Heat Exchange Intensifiers Research Articles

Исследование тепловой работы теплогенератора ротационной хлебопекарной печи

The main technological equipment to produce bread and confectionary is baking ovens. Fuel-based rotary ovens, in which the heat source is a heat generator, have become widespread. Often, the thermal conditions of ovens are characterized by increased fuel and thermal energy costs which depend on the efficiency of the heat generator. Currently, there are no recommendations on the design of a heat generator with the most efficient characteristics and the coefficient of efficiency, namely the distribution of the heat transfer surface between the flame tube and the heat exchanger, the layout and materials of the heat exchanger tubes, the geometry of heat exchange intensifiers, etc. Therefore, there is a need to study the thermal operation of the rotary oven of the heat generator to increase its efficiency due to improving the design. Physical and numerical experiments using mathematical modeling methods are caried out to study thermal operation of the heat generator of a rotary baking oven. The authors have conducted computational and experimental studies of thermal operation of the heat generator. The results have showed a large unevenness of the temperature field of the heat generator, underheating of the baking chamber to the minimum required temperature of 220 ° C, which indicates the low efficiency of the device. The results of field and numerical studies have confirmed the low thermal efficiency of the heat generator. Thus, the development of new technical solutions aimed at improving the design of this device is highly topical.

АНАЛИЗ ТЕХНОЛОГИЧЕСКИХ ВОЗМОЖНОСТЕЙ РАЗВИТИЯ ВНУТРЕННЕЙ ПОВЕРХНОСТИ ТЕПЛООБМЕННЫХ ТРУБ МЕТОДОМ ДЕФОРМИРУЮЩЕГО РЕЗАНИЯ

The analysis of existing methods of surface enhancing for in-tube intensification of heat-exchange processes is presented. Approved variants of using the method of deformational cutting for the increasing the inner surface of heat-exchange tubes are proposed, including principles, schemes of realization, designs of tools and attachments. Photos of macrostructured surfaces and heat exchange intensifiers obtained inside the tubes to increase the efficiency of convective, condensing and boiling heat transfer is presented.

Analysis of increase in efficiency of air-cooled heat exchangers due to intensification of heat exchange

Currently, the issues of improving the heat transfer processes in air-cooled heat exchangers play a huge role in terms of increasing the cooling efficiency and thus reducing the size of heat exchangers. This significantly saves resources. There are several basic methods for increasing the heat transfer of fluids in air coolers, for example, such as: finning of tubes and heat exchange intensification with the help of tube inserts. The purpose of the study is to analyze the efficiency of different fin types and the use of tube inserts, as well as changes in the heat transfer coefficients of air and natural gas, depending on the changes in the types of fins and tube inserts, and their geometry. The application software is Xchanger Suite provided by the company HTRI to ITMO University. The result is the optimally selected geometry of the heat exchange intensifiers based on the analysis, what allows reducing the dimensions of the air- cooled heat exchangers, while providing the necessary heat load, the heat exchange surface reserve coefficient and the heat transfer coefficients.

Computational parametric study on efficiency of low boiling point fluid plants under heat exchange process intensification

One of the main challenges for the energy industry is to improve the reliability and efficiency of heat exchange equipment in heating plants. Phase-change heat exchangers with low boiling point fluid (LBPF) are widely used in both conventional and renewable energy. The main objectives of increasing the efficiency of heat exchange equipment are to reduce the weight and dimensions, to increase the amount of heat transferred and to reduce the electricity consumption spent on pumping the heat transfer agent. These objectives are achieved by implementing various methods of heat exchange intensification in heat exchange equipment. A key aspect concerning application of various types of heat exchange intensifiers in heat exchange equipment is evaluation of possibility to increase their design efficiency. The paper presents the results of a computational parametric study of changes in efficiency of some LBPF-based plants when intensifying heat exchange processes by modifying functional surfaces of heat exchangers by laser ablation.

РАСЧЁТНЫЙ АНАЛИЗ ТЕПЛОГИДРАВЛИЧЕСКОЙ УСТОЙЧИВОСТИ ОБРАТНОГО ПАРОГЕНЕРАТОРА ИССЛЕДОВАТЕЛЬСКОЙ ЯДЕРНОЙ УСТАНОВКИ МБИР

The stability of the circulation in the steam-water circuit, that is, the preservation of the thermohydraulic parameters within acceptable limits for perturbations characteristic of the operation, largely determines the reliability of the steam generator itself. Under certain conditions, pulsating pressure, flow and temperature pulsations may appear in boiling apparatus. For the first time, ripples were encountered during the creation of once-through boilers, and the harmful effect of flow instability on the apparatus design led to the need for a detailed study of the problem. In this work, a computational analysis of the thermal-hydraulic stability of the reverse steam generator (OPG) of the MBIR nuclear research facility (NRF) is carried out. The need for such a study is due to the fact that the OPG consists of three parallel connected steam generating modules. With such a design, water flow rate pulsations may appear, including with overturning flow rates in separate steam-generating channels. To avoid this, it is necessary to conduct throttling at the inlet to each OPG module, therefore, in this study, the hydraulic resistance of the chokes is determined. The research methodology is based on the use of a numerical thermohydraulic model of a reverse steam generator, made by means of a certified thermohydraulic design code HYDRA-IBRAE/LM/V1. The OPG RNU MBIR at the economizer and superheating sections has twisted heat exchange intensifiers that direct water and steam both in the longitudinal and transverse directions relative to the bundle of heat exchange tubes. This circumstance required a special approach in calculating the hydraulic resistance and heat transfer coefficients along the path of the OPG modules. After the creation of the computational model, it had to be verified, and since the design of the OPG of the NRF MBIR is similar to the design of the OPG of the BOR-60 reactor, the experimental data obtained on the OPG BOR-60 were used for verification. The calculations of the normal operation modes of the OPG NRF MBIR after the throttling of the modules confirmed the absence of fluctuations in the flow rate in these modes.

Air breathable thermal insulation with heat transferintensifiers for high-temperature installation

To increase the efficiency of the high-temperature installation (HTI), several design options for air-permeable insulation in the outer furnace body are considered, differing in the location of heat-exchange intensifiers(HEI) - dimples in the form of spherical segments. As a result of a computational experiment, an option was established in which the heat losses are minimal, and the temperature of the heated air directed to combustion is maximum.

Assessment of energy efficiency of channel with nozzles

An algorithm for calculating the energy coefficient has been obtained, which makes it possible to estimate the efficiency of channel with various heat exchange intensifiers in the form of chaotic nozzle elements. The numerical study results are presented in the form of relationship between the energy coefficient Ed and the Reynolds number Ree. This made it possible to assess these heat exchange intensifiers from the point of view of energy efficiency and to determine the most optimal ones.

Gas-cooled nuclear reactor core shaping using heat exchange intensifiers

The need to shape reactor cores in terms of coolant flow distributions arises due to the requirements for temperature fields in the core elements (Safety guide No. NS-G-1.12. 2005, IAEA nuclear energy series No. NP-T-2.9. 2014, Specific safety requirements No. SSR-2/1 (Rev.1) 2014). However, any reactor core shaping inevitably leads to an increase in the core pressure drop and power consumption to ensure the primary coolant circulation. This naturally makes it necessary to select a shaping principle (condition) and install heat exchange intensifiers to meet the safety requirements at the lowest power consumption for the coolant pumping. The result of shaping a nuclear reactor core with identical cooling channels can be predicted at a quality level without detailed calculations. Therefore, it is not normally difficult to select a shaping principle in this case, and detailed calculations are required only where local heat exchange intensifiers are installed. The situation is different if a core has cooling channels of different geometries. In this case, it will be unavoidable to make a detailed calculation of the effects of shaping and heat transfer intensifiers on changes in temperature fields. The aim of this paper is to determine changes in the maximum wall temperatures in cooling channels of high-temperature gas-cooled reactors using the combined effects of shaped coolant mass flows and heat exchange intensifiers installed into the channels. Various shaping conditions have been considered. The authors present the calculated dependences and the procedure for determining the thermal coolant parameters and maximum temperatures of heat exchange surface walls in a system of parallel cooling channels. Variant calculations of the GT-MHR core (NRC project No. 716 2002, Vasyaev et al. 2001, Neylan et al. 1994) with cooling channels of different diameters were carried out. Distributions of coolant flows and temperatures in cooling channels under various shaping conditions were determined using local resistances and heat exchange intensifiers. Preferred options were identified that provide the lowest maximum wall temperature of the most heat-stressed channel at the lowest core pressure drop. The calculation procedure was verified by direct comparison of the results calculated by the proposed algorithm with the CFD simulation results (ANSYS Fluent User’s Guide 2016, ANSYS Fluent. Customization Manual 2016, ANSYS Fluent. Theory Guide 2016, Shaw1992, Anderson et al. 2009, Petrila and Trif 2005, Mohammadi and Pironneau 1994).

Профилирование активной зоны газоохлаждаемого ядерного реактора с использованием интенсификаторов теплообмена

Профилирование активной зоны газоохлаждаемого ядерного реактора с использованием интенсификаторов теплообмена

DESIGN AND STUDY OF EXCHANGERS WITH PRESSURE GRADIENT HEAT INTENSIFIERS

This paper is presented the numerical study of local heat transfer in the turbulent boundary layer with longitudinal pressure gradient. The study is based to free software with open source code (Salome and Code_Saturne) has been based by RANS approach and empirical models of turbulence. Validation of mathematical models and software is based by collation numerical results with the results of experimental study of fl ow characteristics in a turbulent boundary layer of longitudinal pressure gradient and high turbulence intensity (Epik E. Ya., NASc of Ukraine). The validation had a high qualitative coincidence of the fl ow characteristics determined as a result of the simulation with experimental data. We designed two constructive schemes of heat exchangers for air. This study presents a calculation plan for these heat exchangers. Results of the study are showed that the use of gradient heat exchange intensifi ers leads to an increase in the heat transfer coeffi cient from air to 17 %.

Effect of Cellular Lattices, Heat-Exchange Intensifiers, and Coolant Mixing on the Critical Power of VVER FA

The results of one stage in the development of methods for increasing the critical power of water-cooled nuclear reactors – the capacity of a reactor installation with sharp degradation of the heat exchange characteristics of the coolant (crisis of heat exchange) – are presented. This stage included experimental determination of the effect on the crisis of heat exchange of arranging heat-exchange intensifiers in FA and transverse mixing of the coolant flow, for which lattices assembled from properly shaped cellular elements where used. The FA models consisted of an assembly of 19 fuel-element simulators with a non-uniform distribution of heat emission along the length. Freon-12 was used as the coolant. The models of the FA differed by the type of intensifier lattices and the number of FA arranged along the length. The efficacy of the influence of lattices on the critical power as a result of the intensification of heat exchange and transverse mixing of the coolant was determined separately. The optimal rigging of FA with lattices was determined experimentally.

Heat and Mass Transfer and Hydrodynamics in Swirling Flows

Preface for the Sixth International Conference «Heat and Mass Transfer and Hydrodynamics in Swirling Flows», Novosibirsk, November 21-23, 2017.The conference took place in Novosibirsk at the Institute of Thermophysics SB RAS from November 21 to November 23, 2017.The topics were mainly focused on hydrodynamics, heat and mass transfer in swirling flows, but the spectrum of problems discussed was much wider and included thermohydrodynamics on micro- and nanoscale, the application of vortex and heat exchange intensifiers to enhance the heat transfer, swirling flames, various devices based on these types of flows for the power engineering applications and some advances in experimental methods to tackle these problems.The number of participants reached 77 reseachers including scientists from academia and industry with a good share of young members coming from 14 cities in Russia, Belarus, USA, Germany and Belgium. A large number of insightful keynote lectures have been presented by Profs. K. Oberleithner (Germany), M. Vanierschot (Belgium), Ph. Ligrani (USA), N.V. Kornev (Germany), A.A. Khalatov (Ukraine), S.V. Alekseenko, E.E. Son, A, Yu. Varaksin, V.I. Terekhov, E.M. Smirnov, S.K. Nemirovskii, I.A. Popov, S.A. Isaev, V.M. Dulin (Russia). As a results there were 14 keynote and 6 topical lectures followed by 56 oral presentations. The proceedings in this volume contain 43 papers grouped by sections where they were presented.The scientific committee appreciates the enormous work of the editorial board and reviewers during the preparation of this volume. We would like to express our sincere gratitude to all authors for their contributions.

Thermal and Hydraulic Efficiency of Different Modes of the Flow Vortex

The intensification of the heat exchange is always accompanied by an increase in hydraulic losses. To estimate thermal and hydraulic efficiency of heat exchange intensifiers many criteria are used to characterize the ratio of an increase in the heat exchange to the associated losses of the pressure required for the heat carrier pumping. This scientific paper is devoted to the analysis of the following criteria of thermal and hydraulic efficiency, in particular the Reynolds analogy factor and the quality coefficient. The heat hydraulic efficiency of heat-exchange intensifiers with full and partial flow vortex and that of the intensifiers that are characterized both by the flow vortex, the vortex mixing and the flow separation have been studied. The results showed that the studied heat exchange intensifiers of a vortex type have different structural design but a rather common mechanism of heat exchange intensification due to the flow vortex (full and partial), the vortex mixing and the local flow separation, and due to this reason these are summarized by the general relationship on the diagrams of heat hydraulic efficiency. Using the quality coefficient we performed the ranging of heat exchange intensifiers of a vortex type and we arrived at a conclusion that it is reasonable to use the quality coefficient for the domain of f/f0 > 3,0 for practical applications due to the complicated determination of the ultimate values of bounding curves.

A simple model of heat exchange and friction in the channels with spiral near-wall flow swirlers

A model, constructed on the basis of modern concepts, for thermohydraulic calculation of the heat exchanger channels with the heat exchange intensifiers is proposed. Urgent problems of the further investigations in this field are formulated.

Method of adiabatic cross-section and its application for estimating the thermophysical and thermostrength parameters of high density beam dumps in the iter injection system

Abstract For the creation of serviceable designs of technical means for removing driven by vari-ous sources high-intensive heat fluxes with arbitrary spatial-temporal distributions, the method of adiabatic cross-section is proposed for calculating sets of long thin-walled pipes with an arbitrary cross-section cooled by the forced coolant flow and supplied with the heat exchange intensifiers. The arguments in support of the technique feasibility and conditions for its applicability to solve definite engineering tasks are given. The adiabatic cross-section technique efficiency is provided by an organie insertion of experimental correlations, representing the thermophysical heat exchange process parameters with a subsequent analysis of the serviceability and service lives of the structures under design, into a corresponding numerical model composed of a reduced sequence of solutions for thermomechanical piane problems of the mathematical physics. Specific features of the technique are seen in calculations of the thermophysical and thermostrength parameters of heat-removing elements in the beam dumps within the injection plasma heating system of the experimental fusion reactor ITER. The results of calculations are illustrated with distributions of the thermophysical and thermostrength parameters at the most-heat-stressed cross-sections in heat-removing pipes of the calorimeter flaps under the stationary injection conditions.

Modification of the adiabatic crosssection technique for calculation of pipes containing twisted tapes under asymmetric heating by an external stationary heat flux with a high power density

Abstract An expansion of a numerical model for the method of adiabatic cross-section developed previously to study the pulsed asymmetric heating of pipes by an external heat flux’ for the conditions of stationary heating is given to calculate therraophysical parameters of cooled pipes containing twisted tapes. Introduction of the generalized parabolic temperature distribution across the wali matched with conditions of heating and cooling of the pipe cross-section allowed to retain a two-dimensional diagram. Adeauate stationary distributions of thermophysical parameters have been obtained by a time-limited transition for the processes of heating and cooling. The proposed modification for the technique of adiabatic cross-sections is illustrated by the results of calculations for the expected distributions of thermophysical and strength parameters in pipe cross-sections containing heat-exchange intensifiers twisted tapes within the collector of deviated ions in the T-15 tokamak injection system under possibl...

On the development of fuel assemblies

Investigations of RBMK fuel assembly models of various geometries were carried out to develop fuel assemblies with reduced uranium dioxide temperatures and decreased void reactivity effect. The investigations include thermophysical experiments and neutron and physical calculations. The influence of the following factors on bundle thermophysical characteristics was studied: number and diameter of fuel elements located within a channel 80 mm in diameter, relative arrangement of fuel rods within the channel tube, gap between the fuel rods and between the peripheral row of fuel rods and the channel tube, peaking factor of power distribution over the fuel assembly radius, and the use of heat exchange intensifiers. The RBMK fuel assembly of ultimate geometry (18 fuel rods 13.6 mm in diameter within a channel 80 mm in diameter) was compared in neutron and physical calculations with three variants: 36 fuel rods 10.2 mm in diameter within a channel 80 mm in diameter and 18 fuel rods 14.9 mm in diameter without and with holes in the pellets within a channel 86 mm in diameter. It was determined that the fuel assemblies with 36 fuel rods within the ultimate channel 80 mm in diameter give no essential reduction of the void reactivity effect and have little effect of the critical power increase when heat exchange intensifiers are used. Therefore efforts are being made to increase the channel diameter and use the 18-rod fuel assembly with axial holes in the fuel pellets.

Thermohydraulic testing of a model of a sodium-water counter-current steam generator

A design of a modular countercurrent steam generator has been developed at the Scientific-Research Institute (NII) of Power-Generating Plants (Czechoslovakia), with a 26-MW module, with heat-exchange intensification on the water-steam side. To check the efficiency of the heat-exchange intensifiers, test experimentally the thermohydraulic calculations procedure, and study emergency processes where steam in injected into sodium heat-removal tubes, a model of a 625-kW steam generator was designed and built in Czechoslovakia. The design calculations procedure for the steam generator is based on a one-dimensional thermohydraulic model. Thermohydraulic testing of the steam generator model was carried out on a stand of Lenin Scientific-Research Institute of Nuclear Reactors (NIIAR) in the following parameter range: sodium mass flow rate 1.8-2.6 kg/sec; water pressure 7.8-10 MPa; water mass rate 50-85 kg/(m/sup 2/ x sec); sodium inlet temperature 500-525/sup 0/C, and water inlet temperature 160-200/sup 0/C.

Experience in the operation of channels with single-pass steam generation in the reactor at the first nuclear power station

The reactor tests of fuel elements with heat-exchange intensifiers, operating with full evaporation of the water, with superheated steam, and without the use of an intermediate separator, shows that it is possible in principle to design a single-pass steam generator in reactors with tubular fuel elements.