Thermal Field Analysis Research Articles

Impacts of Realistic Urban Heating. Part II: Air Quality and City Breathability

Urban morphology and inter-building shadowing result in a non-uniform distribution of surface heating in urban areas, which can significantly modify the urban flow and thermal field. In Part I, we found that in an idealized three-dimensional urban array, the spatial distribution of the thermal field is correlated with the orientation of surface heating with respect to the wind direction (i.e. leeward or windward heating), while the dispersion field changes more strongly with the vertical temperature gradient in the street canyon. Here, we evaluate these results more closely and translate them into metrics of “city breathability,” with large-eddy simulations coupled with an urban energy-balance model employed for this purpose. First, we quantify breathability by, (i) calculating the pollutant concentration at the pedestrian level (horizontal plane at $$z\approx 1.5$$ –2 m) and averaged over the canopy, and (ii) examining the air exchange rate at the horizontal and vertical ventilating faces of the canyon, such that the in-canopy pollutant advection is distinguished from the vertical removal of pollution. Next, we quantify the change in breathability metrics as a function of previously defined buoyancy parameters, horizontal and vertical Richardson numbers ( $$Ri_\text {h}$$ and $$Ri_\text {v}$$ , respectively), which characterize realistic surface heating. We find that, unlike the analysis of airflow and thermal fields, consideration of the realistic heating distribution is not crucial in the analysis of city breathability, as the pollutant concentration is mainly correlated with the vertical temperature gradient ( $$Ri_\text {v}$$ ) as opposed to the horizontal ( $$Ri_\text {h}$$ ) or bulk ( $$Ri_\text {b}$$ ) thermal forcing. Additionally, we observe that, due to the formation of the primary vortex, the air exchange rate at the roof level (the horizontal ventilating faces of the building canyon) is dominated by the mean flow. Lastly, since $$Ri_\text {h}$$ and $$Ri_\text {v}$$ depend on the meteorological factors (ambient air temperature, wind speed, and wind direction) as well as urban design parameters (such as surface albedo), we propose a methodology for mapping overall outdoor ventilation and city breathability using this characterization method. This methodology helps identify the effects of design on urban microclimate, and ultimately informs urban designers and architects of the impact of their design on air quality, human health, and comfort.

Numerical Simulation of the Electron Beam Welding and Post Welding Heat Treatment Coupling Process

AbstractIn this article, the electron beam welding and post welding heat treatment (PWHT) coupling process of nickel alloy GH80A is carried out using ABAQUS software. The thermo-mechanical coupling (TMC) model is considered in the simulation. The simulation results obtained from finite element method (FEM) including thermal history, heat source sharp, residual stress and stress relaxation. The simulation objectives are analysis of thermal field and heat source sharp which is compared with experimental results. These results also can determine the heat affected zone and residual stress during welding and stress relaxation which is produced by the post welding heat treatment process.

3-D Thermal Field Analysis of 10kV High Voltage Switchgear

A numerical simulation method for 3-D thermal field analysis of 10kV High Voltage Switchgear based on equivalent thermal conductivity is proposed. The equivalent 3-D simulation model of the 10kV High Voltage Switchgear is established by studying the convective heat dissipation of the airflow field during the forced air cooling of the switchgear. The air block is divided and the equivalent thermal conductivity is set up according to the stable working state of 10kV High Voltage Switchgear to complete the modeling process. Compared with the traditional heat flow coupling analysis method, the calculation speed and the convergence is good and the simulation result is accurate enough.

Occupant behavior and thermal comfort field analysis in typical educational research institution: A case study

An experimental field study has been conducted for typical educational research building facility (office building). The research data was gathered by the systematic monitoring of the offices and adaptive occupant behavior during the typical working day in the spring period. Different sensors and data loggers for temperature, relative humidity, CO2 concentration, had been mounted in order to collect data for analysis of thermal comfort conditions. Moreover, occupant surveys and interviews in form of questionnaire were also brought to examine the psychological and social impacts of the occupants? behavior regarding energy consumption. The inductive scientific method is used for data processing, i. e. descriptive and inferential statistical analysis of the results was made. Based on the analysis of the conducted study, it was found that thermal environment of the observed building is within the standards (i. e. specific parameters are within the range) and that the occupants are generally satisfied with thermal conditions in their offices. However, they do not pay much attention to conserving energy which is an important finding as it is directly related to the energy consumption. Thus, more attention should be directed to the education of the users and in general, to enable energy savings in the future.

Numerical simulations of progressive hardening by using ABAQUS FEA software

The paper concerns numerical simulations of progressive hardening include phase transformations in solid state of steel. Abaqus FEA software is used for numerical analysis of temperature field and phase transformations. Numerical subroutines, written in fortran programming language are used in computer simulations where models of the distribution of movable heat source, kinetics of phase transformations in solid state as well as thermal and structural strain are implemented. Model for evaluation of fractions of phases and their kinetics is based on continuous heating diagram and continuous cooling diagram. The numerical analysis of thermal fields, phase fractions and strain associated progressive hardening of elements made of steel were done.

Numerical Analysis of Thermal and Aerodynamic Fields in a Channel with Cascaded Baffles

A computational fluid dynamic analysis of thermal and aerodynamic fields for an incompressible steady-state flow of a Newtonian fluid through a two-dimensional horizontal rectangular section channel with upper and lower wall-attached, vertical, staggered, transverse, cascaded rectangular-triangular (CRT), solid-type baffles is carried out in the present paper using the Commercial, Computational Fluid Dynamics, software FLUENT. The flow model is governed by the Reynolds averaged Navier-Stokes (RANS) equations with the SST k-ω turbulence model and the energy equation. The finite volume method (FVM) with the SIMPLE-discretization algorithm is applied for the solution of the problem. The computations are carried out in the turbulent regime for different Reynolds numbers. In this study, thermo-aeraulic fields, dimensionless axial profiles of velocity, skin friction coefficients, local and average heat transfer coefficients, and thermal enhancement factor were investigated, at constant surface temperature condition along the heated upper wall of the channel, for all the geometry under investigation and chosen for various stations. The impact of the cascaded rectangular-triangular geometry of the baffle on the thermal and dynamic behavior of air is shown and this in comparing the data of this obstacle type with those of the simple flat rectangular-shaped baffle. This CFD analysis can be a real application in the field of heat exchangers, solar air collectors, and electronic equipments.

Infrared Thermography and Image Analysis of Dynamic Processes around the Facial Area

This paper describes the principles of visualization and analysis of thermal fields generated by different physiological processes around the facial area and in the environment. The dynamics of these fields was studied and their possible application for quantitative evaluation of psychophysical parameters is analyzed using infrared thermography with high spatial and temporal resolution. A software module has been developed and tested for combining infrared and visible camera images. A technique was proposed for complex recording and analysis of central and peripheral nervous activities using a thermal camera that captures three types of temperature fields that vary with time around the facial area: exhaled gas flows, cutaneous blood circulation, and sweat gland activity.

The model of double-cage induction motor for the analysis of thermal fields in transient operations

AbstractEmergency motor switch-on happens occasionally while operating a doublesquirrel- cage motor at full supply voltage with the rotor blocked (e.g., in coal mills). After releasing the blockage, the by now heated motor is started up again. However, the mechanical stress caused by the increased temperature poses considerable hazards to the squirrel-cage winding. This paper presents a double-cage induction motor model for analysis of thermal fields in transient operation. The thermal field for the rotor of a doublesquirrel- cage motor of soldered or cast structure, operating in the conditions described, has been calculated in the present paper using a thermal network method. Measurement results have been presented for the double-squirrel-cage winding temperature for a soldered cage construction in the blocked rotor state.

Method of analysis of asymmetrical thermal field in a double insulated wire

PurposeThe purpose of this article is investigating the impact of the spatially variable heat transfer coefficient on the thermal field in the double insulated wire.Design/methodology/approachThe effect of the air boundary layer was modelled by means of changing the total heat transfer coefficient on the external perimeter of the wire. This leads to an elliptical boundary problem with Hankel’s condition dependent on the angular coordinate. The eigenfunctions of the problem were determined analytically. On the other hand, the unknown coefficients of eigenfunctions and the constants were calculated numerically by solving a respective system of algebraic equations. The steady state current rating was determined with an iterative method.FindingsBy means of the presented method, the thermal field distribution deprived of axial symmetry in the double insulated wire was determined. The obtained results have good physical interpretation and were verified with the finite element method (by means of NISA v. 16 software). The determined values of the steady-state current rating were compared with those calculated by means of the equivalent heat transfer coefficient method and the International Electrotechnical Commission (IEC) standard.Research limitations/implicationsThe method is applied to analyse scalar fields in layered cylindrical structures. This could be expanded to the case of a wire of any number of insulation layers. What is more, one could also consider heat sources without axial symmetry and located within the external area.Originality/valueThe analytical method of determining a thermal field deprived of axial symmetry in heterogeneous cylindrical system (the wire composed of three different materials) was developed.

Analysis of Thermal Field in Mineral Transformer Oil Based Magnetic Fluids

Analysis of Thermal Field in Mineral Transformer Oil Based Magnetic Fluids

Calculation and analysis of complex fluid flow and thermal fields in a fully air-cooled hydrogenerator

Fully air-cooled hydrogenerators are applied widely in power stations because of advantages such as high efficiency, simple structure, and easy maintenance. This study investigated fully air-cooled hydrogenerators, and a three-dimensional fluid and thermal coupling analysis model of a hydrogenerator was proposed. Using the finite volume method, the changes in complex fluid velocity in the stator and rotor zones at different times were determined. Additionally, temperature changes in metal parts and insulation in the hydrogenerator were investigated with respect to time from the start to steady state operation of a hydrogenerator. In the study, the time required for the temperatures of different hydrogenerator parts to reach a steady state was predicted. Following the starting of the hydrogenerator, the temperature distribution of different parts at the same time and the changes in the temperature distribution of parts at different times were determined in the hydrogenerator. The surface heat-transfer coefficient distribution law on the surfaces of rotor exciting winding was studied. The calculated temperature result was compared with the measured value, and the results indicated that the calculated value of temperature agreed well with the measured value. Thus, the study indicated the feasibility of designing a fully air-cooled hydrogenerator from a thermal analysis viewpoint.

Models and methods for analysis of temperature and thermomechanical fields in the bodies of complex shape in specialized intelligent system

The design of axisymmetric bodies of complex form, taking into account temperature and thermomechanical fields, is the object of research. To model these fields need to solve boundary value problems for differential equations with partial derivatives. Structural (R-functions) and regional structural methods are used to solve the boundary value problems of thermal conductivity and thermoelasticity. CAD, meeting modern requirements, should include systems based on knowledge. Also, improving the efficiency of CAD is achieved thanks to the development of methods of solution of thermal conductivity and thermoelasticity tasks in the bodies of complex form. Using created structures, we receive more stable and accurate solution of the problem of analysis of thermal and thermomechanical fields in the considered objects. The specialized intelligent system is created. It contains a database of knowledge: a database of geometric forms of designed objects and methods of solving of relevant problems; a database of rules which allow to automate the choice of method and structure of solutions, equations of boundary of its areas; other information, required to increase the degree of automation of computer modelling. Created system creates the program on RL language for some programming system (PS), which solves the problem. Created system is production system. The pictures of temperature and thermomechanical fields are studied with the help of created system in axisymmetric bodies of complex form – pistons of internal combustion engine (ICE), homogeneous and consisting of composite materials. The impact of insert material, form and location on the picture of the temperature and thermomechanical fields in these ICE pistons is researched. These researches help to design these objects in order to reduce the temperature in the critical points of the object. This improves the thermal regimes in these objects, increase their strength, reliability and durability.

Scanning Based Induction Heating for AISI 4340 Steel Spline Shafts-3D Simulation and Experimental Validation

This paper presents an investigation of non-stationary induction heating process applied to AISI 4340 steel spline shafts based on 3D simulation and experimental validation. The study is based on the knowledge, concerning the form of correlations between various induction heating parameters and the final hardness profile, developed in the case of stationary induction heating. The proposed approach focuses on analyzing the effects of variation of frequency, power and especially scanning speed through an extensive 3D finite element method simulation, comprehensive sensitivity study and structured experimental efforts. Based on coupled electromagnetic and thermal fields analysis, the developed 3D model is used to estimate the temperature distribution and the hardness profile. Experimentations conducted on a commercial dual-frequency induction machine for AISI 4340 steel splines confirm the feasibility and the validity of the proposed modelling procedure. The 3D model validation reveals a great concordance between simulated and measured results, confirms that the model can effectively be used as framework for understanding the process and for assessing the effects of various parameters on the hardening process quality and performance and consequently leads to the most relevant variables to use in an eventual hardness profile prediction model.

Analysis of thermal temperature fields and thermal stress under steady temperature field of diesel engine piston

With the improvement of the diesel engine power and performance, the piston in the combustion chamber is subjected to higher thermal load and the thermal stress decreases its working life. Therefore, it is necessary to analyze the subsequent thermal stress on the piston during design process to reach the optimum one. This paper tries to present a new calculation method for the theoretical design of the piston. In this study, the 3D solid model of piston in 16V280 diesel engine was developed and the simulation calculation of the steady-state and the transient-state temperature field is carried out. Based on calculation results, the maximum temperature fluctuation of the piston temperature field is less than 20°, so the steady-state temperature field was used as boundary condition for the thermal stress calculation and the thermal mechanical decoupling method was used to calculate the thermal stress caused only by the uneven temperature distribution. The results show that the maximum temperature is 354°C, which appears at the edge of the combustion chamber. The steady-state temperature field of finite element simulation shows a good agreement with the experimental results. The thermal stress obtained from thermal mechanical decoupling method was within the allowable range, since the maximum value is 270MPa. Danger zone appears at the combustion chamber throat, the contact area of piston head and skirt.

Kinematic and thermal characteristics of Lüders and Portevin-Le Châtelier bands in a medium Mn transformation-induced plasticity steel

This paper focuses on experimental investigations on the kinematic and thermal aspects of the propagative plastic instabilities, namely Lüders band and Portevin–Le Châtelier (PLC) band, observed in a medium Mn transformation-induced plasticity (TRIP) steel. The full-field strain and heat source measurements are used concurrently to investigate in-situ the propagative bands. The kinematic analysis provides the real-time strain field evolution allowing the observation and quantification of the band nucleation and propagation. The local Lüders strain is demonstrated both space and time independent, and its magnitude is equivalent to the macroscopic Lüders strain. The spatio-temporal independent characteristic is also verified on the local strain in the PLC bands. Concerning the thermal field analysis, the heat sources are estimated and used to obtain the geometrical and dynamic parameters of the propagating bands, including the band width, orientation, propagation velocity, and appearance moment. Then the estimated heat sources are applied to establish an experimental energy balance during the plastic deformation. The quantitative energy analysis reveals that the strain-induced martensitic transformation takes place in the Lüders band but barely in the PLC bands. The ex-situ X-ray diffraction measurement on the phase content and surface hardness testing of the material confirm well this determination.

Thermo-Mechanical Coupled Stamping Simulation about the Forming Process of High-Strength Steel Sheet

The developing trend of Automotive Lightweight has brought about the application of High-Strength Steel sheet in the automotive body, but High-Strength Steel sheet has poor formability with cold stamping process, and the existing cold stamping process cannot fully meet the needs of high strength steel forming. The hot stamping technology of High-Strength Steel sheet is the effective method to solve the above-described problem. It can greatly shorten the tryout time of die, and can effectively solve some problems like discarding of die, unreasonable process, and poor forming quality etc. In this paper, mainly for the Thermo-Mechanical Coupling process of sheet metal, introduce the thermal field analysis of High-Strength Steel sheet, the interaction of deformation and temperature field, and the main steps of Thermo-Mechanical Coupling. And for the U Shaped part, built the Finite element model and set process parameters with software ‘Dynaform’. Simulated its forming process of Thermo-Mechanical Coupling with solver ‘LS-DYNA’. The changing temperature field, thickness, and thickness reduction rate were calculated. The results show that, Thermo-Mechanical Coupled Stamping Simulation is an effective method to forecast high temperature formability of High-Strength Steel Sheet.

Analysis of temperature fields of aircraft components

The problem of analyzing of temperature fields of aircraft components is central for ensuring the operational reliability of the latter. The results of developing methods of calculating temperature fields of the existing products and those being designed based on analytical solution of thermal conductivity equations for the principal types of structures are outlined in the paper. The thermal conductivity equation for a parallelepiped and cylinder with heat sources of a similar form is solved using the variable separation method. A common expression of the solution of thermal conductivity equation for bodies of the simplest form ( parallelepiped, cylinder or its segment, sphere or its segment) with spatial, flat, linear or point heat sources is obtained. A mathematical model for the analysis of thermal fields of aircraft components is proposed. Mathematical and thermal models are developed for the analysis of temperature fields of onboard REA.

Study of Frequency Effects on Hardness Profile of Spline Shaft Heat-Treated by Induction

This paper is devoted to the study of frequency effects on hardness profile of AISI 4340 spline shaft heat-treated by induction through an extensive 3D finite element method simulation and structured experimental investigation. Based on coupled electromagnetic and thermal fields analysis, the 3D model is used to estimate the temperature distribution and the hardness profile. The proposed study examines the hardening process parameters, such as frequency, induced current density and heating time, known to have an influence on hardened surface and builds the simulation model step by step. The established model can provide not only an accurate prediction of temperature distribution and hardness profile but also a comprehensive analysis of machine parameters effects, especially the frequency. The numerical results achieved by this model are good and present a great agreement to the experimental data.

Anomalous Magnetic and Electrical Transport Behavior in Intermetallic Co<sub>58.5</sub>Ga<sub>41.5</sub>

Equi-atomic intermetallic Co-Ga compound exhibits unusual properties, such as, non-metallic electrical transport and weakly magnetic behavior. Electronic band structure calculations suggest the presence of deep psuedogap in the density of states near Fermi level. As the cobalt concentration varies over 50–60 at% it presents an interesting magnetic phase diagram along with drastic variation in electronic properties across a critical concentration (x∼58) in Co x Ga 100-x alloy system. The magnetic characteristics observed in these alloy were attributed to antisite defects [1, 2]. Despite several works on this alloy no clear consensus emerged on the nature of magnetic phase transitions observed and the magnetic ground state. A detailed analysis of thermal and magnetic field (H) dependence of magnetization (M) can throw light on magnetic ground state and the origin of anomalous behavior at critical composition. In this work we present dc magnetization, magnetoresistance (MR) and specific heat study of Co 58.5 Ga 41.5 composition prepared under different process conditions to elucidate magnetic ground state.

Analysis of thermal field within an urban canyon with variable thermophysical characteristics of the building's walls

In a typical urban configuration, a microclimatic analysis has been carried out. Using a CFD method, a N-S oriented urban street canyon, with a given H/W ratio, has been examined. The standard k-ε turbulence model has been used to simulate a three-dimensional flow field and to calculate the thermo-fluid dynamics parameters that characterize the street canyon. In this study has been analyzed the thermal flow field when the walls of the building change the properties of solar radiation absorption, in particular for α=0.2 and α=0.8. Solar radiation considered is that of 21/07 in Milan in two different hours: at 11:00 a.m. and at 02:00 p.m. The study shows the importance of the thermophysical properties of a wall, in the development of the thermal field and flow field. This is a very important topic, in terms of improvement of wellbeing and the quality of the air within the cities, through the choice of materials and colors of the facades of buildings.