One-dimensional Heat Conduction Analysis Research Articles

A micromechanical and numerical model for effective thermal conductivity of areca fiber and coconut shell particulate-reinforced hybrid composites

The present investigation reports on the thermal conductivity of areca fiber and coconut shell particulate (CSP)-reinforced polymer composites. The fiber and particulate reinforcement percentages were 10–40wt.% with various weight ratios as 1:1, 1:3, and 3:1. The main focus has been given to the development of a micromechanical model to calculate the effective thermal conductivity of areca fiber and CSP-reinforced hybrid composites. In the numerical study, steady-state one-dimensional heat conduction analysis is performed with a periodic arrangement of cylinders and spherical reinforcement using ANSYS software. Unitherm [Formula: see text]Model 2022 equipment was used to measure the experimental thermal conductivity values of the hybrid composite materials and validated with the micromechanical and numerical values. The experimental results attained for thermal conductivity are supported by the proposed micromechanical model. The measured values of the composites were found to be in very close agreement with the micromechanical model and the numerical analysis. It is concluded from this study that the addition of areca fiber and CSP improves the thermal insulation capability of neat epoxy.

In-depth analysis of reaction kinetics parameters of phenolic resin using molecular dynamics and unsupervised machine learning approach

Reaction kinetics parameters of a material depend on energy dynamics based on breaking and formation of all the types of bonds in the system. While employing molecular dynamics simulation, it can become tedious and a complicated job to use all the bond information for extracting reaction kinetics parameters. With this understanding, in the current study, the use of an unsupervised machine learning technique is demonstrated for extracting the reaction kinetics parameters from the molecular dynamics simulation of an ablative material. Molecular dynamics simulations are performed on crosslinked and non-crosslinked polymers in temperature regime where they would undergo pyrolysis decomposition. Non-negative Matrix Factorization (NMF) technique is used to reduce the bonding environment, obtained during the simulations, to the concentration profiles of a few principal components. A comparative analysis performed with polymers having different degrees of crosslinking reveals that the activation energy reduces with increase in the degree of crosslinking. The effect of heating rate on the reaction kinetics of phenolic polymers during the pyrolysis simulation is investigated in detail. The assumption of chemical equilibrium between gases and porous solid domain is frequently made in continuum level thermal response solvers. It is unknown if this assumption significantly affects the calculated reaction kinetics parameters. To understand the same, a molecular dynamics simulation, which eliminates the generated gas molecules in a systematic manner throughout the pyrolysis process, is carried out. Furthermore, to demonstrate the usefulness of reaction kinetics parameters extracted after manifestation of chemical equilibrium at microscale level, a one-dimensional heat conduction analysis is performed. The results obtained by not considering the gas particles in reaction modeling agree well with experiments. At the end, a multiscale thermal response analysis is performed over an axi-symmetric geometry for which, a relation is derived between pyrolysis gas species and solid material density evolution from MD simulations. Based on the relation, the axi-symmetric domain is segregated into different regions for their contribution in changing pyrolysis gas composition by either adding or consuming gas species.

Estimation of Thickness of Steel Specimens Simulating Corroded Steel Sheet Pile by One-Dimensional Heat Conduction Analysis

Estimation of Thickness of Steel Specimens Simulating Corroded Steel Sheet Pile by One-Dimensional Heat Conduction Analysis

Geothermal study to explain man-made permafrost in tailings with raised surface

Deposition of mine tailings in a cold climate requires precautions as temporary sub-zero temperatures can imply considerable consequences to the storage due to creation of permafrost. The risk of creating man-made permafrost lenses due to tailings deposition exists even in regions with no natural permafrost, as material being frozen during winter might not fully thaw by the following summer. When such frozen layers thaw during later longer warmer periods, excess pore water pressure and large settlements might develop. Such implications close to the dam structure have to be avoided and therefore the risk of generating permafrost should be reduced. This paper describes a geothermal model for one-dimensional heat conduction analysis. The model is able to simulate the temperature profile in tailings where the surface elevation is constantly increased due to deposition. At the tailings surface, the boundary condition is the air temperature changing over time during the year. Air temperatures, tailings deposition schedule and tailings properties are given as input to the model and can easily be changed and applied to specific facilities. The model can be used for tailings facilities in cold regions, where the effects of tailings deposition on the temperature regime are of interest. Findings can improve tailings management by explaining man-made permafrost generation. The model can also aid in setting up appropriate deposition schedules and to prevent generation of permafrost layers.

Numerical Study of Thermal Conductivities of Carbon-Based Mesoporous Composites

The thermal conductivities of ordered mesoporous carbon CMK-3 filled with Al nanoclusters were studied in this article. CMK-3 is a typical example of carbon rods which are arranged in a relatively regular two-dimensional hexagonal array. The initial structure of CMK-3 was generated from the amorphous carbon and validated by XRD simulation which is coincident with experimental data. The thermal conductivities of carbon rods in CMK-3 and Al nanoclusters with 133 atoms were simulated by an equilibrium molecular dynamics method. Then, the effective thermal conductivity (ETC) of a mesoporous composite, CMK-3 filled with $$\text {Al}_{133}$$ , was obtained via one-dimensional heat conduction analysis. The influences of the substrate porosity, nanocluster filling ratio, and temperature were discussed. As an anisotropic material, ETCs along the $$X$$ and $$Y$$ directions are extremely poor, due to the overwhelming effect of the air thermal resistance. However, in the $$Z$$ direction, the ETC improves almost linearly as the porosity decreases, and the value is much higher than those of $$X$$ and $$Y$$ directions. In the case of a 70 % filling ratio, when the porosity is below 59.7 %, the ETC in the $$Z$$ direction exceeds the thermal conductivity of Al nanoclusters and approaches a peak value around the melting temperature of $$\text {Al}_{133}$$ nanoclusters. The results indicate that the carbon-based mesoporous CMK-3 filled with Al nanoclusters might become a promising phase change material.

Raman measurements of optical absorption and heat transfer coefficients of a single carbon fiber in atmosphere environment

In this paper, the optical absorption and heat transfer coefficients of a single suspended 4.3μm diameter carbon fiber have been measured in the experiment. The test fiber was first heated locally by a laser beam and the temperature rise was measured from the shifts in the Raman G-band frequency, and then the laser heating was replaced by an electrical current heating, the electrical power was adjusted to have the same temperature rise. Since the electrical power can be measured accurately, the absorbed laser power can be extracted from one-dimensional heat conduction analysis and the heat transfer coefficient can be obtained as well. The present experimental results show that the optical absorption of 4.3μm diameter carbon fiber is 39.62% and the heat transfer coefficient is 4150Wm−2K−1, which agrees well with the prediction of published experimental empirical formula.

Critical design factors for sector transport maintenance in DEMO

This paper mainly focuses on a sector transport maintenance scheme from the aspects of high plant availability. In this study, three different maintenance schemes are considered based on (1) the number of maintenance ports and (2) the insertion direction. The design study clarifies critical design factors and key engineering issues on the maintenance scheme: (1) how to support an enormous overturning force of the toroidal field coils in the large open port for sector transport and (2) define the transferring mechanism of sectors in the vacuum vessel. On reviewing these assessment factors, the sector transport using a limited number of horizontal maintenance ports is found to be a more realistic maintenance scheme. In addition, evaluating maintenance scenarios under high decay heat is proposed for the first time. The key design factors are the cool-down time in the reactor and the cooling method in the maintenance scheme to keep components under operational temperature. Based on one-dimensional heat conduction analysis, after one month cool-down time, each sector of SlimCS could be transported to the hot cell facility by gas cooling.

A refined model for thermoelastic analysis of initially curved and twisted composite beams

This paper deals with steady state thermoelastic problems in beam structures using the variational asymptotic method. First, we simplify the original three-dimensional heat conduction problem into a two-dimensional thermal cross-sectional analysis along with an optional one-dimensional heat conduction analysis. The refinements up to the second order of the initial curvatures and twist are captured in the model. Having obtained the temperature field, we then construct a generalized Timoshenko model for the one-way coupled thermoelastic analysis. Several examples will be used to demonstrate the application and performance of the present model. The results will be compared with three-dimensional thermoelastic analysis using ANSYS.

A theoretical octet-truss lattice unit cell model for effective thermal conductivity of consolidated porous materials saturated with fluid

A theoretical octet-truss lattice unit cell model for the effective thermal conductivity of consolidated porous materials saturated with fluid was proposed. One-dimensional heat conduction analysis was conducted to derive the explicit expression of effective thermal heat conductivity with isotropic assumption and negligible natural convection inside the solid matrix. By introducing the morphological parameter defined as the ratio of the intersection node radius to the fiber diameter, the effective thermal conductivity was expressed as a function of porosity, thermal conductivity of solids and fluids, and the defined morphological parameter. The limitations in range of the defined morphology parameter were obtained on the basis of the model constraints and implementation examples were formulated. The feasibility of the model was evaluated using the experimental data from previous literature and those obtained in the present study. The effective thermal conductivities of nine sintered metal fiber felts with different morphological parameters were tested in the manner of heating on the top and cooling at the bottom of sample simultaneously to suppress internal natural convection. The validation of applicable porosity range was extended from $$ \varepsilon > 0.9 $$ , used in previous literature, to $$ \varepsilon > 0.8 $$ applied in the present model.

Variational-asymptotic modeling of the thermoelastic behavior of composite beams

This paper deals with steady state thermoelastic problems in composite beam structure by using variational-asymptotic method. First, the original three-dimensional heat conduction problem is reduced to be a two-dimensional thermal cross-sectional analysis along with an optional one-dimensional heat conduction analysis. The one-dimensional heat conduction analysis exists only if the temperature is not prescribed at any point of the cross-section along the span except the end surfaces. Then we reduce the one-way coupled, three-dimensional thermoelasticity problem into a two-dimensional, one-way coupled thermoelastic cross-sectional analysis and a one-dimensional, one-way coupled, thermoelastic beam analysis. The present theory is implemented into the computer program, variational-asymptotic beam sectional analysis (VABS). Several examples are studied using the present theory and the results from VABS are compared with available analytical solutions and the three-dimensional analysis using the commercial finite element package ANSYS.

On errors in thermal conductivity measurements of suspended and supported nanowires using micro-thermometer devices from low to high temperatures

For micro-thermometer devices developed for thermal conductivity measurements of nanowires, it is found using finite element analysis that radiation heat transfer can cause nonlinear temperature profiles in the long supporting beams of the thermometers when the sample stage temperature is considerably higher or lower than room temperature. Although the nonlinearity alone does not introduce errors in the measured thermal conductance, it can cause errors in the measured temperature coefficient of resistance of the thermometers and needs to be minimized with additional radiation shields. For a design where the sample is supported on a silicon dioxide bridge between two micro-thermometers, the numerical analysis reveals that a two-dimensional temperature distribution can cause a 25% error in the sample thermal conductance obtained from a one-dimensional heat conduction analysis for a high-thermal-conductance thin film sample covering only the center part of the oxide bridge. This systematic error is reduced considerably for a low-thermal-conductance nanowire sample. However, care must be taken to ensure that the random uncertainties in the two measured thermal conductance values of the bridge with and without the nanowires are much smaller than the thermal conductance of the nanowires.

Transient Temperature Data Analysis for a Supersonic Flight Test

Determination of transient surface heat flux from the temperature data is one of the traditional techniques applied in many engineering applications. With respect to high speed flight experiments, the time scale of measured temperature data is usually very small (∼ms). So, one-dimensional heat conduction analysis is expensively used to infer surface heating rates on the body. For an analytical modeling, it is necessary to obtain a closed form solution from experimentally measured temperature data. In this paper, a temperature data obtained from a nickel film sensor during a supersonic flight test is considered for analysis. Three different curve fitting techniques are used to recover the temperature history of real time flight, namely, piecewise linear fit, polynomial fitting, and cubic-spline method. A one-dimensional transient heat transfer modeling is used to infer surface heating rates from the closed form temperature solutions. Results obtained from these analysis are compared and it is seen that peak surface heat flux values match very closely for polynomial and cubic-spline fitting of temperature data. But, the piecewise linear fit of temperature data underpredicts the peak surface heat flux value by four times from its counterparts.

Heat Transfer Investigations of a Nano-Porous Silicon Film Deposited on a Flexible Cyclic Olefin Copolymers Substrate

A nano-porous silicon film deposited on a flexible cyclic olefin copolymers substrate is adopted to insulate the structure at high processing temperature during device manufacturing. In this study, the thermal conductivity of nano-porous silicon film modeled by Lysenko et al. [7] is implement to do the one-dimensional heat conduction analysis and to calculate the temperatures theoretically and numerically. In numerical work, the COMSOL finite-element based package is used for the numerical computations and effects of applied temperature loading, thickness of nanoporous silicon layer, and porosity are discussed. As shown in the analysis results, thickness of 200μm has the lowest temperature than other thicknesses, 25μm, 50μm, and 100μm, etc. Porosity plays a vital effect for thermal insulation. From the analyses, the case of 80% porosity has the larger temperature decrement than cases of 40% and 60%. It may be attributed to the lower conduction by higher porosity. Also, these temperatures show good agreement between the theoretical and numerical results and are consistent to the Lysenko et al. [7] statement for nano-porous silicon film for thermal insulating material.

Thermal Conductivity of Xonotlite Insulation Material

A surface-contact hollow cubic model is developed for coupled heat transfer of gas and solid in xonotlite-type calcium silicate insulation material based on its microstructure features. Through one-dimensional heat conduction analysis in the unit cell structure, a conductive thermal conductivity expression is obtained. A transient hot strip method is used to measure the thermal conductivity of xonotlite from 300 to 970K and from 0.045Pa to atmospheric pressure. The spectral specific extinction coefficients are derived from transmission measurements on a thin xonotlite sample performed with a Fourier transform infrared (FTIR) spectrometer. The results show that the specific spectral extinction coefficients are larger than 7m2·kg−1 over the whole measured spectra, and the diffusion approximation equation is a reasonable description of radiative heat transfer in xonotlite insulation material. The effective thermal conductivity model matches extremely well with the experimental data, which is important for the thermal design and thermal analysis of xonotlite insulation material.

Two Effective Thermal Conductivity Models for Porous Media with Hollow Spherical Agglomerates

Based on the microstructure features of xonotlite-type micro-pore calcium silicate, two unit cell models, the point-contact hollow spherical model and the surface-contact hollow cubic model, are developed. As one of several excellent insulation materials, xonotlite is represented as porous media with hollow spherical agglomerates. By one-dimensional heat conduction analysis using theunit cell, the effective thermal conductivity of xonotlite is determined. The results show that both of the models are in agreement with experimental data. The algebraic expressions based on the unit cell models can be used to calculate the effective thermal conductivity of porous media that have similar structure features as xonotlite.

Thermal model for the bolometric response of high- superconducting films to chopped optical radiation

Thermal detectors which convert the incident radiation to heat are frequently used to give a periodic response to the external signal modulated at a fixed low-frequency chopping frequency. Many workers have ascertained the bolometric response of high-quality epitaxial superconducting films on different substrates to chopped laser radiation. Based on these observations we made an a priori assumption that the voltage response of thin film is entirely due to a thermal mechanism, i.e. in the proposed one-dimensional heat conduction analysis any possible non-equilibrium processes are neglected. A new analytical formula is derived for the mean temperature increase in the superconducting film. This formula generalizes the previously well known analytical approximations. Further we explore a specific numerical example based on experimental data for the optical response of a thin () high- Bi-based film on an substrate irradiated by chopped He - Ne laser radiation ( nm). On the basis of the theory and the chopping frequency dependence of the peak voltage response an implementation of a new diagnostic method for evaluation of the thermal Kapitza conductance at the superconducting film - insulator interface is demonstrated.

A Model for First-Wall Thermal Response to Plasma Energy Deposition

A primarily analytical thermal analysis model is presented that allows for calculation of temperatures in fusion reactor first walls. The model utilizes input quantities based on plasma physics calculations and couples a 2 1/2-dimensional geometric analysis with a one-dimensional heat conduction analysis in determining temperature profiles over the surface of and within materials used to confine the plasma and vacuum. Given materials-related temperature limitations, methods are also provided for calculating maximum allowable wall power loadings. The results are primarily applicable to the steady-state operation of magnetic confinement devices such as tokamaks.

Photothermoelastic Investigation of Transient Thermal Stresses in a Multiweb Wing Structure

Summary Photothermoelastic experiments were performed on a long mul­ tiweb wing model for which a theoretical analysis is available in the literature. The experimental procedures utilized to simulate the conditions prescribed in the theory are fully described. Correlation of theory and experiment in terms of dimensionless temperature, stress, time, and Biot Number revealed that the theory predicted values higher than the experimentally observed maximum thermal stresses at the center of the web. Detailed temperature measurements in the flange suggested that the major source of this discrepancy can be traced to the one-dimensional heat conduction analysis of the flange employed in the theory.