Refrigeration engineering and technology

10-13

Authors: А. V. Zimin

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.

22-25

Authors: M. Khmelniuk, N. Zhikhareva, O. Olshevska

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.

34-41

Authors: Amina Abdessemed

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.

53-61

Authors: O.Yu. Rozina, V.B.Rogankov

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.

66-75

Authors: P.V. Borzenkov, V.P. Zhelezny

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).

84-89

Authors: A.A. Kondratenko, B.V. Kosoy

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%.

98-103

Authors: A. A. Gnatovskaya

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.

113-120

Authors: I. Kolumba

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.