ON THE DYNAMICAL THEORY OF HEAT TRANSPORT PROCESS

The powder-bed electron beam additive manufacturing (EBAM) process is a relatively new AM technology that utilizes a high-energy heat source to fabricate metallic parts in a layer by layer fashion by melting metal powder in selected regions. EBAM can be able to produce full density part and complicated components such as near-net-shape parts for medical implants and internal channels. However, the large variation in mechanical properties of AM build parts is an important issue that impedes the mass production ability of AM technology. It is known that the cooling rate in the melt pool directly related to the build part microstructure, which greatly influences the mechanical properties such as strength and hardness. And the cooling rate is correlated to the basic heat transport process physics in EBAM, which includes a moving heat source and rapid self-cooling process. Therefore, a better understanding of the thermal process of the EBAM process is necessary. In this study, a 3D thermal model, using a finite element method (FEM), was utilized for EBAM heat transport process simulations. The process temperature prediction offers information of the cooling rate during the heating-cooling cycle. The thermal model is applied to evaluate, for the case of Ti-6Al-4V in EBAM, the process parameter effects, such as the beam speed and power, on the temperature profile along the melt scan and the corresponding cooling rate characteristics. The relationship between cooling rates and process parameters is systematically investigated, through multiple simulations, by incorporating different combinations of process parameters into the thermal model. The beam scanning speed vs. beam power curves of constant cooling rates can be obtained from 3D surface plots (cooling rate vs. different process parameters), which may facilitate the process parameters selections and achieve consistent build part quality through controlling the cooling rate.

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Analysis of Heat Transfer Through Optically Participating Medium in a Concentric Spherical Enclosure: The Role of Dual-Phase-Lag Conduction and Radiation

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4040283 ◽

2018 ◽

Vol 10 (4) ◽

Cited By ~ 1

Author(s):

Aritra Mukherjee ◽

Pranab Kumar Mondal

Keyword(s):

Heat Conduction ◽

Steady State ◽

Heat Transport ◽

Transport Process ◽

Energy Equation ◽

Spherical Geometry ◽

Phase Lag ◽

Dual Phase ◽

Radial Temperature ◽

Heat Transport Process

This paper deals with the analysis of the effects of combined dual-phase-lag (DPL) heat conduction and radiation in a concentric spherical enclosure with diffuse-gray surfaces. The enclosed medium is optically participating, i.e., it is radiatively absorbing, emitting, and scattering. Lattice Boltzmann method (LBM) is used to solve the energy equation, and finite volume method (FVM) is used to compute the radiative information. To establish the accuracy of this approach, the combined energy equation is also solved with the finite difference method. Radial temperature profiles and energy contributions by conduction and radiation at various instances and prior to steady-state are elaborated for different kind of thermal perturbations Influence of numerous conductive and radiative parameters over the heat transport process have been investigated in detail. It is observed that higher contribution of radiation to the heat transport process can destroy the thermal wave in the medium completely. Sample results for pure non-Fourier heat conduction, pure radiation, and steady-state response of combined Fourier conduction and radiation in spherical geometry are compared with the results available in literature. In all the cases, comparison shows good agreement with the reported results.

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Pore Network Simulation and Experimental Investigation on Water-Heat Transport Process of Soil Porous Media

Journal of Heat Transfer ◽

10.1115/1.4043213 ◽

2019 ◽

Vol 141 (6) ◽

Author(s):

Yuejin Yuan ◽

Libin Tan ◽

Zhe Zhao ◽

Yingying Xu ◽

Miaomiao Bai ◽

...

Keyword(s):

Porous Media ◽

Heat Transport ◽

Sandy Soil ◽

Transport Process ◽

Network Simulation ◽

Pore Network ◽

Two Dimensional ◽

Simulation Results ◽

Heat Transport Process ◽

Good Agreement

The research on water-heat transport of soil porous media has important theoretical and practical significance for the problem of agricultural production and environmental governance. In this work, the water-heat transport characteristics of sandy soil porous media are analyzed. The two-dimensional continuum physical model is constructed by continuum method, and the two-dimensional pore network physical model is constructed directly at pore scale by taking into account the complicated pore and skeleton structures of soil. Mathematical models of water-heat transport process of sandy soil are constructed based on heat-mass transfer mechanism. Mathematical models of the continuum method and pore network method are solved by ANSYS and self-designed solving algorithm, respectively. The numerical simulation results of soil temperature distributions and moisture distributions are in good agreement with the experimental results. The pore network simulation results are in good agreement with the measured data and are superior to the existing continuous scale method. The pore network simulation results can directly present the characteristics of the preferential flow and wetting front during the water-heat transport process of soil.

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INVERSE HEAT TRANSPORT PROBLEMS FOR COEFFICIENTS IN TWO‐LAYER DOMAINS AND METHODS FOR THEIR SOLUTION

Mathematical Modelling and Analysis ◽

10.3846/13926292.2002.9637194 ◽

2002 ◽

Vol 7 (2) ◽

pp. 217-228 ◽

Cited By ~ 2

Author(s):

S. Guseinov ◽

A. Buikis

Keyword(s):

Inverse Problem ◽

Thermal Diffusivity ◽

Inverse Problems ◽

Heat Transport ◽

Transport Process ◽

Direct Problem ◽

Piecewise Constant Function ◽

Algebraic Equations ◽

Heat Transport Process

In various fields of science and technology it is often necessary to solve inverse problems, where from measurements of state of the system or process it is required to determine a certain typesetting of the causal characteristics. It is known that infringement of the natural causal relationships can entail incorrectness of the mathematical stating of inverse problems. Therefore the development of efficient methods for solving such problems allows one to considerably simplify experimental research and to increase the accuracy and reliability of the obtained results due to certain complication of algorithms for processing the experimental data. The problem of determination of thermal diffusivity coefficients considering other known characteristics of heat transport process is among incorrect inverse problems. These inverse problems for coefficients are quite difficult even in the case of homogeneous media. In this paper it is supposed that the heat transport equation is non‐homogeneous and an algorithm for determination of the thermal diffusivity coefficients for both the media is proposed. At the first step, the non‐homogeneous inverse problem with piecewise‐constant function of non‐homogeneity is solved. For this auxiliary inverse problem, the proposed method allows one to determine both the coefficients of thermal diffusivity and to restore the heat transport process without any additional information, i.e. the algorithm also solves the direct problem. Then the initial non‐homogeneous inverse problem with a piecewise‐continuous function of non‐homogeneity is solved. The proposed method reduces the non‐homogeneous inverse problem for coefficients to a set of two transcendent algebraic equations. Finally, the analytical solution to direct problem is obtained using Green's function.

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Electrohydrodynamic Conduction Driven Single- and Two-Phase Flow in Microchannels With Heat Transfer

Journal of Heat Transfer ◽

10.1115/1.4007617 ◽

2013 ◽

Vol 135 (10) ◽

Cited By ~ 13

Author(s):

Matthew R. Pearson ◽

Jamal Seyed-Yagoobi

Keyword(s):

Heat Transfer ◽

Transport Process ◽

Heat Fluxes ◽

Phase Flow ◽

Reverse Effect ◽

Two Phase ◽

Small Areas ◽

Dielectric Liquids ◽

Phase Loop ◽

Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the microscale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The effect of these embedded electrodes on the heat transport process, flow rate, and pressure in the micro-evaporator and on the two-phase loop system is characterized. Local enhancements are found to be up to 30% at low heat fluxes. The reverse effect that phase-change has on the EHD conduction pumping phenomenon is also quantified.

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The Effects of Regional Fluid Flow on Deep Temperatures (Hesse, Germany)

Energies ◽

10.3390/en12112081 ◽

2019 ◽

Vol 12 (11) ◽

pp. 2081 ◽

Cited By ~ 2

Author(s):

Nora Koltzer ◽

Magdalena Scheck-Wenderoth ◽

Judith Bott ◽

Mauro Cacace ◽

Maximilian Frick ◽

...

Keyword(s):

Fluid Flow ◽

Heat Transport ◽

Structural Model ◽

Federal State ◽

Geothermal Resources ◽

Hydrochemical Data ◽

Reservoir Conditions ◽

Deep Fluid ◽

Heat Transport Process ◽

Hydraulic Processes

A successful utilization of deep geothermal resources requires accurate predictions about the distribution of reservoir temperature as well as of the hydraulic processes exerting a direct influence on the productivity of geothermal reservoirs. The aim of this study was to investigate and quantify the influence that regional thermo-hydraulic processes have on the geothermal configuration of potential reservoirs in the German Federal State of Hesse. Specifically, we have addressed the question of how the regional thermal and hydraulic configuration influence the local hydro-thermal reservoir conditions. Therefore, a 3D structural model of Hesse was used as a basis for purely hydraulic, purely thermal and coupled 3D thermo-hydraulic simulations of the deep fluid flow and heat transport. As a result of our numerical simulations, Hesse can be differentiated into sub-areas differing in terms of the dominating heat transport process. In a final attempt to quantify the robustness and reliability of the modelling results, the modelling outcomes were analyzed by comparing them to available subsurface temperature, hydraulic and hydrochemical data.

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Single- and Two-Phase Flow in Microchannels With Heat Transfer and Driven by an EHD Conduction Pump

Volume 10: Heat and Mass Transport Processes, Parts A and B ◽

10.1115/imece2011-64798 ◽

2011 ◽

Author(s):

Matthew R. Pearson ◽

Jamal Seyed-Yagoobi

Keyword(s):

Heat Transfer ◽

Transport Process ◽

Enhancement Effect ◽

Phase Flow ◽

Two Phase ◽

Small Areas ◽

Dielectric Liquids ◽

Phase Loop ◽

Two Phase Heat Transfer ◽

Heat Transport Process

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the micro-scale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The enhancement effect of these embedded electrodes on the heat transport process in the micro-evaporator and on the two-phase loop system is characterized. Single- and two-phase heat transfer regimes are both studied and the effect of applied voltage and heat flux are considered on the overall flow rate and the wall temperature of the microchannel.

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Systematic Reflections and the Two Beam Concept of Extinction Distance

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100061677 ◽

1967 ◽

Vol 25 ◽

pp. 332-333

Author(s):

S. S. Sheinin ◽

C. D. Cann

Keyword(s):

Dynamical Theory ◽

Beam Intensity

The effects of systematic reflections on the variation of diffracted beam intensity with depth in a crystal can only be taken into account by using the multi-beam dynamical theory. The results of calculations of this kind, which are presented here, indicate that the intensity profiles obtained are not periodic. Since extinction distance is a concept strictly applicable only when the diffracted beam intensity varies periodically with depth, its use as a parameter in describing multi-beam intensity profiles must be carefully considered.

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