Finite Element Analysis Of Heat Transfer Research Articles

SU-F-207-05: Excess Heat Corrections in a Prototype Calorimeter for Direct Realization of CT Absorbed Dose to Phantom

Purpose: To reconcile air kerma and calorimetry measurements in a prototype calorimeter for obtaining absorbed dose in diagnostic CT beams. While corrections for thermal artifacts are routine and generally small in calorimetry of radiotherapy beams, large differences in relative stopping powers of calorimeter materials at the lower energies typical of CT beams greatly magnify their effects. Work-to-date on the problem attempts to reconcile laboratory measurements with modeling output from Monte Carlo and finite-element analysis of heat transfer. Methods: Small thermistor beads were embedded in a polystyrene (PS) core element of 1 cm diameter, which was inserted into a cylindrical HDPE phantom of 30 cm diameter and subjected to radiation in a diagnostic CT x-ray imaging system. Resistance changes in the thermistors due to radiation heating were monitored via lock-in amplifier. Multiple 3-second exposures were recorded at 8 different dose-rates from the CT system, and least-squares fits to experimental data were compared to an expected thermal response obtained by finite-element analysis incorporating source terms based on semi-empirical modeling and Monte Carlo simulation. Results: Experimental waveforms exhibited large thermal artifacts with fast time constants, associated with excess heat in wires and glass, and smaller steps attributable to radiation heating of the core material. Preliminary finite-element analysis follows the transient component of the signal qualitatively, but predicts a slower decay of temperature spikes. This was supplemented by non-linear least-squares fits incorporating semi-empirical formulae for heat transfer, which were used to obtain dose-to-PS in reasonable agreement with the output of Monte Carlo calculations that converts air kerma to absorbed dose. Conclusion: Discrepancies between the finite-element analysis and our experimental data testify to the very significant heat transfer correction required for absorbed dose calorimetry of diagnostic CT beams. The results obtained here are being used to refine both simulations and design of calorimeter core components.

A Numerical Study on the Thermal Conductivity of 3D Woven C/C Composites at High Temperature

Experimental data for Carbon/Carbon (C/C) constituent materials are combined with a three dimensional steady state heat transfer finite element analysis to demonstrate the average in-plane and out-of-plane thermal conductivities (TCs) of C/C composites. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibres and (b) a meso scale comparable with the carbon fibre yarns. Micro-scale model calculate the TCs at the fibre yarn scale in the three orthogonal directions (x, y and z). The output results from the micro-scale model are then incorporated in the meso-scale model to obtain the global TCs of the 3D C/C composite. The simulation results are quite consistent with the theoretical and experimental counterparts reported in references. Based on the numerical approach, TCs of the 3D C/C composite are calculated from 300 to 2500 K. Particular attention is given in elucidating the variations of the TCs with temperature. The multi-scale models provide an efficient approach to predict the TCs of 3D textile materials, which is helpful for the thermodynamic property analysis and structure design of the C/C composites.

Simple Method for Predicting Temperatures in Reinforced Concrete Beams Exposed to a Standard Fire

In performance-based fire safety design, the fire performance of a structure needs to be accurately evaluated, which requires the accurate prediction of temperatures in the structure. While a finite-element or a finite-difference analysis may be carried out for this purpose, structural engineers generally prefer a simpler method. This paper therefore presents a simple, design-oriented method for predicting temperatures in RC beams under a standard fire exposure. Results from finite element heat transfer analysis are first examined to identify the key parameters that determine temperature distributions in RC beams. On the basis of this knowledge, a simple method in the form of handy formulae and diagrams is derived from regression analysis of finite element temperature data, with due consideration of the effects of beam geometry and fire exposure duration. The accuracy of the proposed method is demonstrated by comparing its predictions with temperature data from both finite element analysis and laboratory tests. The proposed method is believed to be attractive to practicing engineers for use in the fire resistance evaluation of RC beams exposed to a standard fire because of its simplicity and accuracy.

Laser patterning of transparent conductive metal nanowire coatings: simulation and experiment

Transparent and electrically conductive metal nanowire networks are possible replacements for costly indium tin oxide (ITO) films in many optoelectronic devices. ITO films are regularly patterned using pulsed lasers so similar technologies could be used for nanowire coatings to define electrode structures. Here, the effects of laser irradiation on conducting silver nanowire coatings are simulated and then investigated experimentally for networks formed by spray deposition onto transparent substrates. The ablation threshold fluence is found experimentally for such nanowire networks and is then related to film thickness. An effective model using finite-element heat transfer analysis is examined to look at energy dissipation through these nanowire networks and used to understand mechanisms at play in the laser-material interactions. It is demonstrated that the three-dimensional nature of these coatings and the relative ratios of the rates of lateral to vertical heat diffusion are important controlling parameter affecting the ablation threshold.

Heat Transfer Analysis of the Operation in Delayed Coking Coke Drum

Delayed coking coke drum is the core equipment of delayed coking technology, which experiences almost all the thermal and mechanical loadings during operation. In this study, two coke drum finite element models have been created with four material models and the thermal boundary conditions are determined based on the temperature measurement data. Finite element analysis methods known as function loading and multiple steps analysis are used through the simulation. Temperature distributions and temperature variation curves of different nodes are then obtained by finite element heat transfer analysis. Numerical results show that temperature distribution is complex in the transition section and the water cooling stage has the highest temperature change rate.

Effect of protein denaturation degree on texture and water state of cooked meat

We prepared cooked meat with varied denaturation degrees that were predicted based on 3D finite element heat transfer analysis and reaction kinetics. Using a meat sample with a clear denaturation distribution, we performed stress-relaxation measurements to obtain the elastic modulus and identified the state of water in the meat by using proton magnetic resonance imaging (1H MRI) for quantification of a transverse relaxation time (T2). Even after the complete denaturation of myosin, the elastic modulus did not exceed 14kPa, which is not large compared with 6kPa for unheated meat. However, when actin denaturation was initiated, the elastic modulus dramatically increased while the T2 value at the meat surface remarkably decreased. The difference in the state of water between the surface and the core reflected the uneven denaturation distribution in the meat caused by heating. When actin denaturation was complete, the elastic modulus reached 60kPa, which was the equilibrium value, and T2 decreased and its distribution became more flat.

역열전달해석기법에 의한 LED 조명용 무동력 냉각사이클링 방열기 성능평가

In this study, the performance of a thermo siphon type radiator made of copper for LED lighting system was evaluated by using an inverse heat transfer method. Heating experiments and finite element heat transfer analysis were conducted for three different cases. The data obtained from experiments were compared with the analysis results. Based on the data obtained from experiments, the inverse heat transfer method was used in order to evaluate the heat transfer coefficient. First, the heat transfer analysis was conducted for non-vacuum state, without the refrigerant. The evaluated heat transfer coefficient on the radiator surface was 40W/<TEX>$m^2^{\circ}C$</TEX>. Second, the heat transfer analysis was conducted for non-vacuum state, with the refrigerant, resulting in the heat transfer coefficient of 95W/<TEX>$m^2^{\circ}C$</TEX>. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/<TEX>$m^2^{\circ}C$</TEX>. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/<TEX>$m^2^{\circ}C$</TEX> for the radiator body, 5W/<TEX>$m^2^{\circ}C$</TEX>. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant for the rising position of radiator pipe, 35W/<TEX>$m^2^{\circ}C$</TEX>. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the highest position of radiator pipe, and 120W/<TEX>$m^2^{\circ}C$</TEX> for the downturn position of radiator pipe. As a result of inverse heat transfer analysis, it was confirmed that the thermal performance of the current radiator was best in the case of the vacuum state using the refrigerant.

Enriched finite element spaces for transient conduction heat transfer

This paper presents an alternative approach via finite elements to treat numerically the thermal shocks in heat transfer finite element analysis. The method consists in using the standard enriched finite element approaches with time-interpolation. It will be applied here to the transient conduction heat equation where the classical Galerkin method is shown to be unstable. The proposed method consists in adding and eliminating bubbles to the finite element space and then to interpolate the solution to the real time step. This modification is equivalent to the addition of a stabilizing term tuned by a local time-dependent stability parameter, which ensures an oscillating-free solution. To validate this approach, the numerical results obtained in classical 2D and 3D benchmark problems are compared with the Galerkin and the analytical solutions.

Heat Transfer and Stress Analysis of Coke Drum for a Complete Operating Cycle

Coke drums experience severe thermal and mechanical loadings during operation, and the reliability and safety of the coke drums are critical to the industry. The objective of this study is to analyze temperature and stress of the coke drum for a complete process cycle. The thermal analysis model of the coke drum is first developed incorporating appropriate boundary conditions. The heat transfer coefficients at the inner surface of the coke drum, which change with the operation stages and the levels of oil filling and water quenching, are determined based on the temperature measurement data at a certain location on the outer surface of the coke drum. The temperature history of the coke drum of a complete cycle is then obtained by finite element heat transfer analysis, and computed temperature data are used for the stress analysis of the coke drum, including both thermal and mechanical loadings. It is found from numerical results that the clad experiences a biaxial stress cycling with maximum value higher than the yield limit of the material, which coincide with the low cycle fatigue failure of the structure.

Bimetallic dies with direct metal-deposited steel on Moldmax for high-pressure die casting application

In high-pressure die casting, cooling time greatly affects the total cycle time. As thermal conductivity is the main governing factor, a higher thermal conductive die material allows faster extraction of heat from the casting, thus resulting in shorter cycle time and higher productivity. This paper presents a novel approach to replace a conventional steel die by a bimetallic die made of Moldmax copper alloy coated with a protective layer of steel using laser cladding technology, direct metal deposition on the cavity surface for high-pressure die casting of aluminum alloys. Study includes the investigation of suitable steel layer thickness on Moldmax substrate in terms of porosity, hardness, presence of copper content, and copper particle. Results obtained from the scanning electron microscope and energy dispersive spectroscopy display a metallurgicallly sound and fully dense steel layer on copper alloy. Results of finite element heat transfer analysis also show that bimetallic die offers superior thermal performance compared with monolithic steel die.

An Implicit Fixed-Grid Method for the Finite-Element Analysis of Heat Transfer Involving Phase Changes

The finite-element method is widely used for thermal numerical simulation of heat treatment, casting, or welding processes. The modeling of phase changes requires the simulation of highly nonlinear problems due to latent heat effects. In this article, a finite-element procedure is developed for modeling latent heat effects using an implicit time discretization for transient heat conduction problems involving phase changes for which the enthalpy can be supposed to be a function of temperature only. It is also developed for stationary convection-diffusion problems. Examples are presented to show the efficiency of the method for isothermal and anisothermal transformations. Finally, the method is extended to take couplings with metallurgical transformation kinetics into account.

Considerations in the Design and Analysis of an ASME Section VIII, Div. 2 Reactor Support Skirt

This paper describes the considerations employed in the finite element analysis of a relatively “short” support skirt on a hydrocarbon reactor vessel. The analysis is accomplished in accordance with ASME B&amp;PV Code, Section VIII, Division 2 alternate rules in conjunction with the guidelines outlined in WRC Bulletin 429. This provides a sound basis for the classification of the calculated stress intensities. The support skirt is capable of sustaining the deadweight load in addition to resisting the effects of thermal displacements, wind loadings, overturning moments from external piping loads on the attached hydrocarbon reactor vessel, and friction between the skirt base plate and concrete foundation. The displacement and thermal boundary conditions are well defined and discussed in detail. The effects of multiple scenarios for the displacement boundary conditions are examined. The skirt design also employs a hot-box arrangement whereby the primary mode of heat transfer is by radiation. A discussion of the two-part analysis is included and details the interaction between the heat transfer analysis and the subsequent structural analysis. The heat transfer finite element analysis is utilized to determine the temperatures throughout the bottom of the vessel shell and head, as well as the integrally attached support skirt. Of prime importance during the analysis is the axial thermal gradient present in the skirt from the base plate up to and slightly beyond the skirt-to-shell junction. While the geometry of the subject vessel and skirt is best described as axisymmetric, the imposed loadings are a mixture of axisymmetric and non-axisymmetric. This combination lends itself to the judicious selection and utilization of the harmonic finite element and properly chosen Fourier series representation of the applied loads. Comparison of the thermally induced axial stress gradient results from the FEA to those obtained by the closed form beam-on-elastic-foundation are also tendered and discussed. Finally, recommendations are included for the design and analysis of critical support skirts for large, heavy-wall vessels.

Critical cooling rate for Fe 48Cr 15Mo 14Y 2C 15B 6 bulk metallic glass formation

The critical cooling rate for glass formation was measured for an Fe-based easy glass forming alloy using a wedge casting technique combined with direct temperature measurements and finite element heat transfer analysis. For an alloy with a nominal composition Fe 48Cr 15Mo 14Y 2C 15B 6, the critical cooling rate was measured to be in the range 140–190 K/s. The low critical cooling rate indicates that this alloy may be suitable for use in thermal spray processes. The main crystalline phase competing with glass formation during continuous cooling appears to be a M 23C 6 type phase.

Analysis of Complex Heat Flow Phenomena with Friction Stir Welding Using 3D-Analytical Model

Friction stir welding is being attracted and developed as an efficient joining method in the manufacturing field of Automobile, Aerospace and Ship building industries. As the FSW develops, more scientific research work investigations in this field have also been increased. Recent studies in FSW have revealed that both heat and metal flow characteristics have a non-symmetric complex nature about the tool axis. But until now there is no efficient 3D- heat flow model to be comparable with the experimentally measured values. The body of the work covered FSW of Al6061 and its thermal distribution based on a nonsymmetrical analytical model for the heat input in to the matrix of Al plates from FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 3D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

Full-wave electromagnetic and thermal modeling for the prediction of heat-dissipation-induced RF-MEMS switch failure**This work was supported in part by the National Science Foundation under grant no ECS-01152222.

We propose an extended finite element-boundary integral method (EFE-BI) to model the electromagnetic (EM) behavior of RF-MEMS switches over a wide frequency range from UHF to terahertz. Our new method integrates EM with finite element heat transfer analysis to extract heat dissipation on the micrometer-scale switch beam due to the non-uniform radio frequency (RF) current distribution. The developed EFE-BI technique is an extension of the standard finite element-boundary integral (FE-BI) method to allow for accurate characterization of RF-MEMS structures whose entire size is a small fraction of a wavelength (λ/250 or less) and may contain dimensions in the order of λ/50 000 or less. Our model predictions exhibit good agreement with experimental results obtained independent of the current study.

Effect of Cooling Condition on Deformation of Continuously Cast Stainless Steel 304

This work investigated the effect of the cooling condition on the deformation that was found for continuously cast stainless steel 304 slabs. The transient heat-transfer finite element analysis under various cooling conditions yielded temperature distributions within the slab, which were then used for subsequent calculations of the deformed shape. The asymmetric cooling condition in a cooling pit induced non-uniform and asymmetric thermal gradients with elapsed time. The non-zero final deflection and the reversal of curvature for the slab during cooling were attributed to the combined effect of asymmetric temperature profile and inelastic material property. Parametric studies revealed that a slab material of a low thermal conductivity or yield strength resulted in an increase for final deflection. The present analysis explained the physical cause of the deformation reasonably well.

멤브레인형 LNG선 Cargo의 만선항해시 열전달 해석 및 BOG 평가

Excessive generation of BOG during the LNG transportation not only causes the severe financial loss but also leads to the unexpected disaster. Therefore, the carrier cargo insulating interior LNG should be carefully designed based upon an accurate heat transfer analysis. However. it is not simple to analyze heat transfer of LNG cargo, because it is in a complex insulation structure and LNG carrier experiences a complicated heat transfer according to various kinds of voyage conditions. In this paper, we carried out the transient finite element heat transfer analysis for a cargo of Mark-111 membrane-type LNG carrier during laden voyage, and we compared heat transfer rates between considering natural convection and considering conduction. For this goal, we developed a PCL program incorporating with a commercial MSC/NASTRAN FEM code.

An Investigation of the Reduction in Fire Resistance of Steel Columns Caused by Loss of Spray-Applied Fire Protection

The effect of the loss of fire protection material on the fire resistance of steel columns is examined. A three-dimensional finite element heat transfer analysis is conducted to simulate the ASTM E119 fire resistance test. The predicted temperature distributions within the member over time are used in conjunction with the thermal endpoint criteria specified in ASTM E119 to provide an estimate of the fire resistance of the member. Several variables are then examined with respect to their effect on the fire resistance of a member. For a given exposure, the area of the missing protection and the size of the column are found to have an appreciable effect upon the fire resistance of the column regardless of the protection thickness. The area of the missing protection seems to be the primary factor in the temperature rise and fire resistance assessment of the column. The temperature rise in the column is primarily sensitive to the amount of missing protection, with the size of the column gaining significance only later in the test.

Finite‐element heat‐transfer analysis of a PEEK‐steel sliding pair in a pin‐on‐disc configuration

AbstractFinite‐element (FE) thermal models have been developed in order to study the temperature distribution in a sliding pair comprising a poly(ether ether ketone) (PEEK) pin and a steel disc in a pin‐on‐disc configuration. First, a moving heat source model for the disc was created. An alternative distributed heat source model was also produced in order to reduce computing time for the evaluation of the moving heat source model by some orders of magnitude. This latter model gave the same results as the moving heat source model, except for a small region just below the moving heat source. On the basis of the distributed heat source approach, a complete axisymmetric FE model for the disc side (taking the effect of thermal resistance between the assembled components into consideration) and a steady‐state quarter model for the pin were developed. Water cooling and air cooling of the steel shaft were also compared. It was found that air cooling allowed a higher temperature in the contact region of the two sliding partners. The experimental results obtained with thermocouples and a thermal camera showed good agreement with the model predictions.

Finite element heat transfer analysis of viscoelastic damper for wind applications

Abstract A finite element approach for analyzing the thermal-structural coupling effects of the viscoelastic dampers subjected to steady-state excitation is presented. Nonlinear viscoelastic properties due to temperature rise in the viscoelastic material are considered in the analysis. Examples given in the paper illustrate that the finite element approach can properly predict the temperature distribution in the damper and can be used as a practical design tool.