Dynamic Temperature Field Research Articles

A step-wise method for measuring thermophysical parameters of materials

A version of a transient method for measuring specific heat, thermal diffusivity and thermal conductivity is presented. The dynamic temperature field is generated by the passage of the electrical current through a planar electrical resistance made of thin metallic foil. The heat is produced in the form of a step-wise function. A thermocouple placed apart from the heat source measures the temperature response. The theory of the method, its experimental arrangement and the measuring regime for considering sensitivity coefficients are presented. Experimental data obtained on Perspex are compared with recommended and published data. The data on thermal conductivity agree to within ±0.7% whereas the specific heat is lower on average by 5.2% and the thermal diffusivity is higher by 3.5% when measurements were realized in vacuum. A shift in data of up to 10% was found for measurements made in air.

Thermal Processes in Nonsymmetric Heating of Ingots and Billets before Rolling

The effect of the process of tilting on the dynamics of the temperature field of a solid cylindrical ingot is shown. The selection of the site of location of tilters for annular furnaces that operate in pipe and axle rolling is substantiated.

Temperature Field Regulation in Thermal Cutting for Layered Manufacturing

A general thermal modeling and control methodology for thermal processing of layered materials for rapid prototyping technologies is established in this article. An analytical multivariable model of lumped temperature outputs generated by heat inputs on a surface grid is developed, based on Green’s function and state-space descriptions. The few independent parameters needed in such a linearized formulation are experimentally identified, and their time-variability reflects the heat transfer nonlinearities and process disturbances. A robust controller with thermal feedback is designed by pole placement methods, to obtain a specified dynamic temperature field yielding the desired material structure and properties. The regulated thermal processing is optimized in real time by proper heat source power modulation and torch guidance through a simulated annealing strategy. Its performance is tested on both the computer model and a laboratory station, using robotically guided plasma-arc cutting and infrared thermal sensing, in regulating the sensitized zone during blanking of an elementary contour pattern on stainless steel.

An evaluation of three numerical models used in simulations of the active layer and permafrost temperature regimes

Three numerical models (designated the Goodrich, Guymon/Hromadka, and Seregina models) used for calculations of the ground thermal regime which are based on different numerical methods and employ different treatments of freezing and thawing were compared with each other, with analytical solutions, and with measured temperature data. Comparisons of the models with the Neumann solution show differences generally less than 0.2°C between calculated temperatures using a wide range of time and depth steps. The Goodrich and Guymon/Hromadka models have been shown to predict temperature field dynamics reliably in the active layer and permafrost using small time and depth steps. However, comparisons of the models with each other using large time and depth steps and field data for the surface boundary condition showed significant differences between them (RMS deviations exceeding 1°C) and, in addition, the development of a non-physical feature (thaw bulb after freeze-up). Therefore, with large time and depth steps, the models cannot reproduce the temperature field dynamics in the active layer and permafrost. Consequently, agreement with the Neumann solution is necessary but not sufficient to qualify the models for calculations of real temperature fields. The Goodrich model requires a time step not longer than 1 h and depth step in the upper 1 m not larger than 0.02 m to reproduce the temperature regime with reasonable accuracy. However, the choice of optimum time and depth steps appears to be specific to the application. Using the Guymon/Hromadka model, similar accuracy can be obtained with a 1 h time step and 0.1 m space step within the upper 1 m depth or a 1 day time step and 0.01 m space step. However, the use of larger steps does not necessarily decrease the calculational time compared to the Goodrich model. For the case with unfrozen water present in the frozen soil, the results of calculations using the numerical models were compared with an analytical solution and were found to agree within 0.02°C.

Tool temperatures and crack development in milling cutters

This paper presents a theoretical and experimental study of the dynamic temperature field on a milling cutter tooth. A finite element model is developed to simulate the heat cycle of the cutting tooth by a time-varying heat flux. Forced convection effect has been investigated at exit. Experiments on simulating thermal process of face milling by heating cemented carbide teeth with laser pulses have also been conducted; the dynamic temperature field on a cutting tooth was measured. It has been shown that when the tooth is disengaged its temperature does not decrease to a level which will induce tensile stresses on the rake face. Thus, thermal cracks are not initiated during this stage of cutting. In this paper the authors propose that thermal cracks develop cyclically with increases in the temperature gradient at each entry of the cutter into the workpiece.

Thermal problems in modeling of welding by a fixed fusing electrode

A theoretical description of the thermal processes occurring in the electrode and the base metal is given. Useful mathematical models are suggested for calculating the dynamics of temperature fields, and the reasons for defects in the weld are discussed.

Computer Aided Infrared Imagery for Fabric Surface Temperature Fields Under Simulated Cigarette Exposure

This paper, the first of two parts, describes a technique of measuring dynamic temperature fields on thin, porous textile materials when exposed to a low energy, localized heat source. A methodology is outlined for studying the smoldering process via measurement of surface temperature profiles using calibrated infrared (IR) thermography, a non-intrusive technique for the measurement and analysis of a material's surface temperature. This paper outlines the essential elements necessary for proper use of IR thermography and provides a summary of thermal radiation theory, combined with computer enhancement of the thermographs. An advanced thermal imaging system couples non-contact infrared thermography with personal computer-based image processing routines for the measurement of real-time temperature and heat flow patterns. The instrumental set-up descri bed here facilitates instantaneous scanning, detection, and depiction of temperature variations and isotherms. Such a system allows continuous, real-time or post-experiment processing and analysis of thermal images in color or gray scale, via digitization followed by image enhancement. A typical protocol of computational techniques and image analysis steps are described for obtaining thermographic data and to analyze growth of conditions leading to smolder initiation, typically in a cellulosic fabric. This methodology can be employed for dynamic measurement of temperature and heat flow though porous materials such as upholstery cover fabric, insulation material, protective clothing, etc. Language: en

Heat transfer in He II with stepwise switching on of heater

The problem of the dynamics of temperature and normal velocity fields in He II with stepwise switching on of a plane heater is investigated in this paper using numerical methods. The problem is solved in the framework of the hydrodynamics of superfluid turbulence in which the density of vortex tangle, L, reaches its equilibrium value with respect to the value of the relative velocity, v ns = ( v n - v s). Such an approximation, the so-called adiabatic approximation, is valid at times much larger than the time for development of turbulence, τ v. The results obtained are compared with other known solutions of similar problems and with experimental data.

Simulation of temperature profiles in cylindrical furnaces

The model used for the following calculations is suitable for evaluation of power distribution for given static and dynamic temperature fields in cylindrical furnaces, conclusions and suggestions concerning optimum furnace construction, calculation of coefficients of transfer matrix for furnace control. The aim of this paper is to give some examples of model application which show the influence of furnace geometry on temperature profiles for given thermal properties of materials used for furnace construction

Effect of the percolation heat transfer component on the temperature field and thawing dynamics of soils

The effect of the convective heat transfer component on the temperature field and thawing front dynamics of soils is investigated for high fluid percolation velocities in the thawed zone. The steady state interchange and approximate self-similarity methods are used to obtain upper and lower bounds of the solution of the Stefan problem with a convective heat transfer component in a porous medium. From the results of the calculations conclusions are drawn concerning the accuracy and limits of applicability of the solutions obtained.

Heat flow, heat production and crustal dynamics in the Central Alps, Switzerland

Interrelations between temperature field, crustal structure and crustal dynamics (vertical crustal movements) have been investigated along a selected profile: the Swiss Geotraverse which cross-sects in a NW-SE direction the following tectonic units: Rhine-Graben, Jura Mountains, Molasse Basin, Helvetic Nappes, Central Massifs with autochthonous cover, Penninic units, basement and sedimentary units of the Southern Alps (total length: 220 km). The corrected heat flow is slightly elevated along or close to the traverse (≈ 75 mW/m 2). Thermal effects of Alpine overthrusting and metamorphism on the surface gradient are negligible today. For steady-state calculations of the temperature field heat production has been determined experimentally for surface samples; for deep crustal rocks it was inferred from an empirical relationship between heat production and seismic compressional wave velocity or density. The temperature field shows downwarped isotherms where a pronounced inversion of seismic velocity and density occurs in the upper crust. The same area of the Central Alps (Lepontine gneiss region) exhibits the strongest recent crustal movements (vertical uplift ≈ 1 mm/yr). The Mohorovićič discontinuity is clearly not an isothermal surface; its asymmetric shape found by seismic and gravimetric measurements is likely to be a result of the early Alpine subduction tectonics.

Dynamics of temperature field in the halo of emplaced plutons, during several metamorphic reactions

Dynamics of temperature field in the halo of emplaced plutons, during several metamorphic reactions