Intensification Of Heat Exchange Research Articles

COMPARATIVE ANALYSIS OF ENERGY EFFICIENCY OF THERMAL OPERATION OF ROTARY KILNS WITH DIFFERENT HEATING SYSTEMS

Analysis of the design features of known heating systems for large rotary kilns and modern methods of influencing the formation of the flame and the distribution of the temperature profile is presented. It has been established that most of the known methods of forming the flame and temperature profile of the working space of rotary kilns are based on methods of influencing air flows, in particular secondary air, the share of which in the total volume of combustion air is 70–100 %. On the basis of previous studies and observations, it is proposed to form a flame using additional sideways gas jets from the burner. Examples of modernization of heating systems of existing industrial rotary kilns for firing various materials, including ferronickel ore, fireclay, and lime, are presented. After installing burners with controlled flame parameters and changing the design of the combustion air supply system in the working space of the kilns, an optimal temperature distribution along their length was obtained. It was determined that the required temperature at about half the length of the kilns is almost constant, without significant fluctuations, differing at the beginning and end of the firing zone by 30–70 °C. The decrease in the temperature of the exhaust gases from the kilns after the modernization of the heating systems indicates an intensification of heat exchange in the workspace, which leads to a decrease in specific fuel consumption by 7–15 %, as well as an improvement in the quality of the final material. A comparative analysis of the thermal efficiency of operating rotary kilns depending on the design features of the heating system is presented. Bibl. 24, Fig. 4.

HYDRODYNAMIC MEANS OF HEAT EXCHANGE INTENSIFICATION IN CONSTANT CROSS-SECTION ROUND CHANNELS

The purpose of research is the analysis of innovative designs of hydrodynamic means of intensification of heat exchange in channels of constant cross-section of technological equipment and pipelines, intended for use in the thermal power, chemical, food and related industries. The study of the state of the issue and trends in the development of structural and technological design of hydrodynamic elements of pipes and tubular elements for the intensification of heat exchange are based on a critical analysis of scientific and technical sources of information and, first of all, patent information of the leading countries of the world. The classification of these means for intensification of heat exchange in equipment and pipelines of thermal energy, chemical, food and related industries is proposed. The most interesting designs of these elements proposed by scientists, designers and inventors of the leading countries of the world are considered. A critical assessment of most of the above constructions is provided, their advantages and disadvantages are discussed. Designs of means of intensification of heat exchange in channels are analyzed depending on the change in flow continuity, the degree of mobility of the working element, the nature of the effect on the flow over time, relative length, assembly/disassembly possibilities, the degree of curvature of the channel, material, level of assembly, the degree of rigidity, the degree of mobility of the working element, the possibility of changing the geometry of the working channel , the possibility of temperature regulation, as well as the degree of uniformity of the heat flow in the circular direction of the channel. Means according to the change of flow continuity, namely turbulizers and cavitators, were analyzed in more detail. It is shown that, despite the significant variety of structural and technological design of hydrodynamic means of heat exchange intensification in round channels of constant cross-section, the most demanded by the industry are technologically diverse removable turbulizers that can be replaced or completely removed from the channel if necessary. Less common are cavitators, because they are usually characterized by less versatility and manufacturability, as well as greater sensitivity to the flow rate of the transported flow and its physical properties. Bibl. 44, Fig. 19.

Intensification of Heat Transfer during Steam Condensation in Process Condenser of NPP Unit Cooling System

The paper investigates heat transfer during condensation of water vapor on vertical pipes of the process condenser of the cooling system of a nuclear power unit. The numerical study was performed at different mass flow rates of steam in the range of its change from 20 kg/s to 40 kg/s. Intensification of heat exchange is provided by the use of highly efficient heat exchange profiled tubes. The study used a set of heat exchange tubes (25 mm in diameter and 1.4 mm wall thickness) with the following values of the distance between the grooves of the profiled tube: 0.007075 m, 0.00875 m, 0.00925 m, 0.0105 m. The effect of the groove depth (from 0.0007 to 0.0009 m) on heat transfer during water vapor condensation on vertical pipes was also studied. The study was carried out for the range of changes in the Reynolds number for the condensate film from 5254.2 to 10508.5. The study obtained data indicating an increase in the heat transfer coefficient on the pipe with an intensifier compared to the heat transfer coefficient on a smooth pipe. This analysis did not take into account the change in tube wall temperature.

Modeling of the flow and heat exchange in pipes with turbulators of viscous heat carriers in the laminar region, as well as in the transition to turbulent flow

Objective. Mathematical modeling of heat transfer in pipes with turbulators for viscous heat carriers at Reynolds numbers characteristic of laminar and transient flow regimes is carried out by the calculation method. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multiblock computing technologies based on the solution of the Reynolds equations (closed for the transient mode using the Menter shear stress transfer model) and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method (FCOM) was considered.Method. The calculation was carried out on the basis of a theoretical method based on the solution of the Reynolds equations, closed for transient modes using the Menter shear stress transfer model, and the energy equation on multiscale intersecting structured grids (FCOM), by a factorized finite-volume method.Result. Both local and averaged characteristics of the flow and heat exchange in pipes with turbulators for a viscous coolant for laminar and transient flow modes of the coolant were obtained using the FCOM method in the work, which made it possible to determine for these modes the levels of heat exchange intensification that satisfactorily correlate with the existing experiment.Conclusion. The calculated relative hydraulic resistance for low turbulators increases quite slightly, and for medium-altitude turbulators reaches 2÷2.5 to the critical Reynolds number, and subsequently it increases up to 3 times; for high turbulators, the relative hydraulic resistance increases up to 4 times even before the transition flow regime is reached, after which it increases up to 4.5 times. The calculated relative isothermal intensified heat exchange under the laminar flow regime of a viscous coolant for relatively high turbulators increases almost 2 times; for relatively medium heights of turbulators — almost one and a half, and for low relative heights, the intensification of heat exchange is insignificant.

DEVELOPED SURFACES AS A FACTOR FOR OPTIMIZING THE DESIGN OF HEAT EXCHANGERS

Optimization of the geometric parameters of heat exchangers can be carried out according to many parameters. One of the most important are geometric dimensions. The development of an optimized heat exchanger design using experimental planning methods is an urgent task. This allows you to minimize the cost of materials for the manufacture of devices and transfer heat most efficiently.
 Intensification of heat exchange is always given great attention for any branch of industry and technology. High requirements are put forward to the structures of heat exchange equipment, which are related to the reduction of their mass, occupied volume, etc. A promising direction is the use of heat exchange surfaces with a large area, that is, developed, which is achieved by finning the primary surface. The optimal design of the surface development is determined by the values of the heat transfer coefficients from the hot coolant to the dividing wall of the heat exchanger tube and from the wall to the cold coolant. The most widely used are ribbed surfaces with knurled ribs, which are quite convenient in production and further operation
 The purpose of the work is to determine the influence of such factors as the length of one finned tube, the bearing diameter of the finned tube and the finning ratio on the optimal structural performance of the compressed air heater based on the minimum length of the pipe system.
 In terms of influence, the length of one tube is the most important, and the fin ratio is of secondary importance. With a significant increase in the finning ratio of the pipes, the total length of the pipes decreases.
 The developed technique makes it possible to determine the optimal value of such a parameter as the total length of finned tubes. Also, on the basis of the obtained results, it is possible to develop an appropriate design of the heat exchanger with the accepted number of tubes transverse to the flow of the heat carrier that is heated. With the help of the developed methodology, it is possible to analyze the value of the length of the tubular system of the heat exchanger with various combinations of the above factors and to optimize its design in a fairly simple formulation.

Intensification of heat exchange in the developed surfaces in flat channels

The paper presents the results of an experimental study of heat transfer during forced water flow from microstructured surfaces in a slotted channel. The investigated micro-structured surfaces were obtained by a resource-saving (waste-free) method of deforming cutting with various constructive shapes and sizes. A description of the experimental setup, methods for conducting and processing experimental data are presented. The maximum increase in heat transfer coefficients in comparison with a smooth surface reaches Nu/Nu0 = 16.2.

Intensification of heat-exchange of a direct-flow steam boiler of a coil type based on an educational laboratory stand

In the work under consideration, using an experimental stand formed by a cylindrical coil, the modes of air movement through the flue of a ramjet steam boiler were investigated. Experimental studies have revealed shortcomings in the operation of a direct-flow steam boiler and proposed ways to increase heat transfer in a steam boiler by turbulizing the gas-air flow in the convective part of the boiler flue. The Ansys programmable engineering environment was used to simulate the heat exchange between waste gases and water in the heat exchanger. The Ansys SpaceClaim program was used to design the geometric model. Finite element grid was created using the Ansys Icem CFD program. In the process of creation, materials were selected and designated for each part of the model, water and steam temperatures inside the heat exchanger, exhaust gas temperature, boundary conditions and heat exchange conditions between them were also set. After entering all the parameters the model calculations were carried out and the results were presented in the form of a temperature distribution diagram. In conclusion, a variant of further research of aerodynamic processes in a ramjet steam boiler and a demonstration of the selected option were presented.

Mathematical Modelling of Heat Transfer in Pipes with Turbulators in the Laminar Region and in the Transition to Turbulent Flow

The article presents an analysis of mathematical modeling of heat transfer in pipes with turbulators at low Reynolds numbers characteristic of laminar and transient flow modes of heat carriers. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multi-block computing technologies based on the solution of Reynolds equations closed using the Menter shear stress transfer model and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method is considered. Both local and averaged characteristics of the flow and heat transfer to a pipe with a system of turbulators were obtained, which made it possible to determine the levels of heat exchange intensification for these regime ranges.

Contribution of the Provençal Well for the Improvement of the Thermal Comfort in the Building in Turbulent Regime

In the current energy context, geothermal systems are highly developed in the building field. Among these interesting systems on the energy plan, one finds in particular the earth-to-air heat exchanger commonly called ‘Canadian or Provençal well’. It consists of tubes buried in which the ambient air is pushed in order to be refreshed in contact with the ground whose temperature is quasi-constant throughout the year. In this work, a study of the performance of an earth-to-air heat exchanger was undertaken by means of numerical modeling of heat exchange by forced convection in a buried tube. The transfer equations in the tube are discretized using the finite volume method in turbulent regime and solved using the Thomas algorithm. For the determination of the ground temperature, the model of the semi-infinite mass subjected to a periodic excitation was adopted. The soil temperature was used as a boundary condition for the buried tube.
 The results show that the interest of the earth-to-air heat exchanger is major, since it improves throughout the year, the thermal conditions sought. It intervenes in an effective way on the damping of the thermal amplitudes in the building. The variation of the diameter and the length of earth-to-air heat exchanger does not influence notably the distribution of the streamlines and isotherms but affect significantly the values of stream function and temperature inside de tube of the earth-to-air heat exchanger. When diameter of the pipe increases, the outlet temperature increases. The increase of the length of the earth-to-air heat exchanger leads to the isotherms increase as a result of the intensification of heat exchange between the walls and the convective jet. The temperature in the air outlet compartment is lower as the length of the earth-to-air exchanger increases.

Optimization of the distance between the vertical plates in the convective air heat exchanger

This paper examines the influence of the distance between vertical plates on the intensity of free convective heat transfer along with the optimization of this distance. Experimental tests were carried out for one model channel of such an heat exchanger with widths s=0.045, 0.085 and 0.18 m. This channel, open at the top and sides, was formed by two isothermal symmetrically heated parallel vertical plates of dimensions H=0.5 m and B=0.25 m. The influence of the heating surface temperatures tw=30, 40, 50, 55, 60 and 70 °C on the convective temperature fields and velocity generated inside the channels was investigated. Directly measured temperature fields, as well as velocity fields measured indirectly using the NRP, enabled the thermodynamic parameters of the heat exchanger to be determined. Based on the temperature gradient distribution ∂Tw∂x on the wall, its average value was determined for each of the plates and for the entire channel, after which the heat flux Qw transferred from the plates was calculated. The heat flux transferred with the air Q and the efficiency η=Q/Qw of heat transfer in the channel were determined using the balance method based on the average temperatures and air velocities at the inlet t̄bott and ūin and at the outlet t̄top and ūout of the channel obtained from the temperature and velocity fields. A grid placed vertically in the channel, halfway across the panel width and perpendicular to the heating surfaces was used to detect the temperature field in air. The image and matrix of these temperatures were determined using a thermal imaging camera. The numerical reconstruction procedure (NRP) was used to determine the velocity field.For technical reasons and lack of time it was not possible to test more channels. Since three values of the width s were insufficient to determine sopt, it was decided to use numerical research. For this purpose, numerical results were compared with those obtained experimentally for the channels already tested. As the compliance verification was successful, further studies of the channels were continued numerically. As a result of optimizing the heat exchange intensification, optimal widths of a single channel sopt=0.035 m and n channels s0=0.0123 m, included in the heat exchanger, were obtained.

Thermomagnetic Convection of a Ferrofluid in a Vertical Hydrodynamic Loop: Intensification of Heat Exchange in a Magnetic Field

Thermomagnetic Convection of a Ferrofluid in a Vertical Hydrodynamic Loop: Intensification of Heat Exchange in a Magnetic Field

Possibility of Improving Air Distribution and Heat Flow Conditions in Mechanical Grate Furnaces

Abstract One group of plants commonly used for solids combustion are grate furnaces. These furnaces come in numerous design solutions, dedicated to fuels with different properties and plants with different capacities. The use of grate furnaces presents the as-yet unresolved challenge of how to ensure the most favourable air distribution along the length of the grate. The paper proposes a design solution to ensure proper air distribution along the length of the grate. An additional advantage of the proposed solution is the intensification of heat exchange in the furnace, enabling the boiler's circulating medium to be heated more efficiently. Both of the advantages allow an increase in the energy efficiency of the plant and therefore contribute to a reduction in the amount of fuel burned and CO2 emissions.

Application of the rotating-convection paradigm for tropical cyclones to interpreting medicanes: An example

The rotating-convection paradigm for tropical cyclone behaviour is shown to provide an attractive and consistent framework for interpreting the dynamics of formation and intensification of at least some medicanes. The ideas are illustrated by a case study of the medicane that formed over the eastern Mediterranean in mid-December 2020. This case study is based on analyses of data from the European Centre for Medium Range Weather Forecasts (ECMWF), imagery from the European geostationary meteorological satellite, Meteosat Second Generation, and output from a convection permitting numerical simulation of the event using the United Kingdom (UK) Met Office regional model with the RAL2 physics configuration. Limitations of the currently widely accepted interpretation of medicanes in terms of the so-called Wind-Induced Surface Heat Exchange (WISHE) intensification mechanism are discussed.

Numerical investigation of transient thermal behaviour of fully wet and porous moving semi-spherical fin

A variety of engineering applications demand efficient and adaptable fin structures for the intensification of heat exchange. The semi-spherical fin structures are useful in the field of refrigeration, chemical processing systems, aerospace etc. In this regard, the present article numerically investigates the transient thermal behaviour of a fully wet semi-spherical fin. The study incorporates the Darcy model as the fin is made up of porous material. Further, the fin is exposed to convective-radiative heat exchange and is subject to uniform motion. The heat balance equation has been reduced to get a nonlinear partial differential equation (PDE) which is computed by employing the finite difference method (FDM). The dimensionless terms are grouped together and their influence on the temperature distribution in a semi-spherical fin is studied. Also, the instantaneous heat transfer rate and the transient fin efficiency have been modelled and their variations with relevant parameters have been graphically depicted. And these are found be strong functions of Peclet number, wet porous nature and dimensionless time. As a main outcome the semi-spherical fin efficiency is positively influenced by the Peclet number. Along with the fundamental point of interest the results presented benefit the fin designing purposes.

Buckling and oscillation of the wall layer of the chain two-mass system at the entrance to the apparatus for turbulizing the flow in the heat exchanger

A mathematical model of heat exchange intensification at the entrance to the turbulence apparatus has been developed. Rational formulas for buckling and oscillation of the wall layer of a chain two-mass system are proposed. Distributions of perturbations caused by the internal instability of the pre-central layer after abolishing conditions under a focused shear load in the zones of solidification, crystallization and cooling are obtained.

IMETHODS OF INTENSIFICATION OF HEAT EXCHANGE IN BIOGAS REACTORS

Proposed research method intensification of heat exchange in biogas reactions using alternative energy sources. The distribution of active and passive methods of heat exchange intensification is determined. The three most effective methods of heat exchange intensification are identified: the method of flow turbulence in the adjacent areas, based on purposeful artificial creation of small dry wall zones, which is the source of additional flow turbulence; the method of flow winding inside the twisted oval tubes and at longitudinal and transverse winding of tightly packed beams and tubes; the method of controlled break-out of the boundary layer at transverse tubulars by creating turboblicators on them. It is determined that in practice the most effective is the use of combined methods of intensification. The important conditions for choosing the method of heat exchange intensification are: the amount of permissible energy costs for heat exchange intensification and the type of energy available for this energy; the task of heat exchange intensification in a particular class of equipment; the technological capacity of equipment with heat exchange intensification, availability at purchase and durability in operation of equipment; the nature of distribution, structure of thermal flows and temperature fields, in which there is a need for intensification of heat exchange. The main indicator of intensification of the heat exchange process in the equipment is found – the efficiency of the process, that is, the process should be economically profitable. From the above it appears that the intensification of heat exchange can’t be considered isolated from the necessary energy costs. The determining criterion of optimization is the efficiency of the heat exchange process at a given level of energy consumption at transfer of the working environment through the equipment. Heat exchange intensification during use of gaseous working environments is of particular importance, for which characteristic reduction of intensity of heat exchange processes and high energy consumption for removal of supports at pumping of gases is characteristic. Tasks of heat exchange intensification are usually set: to reduce the size and weight of heat exchange devices; to decrease the temperature pressure, i.e. to decrease the temperature of the walls at the given temperature of heat carrier or to increase the temperature of heat carrier at the given temperature of walls. Reduction of thickness of heat transfer wall and increase of its thermal conductivity, as well as prevention waste contamination on the wall is an obvious method of intensification of heat exchange.

JUSTIFICATION OF POWER PARAMETERS OF THE PROCESS OF SEMI-FLUIDISATION FREEZING OF FRUIT AND BERRY PRODUCTS

The existing semi-fluidisation devices are described by high-energy consumption during operation, heavy metal structure, and complexity of the drive mechanism. Therefore, the search for effective heat exchange schemes in low-temperature processing of fruit and vegetable products, provided that its damage and energy consumption for the process are minimised, constitutes the relevance of this study. The purpose of this study was to determine and substantiate the amplitude-frequency and power mode parameters of the vibration wave driving organ of the semi-fluidisation machine for freezing fruit and berry products, the regularities of changes in the main characteristics of low-frequency vibrations in the process under study. To perform these tasks, an experimental model of a semi-fluidisation machine with a vibration wave driving organ was developed and a set of special devices was manufactured in the form of a microcontroller system that provides measurement and automatic adjustment of the main parameters of the process under study. Intensification of heat exchange in the process of fluidisation freezing in the conditions of a pseudo-suspended state of products is described by a high heat transfer coefficient, which can exceed typical convective processes by several orders of magnitude; an increase in the active heat exchange surface up to 100% is observed; the contact surface with the energy carrier increases proportionally, which leads to a decrease in the active temperature difference; there is a 2-3 times decrease in internal friction in the mass of products and, accordingly, the technological resistance in the mass of loading is reduced, which is a potential for increasing the technical and economic characteristics of the low-temperature processing under study. The practical value of this study can be attributed to the application of vibro-slush freezing of the proposed structure with a vibration-wave product driver and a spatial elastic system for levelling out parasitic vibrations, which allows simplifying the structure, reducing power loads and, accordingly, energy costs

Heat and Mass Exchange Intensification in Liquid Phase of Oxygen Converter Using Bottom Inert Gas Pulsations

Heat and Mass Exchange Intensification in Liquid Phase of Oxygen Converter Using Bottom Inert Gas Pulsations

Approximate analytical solution of the integro‐differential model of bulk crystallization in a metastable liquid with mass supply (heat dissipation) and crystal withdrawal mechanism

This paper deals with an approximate analytical solution of an integro‐differential model describing nucleation and growth of particles. The model includes a thermal‐mass exchange with the environment and the removal of product crystals from a metastable medium. The method developed for solving model equations (kinetic equation for the particle‐size distribution function and balance equations for temperature/impurity concentration) is based on the saddle point technique for calculating the Laplace‐type integral. We show that the metastability degree decreases with time at a fixed mass (heat) flux. The crystal‐size distribution function is an irregular bell‐shaped curve increasing with the intensification of heat and mass exchange.

The Thermohydraulic Characteristics Investigation of the Aluminum Alloy Monometallic Plate-finned Tube in Together with Numerical Simulation of Heat and Mass Transfer Processes

The article is devoted to the investigation of aluminium alloy plate-finned tube characteristics regarding to the heat exchange intensification. Outer thick finning, inner ribs quantity and rib shape allow to increase heat exchange efficiency. However, the most important task is finding an optimal combination of pipe geometry parameters. Seven different ribbed tube samples were investigated during the experiment. The samples differed by geometry, quality and quantity of ribbing, and consequently hydraulic and thermodynamic characteristics. The main criteria for an integrated assessment of pressure losses and energy indicators were the criteria of Kirpichev and Antufiev. The above evaluation criteria were intended for an overall assessment of sample effectiveness based on experimental data. In advance and parallel with a natural experiment, a numerical experiment was conducted. The purpose of the numerical experiment was obtaining an adequate model of the heat exchange section to be used in a full-sized oil cooler model in the future. Thus, the article discusses the results of comparing natural and numerical investigations and the prospect of using the best sample in the oil cooler composition. The ultimate goal is the development of an automatic air-cooling apparatus with a compact high-performance oil cooler.