Optimal Temperature Distribution Research Articles

A fast adaptive power scheme based on temperature distribution and convergence value for optimal hyperthermia treatment

Abstract To elevate tissue temperature to therapeutic level fast with optimal power deposition during hyperthermia treatment (HT) is a key treatment processing step. Traditionally we have treated the tumor volume, without considering possible existing thermally significant vessels, using a simple 1st-order temperature-based adaptive power scheme to determine optimal power deposition distributions. The objectives of this study were to reveal the difficulty of that approach when considering single large blood vessel, and proposed a novel fast scheme that could improve upon and substitute for the traditional temperature-based adaptive power scheme. In this study, we presented a novel three-coefficient-and-two-SCV 5th-order temperature-based adaptive power scheme to resolve the induced large blood vessel problem in 3-D temperature distribution and introduced the parameter, SCV (Sentinel Convergence Value), to handle interior scheme shift. Results of the novel adaptive power scheme has shown its robustness to fast approach optimal temperature distribution and power density distribution with high precision in the tumor volume when considering the existence of thermally significant blood vessel. Ultimately, we may be able to effectively calculate the absorbed power density distribution of 3-D biological tissues with a complicated vasculature [1] in the volume.

Effect of Rolling Speed on Instantaneous Temperature Distribution and Thermal Expansion of Work Roll in Hot Strip Rolling

In the unsteady state, work roll temperature distribution and thermal expansion have an enormous effect on the process of hot rolling. The rolling speed in the finish rolling as an important rolling parameter plays a crucial role of obtaining the optimum temperature distribution and thermal expansion. Using the finite element method, it solves the regularity of temperature distribution and thermal expansion with thermal-structural coupling analysis, which provide theoretic proof of optimizing gauge and profile control.

Theoretical and Experimental Study of Thermoelectric Generators for Vehicles

The general physical laws for reaching the maximum efficiency of a generator using vehicular exhaust heat have been studied. Based on the physical models of a generator with lumped and distributed parameters, the optimal gas temperature at the outlet of the thermoelectric generator (TEG) and the optimal distribution of gas temperature in the heat exchanger have been found. The basic generator parameters, namely the voltage, power, and efficiency, have been calculated in the steady-state and dynamic modes. The possibility of efficiency improvement by a factor of 1.5 through use of an exponential as compared with an isothermal distribution of heat exchanger temperature has been revealed. Calculations are confirmed by results from testing a prototype vehicular thermoelectric generator.

Numerical and Experimental Analysis of the Temperature Distribution in a Hydrogen Fuelled Combustor for a 10 MW Gas Turbine

Proper cooling of the hot components and an optimal temperature distribution at the turbine inlet are fundamental targets for gas turbine combustors. In particular, the temperature distribution at the combustor discharge is a critical issue for the durability of the turbine blades and the high performance of the engine. At present, CFD is a widely used tool to simulate the reacting flow inside gas turbine combustors. This paper presents a numerical analysis of a single can type combustor designed to be fed both with hydrogen and natural gas. The combustor also features a steam injection system to restrain the NOx pollutants. The simulations were carried out to quantify the effect of fuel type and steam injection on the temperature field. The CFD model employs a computationally low cost approach, thus the physical domain is meshed with a coarse grid. A full-scale test campaign was performed on the combustor: temperatures at the liner wall and the combustor outlet were acquired at different operating conditions. These experimental data, which are discussed, were used to evaluate the capability of the present CFD model to predict temperature values for combustor operation with different fuels and steam to fuel ratios.

Multi-Objective Optimization of the Heating Rods Layout for Rapid Electrical Heating Cycle Injection Mold

Rapid electrical heating cycle injection molding (ERHCM) technology is a promising green manufacturing technology for plastic parts. By using this technology, the defects that usually appear on the surface of conventionally injected parts, such as weld and flow marks, can be avoided effectively. This paper studies rapid electrical heating cycle injection molding technology and its mold structure design techniques. Temperature distribution uniformity and heating efficiency on the mold cavity surface are considered as the major influencing factors on product quality and production efficiency. A multi-objective optimization model for the heating rods layout in the mold cavity plate is formulated to optimize temperature distribution uniformity and heating efficiency with respect to the heating rods layout. An application to a liquid crystal display TV panel is implemented successfully using a genetic algorithm.

Modeling and Optimization of MeOH to DME in Isothermal Fixed-bed Reactor

Dimethyl ether (DME) is a green fuel that commercially produced in an adiabatic fixed bed reactor by methanol dehydration. In the present work, a shell and tube fixed bed reactor is modeled and optimized for DME production. The reactor is modeled based on mass and energy conservation equations as well as auxiliary equations. In order to estimate the DME production and temperature profile along the reactor, a one dimensional heterogeneous model consist of a set of nonlinear differential and algebraic equations has been solved numerically. Also, The DME production in the isothermal reactor is maximized by adjusting the optimal temperature distribution along the reactor using genetic algorithm. Then, the performance of the proposed isothermal reactor is compared with industrial adiabatic fixed bed reactor. Results showed the higher DME production rate and methanol conversion in the optimized reactor.

Sapphire needle capillaries for laser medicine

New devices for laser photochemical and thermal methods of treatment of tumors of the prostate, liver, thyroid gland, and brain are developed on the basis of sapphire needle capillaries. These needles allow one to increase the irradiation volume substantially, to obtain an optimal temperature distribution, to simplify the design, and to eliminate a system for cooling the device.

Energy saving and thermal comfort studies of a regional air-conditioning mechanism

Making the workroom a more pleasant, comfortable, healthy, safe, and energy-efficient place is an important goal. This article presents an airflow management technique that uses a regional air-conditioning mechanism (RACM) to control the airflow in the workroom with the aim of achieving a regional steady-state temperature. This concept means that each member of staff in a different area of the location can be satisfied with respect to their own local environment. A system of RACM consists of a main duct with an upper round inlet port and a lower round outlet port that was located in the centre of a cylindrical room. In simulations for this study, the change of the distance between the inlet and outlet ports as well as that of the heights of the inlet and outlet ports were considered in order to obtain the optimal airflow, temperature distribution, and thermal comfort indices in the occupied zone. The computational fluid dynamics simulation results predict that the RACM could successfully establish a regional air-conditioning cell, an individual thermal comfort zone, and also that RACM can be inferred to be more energy efficient than a typical air-conditioning system. The concepts in this study are relevant to all kinds of regional air-conditioning in any enclosed space.

Fast temperature optimization of multi-source hyperthermia applicators with reduced-order modeling of ‘virtual sources’

The goal of this work is to build the foundation for facilitating real-time magnetic resonance image guided patient treatment for heating systems with a large number of physical sources (e.g. antennas). Achieving this goal requires knowledge of how the temperature distribution will be affected by changing each source individually, which requires time expenditure on the order of the square of the number of sources. To reduce computation time, we propose a model reduction approach that combines a smaller number of predefined source configurations (fewer than the number of actual sources) that are most likely to heat tumor. The source configurations consist of magnitude and phase source excitation values for each actual source and may be computed from a CT scan based plan or a simplified generic model of the corresponding patient anatomy. Each pre-calculated source configuration is considered a ‘virtual source’. We assume that the actual best source settings can be represented effectively as weighted combinations of the virtual sources. In the context of optimization, each source configuration is treated equivalently to one physical source. This model reduction approach is tested on a patient upper-leg tumor model (with and without temperature-dependent perfusion), heated using a 140 MHz ten-antenna cylindrical mini-annular phased array. Numerical simulations demonstrate that using only a few pre-defined source configurations can achieve temperature distributions that are comparable to those from full optimizations using all physical sources. The method yields close to optimal temperature distributions when using source configurations determined from a simplified model of the tumor, even when tumor position is erroneously assumed to be ∼2.0 cm away from the actual position as often happens in practical clinical application of pre-treatment planning. The method also appears to be robust under conditions of changing, nonlinear, temperature-dependent perfusion. The proposed approach of using virtual sources reduces the number of variables that must be optimized to achieve a tumor-focused temperature distribution, thereby reducing the calculation time required in real-time control applications to about 1/3 to 1/4 of that required for full optimization.

Regular solution of inverse optimal design problems for axisymmetric systems of radiative heat transfer

Inverse optimal design problems are considered for axisymmetric systems of heat transfer with only radiative heat transfer. In these problems, the geometry of thermal system is preassigned, and it is required to find the optimal distribution of temperature on the heater surface, which provides for the preassigned distribution of radiative heat flux (at a given temperature) on the surface being heated. Variational methods of regularization are employed for solving these problems, namely, Tikhonov’s regularization method and parametric regularization. Minimization problems are solved numerically by gradient methods. The conjugate problem method is used for calculating the gradient of discrepancy functional. Examples of solution of model problems are given.

Experimentally and Numerical Study on Deep Drawing Process for Magnesium Alloy Sheet at Elevated Temperatures

Recently, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications because of its advantages such as low density, high specific strength etc. However, the application of formed magnesium wrought alloys components is restricted due to lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, the deformation behavior of a cylindrical deep drawing of magnesium alloy sheets at elevated temperatures are simulated by using a non-isothermal finite element based on DEFORM 3D commercial software. In order to validate the finite element analysis, deep drawing test of cylindrical cup of AZ31 and AZ52 rolled sheets at given conditions was also performed. The experimental results show a good agreement with the finite element simulation predictions. The optimal forming temperature, thickness distribution of the cup and punch force were determined for the process. (doi:10.2320/matertrans.MC200761) Weight reduction has long been identified as a key priority for improving automotive fuel economy, and many studies often suggest substituting lightweight materials for typical steel applications. In recent years, magnesium alloys have been paid much attention due to its advantages such as low density, high specific strength etc. Therefore, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications and expected to be widely used for structural components, notably in the automotive and aerospace industry in the near future. 1-3) The application of formed magnesium wrought alloys components, however, is restricted due to lack of knowledge for processing magnesium alloys, especially forming process, at elevated temperatures. Traditionally, forming processes are usually carried out in isothermal conditions. In other words, the processes are conducted under the conditions of constant and homogeneous temperatures of tools and workpiece. However, deep drawing tests with magnesium alloy sheets show that the drawability of sheets can be improved by local heating based on the change of material property with respect to temperatures. 4-6) This means the process is ultimately non-isothermal. Moreover, during the forming process, heat is generated by plastic deformation and the heat loss by conduction and by radiation and convection to the punch as well as to the environment can result in several property changes of the workpiece. There- fore, this underscores the need for accurate methods to investigate a forming process of magnesium alloy not only deformation behavior but also heat transfer process, a task to which the finite element method is well suited. In this study, a thermo-rigid-viscoplastic FEM, based on DEFORM 3D codes, with anisotropic Hill's non-quadratic yield criterion is applied to analyze the warm deep drawing of AZ31 and AZ52 rolled sheets. The load-stroke curves, optimal process parameters and temperature distribution in the sheets obtained in the FE simulation were compared with experimental results for various forming conditions. 2. Experimental Procedure The magnesium alloys used in this study are AZ31 and AZ52 rolled sheets with a thickness of 0.83 mm. The chemical composition and microstructure images of the sheets are shown in Table 1 and Fig. 1, respectively.

Optimal temperature distribution in a 3D triple-layered skin structure embedded with artery and vein vasculature and induced by electromagnetic radiation

In hyperthermia cancer treatments, a crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Thus, obtaining a temperature field of the entire treatment region is important to control the process. In this study we develop a model and a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure embedded with multi-level blood vessels. The heat is induced by electromagnetic (EM) radiation. The dimensions and blood flow of multi-level blood vessels are determined based on the constructal theory.

Optimal Temperature Distribution in a Three-Dimensional Triple-Layered Skin Structure Embedded with Artery and Vein Vasculature

In recent years there has been interest in research related to hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. When heating the tumor tissue, the crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Hence, in order to control the process, it is important to obtain a temperature field of the entire treatment region. In this article, we develop a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure embedded with two countercurrent, multilevel blood vessels: artery and vein.

A Numerical Method for Obtaining an Optimal Temperature Distribution in a 3-D Triple-Layered Cylindrical Skin Structure Embedded with a Blood Vessel

ABSTRACT In hyperthermia cancer treatments, the crucial problem, when heating the tumor tissue, is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Thus, it is important to optimize the temperature field of the entire treatment region. Recently, we have developed a numerical method for obtaining an optimal temperature distribution in a triple-layered cylindrical skin structure. In this article, we extend our method to a case involving a triple-layered cylindrical skin structure embedded with a blood vessel. The method is illustrated by a numerical example.

A hybrid multi-fidelity approach to the optimal design of warm forming processes using a knowledge-based artificial neural network

In this paper, a hybrid multi-fidelity optimization approach based on a knowledge-based artificial neural network (KBNN) was used to determine the optimal heating strategy in warm forming processes. First, a less costly, but less accurate isothermal finite element analysis (FEA), which neglected the complex heat transfer between the part and tooling elements, was performed to obtain overall knowledge about the effect of temperature on forming performance. Then, a small number of more accurate and expensive (i.e., longer computational time) non-isothermal FEA results were utilized in an artificial neural network (ANN), along with the prior knowledge from the isothermal FEA, to improve the accuracy in defining the non-linear relationship between the design variables (i.e., regional temperatures on the tooling) and the response (i.e., part depth value before failure). The accuracy of the non-isothermal FEA was validated by comparing its prediction results to the experimental findings. This approach was demonstrated for forming a rectangular cup, where it offered a rapid and accurate recommendation of the optimal temperature distribution on the tooling elements for improved formability. The individual and interaction effects of the regional temperatures on formability were also evaluated in detail by constructing the response surfaces near the optimal design point using the multi-fidelity system developed. Finally, a comparison of the temperature and thickness strain distributions on the formed parts was made under various operating conditions, to acquire detailed information on the deformation characteristics of the material.

Optimal temperature distribution in a three dimensional triple-layered skin structure with embedded vasculature

In recent years there has been interest in research related to hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. When heating the tumor tissue, the crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Hence, in order to control the process, it is important to obtain a temperature field of the entire treatment region. Recently, we have developed a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure. In this article, we extend our study to a triple-layered skin structure embedded with multilevel blood vessels, and develop a numerical method for obtaining an optimal temperature distribution.

Parametric analysis of warm forming of aluminum blanks with FEA and DOE

The effect of temperature distribution on warm forming performance was investigated for 5083-O (Al-Mg) sheet metal blanks. Combined isothermal/non-isothermal FEA with design of experiments tools were used to predict appropriate warm forming temperature conditions for deep drawing and two-dimensional stamping cases. In the investigated temperature range of 25–250 °C, the formability of Al-5083 alloy is found to be greatly dependent on the temperature distribution of the die and punch. To achieve increased degrees of forming, different temperature levels should be assigned to the corner and body of the die and punch. And the optimal temperature distributions for warm deep drawing and warm two-dimensional stamping are not identical.

Second-law analysis and optimization of microchannel flows subjected to different thermal boundary conditions

Entropy generation and transfer in microchannel flows were calculated and analyzed for different thermal boundary conditions. Due to the small flow cross-sectional area, fluid temperature variation in the lateral direction was neglected and a laterally lumped model was developed and used in the first- and second-law analyses. Since the Peclet numbers of microchannel flows are typically low, heat conduction in the flow direction was taken into consideration. Computed fluid temperature and entropy generation rate were cast into dimensionless forms, thus can be applied to different fluids and channels of different sizes and configurations. Local entropy generation rate was found to be only dependent upon the temperature gradient in the flow direction. The optimization results of microchannel flows exchanging heat with their surroundings indicate the optimal fluid temperature distribution is a linear one. Copyright © 2004 John Wiley & Sons, Ltd.

Optimization of surface temperature distribution for control of point defects in the silicon single crystal

Optimization of crystal surface temperature distribution is performed for the control of point defects in a silicon single crystal grown by the Czochralski process. In the optimization problem, we seek an optimal solution that minimizes the level of point defects while the radial uniformity of temperature is maximized. In order to solve the optimization problem with the equality constraints described by partial differential equations, the variational principle is used. Based on the calculus of variations and the method of Lagrange multiplier, the Euler–Lagrange equations are derived and solved by the finite difference method. In order to handle inequality constraints, the penalty function method is also applied. The optimal distribution of the crystal surface temperature is expected to provide an insight for the design of thermal surroundings such as the thermal shield configuration and the heater/cooler position.

Evolutionary optimization in thermoelastic problems using the boundary element method

The paper is devoted to application of evolutionary algorithms and the boundary element method to shape optimization of structures for various thermomechanical criteria, inverse problems of finding an optimal distribution of temperature on the boundary and identification of unknown boundary. Design variables are specified by Bezier curves. Several numerical examples of evolutionary computation are presented.