Search Results for transient heat conduction

For most nondestructive evaluation (NDE) applications, the term thermography actually refers to surface-excited thermography (SET) that involves thermal mapping of surface temperature as heat flows from, to, or through a test object in response to excitation applied to the sample surface. This article discusses the strategies for implementing thermography for NDE, including the steady-state/whole-body approach and transient heat conduction. It describes the most common signal-processing methods, such as thermographic signal reconstruction, lock-in thermography, and pulsed-phase thermography. The article concludes with a discussion on the use of thermal methods for thermal diffusivity measurement and characterization of multilayer structures.

Thermal nondestructive evaluation (TNDE) is an indirect process, so that regardless of the form of energy used to excite the sample, interaction with the internal structure of a part occurs through the process of heat conduction. This article discusses the steady-state configuration and selective excitation configuration of the signal-generation mechanisms in thermal nondestructive evaluation methods. The three widely used approaches to TNDE are surface-excited thermography, vibrothermography, and thermoelastic stress analysis. The article provides information on the common features, characteristics, and limitations of these approaches.

This article provides an overview of the models of two induction heating devices, namely, induction crucible furnace (ICF) and induction furnace with slits, or segmented and water-cooled induction furnace with cold crucible (IFCC). These devices are used for melting with skull formation of low-conductivity materials such as glasses and oxides. The article presents the governing equations and boundary conditions for ICF and IFCC modeling. It includes a discussion on three electromagnetic field models in IFCC, namely, two-dimensional (2-D), quasi-three-dimensional, and three-dimensional (3-D) models. The article provides information on the simulation of skull formation in IFCC, and elucidates the transient axisymmetrical 2-D model and the transient 3-D model, including the primary results achieved for both glasses and skull formation.

Induction heating is a combination of several interrelated physical phenomena, including heat transfer, electromagnetics, and metallurgy. This article presents a brief review of different heat transfer modes, namely, heat conduction, thermal radiation, and convection. It focuses on the specifics of induction heating and heat treating applications. The article discusses the nonlinear and interrelated nature of a particular heat transfer phenomenon, physical property, and skin effect. It also presents simple case studies and general physical laws governing different heat transfer modes. The article also discusses the basic concepts of direct current and alternating current circuits, and reviews the theory of electromagnetic fields.

This article presents the modes of heat transfer and the stages of cooling during quenching. It provides an overview on the wetting process and then focuses on the evaluation of heat transfer during quenching. It also presents the challenges of thermal process evaluation based on an inverse heat conduction analysis. The article contains a compilation of best practice examples on heat transfer evaluation, which are intended to represent the practical aspects and applicability of the methods aiming the prediction of heat-transfer coefficients.

The finished product, after fusion welding, may contain physical discontinuities due to excessively rapid solidification, adverse microstructures due to inappropriate cooling, or residual stress and distortion due to the existence of incompatible plastic strains. To analyze these problems, this article presents an analysis of the welding heat flow, with focus on the fusion welding process. It discusses the analytical heat-flow solutions and their practical applications. The article concludes with a description of the effects of material property and welding condition on the temperature distribution of weldments.

During fusion welding, the thermal cycles produced by the moving heat source cause physical state changes, metallurgical phase transformation, and transient thermal stress and metal movement. This article presents an analysis of heat flow in the fusion welding process. The primary objective of welding heat flow modeling is to provide a mathematical tool for thermal data analysis, design iterations, or the systematic investigation of the thermal characteristics of any welding parameters. The article addresses analytical heat-flow solutions and their practical applications. It describes the effects of material property and welding condition on the temperature distribution of weldments. The thermal properties of selected engineering materials are provided in a table.

Intensive quenching (IQ) is an alternative method of hardening steel parts. Two types of IQ methods are used in heat treating practice: IQ-2 and IQ-3. IQ-2 is implemented in IQ water tanks, which are usually used for batch quenching of steel parts. IQ-3 is conducted in single-part processing using high-velocity water flow IQ units. This article presents a detailed description of IQ technology, related equipment, and IQ applications. A review of intensive quench system design and processing is provided, including numerical design criteria, steel selection, quenchants, properties (especially optimal residual stress profiles). Several specific applications of intensive quenching are also provided.

Welding and joining processes are essential for the development of virtually every manufactured product. This article discusses the fundamentals of fusion welding processes, with an emphasis on the underlying scientific principles. It reviews the role of energy-source intensity and the width of the heat-affected zone in fusion welding processes. The article contains figures from which the properties of any heat source can be estimated readily.

This article introduces the fundamental sources of residual stresses common to most manufacturing processes. It explains the effect of material removal on residual stresses and distortions in a part. The article assists the reader in making a choice between trial-and-error and computer-simulation approaches for the control of residual stresses. It provides a summary of the commonly used techniques of measuring residual stresses. The article also describes the finite element method for predicting residual stresses caused by various manufacturing processes. It concludes with a discussion on the operations involved in thermal and mechanical stress-relief methods.

The article discusses the fundamentals of fusion welding processes with an emphasis on the underlying scientific principles. It describes how surface temperature varies on steel with surface power densities that range from 400 to 8000 W/cm2. The article illustrates the spectrum of practical heat intensities used for fusion welding. It contains tables that present information on the thermal diffusivities of common elements and alloys from 20 to 100 °C.

This article provides a detailed overview of the thermomechanical modeling of additive manufacturing (AM) process. It begins with information on a basic understanding of the formation of residual stress during AM processing followed by a discussion on models commonly applied in AM modeling, such as heat-input models, material models, and material activation models. Information on experimental setup for validation and simulation of directed-energy deposition model is then included. The article also provides information on moving-source and part-scale analyses to simulate the laser powder-bed fusion AM process.

The measurement of thermophysical properties of metal alloys, especially at high temperatures, is difficult because of the reactivity of some alloys. This article reviews the methods available for measurement of thermal and other physical properties for liquid, semi-solid, and solid commercial alloys, including adiabatic calorimetry, modulated calorimetry, Calvet calorimetry, single-pan calorimetry, and drop calorimetry. It describes differential scanning calorimetry and differential temperature analysis for measuring transition temperatures such as phase transformation or glass transition temperatures. The article schematically illustrates the laser flash apparatus for measuring the thermal diffusivity of solids and oscillation viscometer for measurements of the viscosity of metals. A summary of the measurement methods is presented in tables.

Spray quenching (or jet impingement) is the most common technique employed to improve the uniformity of heat removal and break the vapor layer, allowing for a high cooling rate to be achieved. This article presents the heat transfer characteristics of quenching a hot surface, which can be expressed by the boiling and quench curve. It discusses three major spray parameters that have a substantial role in the quantification of spray cooling performance: droplet size, droplet velocity, and volumetric flux. The article also presents the available models and correlations to predict the cooling rate in spray quenching of hot surfaces during different boiling phases. It then discusses the effect of surface roughness on spray cooling performance.

This article provides a comprehensive review and critical assessment of numerical modeling of heat and mass transfer in fusion welding. The different fusion welding processes are gas tungsten arc welding, gas metal arc welding, laser welding, electron beam welding, and laser-arc hybrid welding. The article presents the mathematical equations of mass, momentum, energy, and species conservation. It reviews the applications of heat transfer and fluid flow models for different welding processes. Finally, the article discusses the approaches to improve reliability of, and reduce uncertainty in, numerical models.

This article describes the mechanisms and characteristics of heat transfer in the quenching of steel. This article describes the characterization of boiling heat transfer, including pool boiling, forced convective boiling, and rewetting, which plays a key role in defining the heat-extraction characteristics of a liquid quenchant. It provides information on heat generated microstructural field evolution and information on the analysis and characterization of heat transfer boundary conditions.