and active aeration. The channel-less systems are based on separate unit coolers that is up-diffused on the area of chambers. Such systems are the simplest and cheapest. The channel systems have one or a few forcing and suction channels. Placing of channels provides the even temperature-humidity field in a chamber. Such systems are more difficult and expensive. Principle of work of the systems of active aeration is based on creation of the set technological mode directly in the stack of fruit and vegetables. The use of such technology allows taking the losses of product to the minimum.
Key words: storage of fruit and vegetables; systems of air-distribution; active aeration.
V.Y. Labay, D.I. Harasym
THE DEPENDENCE OF THE EXERGETIC OUTPUT-INPUT RATIO OF AIR CONDITIONING SYSTEM FOR OPERATING CLEANROOMS ON COEFFICIENT OF TRANSFORMATION OF REFRIGERATION MACHINE
Exergetic method is a universal way of thermodynamic research of various processes of energy transformation in energy technological systems, to which air conditioning system for cleanroom belongs. Implementation of exergetic analysis for energy technological system makes it possible to determine the influence of various elements of its system on its work and because of this to increase the effectiveness of work of energy technological system in general. Effectiveness of work of any air conditioning system depends on energy effectiveness of refrigeration machine, which serves it and consumes electricity for reducing the heat of supply air which enters the room. And it means that the main purpose of selection of certain refrigeration machine for air conditioning system is to reach the maximum cooling capacity with minimum energy consumption. Innovation mathematical research model of the implemented central straight flow air conditioning system for operating cleanrooms was used in this article. The aim of the model is to make computer estimation of exergy efficiency of existing air conditioning system depending on different factors, which have influence on its work, in particular the coefficient of transformation EER of its refrigeration machine. The dependence of the exergetic output-input ratio of implemented air conditioning system for operating cleanrooms on coefficient of transformation EER of its refrigeration machine by different parameters of outdoor and indoor air and the temperature difference between the indoor and supply air were presented. It is shown, that the implemented air conditioning system should be preferably used by higher coefficient of transformation EER of its refrigeration machine and higher difference between temperatures of indoor and supply air by various temperatures of outdoor air, that will give the opportunity to gain the highest exergetic output-input ratio , which means to gain the most advantageous economical variant of exploitation of implemented air conditioning system.
Key words: Exergetic balance; Air conditioning systems; Cleanrooms; Exergetic efficiency; Coefficient of transformation EER
M. Khmelniuk, N. Zhikhareva, O. Olshevska
EXPEDIENT-ECONOMIC THICKNESS OF MODERN INSULATING MATERIAL FOR FRUIT-VEGETABLE WAREHOUSES
The impact of expedient-economic insulation thickness on energy and resource saving fruit-vegetable warehouses cooling systems optimization is examined in the paper. The method of cal-culation is presented. The calculation results for expedient-economic thickness of modern insulating materials are introduced.
Key words: insulating materials; optimization; heat-mass exchange; energy loses; fruit-vegetable warehouses
V. Trandafilov, O. Yakovleva, M. Khmelniuk
MEDIUM-TEMPERATURE STIRLING GAS-REFRIGERATING MACHINES DEVELOPMENT TRENDS
Fuel and energy resources price surge as well as global warming pushes us to set problem of searching innovative technologies for energy transformation, to develop new technologies on the base of thermodynamic cycles with high efficiency, to use new working mediums in order to develop ecologically safe energy system, which can satisfy industrial sector alone with housing and utilities for minimum amount used. In this paper we describe Stirling refrigeration system for medium-temperature cooling. Stirling-engine embodiment characteristics are analyzed in order to derive defects, limitations as well as to propose the way of disadvantages removal. Principal advantages of Stirling refrigeration system are represented such as environmental safety, higher energy coefficient, overall detentions reducing and lower energy consumption. Construction problems and Stirling refrigeration system production with high efficiency are analyzed. Defined data let us to claim that The Medium-Temperature Stirling Refrigeration Systems use offers a bundle of benefits and opportunities for medium-temperature cooling.
Key words: Environmental safety – Energy efficiency – Stirling refrigerating machine – Medium-temperature refrigeration – Vapor-compression refrigerating machine – Mathematical model
Section 2. Power engineering and energy saving
LOW-TEMPERATURE WATER EVAPORATIVE CHILLERS DEVELOPMENT AND THEIR FUNDAMENTAL CAPABILITIES ANALYSIS
Conception of creation of the water evaporative chillers of new generation is worked out with the use of air-water heat-exchanger for the preliminary cooling of entering air, at its unchanging moisture content. The natural limit of cooling in such systems is a dew of outward air point, that substantially extends capabilities of the evaporative cooling technique practical use as a whole and allows to decide the tasks of refrigeration and air-conditioning systems with a substantial power cost cutout on realization of processes and simultaneous decline of level of harmful ecological influence on an environment. In the evaporated cooler multichannel structures are used from polymeric materials. Traditional type and new generation water chillers capabilities comparison is executed at varying of initial parameters and correlation of gas streams and liquid in the basic contours of the evaporative chillers.The special attention is spared to the issue of water vapor condensation on the satiation line in transition on the deep evaporative cooling of environments. The comparative analysis of such coolers capabilities is executed on the basis of theoretical and experimental data of the author, as it applies to the solution of evaporative cooling tasks.
Key words: Evaporative chiller; Multi-channel packing; Polymeric materials; Combined heat and mass transfer; Recondensation
A.V. Doroshenko, K.V. Lyudnitskij
SOLAR REFRIGERATION SYSTEMS BASED ON THE ABSORBER WITH INTERNAL EVAPORATIVE COOLING
The paper presents the developed schematics for alternative refrigeration systems and air condi-tioning systems based on the use of heat-absorption cycle and solar energy for regeneration (re-covery) of the absorbent solution. Cascade principle of construction of the drying and cooling circuits with absorbent concentration increasing on the steps of the cascade is used. The absorber with internal evaporative cooling that eliminates a separate evaporative cooler, typically comprised after the corresponding absorber is worked out. Heat mass transfer film-type equipment which is part of the drying and cooling circuits is unified and executed on the basis of mono-block multi-channel compositions of polymeric materials. A preliminary comparative analysis of the possibilities of solar refrigeration systems, solved by the formulas ADB and ADB-IO / IO-R is carried out.
Key words: Solar systems; Dehumidification; Cooling fluids; Heat masoobmennaya apparatus; Absorption; Stripping; Evaporative cooling
O.Yu. Rozina, V.B.Rogankov
GENERATION OF HEAT FLUX NEAR THE CAPILLARY IMMERSED INTO THE CAVITATING LIQUID DUE TO THE EXTERNAL ACOUSTICAL FIELD
We propose the simple model of the heat flux generation throw the open end of the capillary cannel submersed into liquid, where an ultrasonic field is formed. This model is based on the previous experimental research of the sonic-capillary effect. The peculiarities of them are: the excitation of cavitations strongly under the capillary cannel; the translation motion of cavities to the capillary cannel, recorded by mean of the moving image camera with the velocity of about 160000 frames per second; the local heating of liquid in capillary and temperature distribution in the capillary cannel; the gradient of temperature directed according the translation motion of the cavities. The principal distinction of our model is that the cavitation process is connected with a periodical phase transitions. Due to the directional motion of cavities to the capillary cannel, all thermodynamic processes, connected with extension of cavities and which need some quality of heat are located under the capillary cannel; the decreasing of cavities and the return of heat are located in the capillary cannel. Thus, the result heat flux forms throw the open capillary section. The proposed model is realized as a software and calculated in wide ranges of temperature, diameters of cavities, frequencies of ultrasonic. The density of heat flux was calculated for the conditions of based experiments.
Key words: Heat flux; Capillary; Ultrasonic cavitation; Phase transition
A.S.Titlov, D.P. Gozhelov, G.V. Shlapak, G.M. Redunov
ANALYSIS OF PROSPECTS FOR USE ON VESSELS PUMPLESS ABSORPTION-TYPE REFRIGERATING UNITS
The issues of the heat-utilizing low-capacity refrigerating machines utilization on the vessels for storage of food, raw materials and semi-finished products are discussed in the paper. The exhaust gases of diesel generators may be used for such units operation on the vessels. Two schemes of pumpless absorption-type refrigerating units – with air- and liquid-cooling of heat dissipating elements are examined.
Key words: exhaust gases heat recycling; absorption-type refrigerating unit; marine refrigeration equipment.
Section 3. Refrigerating and accompanying technologies
P.V. Borzenkov, V.P. Zhelezny
THE NANOPARTICLES EFFECT ON THE LIQUID-LIQUID PHASE EQUILIBRIUM PARAMETERS. PART 2.
Issues of nanoparticles impact on the parameters of the phase liquid-liquid equilibria in the gen-eral vicinity of the critical point are considered in the paper. Binary system exfoliating nitroben-zene/n-heptane and nitrobenzene / nanogeptan are been objects of study. Simulation results of phase equilibrium liquid-liquid using the extended scaling equations are given. It is shown that for an adequate description only three coefficients and critical system parameters are necessary. The rule of rectilinear diameter for exfoliating systems is applied. Critical phenomena in the curves for the three-component separation nanofluids (nitrobenzene / heptane / nanoparticles TiO2) are isomorphic phenomena on the curves of the bundle of binary solutions (nitrobenzene / heptane).
Key words: Coexistence curve; Nanoparticle; Concentration; Nanofluid; Experiment; The equations of the extended scaling.
NUMERICAL SIMULATION OF TEMPERATURE SEPARATION IN METHANE STREAM IN RANQUE-HILSCH VORTEX TUBE
In present numerical research, the temperature separation in methane stream within a counter flow Ranque-Hilsch vortex tube was investigated. A complete three-dimensional geometry of the vortex tube was used to generate a high-density computational grid. A vortex tube with two tangential inlet nozzles, an axial cold stream outlet and a circumferential hot stream outlet was considered. Methane was used as a fluid along with Peng-Robinson cubic equation of state. Fluid properties like total temperature and total pressure were analyzed for a range of inlet mass flow rates and inlet total pressure values. Also the total pressure and total temperature distribution along the axial direction was investigated. The temperature separation effect is more significant for air then for methane at all investigated pressures. Created model can be used to design industrial vortex tubes for oil and gas industry where methane is a main product.
Key words: Ranque-Hilsch vortex tube; Energy separation; Large eddy simulation; Real gas equation of state; Methane
A.A. Kondratenko, B.V. Kosoy
EXPERIMENTAL STUDIES OF CAPABILITIES FOR ENHANCEMENT OF VAPORIZA-TION HEAT TRANSFER AT THE MICROCHANNEL SURFACES
The use of grooves, as the structure of flat plate heat pipe is widespread and is a popular and effective technical solution in the practical implementation of various design systems for thermal control of electronic equipment. Advanced thermal control system must meet two criteria: 1) have a high heat transfer coefficient; 2) remove heat of high density. However, the last criterion leads to the fact that the high density heat flux may lead to a boiling limit, which leads to a drastic decrease in heat transfer coefficient, and conducts to a rapid increase of surface temperature. The paper presents an experimental investigation of the heat transfer characteristics of the microgrooved structures at vaporization of water and ethanol. The structures are represented in the form of axial grooves with a square section dimensions of 0.3, 0.5 and 0.7 mm, and a rectangular cross section with the same width and pitch parameters of the channel but with double depth of channels. Studies showed that in the grooved structures three modes of vaporization occur as follows: evaporation, evaporation-pulsation and boiling. The experiment revealed the area having constancy of the heat transfer coefficient at varying specific heat flux that is typical for evaporation. At certain heat flux value the nucleate boiling in the grooves is initiated, and heat transfer coefficient is growing at increasing heat flux. Boiling in the channels of micro-grooved surface is accompanied by a slug boiling regime, and formation of a thin liquid film on the surface of the channel. It is essentially increasing the heat transfer characteristics of the micro-grooved structures. Double of the channel depth leads to increase in heat transfer coefficient up to 30 - 40% for both water and ethanol. Increase of the heat transfer coefficient could be explained by the enlargement of the heat transfer surface of the channels. Increasing of the effective pore radius by the increasing of the channels depth leads to reduction in the hydraulic resistance of the channels that accompanies increase of the critical heat flux up to 50 - 60%.
Key words: micro-grooved structure – vaporization – heat transfer – critical heat flux.
NEW CYCLE OF AVERAGE PRESSURE FOR AIR LIQUEFYING AND POSSIBILITY OF ITS APPLICATION IN VRU
The new cycle of average pressure for air liquefaction permitting lowering of thermodynamic losses in heat exchange devices is offered. On specific examples with application of the q-1/T diagrams analysis and comparison of thermodynamic losses in a classical Clothe cycle, in air separation units cycle and offered cycle is carried out. The opportunity to use offered cycle in air separation units for obtaining the liquid components of air fractionation is considered.
Key words: cryogenic engineering; thermodynamic losses; air fractionation.
Section 4. Automatic, computer and telecommunication technologies
A. A. Gnatovskaya
SIMULATION OF HEAT-LOADED MEANS WITH RESERVATION OF CRITICAL SYS-TEMS IN CAD SYSTEMS
The article represents the issues of simulation of heat-loaded means with reservation of critical systems in CAD systems. The reliability parameters of heat-loaded devices cannot be achieved only by parametric methods and require to ensure efficient management of their reliability. Achievement of this level of reliability for heat-loaded systems is possible by hardware redundancy, i.e. redundant. The model which could improve the heat-loaded system reliability through the use of hardware redundancy, based on the use of redundancy techniques was presented. The effectiveness of reservation techniques in the early stages of development and design determines its usage for reliability improving as critical thermally loaded elements and the system as a whole. Application of the proposed model of reliability improvement of heat-loaded means due to hardware redundancy in the CAD subsystem allows evaluating the effectiveness of different methods of hardware reservation to improve the reliability of heat-loaded system.
Key words: Reliability; Thermoelectric devices; Critical Systems; Heat-loaded means.
V.P. Zaykov, V.I. Mescheryakov, Yu.I. Zhuravlev
IMPROVING THE RELIABILITY OF SINGLE-STAGE THERMOELECTRIC COOLING DEVICES BY THE USE OF VARIOUS COMBINATIONS OF ORIGINAL MATERIALS OF EQUAL EFFICIENCY
The article represents possibilities of improving the reliability of single-stage thermoelectric cooling device by using different combinations of the original materials averaged parameters of the same efficiency, namely, thermoelectric power factor, electrical conductivity and the thermal conductivity for various changes in temperature and operating modes for a given height to the cross-sectional area branches of the thermocouple. There were obtained simple analytical expressions that provide the interconnection of reliability, namely, failure rate, the number of thermocouples of thermoelectric cooling capacity single-stage thermoelectric cooling device for different combinations of parameters of the source material. The calculations of single-stage thermoelectric devices basic parameters for different operating modes on the mode of maximum cooling capacity to minimum failure rates for different ranges of temperature changes from 0 to 60 K, and various combinations of options thermoelectric materials with differing efficiency parameters, electrical conductivity, thermoelectric power factors, the geometric parameters of thermocouples are presented. It is shown the possibility of failure rate reducing and increasing of cooler failure-free operation probability through the use of original materials with the same efficiency for greater conductivity.
Key words: Reliability – Thermoelectric devices – Materials – Failure rate – Cooling capacity
APPROACHES TO SERVICE REQUESTS IN INTELLECTUAL SUPERSTRUCTURE IN NEXT GENERATION NETWORKS
The paper considers the existing principles of management services in intellectual add-in of NGN - centralized and decentralized management, shows their advantages and disadvantages. The architecture of intellectual add-in with a mixed control strategy was proposed which presents several hierarchy levels, which are key nodes of intellectual add-in. The lower level has a few Softswitch, which are connected to each other. At the top level of the hierarchy there is a universal server, which is a single control center. At an average level there are specialized server services, connected with the central control device and a Softswitch. Intellectual add-in with a mixed architecture offers several approaches to service requests. According to the first approach, the request for service arrives at one of the dedicated servers through the connected Softswitch installed in a separate area. In the other, the request is taken Softswitch, which is connected to the universal server services. The choice of management approach to intellectual add-in builds on the assessment of management effectiveness of intelligent services, the calculation of which is necessary to consider individual indicators of quality. As partial indicators of intellectual services provision quality the author proposed to use the total residence time of request for intelligent service in management system, the total waiting time of request service, the probability of request blocking on the server on the upper level of intellectual add-in, the probability of request service on the server on the middle level of intellectual add-in, the control system cost. The calculation of the final effectiveness based on the proposed specific indicators for each of the presented approaches to architecture of the intellectual add-in will provide an opportunity to determine the best management option.
Key words: Intellectual services; Intellectual superstructure; Next-generation networks; Mixed management principle.