Toward an Improved Understanding of Effect of Linear Heat Input on Heat-Affected Zone Tempering in Temper Bead Welding

2016 ◽  
Author(s):  
Kaiwen Zhang ◽  
Jeffrey A. Enneking ◽  
Bennett B. Grimmett ◽  
Wei Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Affected Zone ◽  
Heat Input ◽  
Experimental Testing ◽  
Transfer Model ◽  
Power Ratio ◽  
Hardness Distribution ◽  
Micro Hardness ◽  
Linear Heat

In temper bead welding, the heat input from welding is purposefully utilized to temper the hard microstructure for improving toughness. An optimal temper bead welding requires careful control of heat input and bead placement. In this study, the effect of linear heat input on heat-affected zone (HAZ) tempering was studied by a combination of experimental testing and numerical modeling. Temper bead welding experiments were performed on SA-533 steel using three different heat inputs while keeping the power ratio constant. The extent of tempering in the HAZ was quantified using micro-hardness mapping. A 2-D weld heat transfer model, using the double-ellipsoidal heat flux equation, was developed to calculate the temperature evolution. The peak temperatures experienced in the substrate’s HAZ was correlated to the hardness distribution. The results indicate that the linear heat input can have a significant influence on the extent of tempering in temper bead welding.

The Infrared Characteristics of the Wall Temperature of Boiling Heat Transfer in Microchannel

2011 ◽  
Vol 383-390 ◽  
pp. 811-815
Author(s):  
Hu Gen Ma ◽  
Jian Mei Bai ◽  
Rong Jian Xie ◽  
Wen Jing Tu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Boiling Heat Transfer ◽  
Transfer Test ◽  
Axial Direction ◽  
Transfer Model ◽  
Micro Channel ◽  
Vapor Quality ◽  
Test Rig

In this paper, the boiling heat transfer test rig was designed and built, while the characteristics of boiling Heat Transfer of refrigerants in micro-channel was researched. The wall temperature of micro-channel was measured by TH5104 Infrared thermography. The results showed that there were obvious variations for wall temperature of micro-channel along the axial direction when boiling heat transfer occurred in the micro-channel. The temperature distribution affected obviously by the heat flux, mass flow rate; vapor quality and heat transfer model.

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

2011 ◽  
Vol 199-200 ◽  
pp. 1604-1608
Author(s):  
Yun Fu Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Fractal Model ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
Small Contact Angle ◽  
Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

Application of a Complex Nusselt Number to Heat Transfer During Compression and Expansion

1994 ◽  
Vol 116 (3) ◽  
pp. 536-542 ◽  
Author(s):  
A. A. Kornhauser ◽  
J. L. Smith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Temperature Difference ◽  
Rate Of Change ◽  
Transfer Model ◽  
Volume Data ◽  
Piston Cylinder ◽  
Compression And Expansion ◽  
Experimental Pressure

Heat transfer during compression and expansion can be out of phase with bulk gas-wall temperature difference. An ordinary convective heat transfer model is incapable of predicting this phenomenon. Expressions for compression/expansion heat transfer developed from simple conduction models use a complex heat transfer coefficient. Thus, heat flux consists of one part proportional to temperature difference plus a second part proportional to rate of change of temperature. Surface-averaged heat flux was calculated from experimental pressure-volume data for piston-cylinder gas springs over a range of speeds, pressures, gases, and geometries. The complex Nusselt number model proved capable of correlating both magnitude and phase of the measured heat transfer as functions of an oscillation Peclet number.

Numerical Investigation of an Induced Draft Air-Cooled Condenser Under Crosswind Conditions

2021 ◽  
Author(s):  
Daniel L. Louw ◽  
C. J. Meyer ◽  
S. J. van der Spuy
Keyword(s):  
Heat Transfer ◽  
Axial Flow ◽  
Transfer Model ◽  
Power Ratio ◽  
Reference Case ◽  
Disk Model ◽  
Primary Direction ◽  
The Mean ◽  
Multiple Reference ◽  
Porosity Model

Abstract This study numerically investigated the performance of a 64-fan induced draft Air-Cooled Condenser (ACC) subjected to crosswind conditions. An Actuator Disk Model (ADM) was used to model the axial flow fans and a combination of the Darcy-Forchheimer porosity model and the Effectiveness Number of Transfer Units (ε-NTU) heat transfer model were used to model the heat exchangers. Crosswind conditions were applied to the ACC model in multiple directions and multiple reference velocities, with the results compared to a reference case where no wind was present. The induced draft ACC attained a mean fan volumetric effectiveness of 1.065, a mean heat transfer effectiveness of 1.039 and a mean heat-to-power ratio of 120.6 when no crosswinds were present. At relatively high crosswind velocities of 9 m/s the mean volumetric effectiveness decreased by 10.1% from wind coming from the primary direction, and by 10.3% from wind coming from the secondary direction. Similarly, the mean heat transfer effectiveness decreased by 21.7% under primary cross-winds, and by 31.3% under secondary crosswinds. Finally, the heat-to-power ratio of the ACC decreased to 92.5 under primary crosswinds, and by 77.6 under secondary crosswinds.

Heat Transfer and Air Diffusion Phenomena in a Bed of Polymer Powder Using Apparent Heat Capacity Method: Application to the Rotational Molding Process

2007 ◽  
Author(s):  
M. Boutaous ◽  
E. Pe´rot ◽  
A. Maazouz ◽  
P. Bourgin ◽  
P. Chantrenne
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Heat And Mass Transfer ◽  
Granular Media ◽  
Transfer Model ◽  
Melting Front ◽  
Polymer Powder ◽  
Air Diffusion

The process of rotational moulding consists in manufacturing plastic parts by heating a polymer powder in a biaxial rotating mould. In order to optimise the production cycle of this process, a complete simulation model has to be used. This model should describe the phenomena of heat and mass transfer in a moving granular media with phase change, coalescence, sintering, air evacuation and crystallization during the cooling stage. This paper focus on the study of heat and mass transfer in a quiescent polymer powder during the heating stage. An experimental device has been built. It consists in an open plane static mold on which an initial thickness, e, of a polymer powder is deposited. This powder is then heated until it melts. An inverse heat conduction method is used to determine the heat flux and temperature at the interface between the mold and the powder. This interfacial heat flux is taken as a boundary condition in a numerical heat transfer model witch takes into account the heat transfer in granular media with phase change, coalescence, sintering, air bubbles evacuation and rheological behaviour of the polymer. For the numerical simulation of the heat transfer, the apparent specific heat method is used. This approach allows to solve the same energy equation for all the material phases, so one do not have to calculate the melting front evolution. This fine modelling, close to the real physical phenomena makes it possible to estimate the temperature profile and the evolution of the polymer powder characteristics (phase change, air diffusion, viscosity, evolution of the thermophysical properties of the equivalent homogeneous medium, thickness reduction, air volume fraction...). Several results are then presented, and the influence of different parameters, like the thermal contact resistance, the process initial conditions and the polymer’s rheological characteristics are studied and commented. Indeed the predictions of the temperature rises in the polymer bed, agree well with the experimental measurements.

Numerical Simulation of Flow Boiling of Binary Mixtures Using Multi-Fluid Modeling Approach

2011 ◽  
Author(s):  
Vedanth Srinivasan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Interfacial Area ◽  
Transfer Model ◽  
Mass Transfer Model ◽  
Number Density ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

In this paper, the development of a new mass transfer model to simulate the thermal and phase change characteristics encountered by binary mixtures during flow boiling process is discussed. A new boiling mass transfer model based on detailed bubble dynamic effects, inclusive of local bubble shear, drag and buoyancy dynamics, has been developed and full implemented within the commercial CFD code AVL FIRE v2010. In the present study the phasic mass, momentum and energy equations are solved in a segregated fashion in conjunction with an interfacial area transport and a number density equation to study the heat and mass transfer characteristics of binary flow boiling inside a rectangular duct. Turbulence in the fluidic system and those generated by the bubbly flow are treated using an advanced k-ζ-f model. The simulation results comprising of flow variables such as volume fraction, fluidic velocities and temperature and the resultant heat flux generated on the heated wall section clearly monitors the suppression in heat transfer coefficients with enhancement in flow convection. Competing mechanisms such as phase change process and turbulent convection are identified to influence the heat transfer characteristics. In particular, the varying influence of the mass transfer effects on the heat flux characteristics with alteration in wall temperature is well demonstrated. Comparisons of the predicted heat transfer coefficients for varying wall superheat and varying fluidic velocity indicates a very good agreement with experimental data, wherever available. Description of the flow field inclusive of interfacial area and number density distribution is provided. The current model can be easily extended to simulate multiphase flow in complex systems such as a cooling water jacket for automotive applications.

Flow and Heat Transfer Study in an Autoclave for Hydrothermal Crystal Growth With a Three-Dimensional Conjugate Heat Transfer Model

2002 ◽  
Author(s):  
Hongmin Li ◽  
Edward A. Evans ◽  
G.-X. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Crystal Growth ◽  
Conjugate Heat Transfer ◽  
Heat Transfer Model ◽  
Thick Wall ◽  
Transfer Model ◽  
Hydrothermal Crystal Growth ◽  
Flow And Heat Transfer ◽  
Isothermal Wall

Numerical modeling becomes an important technique to study hydrothermal crystal growth since experimental measurements in hydrothermal autoclaves are extremely difficult due to the high pressure and high temperature growth conditions. In all existing models for hydrothermal growth, isothermal boundary conditions are assumed, although electric heaters are employed around the outside surface of the thick autoclave wall in practice. In this paper, a conjugate heat transfer model based on an industry size autoclave is developed to investigate the validity of such an assumption. The model includes not only turbulent fluid flow and heat transfer of the solution but also the heat conduction in the thick wall. The outside surfaces of the wall are under constant heat flux conditions, simulating electric resistance heating used in practice. Non-uniformity of the heat flux in the circumferential direction is also introduced in the model. The results indicate that the temperature at the solution/wall interface is far away from uniform. The isothermal wall boundary condition in previous efforts is questionable. Predictions of the isothermal wall model are analyzed. Parametric studies with the conjugate model show that total heat supply rate does not affect vertical uniformity dramatically. Heat loss can be lowered without affecting the flow and temperature fields if heaters are put half diameter or further away from the middle height (baffle) plane.

Progress in the Modeling and Simulation of Flow Boiling Heat Transfer of Binary Fluids Using Advanced Multi-Fluid Modeling Techniques

2012 ◽  
Author(s):  
Vedanth Srinivasan ◽  
Rok Kopun
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Wide Range

In this paper, we discuss the implementation and testing of a novel boiling mass transfer model to simulate the thermal and phase transformation behavior, generated due to boiling of binary mixtures, using the commercial CFD code AVL FIRE® v2011. The phase change model, based on detailed bubble dynamics effects, is solved in conjunction with incompressible phasic momentum, turbulence and energy equations in a segregated fashion, to study the flow boiling process inside a rectangular duct. Full three dimensional validation studies including the effect of flow velocity and exit pressure conditions, acting on a wide range of operating wall (superheat) temperatures, clearly shows the suppression of heat and mass transfer coefficients with enhancement in flow convection. Competing mechanisms such as phase change process and turbulent convection are identified to influence the heat transfer characteristics. In particular, the varying influence of the mass transfer effects on the heat flux characteristics with alteration in wall temperature is well demonstrated. Comparisons of the predicted total heat flux, computed as the sum of the convection and phase change components, indicate a very good agreement with experimental data, wherever available. Description of the flow field inclusive of phasic fraction, temperature and velocity field provides extensive details of the multiphase behavior of the boiling flow. Some preliminary results on the phase change work flow to model heat transfer in cooling jackets, for automotive applications, is also discussed.

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