Inclusion Of Heat Conduction Research Articles

A dual-solver CFD model for conjugate heat transfer in continuous thermal processing

High temperature heat treatment of powders is a common operation in the manufacturing of a range of commercial products. Often, powders are heated or cooled in discrete quantities while being conveyed through a continuous furnace or oven, where a certain temperature–time profile is required for product quality reasons. For powders that are contained and conveyed in oven-ware (saggars), heat-transfer occurs between the surrounding gas phase and the powder material and oven-ware, as well as between oven ware that is vertically stacked.The large physical size and long transit times through typical industrial furnaces (up to 40 m length) means that a full transient CFD solution for both gas and solid phases is computationally very expensive . In this study, a novel CFD simulation model is developed for conjugate heat transfer in the cooling section at the outlet of a continuous furnace. A particular novel feature in this model is the inclusion of heat conduction in multiple solid domains. A dual-solver approach enables the convective and radiant heat-transfer processes in the gas phase are modelled using a steady-state conjugate solver, while the heat conduction processes within the powders and saggars are modelled using a time-dependent conjugate solver that solves for heat conduction only. Using only steady-state solution for the gas phase enables a “snap-shot” of the thermal performance of the system to be generated in a reasonable time frame, which has practical implications for modelling of large-scale industrial equipment. In the “dual-solver” approach, heat fluxes at solid boundaries from the steady-state model are applied as boundary conditions to the transient solver, while the temperature field resulting from the solution of the transient solver is then applied to the steady-state model. Radiative cooling effects are accounted for using a discrete-ordinates model.

Modeling of icing on a planar surface due to Sea spray and blowing Snow

Two main extensions of the time-dependent two-dimensional sea spray icing model ICEMOD2.1 (Horjen, 2015) is presented. The first extension, called ICEMOD2.2, is the inclusion of heat conduction through the accreted ice. This quantity has been calculated from the temperature distribution in the ice which varies with time. The second extension, called ICEMOD2.3, is the combined effect of sea spray and snow. No other icing models have ever before included this effect. The new models have been applied for some reported icing cases on the nearly vertical wall of the bulkhead of the large Norwegian coast guard vessel KV Nordkapp from 1983 to 1997. Local wind field above the boundary layer, heat loss by forced convection and wind stress have been approximated by using analytical formulas for the wind field around a single plate. The physics of instantaneous freezing of a fraction of supercooled droplets upon impact has been discussed and implemented in the model.The most severe icing conditions in Norwegian Arctic water often occur during polar lows, which are often followed up with heavy snow fall. Due to the inclusion of snow the thermal conductivity of the ice accretion is modified. Using an electrical analogy it is shown that this parameter decreases during snow conditions. Overall ice salinity and density are also affected by the snow.

The required level of thermal protection of enclosing structures of administrative buildings in the transport infrastructure in Russia and European countries

Comparison of various standard values and calculation methods adopted in Russia and European countries has always aroused quite a lot of interest, and many works are devoted to this topic. However, the last comparisons were carried out quite a long time ago, and the purpose of this study is to compare the required level of thermal protection of the building envelopes of administrative buildings in the transport infrastructure in Russia and European countries according to the current regulatory documents to determine the ratio of these values to each other. The normalized values of the level of thermal protection of external enclosing structures are related to the degree-days of the heating period. Moreover, the definition of this value in Russia and the EU countries differ from each other. And it is possible to compare the level of thermal protection of enclosing structures in different countries only according to the same characteristic, that is, with the same (or very close) value of the degree-day of the heating period. Also, the level of required resistance to heat transfer of external enclosing structures in Russia is set taking into account heat-conducting inclusions in the enclosing structure, and in European countries without taking into account. That is, it is impossible to compare these two quantities in the original form - you need to take into account the design of the outer shell of the building.

MODERN ARCHITECTURE AND ENERGY EFFICIENCY

The article analyzes the design solutions for the outer walls of residential buildings built in 2020-2022 in a city that belongs to the II temperature zone of Ukraine. The outer walls of the monolithic reinforced concrete frame of the building are made of hollow brick 250 mm thick with a façade system of heat-insulating and finishing class A. A verification thermotechnical calculation of the outer wall was carried out, taking into account heat-conducting inclusions, the reduced heat transfer resistance of an opaque enclosing structure (wall) does not correspond to the minimum allowable value of heat transfer resistance of the corresponding structure according to DBN V.2.6 – 31:2016 for the II temperature zone. When taking into account the effect of air permeability on reducing the overall level of thermal protection of the fence, it was determined that the calculated reduced value of the resistance to heat transfer of the outer wall will be even lower due to the fact that the structure consists of light cellular materials with a significant breathability. External enclosing structures and internal, dividing rooms with a temperature difference of 4 ° C or more, have insufficient insulation thickness. When developing insulation measures, the effect of air filtration through wall structures made of lightweight materials is not taken into account. The requirements for the insulation of complex structural units of enclosing structures to prevent the formation of "cold bridges", for example, a balcony slab, are not met. Translucent structures, which occupy more than 50% of the facades, are the cheapest, their heat transfer resistance is less than the minimum allowable value. Based on the results of the analysis, the main measures to improve the energy efficiency of residential multi-storey buildings were identified to enable the installation of large windows in residential and public buildings in the climatic conditions of Ukraine.

Calculation of heat resistance of external enclosing structures with heat-conducting inclusions

Calculation of heat resistance of external enclosing structures with heat-conducting inclusions

Blast Waves in Two and Three Dimensions: Euler Versus Navier–Stokes Equations

The exact solution of the Euler equation, which describes the time evolution of a blast wave created by an intense explosion, is a classic problem in gas dynamics. However, it has been found that the analytical results do not match with results from molecular dynamics simulation of hard spheres in two and three dimensions. In this paper, we show that the mismatch between theory and simulations can be resolved by considering the Navier–Stokes equation. From the direct numerical simulation of the Navier–Stokes equation in two and three dimensions, we show that the inclusion of heat conduction and viscosity terms is essential to capture the results from molecular dynamics simulations.

Повышение теплотехнической однородности стен из ячеистобетонных блоков

The development of effective protecting structures is currently one of the most popular areas in the construction industry. Masonry made of aerated concrete blocks is used in conditions of ensuring energy efficiency and environmental safety in the construction of civil buildings as enclosing structures. It has high thermal protection properties. The issue of filling through seams of aerated concrete masonry is acute, since adhesive and cement-sand mortars in masonry have low thermal conductivity and are temperature bridges. The authors have developed a two-row energy-efficient wall masonry made of aerated concrete blocks using polyurethane glue as a filler for through and dressing joints. The article discusses the effect of horizontal through joints made of cement-sand mortar and blocking of blocks on the resistance to heat transfer of masonry from aerated concrete blocks. In addition, it presents a study of the reduced resistance to heat transfer of the enclosing structure, taking into account heat-conducting inclusions, presented in the form of a traditional two-row aerated concrete masonry through a row, made on a thin-layer adhesive solution, as well as the masonry developed by the authors. It is concluded that the energy efficiency of the developed wall fencing is ensured due to the increased thermal homogeneity of the masonry.

Experimental and theoretical studies of the thermal efficiency of multilayer non-uniform building enclosures

External vertical enclosures of contemporary buildings represent heterogeneous multilayer systems, whose thermal efficiency to a significant extent determines building heat insulation. The article addresses the results of research on the thermal efficiency of a multilayer enclosure, having heat-conducting inclusions. In the article, the co-authors analyze the case of a wall, whose bearing layer is made of aerated concrete blocks. Experimental and numerical methods of research were used by the co-authors, who applied TEPL software package that had the control volume method implemented to perform the numerical research of 3D temperature fields. The comparative analysis of numerical studies and the experiment has proven the qualitative convergence of their results. In addition, quantitative discrepancies did not exceed 5–20%. The co-authors conducted numerical studies of the thermal efficiency of external walls with windows to discover that the insulation of window jambs can reduce heat loss by 28%, nearly double the wall's reduced heat transfer resistance and prevent the condensation on its inner surface, and, thus, to improve its maintainability.

Influence of matrix-filler thermal conductivity on micro heat transfer in two-component composites

The maps of local heat fluxes in the composite matrix with randomly located heat-insulating and heat-conducting inclusions have been calculated in this work. It was shown that with a significant difference in the thermal conductivity of inclusions and matrix, the main heat transfer occurs through the induced heat-conducting channels. It was found that the weighted average angles of local heat fluxes deviation from the direction of the temperature difference between the sample faces depend on the concentration of heat-insulating and heat-conducting inclusions of various sizes. A sublinear decrease or super linear increase in the effective thermal conductivity of the composite with an increase in the concentration of heat-insulating or heat-conducting inclusions, respectively, was associated with a change in the path length of local heat fluxes due to the flow at an angle to the direction of the temperature difference. An approximation formula for the dependence of the composite effective thermal conductivity on the filler concentration has been proposed, which makes it possible to take into account the presence of both heat-conducting and heat-insulating inclusions.

Problems of thermal protection of two-layer external walls with hinged facade systems

Currently, in the Republic of Khakassia, much attention is paid to research aimed at reducing air pollution due to fuel combustion. In this aspect, the issue of increasing the energy efficiency of buildings is relevant. The use of ventilated facade systems with an air gap makes it possible to improve the energy efficiency class of buildings and modernize the facades. However, these facade systems have weak points that require detailed and high-quality study. Often, design solutions are used that are used in warm climates without taking into account the peculiarities of a cold climate - frequent changes in temperature, humidity, wind loads, and other influences, which can lead to negative manifestations. Facade systems with a ventilated air gap must provide the ability to monitor the operability of all system elements and, if necessary, carry out repair and reconstruction work with minimal operating costs. The article presents an analysis of the thermal properties of an external fence using a hinged facade structure. The influence of installation defects and heat-conducting inclusions on the heat-shielding properties of the building envelope is shown. It was determined that during operation the moisture-windproof membrane loses its vapor-permeable properties.

STUDY OF SPATIAL HEAT TRANSFER IN A CORNER FRAGMENT OF AN EXTERNAL FENCE WITH CONNECTORS

Increasing energy efficiency and reducing heat loss in buildings are the main challenges of the modern construction sector. For this reason, it is recommended to design buildings using modern energy-saving materials and technologies. When using multilayer walls in housing construction, the problem of thermal bridges arises. Therefore, you need to understand how the thermal behavior of the enclosing structure changes when thermal engineering inhomogeneities are included in it. The aim of this work is to study the effect of heat-conducting inclusions located in external enclosing structures on the change in the values of temperature and heat flux density. The paper considers the importance of increasing the energy efficiency of outdoor fences. A numerical study of the heat transfer process for corner fragments of enclosing structures used in housing construction using the VELOX technology has been carried out. The influence of the design features of the considered corner fragments on the characteristics of temperature fields is shown. Mathematical modeling of spatial heat transfer in the corner fragment of the outer enclosure is carried out using a nonlinear system of differential equations of heat conduction with specified boundary conditions using the finite element method. The problem was solved using the ANSYS software package. The influence of metal and fiberglass connectors on the change in the fields of temperature and heat flux density in the enclosing structure has been investigated. The change in the thermal state is considered both in the thickness of the outer wall and along the inner surface of the fence from the corner area and along the smooth surface of the wall. Analysis of the calculations showed that the maximum disturbance is introduced by the connector made of metal, and the minimum — from fiberglass. The presence of highly heat-conducting inclusions in the thickness of the structure leads to a distortion of the density field of the heat flux of the fence.

Heat and mass transfer in laminated glued timber bar

The main prerequisites for the development of wooden housing construction in Russia are given, which determined the goal of this study - to develop a mathematical model of heat and mass transfer (moisture transfer) in glued timber for rational design of enclosing structures. Lamellas can be classified as a capillary ‒ porous body. leaning on theory of academician A.V. Lykov, the formulation of the problem of heat and mass transfer in a multilayer glued laminated timber is presented a system of equations describing non-stationary heat, mass and pressure transfer under real possible operating conditions of enclosing structures is considered. An analytical method is proposed for calculating both individual lamellas and the entire multilayer glued beam. The proposed technique allows the method of solving the inverse problem to directly calculate the resistance value of the entire bar from the unsteady temperature field. The system of equations describing the process is nonlinear and analytically insoluble. To solve the problem, a combined method for solving boundary value problems of heat transfer was used, which is based on a combination of elements of analytical and numerical solutions. A feature of the problem under consideration is that the middle lamella has heat-conducting inclusions in the form of a bough. Method is that the entire heat transfer process is divided into a number of small time intervals. Within each interval, we assume that the temperature is constant at the interface between layers and a constant heat flux through the contacting surfaces, i.e. perfect thermal contact.

ADDITIONAL HEAT LOSSES AT THE JUNCTIONS OF THE WINDOW FRAMES AND ENCLOSING STRUCTURES

The current state of housing and communal services, which have been built by the end of the 90s, requires complete modernization and a significant increase of energy efficiency. Global trends in energy efficiency of buildings are aimed at changing energy consumption to almost zero level (nZEB). Most of the measures aimed at achieving nZEB refer to measures of improvement the thermophysical properties of enclosures. With the improvement of the thermophysical properties of the enclosures, the influence of the thermally conductive inclusions that occur at the junctions of the window structures / reinforced concrete slab of the ceiling to the outer wall, etc., increases significantly.The paper contains 2D-models built in the THERM – a software for studying temperature fields at the junctions of linear heat-conducting inclusions. We have simulated heat-conducting fields for two variants of external walls with improved thermophysical properties of enclosures that conform to modern requirements for thermal protection. The calculation was made for the climatic conditions of Kyiv.It is established that for the same thickness of the outer wall, the replacement of the bearing layer of the silicate bricks structure with a aerocrete blocks improves the resistance to heat transfer by 2 times. From the point of view of influence of linear heat-conducting inclusions in places of adjunction of a window frame to an external wall is observed the opposite effect, when there is a bigger influence in a wall made of the aerocrete blocks. Taking into account linear and point heat-conducting inclusions leads to a deterioration of the resistance to heat transfer of the outer wall made of silicate bricks by 20%, and of the aerocrete blocks - by 33%. Consideration of heat-conducting inclusions even for a construction without difficult constructive decisions of protections leads to increase in heat losses.

АНАЛИЗ ФАКТОРОВ, ВЛИЯЮЩИХ НА ВЫБОР СИСТЕМ УТЕПЛЕНИЯ ОБРАЗОВАТЕЛЬНЫХ УЧРЕЖДЕНИЙ

the article raises the problem of improving the energy efficiency of buildings in operation with a constant increase in energy prices, which is now becoming increasingly important. The analysis of the design decisions of the buildings of educational institutions of Donetsk region was carried out; the main typical series of the region were highlighted and given. The issues and the factors affecting the heat and moisture characteristics of enclosing structures of educational institutions were discussed. The values of resistance to heat transfer for the most common standard series of secondary schools are given. The modeling of temperature fields of nodes of public buildings of standard series was made. The most unfavorable design solutions of serial buildings were identified by the following factors: the temperature of the inner surface of the outer enclosures and the temperature difference between the average temperature at the surface and the air temperature in the room. Possible ways of thermo-modernization of such buildings with consideration of the requirements for temperature and breathability are considered. The influence of heat-conducting inclusions on the heat-moisture regime of external enclosing structures during partial and full thermal modernization is estimated. The analysis of various methods and ways of warming the buildings of educational institutions are performed. The advantages and disadvantages of the proposed options from an economic point of view are indicated, as well as on the basis of the requirements of fire regulations.

REDUCTION OF HEAT-MOISTURE IMPACT ON REINFORCED CONCRETE SILO FOR STORING CEMENT CLINKER

The paper analyzes various constructional options for insulation of load-bearing structures of reinforced concrete silo. Based on the analysis, the optimum insulation was selected according to the minimum temperature difference in the wall thickness. Factors affecting the heat-moisture characteristics of the walls of reinforced concrete silo are identified. The influence of heat-conducting inclusions on the heat-moisture characteristics of the building envelope is estimated. The temperature differences in the silo wall thickness are detected. The temperature and humidity are calculated for various design options and the moisture accumulation percentage of the con-struction is calculated for the specified time period.

Thermal protection of buildings from sandwich panels for Southern Siberia conditions

Article represents recommendations on decrease in heat losses through heat-conducting inclusions of sandwich panels. Recommendations are based on the analysis of calculations by a finite element method in software package Elcut and thermal imaging. The purpose of this study is to increase the thermal protection of buildings built with sandwich panels for the South Siberia conditions. The way of decrease in the factor of cold bridges is studied by adding thermal insulation of panel node connections. The authors analyzed constructive joints: roof parapet, roof cornice and junction of wall panels.

Functional Polystyrene Materials

The article presents successful technologies for isolation of functional polystyrene materials. The results of analysis of a material with current and heat-conducting inclusions, of an antibacterial component for medical purpose are given. The material has polymer characteristics and is suitable for obtaining a product with specified functional properties. Ways of copper formation having nanometer dimensions, a brief methodology and possible structure of the resulting filler are shown. Copper nanoparticles have unique anti-bacterial, current and heat-conducting properties. These properties are largely retained in the polymer material. The used carrying agent - polystyrene - is a product of large-capacity production; therefore the resulting materials are based on developed raw materials base all over the world. Isolation of copper ions from nanoparticles depends on the type of stabilizing agent and chemical nature of the environment. Implementation of antimicrobial properties in polymer materials is achieved by the dosage of copper in the amount of 1-2% by weight. Giving to material the conducting properties of copper nanoparticles requires higher concentration of metal. The shown way of synthesis of copper nanoparticles is suitable for implementation in polystyrene.physical properties of the catalyst, so that an efficient, industrially applicable process.

Estimation of influence of heat-conducting inclusions on thermal protection of filler constructions of buildings

Article represents recommendations on decrease in heat losses through heat-conducting inclusions of filler constructions of buildings. Recommendations are based on the analysis of calculations by a finite element method in software package Elcut. The purpose consists in the analysis of expediency of replacement of a steel reinforcement on glass composite reinforcement in design decisions of filler constructions in view of calculation of thermal fields. The way of decrease in the factor of cold bridges is researched by replacement of a steel reinforcement by glass composite reinforcement. It is analysed constructive units: fastenings of facing verst to a diaphragm of rigidity; adjunctions of an external wall to a column. On a result efficiency of replacement of a steel reinforcement on glass composite reinforcement in filler constructions of walls is revealed, and also results of calculation of thermal losses of design decisions of filler constructions of a building are resulted.

Thermal Modernization of the Panel Buildings External Walls

The thermal protection level of the first mass series panel buildings (series 111-94) is the lowest among residential buildings in Poltava. The problems of these buildings’ thermal modernization, is consideration of heat-conducting inclusions effect on the reduced resistance to heat transfer. In the studies such heat-conducting inclusions as the panel joints’ design, the window slope and the external wall geometry (the external corner) were taken into account. Studies were performed for the four pattern sections of the outer wall. Panels of two thickness variants with two joint designs were under consideration.To analyze the thermal protection level, the results of the two-dimensional temperature fields’ calculations were used. The analysis of the wall panels’ thermal protection level before the thermal modernization was performed. The magnitude of the heat conducting inclusions effect on reduced resistance of the walling to the heat transfer before and after the thermal modernization is determined. Possible ways of improving the wall panels’ heat-protective properties to the level of the standards in Ukraine are considered. The optimal variant of insulation for each pattern was chosen.

Analysis of heat-conducting inclusions in exterior walls of residential building

The study is aimed at detecting the zones of major heat losses in exterior walls of residential buildings and developing recommendations on their elimination. The “ELCUT” software program calculated the temperature fields of the external wall under the design temperature of the outside air. The calculation was carried out for three options: the thermal characteristics of the materials of the layers of the outer wall correspond to the design parameters; thermal characteristics of the materials of the layers of the outer wall correspond to the actual measured values; Thermal technical characteristics of the materials of the layers of the outer wall correspond to the actual indicators and additional insulation is made. It is established that with additional insulation, the irregularity of the temperature field on the external surface of the wall is eliminated and normalized thermal resistance complies with the requirements.