Thermal Calculation Method Research Articles

Thermal calculation and experimental study of a double-disk magnetic coupler

Aiming to tackle the difficulties and inaccuracies in calculating the temperature field of double-disk magnetic coupler, a novel thermal calculation method is proposed, integrating the equivalent thermal network method and CFD method. This approach deviates from traditional methods that substitute empirical formulas with rotational speed. An equivalent thermal network model is established to ascertain the temperature rise at each network node. Additionally, a fluid-solid coupling model is constructed, and the impact of uneven air temperature distribution on air density, specific heat capacity, dynamic viscosity, and thermal conductivity is analyzed using the least squares method. The results reveal that after incorporating variable temperature air physical properties, the high-temperature area of the copper conductor decreases, the calculated temperature rise aligns closer to actual values, and air friction loss on the copper surface is reduced by 6.5 %. Experimental verification, conducted on a 55 kW double-disk magnetic coupler, demonstrates maximum errors of 8.86 % and 6.53 % when comparing experimental values to those calculated by the equivalent thermal network method and CFD method, respectively, thereby validating the proposed method. This research provides a theoretical reference for thermal calculations in double-disk magnetic coupler.

Development of multi-physics calculation method in lead cooled fast reactor code system MOSASAUR

A full-core three-dimensional multi-physics calculation method was researched based on the Lead cooled fast reactor (LFR) code system MOSASAUR, which is focused on both core steady-state and transient analyses of LFR. In the previous version of MOSASAUR, cross-sections generation module and core steady-state simulation module have been developed. In this research, the stiffness confinement method is employed to solve the time-dependent multi-group neutron transport equation to expand the capabilities of core transient analyses. And the thermal hydraulic calculation method is developed as thermal feedback module for core steady-state and transient analyses. Based on the fixed-point iteration scheme, the neutron module and thermal hydraulic module are coupled at each time step. The LMW benchmark and the problem based on ORAL 19-rod bundle are employed to verify the accuracy of transient calculation and thermal hydraulic module respectively. Finally, the multi-physics calculation method is utilized to simulate the transient process of the MicroURANUS core. The simulation results demonstrate the capability of the constructed multi-physics calculation framework to accurately simulate the transient behaviors of LMRs. Numerical results showed the good accuracy of the newly-developed multi-physics calculation module with MOSASAUR.

CHOICE OF THERMAL INSULATION MATERIAL PRESS FORM FOR MANUFACTURING PRODUCTS FROM COMPOSITE MATERIALS

Purpose. The development of a method of thermal calculation of molds for the manufacture of products from composite materials, which allows you to choose an insulating material that ensures effective savings in heat consumption. Research methods. A theoretical analysis of the existing thermal calculations of the molds was carried out; an analysis of the theory of heat exchange based on the theory of similarity was carried out, using dimensionless criteria of Nusselt, Grashof and Prandtl; an analysis of reference data on the properties of insulating materials was carried out. Results. In the course of the work, the processes of convective heat transfer from the side surface of the mold were clarified and described; a method of calculating energy losses through heat transfer at a certain temperature on the outer surface of an uninsulated mold was developed; it was established that the temperature of the wall, from which the heat transfer is actually carried out, plays a decisive role in the selection of the insulating material; a method of reducing energy consumption is determined by applying a layer of heat-insulating material on the heat transfer surface of the mold, reaching a given temperature on the isolated surface of the mold; on the example of a mold of specific dimensions, the optimal materials were selected and their effectiveness in reducing heat consumption was determined. Scientific novelty. Developed methods for evaluating the effectiveness of heat-insulating material by calculating the temperature on the insulated surface of the mold; in this connection, the reduction of heat loss through heat transfer is achieved with the help of the selected optimal heat-insulating material, which has the appropriate thermophysical and technological properties. Practical value. Information on the impact of the design of the mold matrix and reference information on the thermal conductivity of heat-insulating materials are provided; the proposed calculation method can be used in the design of energy-saving molds for the manufacture of products from composite materials.

О ВЛИЯНИИ ТЕПЛОИНЕРЦИОННЫХ СВОЙСТВ ИЗОЛЯЦИОННЫХ МАТЕРИАЛОВ РЕЗЕРВУАРОВ СЖИЖЕННОГО ПРИРОДНОГО ГАЗА В РАСЧЕТЕ ТЕПЛОВЫХ ПОТЕРЬ

Negative factors in ensuring the safe operation of liquefied natural gas reservoirs are identified, which manifest themselves during liquefaction, unloading, receiving and regasification of the product. The role of heat losses in ensuring the safe operation of tanks is shown. Methods are analyzed in terms of considering possible variable thermal effects on the outer surface of a tank with liquefied natural gas. A method for thermal calculation of an isothermal tank is presented, which makes it possible to consider the thermal inertia of multilayer insulation when exposed to thermal radiation from a fire of variable intensity.

Improved Research on Two-Step Thermal Stress Calculation Method for Asphalt Mixture: Extended Creep Compliance Test.

The two-step thermal stress calculation method (TTSCM) is commonly used to predict the cracking temperature of asphalt mixture. The aim of this study is to improve TTSCM's mathematical model so as to enhance its prediction accuracy. First, this study evaluated the errors of predicted cracking temperatures of original TTSCM for AC-16 and AC-25 asphalt mixtures by thermal stress-restrained specimen test (TSRST). Then, an improved method called the extended creep compliance test (ECCT) was developed to modify the TTSCM. The test results show that the cracking predictions of the original TTSCM are not always accurate. Particularly for AC-16 asphalt mixture, the predicted cracking temperature is 2.9 °C (-10.6%) higher than the measured value by the TSRST. The ECCT method has been proven to be an effective way to enhance the prediction accuracy of the TTSCM. The predicted cracking temperatures modified by the ECCT method for both asphalt mixtures are relatively accurate, having an error within ±2%. The ECCT method changed the calculated thermal stress values at different temperatures of the TTSCM; however, they still conformed to a basic changing trend with respect to the initial temperature and cooling rate. Finally, a recommendation regarding the ECCT method was presented.

ТЕПЛОВИЙ РОЗРАХУНОК СУХИХ ТРАНСФОРМАТОРІВ З ЛИТОЮ ІЗОЛЯЦІЄЮ ТА З ФОЛЬГОВИМИ ОБМОТКАМИ

The method of analytical thermal calculation of dry transformers with cylindrical conductors with cast insulation and foil windings is presented. The surface and volume averaged temperatures of the magnetic system core and the wind-ings are determined from the one-dimensional non-linear substitute thermal circuit of the transformer. To clarify the temperature distribution across the cross-section of the anisotropic foil winding, the solution of the boundary value problem in the form of a two-dimensional Poisson equation with heat transfer coefficients calculated from the substitute scheme is used. Calculation example of a dry transformer with a capacity of 2500 kVA is given. Numerical CFD model-ing was performed to verify the calculation results. Bibl. 10, fig. 9, tab. 3.

Development of a 2-dimensional thermal calculation method to estimate silicone oil's temperature distribution in viscous torsional vibration dampers

AbstractHigh-performance internal combustion engines are subject to severe torsional vibrations which result from uneven gas and inertial loads. Fatigue damage occurs if the frequency of these undesired oscillations matches the resonance frequency of the crankshaft and the driven engine elements. This phenomenon can be avoided by the application of visco-dampers whose working fluid is high-viscosity silicone oil. Since silicone oil is exposed to a significant amount of heat load during operation, it is essential to calculate the temperature distribution in a relatively easy, quick, and cost-efficient way for lifetime estimation purposes. The aim of this article is to develop a reliable, fast, and accurate finite difference-based numerical method for steady-state thermal calculations for arbitrary damper sections. The developed MATLAB code calculates the temperature field of the damping fluid together with all components in a radial cross-section at given operational conditions. The accuracy of the developed thermal calculation method has been tested in a 3-dimensional – 2-dimensional two-step verification process by finite element and finite volume-based advanced engineering software in ANSYS environment. Furthermore, the original Iwamoto equation available in the literature has been updated to provide more accurate surface temperature results based on the simulations' outcome gained by the finite volume method.

The method of calculating the parameters of a heat exchanger with porous inserts based on the obtained criterion equation

The issues of improving the efficiency of heat exchange equipment are relevant. Heat exchange equipment is used in various industries. Porous metals have proven themselves well when used in heat exchange systems of gas turbine and rocket engines, laser mirror systems, nuclear reactors and other similar systems to increase the efficiency of heat exchange. The use of porous structures is effective due to a significant increase in the heat exchange area. The paper presents the results of experimental and theoretical studies of the efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger. The efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger has been experimentally shown. A similarity equation is obtained for calculating the Nusselt criterion, which makes it possible to find the heat transfer coefficient, and as a consequence, heat transfer for the coolant flowing through porous inserts in the inter-tube space of the heat exchanger. A cluster model was used to calculate the heat exchange area from the side of the coolant flowing through the pairs. The correspondence of the obtained calculation formula with the results of the experimental work is shown. A method of thermal calculation of a heat exchanger with porous aluminum inserts using a cluster model and the obtained criterion equation for calculating the heat transfer coefficient is proposed. The conclusion is made about the expediency of using porous metals in heat exchange structures.

RC-Network based thermal bridge calculation method for transient heat transfer analysis of multidimensional building envelope details: A frequency response analysis-based method

Thermal bridges have a significant impact on the overall energy performance and thermal comfort of buildings. Proper accounting of thermal bridge effects through model coupling leads to more accurate predictions of heating and cooling loads and narrows the performance gap between the design and the actual energy consumption of buildings. In this paper, a dynamic thermal bridge calculation method is introduced in a frequency domain to transform a broad range of multidimensional building envelope assemblies to thermally equivalent RC-Network simple models. RC-Network model with three resistances, four capacitances, and internal and external surface resistances at the ends is found to represent multidimensional thermal bridge assemblies more accurately with minimal computational time. The method is applied for the simulation of diverse two- and three-dimensional thermal bridge details of lightweight and mass constructions exposed to hourly varying sol–air temperature boundary conditions, and the results are compared to reference solutions obtained from transient finite element modeling of the original thermal bridge details. The highest RMSE of the proposed RC-Network model for the lightweight and mass construction details are 0.12 W/m2 and 0.37 W/m2, respectively. The low RMSE values reaffirm the good performance of the method and its appropriateness for the calculation of hourly heat flux through multidimensional thermal bridge details.

The apparent effusivity method for normalized thermal contrast evaluation in infrared thermographic testing

Thermographic nondestructive testing is used for the detection of near-surface discontinuities in materials, where indications of potential defects or discontinuities are detected and evaluated by their thermal contrast. The key requirements for successful thermographic data processing include managing non-uniform heating and identifying nominal areas. Advanced methods often rely on numerical simulation, which can be challenging and time-consuming. This study suggests a new simple method of thermal contrast calculation for flash-pulse thermography. It is based on the analysis of the inverse apparent effusivity. It includes an automated indication of the sound (defect-free) area and the creation of an artificial reference sequence, which is based on a temperature profile of the sound area and the non-uniform heating map. Derivative analysis of the smoothed contrast data is applied to improve detectability and Contrast/Noise Ratio (CNR). An experimental comparison of the proposed method with other known methods is presented. In the presented example, it allowed detection of 23 defects with an average CNR of 6.13 dB, against the traditional differential absolute contrast method, which detected only 13 defects with an average CNR of 0.53 dB. Thus, high detectability and high CNR values provided by the proposed method are demonstrated.

APPLICATION OF VACUUM SUCTION CASTING OF IRON-CARBON ALLOYS FOR THE PRODUCTION OF ENGINE PARTS

The use of vacuum suction casting technology for iron-carbon alloys for the production of internal combustion engine parts will improve their quality and wear resistance, preserve metal, and reduce emissions. The technology is widely used for non-ferrous alloys. At the same time, its implementation for iron-carbon alloys (including cast iron) in modern engine construction requires careful scientific and practical preparation. Problematic tasks arise when improving the pneumatic system of vacuum suction (large volumes of gas release), the stability of the metal pipeline (thermal overload in a high-temperature cast iron melt), and the stabilization of the casting microstructure (high-speed crystallization). The authors suggest using a specialized titanium alloy VT3-1 for the metal pipeline, for which the article calculates thermal loads during cyclic operation in the “Deep – take-out” mode for the use of cast irons of the SCH25 and VCH50-1.5 grades. For reliable operation of the metal pipeline and the absence of solidification of the melt on its inner surface, a thermal calculation method was develop, which allows determining the time of heat removal of overheating of the melt according to the diameter of the metal pipeline. The pneumatic system of the vacuum unit is supplement with a patented gas jet ejector, which, in combination with a powerful shop compressed air system, provides a full gas outlet. Applying the developed law of change in the discharge between atmospheric pressure and pressure in the mold cavity, the authors of the article regulate the rate of crystallization of castings, which makes it possible to form much smaller phases of perlite in the microstructure and reduce the presence of Ferrite. At the Enterprise "Pervomaiskdizelmash" using vacuum casting technology, blanks of guide bushings of engine valves 6CHN25/34 made of cast iron SCH25 and VCH50-1,5, as well as oils of piston rings made of cast iron VCH50-1,5 were obtained. The obtained parts showed an increased service life by 15-30%. Vacuum casting technology is recommend for iron-carbon alloys in the production of engine parts.

Real-time indoor thermal comfort prediction in campus buildings driven by deep learning algorithms

Thermal comfort prediction is vital in achieving a good indoor environment and efficient energy management. However, thermal comfort is strongly nonlinear and dynamically changing over time, making it difficult to predict thermal comfort accurately. Two real-time thermal comfort prediction models on multi-time scales are proposed based on deep learning algorithms. The indirect prediction model for thermal comfort integrates the bidirectional long and short-term memory network to predict real-time environmental parameters. It subsequently combines the thermal comfort calculation method with the predicted environmental parameters to obtain the predicted thermal comfort value. The indirect prediction model for thermal comfort combines the bidirectional long and short-term memory network to realize real-time prediction of environmental parameters and then calculates thermal comfort by the thermal comfort calculation method to realize indirect thermal comfort prediction. The other is the direct prediction model of thermal comfort, which is realized using the bidirectional long short-term memory network for real-time thermal comfort prediction. The two real-time prediction models are compared and analyzed for 10-min, 30-min, and 60-min scales. Experimental results show that the prediction accuracy of the indirect prediction model is better than the direct prediction model, but the robustness of the indirect prediction model is lower than the direct prediction model. In addition, the accuracy of the thermal comfort prediction model on the small time scale is higher than that on the large time scale, in which the RMSE and MAE reached 0.0551 and 0.0543 (10-min scale), respectively. Therefore, the proposed thermal comfort prediction models can be integrated into the control model of heating, ventilation and air conditioning systems, providing a reference for optimizing indoor thermal comfort.

Method of thermal calculation of the locomotive traction engine armature

A verification calculation of traction engines of locomotives is proposed, taking into account the temperature mode. Analytical expressions for the static thermal state of the engine are obtained, reflecting the balance of heat release and heat removal powers. Keywords: locomotive, engine, armature, reliability, electric drive, heating, operation, heat flow, mathematical model. lam75@mail.ru, glazunovdm@yandex.ru, ats@rgups.ru

Thermal Conductivity of Fractal-Textured Foamed Concrete

To provide scientific guidance for the use of foamed concrete (FC) in construction engineering, a thermal conductivity calculation method, based on the fractal model of FC, has been developed. The thermal conductivity (TC) of FC has been tested by the transient planar heat source method in order to verify the reliability of the proposed calculation model. The FC was made of cement, fly ash, and ore powder, and cured under natural conditions for 7 d, 14 d, 28 d, and 42 d, respectively. The TC of FC gradually decreases with the increase in age. The fractal dimension of FC can be determined by both the box-counting method and compressive strength test, and the dimensions determined by both methods are similar. The TC of FC at different porosities and curing ages can be calculated by the fractal dimension, and the estimated values are basically consistent with the test data.

OPERATION FEATURES OF ENVIRONMENTALLY EFFICIENT BOILER PLANTS OF MUNICIPAL THERMAL POWER ENGINEERING

The work is devoted to research on the improvement of thermal energy production technologies in gas-consuming heating boiler installations while improving their environmental performance and increasing the operation reliability. The work purpose is to study the heat and humidity modes of the air-supply ducts of boiler plants with exhaust gases recirculation systems into the blown air. The main objectives of the study are: to determine the thermal parameters of a heating boiler with a 2 MW heating capacity with a exhaust gases recirculation system mixed with blown air into its furnace space under conditions of using heat recovery technologies and without them; determination and analysis the heat and humidity parameters of this mixture in different operating modes of boiler plants. Known thermal calculation methods of boiler plants and data from our own experimental studies of heat transfer during deep cooling of boiler plant exhaust gases were used. The thermal calculation results of the heating boiler with a system for exhaust gas recirculation into its furnace space mixed with blown air are presented. The regularities of changes in the adiabatic combustion temperature and heat-humidity characteristics of the above mixture depending on the boiler heat load in different its operation modes during the heating period and the share of flue gas recirculation from 10 to 20 % were established. The research results show that the introduction of recirculation gases leads to a decrease by 150 – 250 °С of the adiabatic combustion temperature tad due to the need to consume fuel heat for heating the introduced ballast and the greater of the recirculation share s the lower the level of the indicated temperature. The research results also showed that gas recirculation causes insignificant (in the range of 0.5 – 4.7 °С) changes in the temperature of the boiler exhaust gases. Based on the data obtained, the change regularities in the heat-humidity characteristics (temperature and dew point) of the mixture of recirculated gases and air in different boiler operating modes during the heating period and under the studied recirculation shares were established. It is shown that recirculation causes condensate formation on the surfaces of air ducts in all operating modes of boiler and in some modes their icing is possible. To prevent these negative phenomena, it is necessary to apply measures to increase the temperature of the gas-air mixture by a value not less than Δtsum = 15 – 35 °С.

Summary Study on Temperature Calculation Method for Water Accumulation in Permafrost Regions

With permafrost degeneration caused by climate change, water accumulation has increased in permafrost regions during recent decades. Water accumulation will deteriorate the existing status of engineering in cold regions. Water accumulation can have a thermal effect on permafrost during its formation, even resulting in failure of the subgrade. Moreover, the thermal effect is related to water temperature. However, temperature variation of water accumulation is complex, and its influencing factors include air temperature, environment, scope of water accumulation and so on. In order to conduct analysis of the damage mechanism of water accumulation on permafrost, it is necessary to explore the internal temperature change of water accumulation. This paper proposes a review of temperature calculation method for water accumulation in cold environment. The thermal calculation method for the space between the air and the water boundary of water accumulation is summarized. Water temperature change of water accumulation of various types is analyzed. The thermal calculation considering phase transformation in water accumulation is discussed, and heat transfer from the bottom of the water accumulation to the underlying soil is further studied. Finally, the key factors that are advantageous for conducting research about the thermal effect of water accumulation in permafrost are proposed to optimize the calculation method.

Evaluating the Effect of Ammonia Co-Firing on the Performance of a Pulverized Coal-Fired Utility Boiler

Ammonia (NH3), as a derivative of hydrogen and energy carrier, is regarded as a low-carbon fuel provided that it is produced from a renewable source or a carbon abated process of fossil fuel. Co-firing ammonia with coal is a promising option for pulverized coal-fired power plants to reduce CO2 emission. Applying the co-firing in an existing pulverized coal-fired boiler can achieve satisfying combustion performance in the furnace but may affect the boiler performance. In the present work, a thermal calculation method was employed to evaluate the impact of ammonia co-firing on the boiler performance of an existing 600 MW supercritical utility boiler, covering the co-firing ratio range up to 40% (on heat basis). The calculations indicated that, as compared to sole coal combustion, co-firing ammonia changed the volume and composition and consequently the temperature and heat transfer characteristics of the flue gas. These resulted in increased variations in the heat transfer performance of the boiler with increasing of the co-firing ratio. The evaluations revealed that co-firing up to 20% ammonia in the existing boiler is feasible with the boiler performance not being considerably affected. However, the distribution of the heat transferred from the flue gas to boiler heat exchangers is significantly deteriorated at higher ratios (30% and 40%), resulting in over-temperature of the superheated steam, under-temperature of the reheated steam and considerable reduction in boiler thermal efficiency. It implies retrofits on the heat exchangers required for accommodating higher ratio co-firing in the existing boiler. The comparison study showed that co-firing 20% ammonia provides a superior boiler performance over co-firing 20% biomass producing gases and blast furnace gas.

Computational Analysis of Tube Wall Temperature of Superheater in 1000 MW Ultra-Supercritical Boiler Based on the Inlet Thermal Deviation

Local over-temperature is one of the main reasons for boiler tube failures (BTF). By accurately monitoring and controlling tube wall temperature, local over-temperature can be avoided. Based on the measured flue gas parameters and numerical simulation, a method of thermal deviation calculation is proposed in this study for the on-line calculation of the tube wall temperature of boiler superheaters. The full-size three-dimensional numerical simulation was presented on the combustion in a pulverized coal-fired boiler of 1000 MW ultra-supercritical (USC) unit. A difference in the thermal deviation of the vertical direction was innovatively introduced into a segmented discrete model, and the thermal deviation condition conforming to reality was introduced into the calculation. An on-line calculation system developed based on the current calculation method was applied in a 1000 MW USC unit. The calculated local high-temperature zone was consistent with the actual over-temperature position and conformed to the law of the allowable metal temperature of the final superheater (FSH) serpentines segment. The comparison results showed that the calculated data by this method were more reflective of tube wall temperature change with boiler loads than the measured data. According to the calculated local over-temperature zone, the immediate warning response can effectively reduce the possibility of over-temperature BTF.

Thermal stress calculation of wax-based warm mix asphalt considering thermorheologically complex behavior

The warm mix asphalts which reduce the environmental pollution always show thermorheologically complex behavior under the realistic working conditions (the long-term loading at the low temperature) in the cold region. However, many scholars ignore the thermorheologically complex behavior when calculating thermal stresses. In this paper, the new thermal stresses calculation method considering thermorheological complexity of four wax-based warm mix additives (Fischer-Tropsch (F-T) based wax, fatty acid amides (FAA) based wax, polyethylene (PE)-based wax, and linear aliphatic hydrocarbon (LAH)-based wax) modified asphalt binders were proposed, which was the process of incremental iterative (Named as ‘the incremental method’). The results show that the warm mix asphalt exhibits the thermorheologically complex behavior under long-term loading condition at the low temperature through the tail of the master curve of stiffness modulus, and the thermal stresses considering thermorheologically complex characteristics calculated by the incremental method are greater than that calculated by the traditional Monismith method. Therefore, the incremental method should be used to calculate the thermal stress of asphalt binders under the long-term loading condition instead of the Monismith method, otherwise the cracking risk of the asphalt binder will be underestimated. The wax-based warm mix additives with longer chain molecules and cold storage time can increase the thermorheological complexity more evidently, and the thermal stresses of asphalts with thermorheologically complex characteristics are more sensitive to cooling rate. All in all, the proposed incremental method will provide a supplement to the calculation method of the thermal stresses in the asphalt binder.

Approximate analytical method for calculating the heating process of concrete structures in heating formwork

The use of electric heating of concrete during construction in winter makes it possible to create an optimal thermal regime in which the hardening process takes place, and to obtain a structure of the required quality. When developing a system for automatic control of the heating process, it is necessary to determine the law of regulating the power of heaters. This article presents a method for calculating the thermal heating regime of concrete structures in heating formwork, the essence of which is to reduce the boundary value problem of thermal conductivity to a system of equivalent integral equations. To solve this problem, a theoretical study was carried out, a theoretical study of the heat transfer process in concrete structures heated during winter concreting was carried out, and a mathematical description of this process was presented in the form of a system of differential equations. After the transformations of the above system of equations and the application of the Green function of the second kind to it for the plate and rod, an approximate solution of the equivalent equation was obtained. As a result of the application of the asymptotic method to the solution of the integral equation, an analytical solution of the problem under consideration is obtained. The resulting solution makes it possible to determine the temperature fields on the concrete surface, as well as the value of the specific heat flux from electric heaters. In order to automate the process of performing the thermal calculation of heating concrete structures with the help of heating forms, a program for calculating temperature fields in heating forms has been developed based on the solution obtained, which makes it possible to effectively solve the tasks of monitoring and controlling the concrete hardening process. The developed program makes it possible to calculate temperature fields not only at constant heater power, but also when it changes with the help of regulators. The presented method of thermal calculation with a hardware and software complex for regulating the power of electric heaters allows solving a fairly wide range of tasks related to maintaining a constant temperature field.