Radiation heat transfer model for complex superalloy turbine blade in directional solidification process based on finite element method

For the sake of a more accurate shell boundary and calculation of radiation heat transfer in the Directional Solidification(DS) process, a radiation heat transfer model based on the Finite Element Method(FEM)is developed in this study. Key technologies, such as distinguishing boundaries automatically, local matrix and lumped heat capacity matrix, are also stated. In order to analyze the effect of withdrawing rate on DS process,the solidification processes of a complex superalloy turbine blade in the High Rate Solidification(HRS) process with different withdrawing rates are simulated; and by comparing the simulation results, it is found that the most suitable withdrawing rate is determined to be 5.0 mm·min^(-1). Finally, the accuracy and reliability of the radiation heat transfer model are verified, because of the accordance of simulation results with practical process.

Effect of Thermal Radiation Heat Transfer on the Temperature Measurement by the Thermocouple in Premixed Laminar Flames

In the past 30 years,the effect of thermal radiation and convection heat transfer,which are predominant at high temperature and can affect the measurement accuracy of thermocouple,were not fully considered in the field of laminar flame researches.In this work,the effect of thermal radiation heat transfer was newly calculated by determining the spectral irradiation heat flux from the whole space to thermocouple and the radiation heat loss from thermocouple junction to surroundings.Analysis reveals that the thermocouple itself maintains at high temperature,resulting serious thermal radiation heat loss,which can be compensated via receiving energy from convection-transferred heat as well as thermal radiation emitted by flame and burner surface.Such method was applied to correct the temperatures measured by thermocouple in rich nitromethane flame as reference.The results indicate that the radiation heat loss plays a dominant role,while the radiations emitted by flame and burner surface account for minor contribution with the percentage of 20.78%at the height above burner(HAB)of 0.4 mm,3.63%at HAB of 2.0 mm and even smaller at higher HAB.Temperature correction states that the maximum temperature error is 117.60 K,where the effect of thermal radiation emitted by flame and burner surface is less than 1.75 K.Consequently,it is provably reasonable and feasible to concentrate on the radiation heat loss and ignore the effect of thermal radiation emitted by flame and burner in real combustion processes.

Characteristics of radiation and convection heat transfer in indirect near-infrared-ray heating chamber

Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation, conduction and convection in indirect near infrared ray （N/R） heating chamber. The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers. The Reynolds numbers were varied from 103 to 3x106, which was defined based on the hydraulic diameter of the heat absorbing cylinder. Analyses were performed to obtain the inner and outer flow and the temperature distributions in the heat absorbing cylinder and the rates of radiation heat transfer and convection heat transfer. As the Reynolds number increases, the convection heat transfer rate is increased while the radiation heat transfer rate is decreased. The average convection heat transfer rate follows a power rule of the Reynolds number. Addition of three-dimensional heat releasing fin to the outside of the heat absorbing cylinder enhances the convection heat transfer.

Numerical Study of Convective and Radiation Heat Transfer Characteristics in an Upward-Facing Cylindrical Cavity under Back-Side Windy Condition

Under the back-side windy condition,the convection and radiation heat transfer characteristics in an iso-flux upward-facing cylindrical cavity were studied by three-dimensional numerical simulation.The impacts of cavity tilt angle,wind incident angle and wind speed on convection and radiation heat transfer Nusselt number Nuc and Nur were analyzed,and the possible explanations for their impacts were presented.Results show that due to the disturbance of wind,the influence of cavity tilt angle becomes more complicated and is related to wind incident angle and wind speed.The variation of Nuc or Nur with wind incident angle is different for different cavity tilt angles.Despite of the changes of cavity tilt angle or wind incident angle,the Nuc increases with the wind speed while the Nur presents a declination with the increasing of wind speed.Hence,compared with cavity tilt angle and wind incident angle,wind speed may be the dominant factor affecting or controlling the convective and radiation heat transfer of cavity.

A new hybrid method—combined heat flux method with Monte-Carlo method to analyze thermal radiation

A new hybrid method, Monte-Carlo-Heat-Flux （MCHF） method, was presented to analyze the radiative heat transfer of participating medium in a three-dimensional rectangular enclosure using combined the Monte-Carlo method with the heat flux method. Its accuracy and reliability was proved by comparing the computational results with exact results from classical ＂Zone Method＂.

Thermal energy storage inside the chamber with a brick wall using the phase change process of paraffinic materials:A numerical simulation

Phase change materials are one of the potential resources to replace fossil fuels in regards of supplying the energy of buildings.Basically,these materials absorb or release heat energy with the help of their latent heat.Phase change materials have low thermal conductivity and this makes it possible to use the physical properties of these materials in the tropical regions where the solar radiation is more direct and concentrated over a smaller area.In this theoretical work,an attempt has been made to study the melting process of these materials by applying constant heat flux and temperature.It was found that by increasing the thickness of phase change materials’layers,due to the melting,more thermal energy is stored.Simultaneously it reduces the penetration of excessive heat into the chamber,so that by increasing the thickness of paraffin materials up to 20 mm,the rate of temperature reduction reaches more than 18%.It was also recognized that increasing the values of constant input heat flux increases buoyancy effects.Increasing the Stefan number from 0.1 to 0.3,increases the temperature by 6%.

Thermally Induced Vibration Analysis of Flexible Beams Based on Isogeometric Analysis

Spacecraft flexible appendages may experience thermally induced vibrations(TIV)under sudden heating loads,which in consequence will be unable to complete their intended missions.Isogeometric analysis(IGA)utilizes,in an isoparametric concept,the same high order and high continuity non-uniform rational B-splines(NURBS)to represent both the geometry and the physical field of the structure.Compared to the traditional Lagrange polynomial based finite element method where only C0-continuity across elements can be achieved,IGA is geometrically exact and naturally fulfills the C1-continuity requirement of Euler–Bernoulli(EB)beam elements,therefore,does not need extra rotational degrees-of-freedom.In this paper,we present a thermally induced vibration analysis framework based on the isogeometric method where thermal and structural behaviors are coupled.We fully exploited the higher order,higher continuous and geometric exactness of the NURBS basis with both benchmarks and sophisticated problems.In particular,we studied the thermally induced vibrations of the Hubble Space Telescope(HST)solar panel where main factors influencing thermal flutters are studied,and where possible improvements of the analytical reference methods are discussed.Additionally,thermally induced vibrations of the thin-walled lenticular tubes are studied and two new configurations of the tube are proposed to effectively suppress the thermally induced vibrations.Numerical examples of both benchmarks and sophisticated problems confirm the accuracy and efficiency of the isogeometric analysis framework for thermally induced vibration analysis of space structures.

Effects of thermal transport properties on temperature distribution within silicon wafer

A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface. It is found that the increased conductivities in both doped and undoped regions help reduce the temperature difference across the wafer surface. However, the doped layer conductivity has little effect on the overall temperature distribution and difference. The temperature level and difference on the top surface drop suddenly when absorption coefficient changes from 104 to 103 m-1. When the absorption coefficient is less or equal to 103 m-1, the temperature level and difference do not change much. The emissivity has the dominant effect on the top surface temperature level and difference. Higher surface emissivity can easily increase the temperature level of the wafer surface. After using the improved property data, the overall temperature level reduces by about 200 K from the basis case. The results will help improve the current understanding of the energy transport in the rapid thermal processing and the wafer temperature monitor and control level.

Comparative studies for two different orientations of pebble bed in an HCCB blanket

The Indian Test Blanket Module（TBM） program in ITER is one of the major steps in its fusion reactor program towards DEMO and the future fusion power reactor vision. Research and development（RD） is focused on two types of breeding blanket concepts： lead–lithium ceramic breeder（LLCB） and helium-cooled ceramic breeder（HCCB） blanket systems for the DEMO reactor. As part of the ITER-TBM program, the LLCB concept will be tested in one-half of ITER port no. 2, whose materials and technologies will be tested during ITER operation. The HCCB concept is a variant of the solid breeder blanket, which is presently part of our domestic RD program for DEMO relevant technology development. In the HCCB concept Li_2TiO_3 and beryllium are used as the tritium breeder and neutron multiplier, respectively, in the form of a packed bed having edge-on configuration with reduced activation ferritic martensitic steel as the structural material. In this paper two design schemes, mainly two different orientations of pebble beds, are discussed. In the current concept（case-1）, the ceramic breeder beds are kept horizontal in the toroidal–radial direction. Due to gravity, the pebbles may settle down at the bottom and create a finite gap between the pebbles and the top cooling plate, which will affect the heat transfer between them. In the alternate design concept（case-2）, the pebble bed is vertically（poloidal–radial） orientated where the side plates act as cooling plates instead of top and bottom plates. These two design variants are analyzed analytically and 2 D thermal-hydraulic simulation studies are carried out with ANSYS, using the heat loads obtained from neutronic calculations.Based on the analysis the performance is compared and details of the thermal and radiative heat transfer studies are also discussed in this paper.

Materials Response to High Power Energy Lasers(A Short Course—Part I)

With recent attention to high power energy and its interaction with materials of different type,both in industry and military application,this paper covers a short review course into subject of materials response in respect to such high power energy lasers.In this paper,we are covering laser interaction with solid and going through steps of phase changes,from solid to liquid and finally vapor stage.We describe the radiation wave,propagation wave in a complex form solution,utilizing Maxwell’s equation within dielectric materials,then we look at compression of materials,due to melting and boiling driven by heat transfer energy radiation and conduction induced by these high power energy lasers such is Nd Ya and CO2 lasers with wavelengths anywhere from 1.6μm to 10.6μm.We also look at Hugoniot Elastic Limit(HEL)and spall strength of materials,with the energy lasers dueling with targeted material,where also,physics of hydrodynamics effects due to strong shock is involved.We also talk about certain available computer that allows end user to calculate these phenomena in 1-D to 3-D type scenarios.Although covering all these above issues that are very lengthy write-up proposition,we have tried to be very brief,yet to the point presentation in form of a short course in this paper.

Materials Response to High Power Energy Lasers(A Short Course—Part II)

With recent attention to high power energy and its interaction with materials of different types,both in industry and military application,this paper covers a short review course into subject of materials response in respect to such high power energy lasers.In this paper,we are covering laser interaction with solid and going through steps of phase changes,from solid to liquid and finally vapor stage.As we indicated in this part of short course mainly Part I,we have stated of series of article on the subject of Materials Responses to High Power Energy Lasers and continue these series by starting to introduce the Laser Light Propagation either in vacuum or through atmosphere by also introducing thermal blooming effects as well,then we cover,subjects such as Optical Reflectivity,thermal responses of materials by looking at Latent Heat of Fusion as well as Vaporization,No Phase Changes in both Semi-Infinite Solid or Slab of Finite Thickness,Melting and Vaporization and then move on to Effects of Pulsed or Continuous Laser Radiation as well,throughout of next few parts that we report them as further Short Courses content.

Materials Response to High Power Energy Lasers (A Short Course-Part III)

With recent attention to high power energy and its interaction with materials of different type,both in industry and military application,this paper covers a short review course into subject of materials response in respect to such high power energy lasers.In this paper,we are covering laser interaction with solid and going through steps of phase changes,from solid to liquid and finally vapor stage.As we indicated in this part of short course mainly Part I and Part II,we have started a series of articles on the subject of Materials Responses to High Power Energy Lasers and continue these series by starting to introduce the Laser Light Propagation into materials.In this part namely Part III,we are discussing,one of the most important effects of intense laser irradiation is the conversion of the optical energy in the beam into thermal energy in the material.This is the basis of many applications of lasers,such as welding and cutting.We shall summarize here this thermal response.It is basically a classical problem,namely heat flow,in a usual manner of heat conduction,we show solutions to the equation which governs the flow of heat and discuss change of phases in targeting material from solid to liquid and finally vapor and plasma stages step by step.

Materials Response to High Power Energy Lasers(A Short Course—PartⅣ)

A complete understanding of laser interaction with materials is still a matter of trials and adjustments.The real physical processes of laser beam interaction(drilling,cutting,welding,or being used as a directed energy weapon application)with materials are very complex.Problem of laser interaction with materials presents many difficulties,both from modeling as well as from experimental sides.One would expect a reasonable description of the main phenomena occurring during laser interaction,but this is complicated because many of physical processes equally contribute to the development of conservation equations,producing drawback because of a great complexity of the equations to be solved.In most instances,this leads to formulation of a model needed to be solved numerically.A lack of pertinent experimental data to compare with,forces one to simplify some equations and use previous analytical and computational work done in this field.In Part IV here,we cover the absorption coefficient,which can be derived from the material’s dielectric function and conductivity,determines the absorption of light as a function of depth.However,the specific mechanisms by which the absorption occurs will depend on the type of material.In general,photons will couple into the available electronic or vibrational states in the material depending on the photon energy.In insulators and semiconductors,the absorption of laser light predominantly occurs through resonant excitations such as transitions of valence band electrons to the conduction band(inter-band transitions)or within bands(inter-sub-band transitions).In this part we cover all the aspect of the“Mathematical of Laser Absorption in Metals”that fits into this part of our suggesting short courses in different parts so far.

Modeling of Strip Heating Process in Vertical Continuous Annealing Furnace

The mechanism for heat transfer of radiation is usually adopted to heat strip in vertical continuous annealing furnace. The rate of heat transfer among strip and other objects can be hugely affected by the parameters of strip speed, geometry factors and radiating characteristic of surfaces of strip, radiating tubes and walls of furnace. A model including all parameters is proposed for calculating the heat transfer coefficient, predicting the strip tempera- ture and boundary temperature of strip through analyzing these parameters. The boundary temperature is a important datum and different from average arithmetic value of temperature of strip and temperature in furnace. Also, the model can be used to analyze the relation for temperature of strip and heat transfer coefficient, total heat transfer quantity and heating time. The model is built by using the radiating heat transfer rate, the Newtonrs law of cooling, and lumped system analysis. The results of calculation are compared to the data from production line. The comparisons indicate that the model can well predict the heating process. The model is already applied for process control in pro- duction line. Also, this research will provide a new method for analyzing the radiation heat transfer.

Investigation on the Synthesis Mechanism of β-FeSi_2 Prepared by Pulsed Laser Deposition

The FeSi2 target alloy was fabricated by conventional powder metallurgy technology, and then, β-FeSi2 thin films was successfully prepared by pulsed laser deposition （PLD）. X-ray diffraction （XRD） and field emission scanning electron microscopy （FESEM） were used to characterize the structure, composition, and their changes in the process of β-FeSi2 preparation. In addition, a laser sintering process was also employed to prepare FeSi2 alloy. The analysis of radiation heat transfers in different-sized FeSi2 melt indicates that the cooling rate of the melt depends on the size, i.e., the cooling rate of the micron sized melt is 103 times greater than that of the millimeter-sized melt. The product a-FeSi2 by laser sintering and β-FeSi2 by PLD reveals the different phase transition process in crystallization of millimeter-sized and micron-sized （or submicron-sized） FeSi2 melt. The results of PLD preparation process shows that β-FeSi2 could be prepared through a liquid-phase sintering, followed by a rapid cooling.