Thermal Field Simulation Research Articles

A Kind of Improved Pass Structure of Double Regenerative Burner with the Numerical Simulation of Thermal Stress Field

In order to solve the problem of cracks of the double regenerative burner, a kind of new low stress pass structures was developed, and the corresponding 3D CAE model was set up. The results of numerical simulation of thermal stress field of the new pass structure showed that the thermal stress and stress amplitude of the new pass structure is relatively lower and thus can improve the service life of burner.

Laminated fabrication of micro-stepped gear mold based on femtosecond laser cutting of stainless steel foil

This paper proposes that a micro-stepped structure is fabricated based on the characteristics of femtosecond laser (high-precision and cold machining) and the laminated manufacturing principle in rapid prototyping. This process is composed of two parts: the single-layer graphics cutting and the layer laminating. The cutting experiment results show that when the femtosecond laser power is 230 mW and the cutting speed is 50 μm/s, the cutting effect of the 20 μm thick 0Cr18Ni9 stainless steel foil is guaranteed and the over-ablation of the lower layer steel foil caused by excessive power is avoided. During the experiment, the principles and error of focus adjustment are analyzed and a compensation plan is proposed. When the laminated procedure is finished, the overall intensive spot welding is performed on the area surrounding the mold cavity to reinforce the mold cavity and reduce the gap between layers. For a six-layer micro-mold, the nugget thermal field simulations and the metallographic analyses showed that when the welding time is 10 ms, the pressure is 20 N and the voltage reaches 0.22 V, the overall welding effect is satisfactory. Eventually, three kinds of micro-stepped gear molds are prepared and a micro-mold is bulged and replicated by Cu foils.

Thermal and Fluid Field Simulation of Single Pulse Discharge in Dry EDM

Dry Wire Electrical Discharge Machining (WEDM) is a newly developed technology that uses gases as dielectric and is in favor of environmental protection. Dry finishing of WEDM offers advantages such as better straightness, lower surface roughness and shorter gap length. Experimental studies show that the machining behaviors in dry conditions are quite different from those in conventional liquid dielectric. In order to explore the processing mechanism of dry WEDM, this paper studies the single pulse discharge mechanism in gas with finite element method. In order to obtain the crater morphology with edge raised, the fluid field was simulated by ANAYS on the basis of thermal analysis of a single pulse generated by the instantaneous discharge in gas.

Application of CFD to Building Thermal Control Analysis

Building-integrated photovoltaic system is to import a photovoltaic panel system into the shell structure of a building by using building design techniques, so that the system constituents not only generate power, but are also a part of the building’s shell. If the photovoltaic panel is integrated with a sun shield, a power benefit could be obtained and both solar irradiation and the cooling load could be reduced. This study aimed to use CFD technology for analysis of building surface thermal control and flow field simulation, and further discuss the effects of the relative position of the sun and atmospheric wind flow field on the distribution of building surface temperatures and flow fields at different hours and in different seasons. Understanding the sun's position and other climatic conditions accurately is helpful for locating solar panels and solar collectors on buildings.

Crystallizer's Heat-Transferring Theory Analysis and Thermal Field Simulation

Crystallizer's Heat-Transferring Theory Analysis and Thermal Field Simulation

The characteristics of gas–solid flow and wall heat transfer in a fluidized bed reactor

Numerical study using computational fluid dynamics has been carried out to investigate the heat transfer characteristics of a laboratory fluidized bed reactor. The fluidized bed reactor of vTI (Johann Heinrich von Thunen-Institute)-Institute of Wood Technology and Wood Biology is modeled. For the simulation of multiphase flow and thermal fields, an Eulerian–Eulerian approach is applied. The flow and thermal characteristics of the reactor are fully investigated for the wide range of superficial gas velocities and two different particle diameters. In particular, the contributions of the gas bubble and emulsion phase flows on the wall heat transfer are scrutinized. From the predicted results, it is fully elucidated that particular near-wall bubble motions mainly govern the wall heat transfer.

Antimicrobial photodynamic therapy: The impact of laser radiation on mucous tissue stained with photosensitizer methylene blue

We have calculated the spatial distribution of absorbed light energy within layers of a mucous tissue that contains photosensitizer methylene blue. Under irradiation regimes that are typical of antimicrobial photodynamic therapy (laser radiation wavelength, 670 nm; power density, 150–300 mW/cm2; dose, 9–18 J/cm2), we have analyzed conditions that are necessary for the light penetration and delivery of methylene blue to a nidus of infection on a mucosal surface. We have performed a computer simulation of thermal fields, estimated maximal heating temperatures, and considered the degree at which the heating affects the trans-mission of light through a stained tissue.

Heat transfer characteristics of KIMM‐fast pyrolysis reactor

AbstractNumerical study using computational fluid dynamics (CFD) was carried out to investigate the heat transfer characteristics of an innovative inclined gravity‐driven reactor (KIMM‐fast pyrolysis reactor). For the simulation of multiphase flow and thermal fields, we applied an Eulerian–Eulerian approach. The flow and thermal characteristics of the reactor were fully investigated with varying inlet width, inlet location, and inclined angle of the reactor. In particular, the contributions of the solid particle flows on the wall heat transfer were studied. To scrutinize the wall heat transfer, time‐averaged wall heat transfer coefficient was obtained and probability density function between gas volume fraction and wall heat transfer coefficient was analyzed. From the predicted results, it is fully elucidated that the particle packing density and gas volume fraction mainly govern the wall heat transfer, which are closely related to particular near‐wall solid motions. © 2012 American Institute of Chemical Engineers Environ Prog, 2012

Performance of an adaptive liquid microlens controlled by a microcoil actuator

We present an optofluidic system based on electromagnetic manipulation of a ferrofluid to tune a liquid lens. Both studies of the dynamics of fluid transport and of the optical properties of the liquid lens have been carried out. Thermal and magnetic field simulations of the microcoil actuators are presented. Proof-of-principle experiments demonstrating the adaption of the focal length of the lens have been carried out. It is shown that the lens adaption proceeds in a reversible and reproducible manner, given that the ferrofluid plug moves with a speed below a specific threshold value. Furthermore, the time delay between the actuation and the deflection of the lens surface is studied.

Surface Topography Prediction on Laser Processed Tool Steel

In laser surface treatment the laser beam is used as energy source for surface modification improving aspects such as mechanical properties, tribology or surface texture. Modeling tools have special interest in processes with many variables, like laser surface processing, in order to minimize the tryout testing to find the optimal process parameters. The work presented here focuses on the prediction of the final topography in laser polishing process. By FFT analysis of the surface profile it is possible to get the different frequency components of the initial topography. On the other hand, thermal field simulation was carried out to evaluate the melt duration. Matching this with the spatial frequency damping during process, the reconstruction of the processed topography was obtained.

Simulation Analysis of Concrete Temperature and Stress of Plant Elbow Section of Sluice Dam

In view of concrete structure of dam plant elbows section is complex and strong external constraints, the study of concrete temperature and stress during construction should be carried out by computer simulation. A case of plant elbow section of a sluice dam project is presented where the 3D FEM simulation of instability thermal field and stress field of the concrete structure is adopted after building the 3D finite element model, and the changes and distribution characteristics of temperature and stress during whole process of construction is obtained. The results show that, under the complex constraints condition, the concrete of plant elbow section has greater tensile stress, it can lead to structural cracking, and it is necessary to take appropriate temperature control measures.

Theoretical Study of Bone Cancer Therapy By Plasmonic Nanoparticles

Progress made by the scientific community in the understanding of cell receptors and metabolic pathways has led to discovery of chemical and protein agents which act as delivery vectors to specific tissues. Conjugating these agents to noble-metal nanoparticles allows for subsequent accumulation on or within targeted cells. Utilizing the unique light absorption properties of these nanoparticles then allows for photothermal heating of the particles and surrounding tissue. The heat equations are solved for the case of gold nanoparticles in biological hard tissues, such as bone, for applications to two future cancer therapies: nanophotothermolysis and nanophotohyperthermia. A survey of recent research in bone-targeting bioconjugates and simulations of nanoparticle thermal fields shows promise for these therapies in the near future.

Numerical Simulation of Thermal Fields Within Earth Surface Layers in the Region of South Urals

A mathematical model of thermal conductivity within the Earth near-surface layers has been studied in stationary mode relative to South Ural region. A purpose of the work is to identify cause of local heat flow density anomalies observed on the surface. Reconstruction of thermal field and heat production field is represented as numerical solution of the variational problems formulated according to boundary observation data

Thermophysical properties and thermal simulation of Bridgman crystal growth process of Ni–Mn–Ga magnetic shape memory alloys

Ni–Mn–Ga magnetic shape memory alloys (MSMA) are well-known smart materials for actuation applications, due to their large magnetic field-induced shape change of up to 10%. The production of larger amounts of single-crystalline material from these alloys with reproducible and homogeneous properties is demanding and calls for optimization of the corresponding crystal growth process. In order to support this optimization, sensitive process parameters are varied in simulations and their effects are studied. Here, we report on thermal field simulations in a Bridgman–Stockbarger furnace. The lab furnace is equipped with liquid metal cooling (LMC) to achieve high and homogeneous thermal gradients at the crystallization front during crystal growth of cylindrical Ni–Mn–Ga-rods. The calibration of the thermal simulation model requires (i) the knowledge/measurement of the relevant thermophysical properties of the Ni–Mn–Ga alloy as functions of temperature and (ii) thermal data from a reference benchmark experiment in the lab furnace using the same alloy. The calibrated simulation model is used for the simulation of a specific virtual Bridgman-experiment and for the determination of the temperature distributions. Moreover, the influence of the type of liquid metal coolant on the simulation results is investigated.

Contribution to Numerical Simulation of Laser Welding

Contribution deals with numerical simulation of thermal and stress fields in welding tubes made of austenitic stainless CrNi steel type AISI 304 with a pulsed Nd:YAG laser. Process simulation was realised by use of ANSYS 10 software. Experiments were aimed at solution of asymptotic, standard and the so-called shell model. Thermally dependent properties of AISI 304 steel were considered. Thermal fields developed in the course of welding process and also shape of weld pool were assessed. Contribution is aimed at simulation of technological welding process with input parameters regarding the thermal and strain task and comparison of attained results with real experiment. The achieved results of numerical simulation were almost identical with a real weldment thermally affected by welding process.

Simulation of temperature and magnetic field distribution in superconducting bulk duringpulsed field magnetization

A theoretical simulation of electromagnetic and thermal fields was performedfor a cryocooled superconducting bulk disc after applying a magnetic pulse.The results of the simulation qualitatively reproduced the experimentalones for the time and applied field dependences of the trapped fieldBz and thetemperature T on the bulk surface. For magnetic pulse application with a rise time ofτ = 0.01 s, the magnetic flux propagation was about two orders of magnitude fasterthan the heat propagation because of the low thermal conductivity of thebulk. The results show that the intruding magnetic flux escaped because ofthe delayed temperature rise. For a longer magnetic pulse application withτ = 1 or 10 s, the flux propagation speed becomes slow and approaches the heat propagationspeed. In this case, the magnetic flux escape attributable to the flux creep becomessmall and a higher trapped field can be achieved. The method of exploring theenhancement of the trapped field using pulsed field magnetization is discussed.

Three‐dimensional ultrasound image‐guided robotic system for accurate microwave coagulation of malignant liver tumours

The further application of conventional ultrasound (US) image-guided microwave (MW) ablation of liver cancer is often limited by two-dimensional (2D) imaging, inaccurate needle placement and the resulting skill requirement. The three-dimensional (3D) image-guided robotic-assisted system provides an appealing alternative option, enabling the physician to perform consistent, accurate therapy with improved treatment effectiveness. Our robotic system is constructed by integrating an imaging module, a needle-driven robot, a MW thermal field simulation module, and surgical navigation software in a practical and user-friendly manner. The robot executes precise needle placement based on the 3D model reconstructed from freehand-tracked 2D B-scans. A qualitative slice guidance method for fine registration is introduced to reduce the placement error caused by target motion. By incorporating the 3D MW specific absorption rate (SAR) model into the heat transfer equation, the MW thermal field simulation module determines the MW power level and the coagulation time for improved ablation therapy. Two types of wrists are developed for the robot: a 'remote centre of motion' (RCM) wrist and a non-RCM wrist, which is preferred in real applications. The needle placement accuracies were < 3 mm for both wrists in the mechanical phantom experiment. The target accuracy for the robot with the RCM wrist was improved to 1.6 +/- 1.0 mm when real-time 2D US feedback was used in the artificial-tissue phantom experiment. By using the slice guidance method, the robot with the non-RCM wrist achieved accuracy of 1.8 +/- 0.9 mm in the ex vivo experiment; even target motion was introduced. In the thermal field experiment, a 5.6% relative mean error was observed between the experimental coagulated neurosis volume and the simulation result. The proposed robotic system holds promise to enhance the clinical performance of percutaneous MW ablation of malignant liver tumours.

Thermal field simulation and heat zone optimization for the growth of 50-mm basal-plane-faceted sapphire ribbons

The global heat transfer during growth of 50-mm basal-plane-faced sapphire ribbons in a cylindrical heat zone has been numerically simulated for different heat shield configurations. The ribbon thermoelastic strains were computated to estimate the heat zone quality. It is shown that shield adjustment and redistribution of radiative heat fluxes inside the heat zone make it possible to essentially decrease the thermal field curvature in the ribbon around the crystallization front and, therefore, decrease the thermoelastic strains by a factor of 2 to 3 (to 20 MPa).

Numerical Simulation of Thermal and Flow Fields in Induction Skull Melting Process

The electromagnetic, thermal and fluid fields during ISM (Induction Skull Melting)of TiAl alloy are simulated. The effects of ampere-turn, frequency and relative position between crucible and coil on the distribution of thermal and flow fields are numerically studied. The simulation model is verified by experiments and the simulation results are discussed in detail.

FEM simulation of the Nitinol wire

In recent years, one of the most promising new actuator technologies is based on the use of Shape Memory Alloys (SMA). The main challenge for the application of devices that use these materials is the hysteresis in the phase transition they suffer during actuation. Finite element analysis (FEA) is an important aid in the simulation of mechanical properties and thermal fields in actuators. Dynamic simulations give in many cases enough information without the necessity of building a prototype. We have used ABAQUS to simulate a Nitinol wire used in a micropositioning actuator. The model parameters, not given by the supplier but required by the FEA program, have been obtained by thermal and mechanical characterization of the material used. The output force is computed and compared with the measurements.