Uniform Thermal Distribution Research Articles

Multicoils Design for Induction Cookers With Applying Switched Exciting Method

This paper investigates induction cookers with multicoils to improve their heating performances. Two multicoils solutions are proposed to replace the traditional single coil design. The eddy currents and power losses distributions of the systems are analyzed using finite-element method. A switched exciting method for driving the multicoils is adopted. Furthermore, thermal fields on the induction pan are computed to evaluate the thermal performances of the proposed multicoils systems. A prototype of the proposed multicoils system has been developed and undergone validation experiments. The testing results indicate that the proposed solution is capable of providing more uniform thermal distribution, as well as flexible and sound heating-control functions.

Emissivity study of the array shaped blackbody in the microwave band

Different from that in the optical band, the blackbody in the microwave band is constructed in a coated cone array structure. The blackbody of this type can be used in calibrating microwave radiometers with standard brightness radiations, and needs to have a uniform surface thermal distribution and high emissivity. The emissivity study of such a blackbody can be performed based on the Kirchhoff's law of thermal equilibrium, in a reflection determination routine. The emissivity characteristics varying with frequency have been intensively studied, but their variations with direction and polarization have not received much attentions. Starting from the Floquet mode analysis, a reflection evaluation scheme for the blackbody is presented, which is more robust than that based on the back-ward RCS determination. Based on the presented scheme, the trends of emissivity varying with frequency, direction, polarization are studied, for a microwave blackbody design. Results show that the emissivity rises as the frequency rises in a range from X band to K band; and in the low frequency band, the trend of the vertical polarization emissivity varying with elevation angle is different from that of the horizontal polarization emissivity, and there exists an obvious phenomenon that the vertical polarization emissivity declines with the increase of elevation angle. These phenomena are related to the electromagnetic absorption characteristics of the coating layer.

THERMAL BUCKLING OF RECTANGULAR PLATES WITH DIFFERENT TEMPERATURE DISTRIBUTION USING STRAIN ENERGY METHOD

By using governing differential equation and the Rayleigh-Ritz method of minimizing the total potential energy of a thermoelastic structural system of isotropic thermoelastic thin plates, thermal buckling equations were established for rectangular plate with different fixing edge conditions and with different aspect ratio. The strain energy stored in a plate element due to bending, mid-plane thermal force and thermal bending was obtained. Three types of thermal distribution have been considered these are: uniform temperature, linear distribution and non-linear thermal distribution across thickness. It is observed that the buckling strength enhanced considerably by additional clamping of edges. Also, the thermal buckling temperatures and thermal buckling load have lowest values at first mode of buckling for all types of ends condition and with all values of aspect ratios

Study on Thermal Placement Optimization of Embedded MCM

In the thermal design of embedded multi-chip module (MCM), the placement of chips has a significant effect on temperature field distributing, thus influences the reliability of the embedded MCM. The thermal placement optimization of chips in embedded MCM was studied in this paper, the goal of this work is to decrease temperature and achieve uniform thermal field distribution within embedded MCM. By using ANSYS the finite element analysis model of embedded MCM was developed, the temperature field distributing was calculated. Based on genetic algorithms, chips placement optimization algorithm of embedded MCM was proposed and the optimization chips placement of embedded MCM was achieved by corresponding optimization program. To demonstrate the effectiveness of the obtained optimization chips placement, finite element analysis (FEA) was carried out to assess the thermal field distribution of the optimization chips placement in embedded MCM by using ANSYS. The result shows that without chips placement optimizing the maximum temperature and temperature difference in embedded MCM model are 87.963°C and 2.189°C respectively, by using chips placement optimization algorithm the maximum temperature drop than the original 0.583°C and the temperature difference is only 0.694°C . It turns out that the chip placement optimization approach proposed in this work can be effective in providing thermal optimal design of chip placement in embedded MCM.

Active Control of Thermal Buckling of Shells of Revolution Using Piezoelectric Patches

In this paper, the thermal buckling of piezoelectric composite shells of revolution under uniform and linear thermal distributions and selected boundary conditions is investigated by using the semi-analytical finite element. The effects of different parameters such as the type of temperature distributions through the thickness, fiber angles, arrangements of piezoelectric patches and amount of displacement feedback control gain are examined. The results obtained from the present analysis are validated, where possible, with those available in the literature.

Effect of Electromagnetic Field on Horizontal Direct Chill Casting of 7075 Aluminum Alloy

The influence of different electromagnetic fields on the horizontal direct chill (HDC) casting of aluminum alloy is studied. 7075 aluminum alloy with 100-mm in diameter is produced by HDC casting process; single electromagnetic field located before or around the mold and an out-phase electromagnetic field (OPEMF) are applied in the HDC casting process. The effect of different electromagnetic fields on the HDC casting solidification behavior and as-cast structure is investigated. The electromagnetic field can effectively make uniform thermal distribution in the molten pool and refine the as-cast structure. The OPEMF is more efficient than the single electromagnetic field in improving the as-cast structure of HDC cast ingots.

A Study of Heating Duration and Scanning Path in Focused Ultrasound Surgery

A conventional method of avoiding normal tissue overheating during focused ultrasound surgery (FUS) is to apply equal heating duration for each sonication in between cooling intervals. However, this method is time-consuming and expensive. A novel method with unequal heating duration in different scanning paths without cooling intervals was investigated in this paper. This method was compared with the conventional method through the ablation of a 10 × 10 cm(2) target. The simulation results indicated that the new method was able to reduce treatment time by more than 50%, with higher than 95% coverage index, and more uniform thermal dose distribution. The method was further verified through the ablation of a circular lesion. Ex vivo experiments were also performed to confirm the simulation results. Both simulation and experimental results have proven that the new method can increase heating efficiency, and are a promising new approach in FUS.

Application of indium tin oxide (ITO)-based microheater chip with uniform thermal distribution for perfusion cell culture outside a cell incubator

This study reports a transparent indium tin oxide (ITO)-based microheater chip and its applicability for perfusion cell culture outside a cell incubator. The attempt of the proposed ITO microheater is to take the role of conventional bulky incubator for cell culture in order to improve integratability with the experimental setup for continuous/perfusion cell culture, to facilitate microscopic observation or other online monitoring activities during cell culture, or even to provide portability of cell culture operation. In this work, numerical simulation and experimental evaluation have been conducted to justify that the presented device is capable of providing a spatially uniform thermal environment and precise temperature control with a mild deviation of +/-0.2 degrees C, which is suitable for a general cell culture practice. Besides, to testify that the thermal environment generated by the presented device is well compatible with conventional cell incubator, chondrocyte perfusion culture was carried out. Results demonstrated that the physiology of the cultured chondrocytes on the developed ITO microheater chip was consistent with that of an incubator. All these not only demonstrate the feasibility of using the presented ITO microheater as a thermal control system for cell culture outside a cell incubator but also reveal its potential for other applications in which excellent thermal control is required.

Silicon-based micro-gas sensors for detecting formaldehyde

Micro-formaldehyde gas sensor of palladium doped tin dioxide was fabricated on silicon substrate. Finite element software ANSYS was used to analyze the thermal field distribution. In order to obtain a uniform thermal field distribution in the micro-gas sensor, the width of the marginal four strips of the heating electrode was designed to be 50 μm and the width of the central seven strips 25 μm. Undoped and 1 mol% Pd-doped SnO 2 thin films were synthesized by sol–gel method on silicon substrates. XRD and XPS spectra of the films were analyzed. The response of the 1 mol% Pd-doped SnO 2 micro-gas sensor to formaldehyde was much higher than that of the undoped SnO 2 micro-gas sensor. This experimental observation was also supported by the XPS O (1s) patterns of the films which showed that doping 1 mol% Pd into SnO 2 increased the value of O a/O l, i.e., the ratio of adsorption and lattice oxygens. Formaldehyde of 0.03 ppm concentration was detected by the 1 mol% Pd-doped SnO 2 micro-gas sensor.

Polydimethylsiloxane microfluidic chip with integrated microheater and thermal sensor

A microheater and a thermal sensor were fabricated inside elastomeric polydimethylsiloxane microchannels by injecting silver paint (or other conductive materials) into the channels. With a high-precision control scheme, microheaters can be used for rapid heating, with precise temperature control and uniform thermal distribution. Using such a microheater and feedback system, a polymerase chain reaction experiment was carried out whereas the DNA was successfully amplified in 25 cycles, with 1 min per cycle.

The Simulation of Thermal Field in Induction Melting with Cold-Crucible and Dual Frequencies

A study of thermal field in induction melting with cold crucible and dual induction frequencies is presented in this paper. Numerical simulation was done by finite element based software COMSOL with use of multi-physical modeling. A method of superposing of magnetic vector potential is proposed to solve the complexity of dual induction frequencies. Different conditions of high and low frequencies were given in the calculation to find the effects on distribution of thermal fields. The computed temperature distribution was compared with the macro etched section of solidified ingots and the results showed that the orientation of dendritic grain structures follow to the similar direction of heat flow. This indicates that proper set of induction coils could enable more uniform thermal field distribution and attaining controlled solidification morphology in the ingots.

Pressure-loss reduction and velocity-profile improvement in a catalytic converter by a flow deflector

In automobile exhaust systems, catalytic converters have become essential in reducing environmental pollution. However, the main components of catalytic converters produce large pressure drops in exhaust systems, which decrease engine power and increase fuel consumption. In addition to the need to reduce pressure loss, the flow passing through the catalytic substrate strate should be as uniform as possible, which provides a uniform thermal distribution and high catalytic conversion efficiency. The goal of the present study is simultaneously to reduce the pressure loss and to improve the flow distribution under spatial constraints. The authors herein propose new types of device and investigate their performances experimentally. Specifically, the possibilities of two types of flow deflector with a shell structure, which are placed inside the diffuser part of the catalytic converter in order to reduce flow separation, were investigated. In addition, using the particle image velocimetry technique and Pitot tube velocimetry, flow features such as the velocity profiles were elucidated. The tested converter has a standard cylindrical ceramic monolith substrate with channels of square cross-section. As a result, the two flow deflectors can reduce the pressure loss by 17 per cent and 22 per cent, compared with a no-deflector converter and can effectively improve the velocity profile.

Thermal neutron irradiation field design for boron neutron capture therapy of human explanted liver

The selective uptake of boron by tumors compared to that by healthy tissue makes boron neutron capture therapy (BNCT) an extremely advantageous technique for the treatment of tumors that affect a whole vital organ. An example is represented by colon adenocarcinoma metastases invading the liver, often resulting in a fatal outcome, even if surgical resection of the primary tumor is successful. BNCT can be performed by irradiating the explanted organ in a suitable neutron field. In the thermal column of the Triga Mark II reactor at Pavia University, a facility was created for this purpose and used for the irradiation of explanted human livers. The neutron field distribution inside the organ was studied both experimentally and by means of the Monte Carlo N-particle transport code (MCNP). The liver was modeled as a spherical segment in MCNP and a hepatic-equivalent solution was used as an experimental phantom. In the as-built facility, the ratio between maximum and minimum flux values inside the phantom ((phi(max)/phi(min)) was 3.8; this value can be lowered to 2.3 by rotating the liver during the irradiation. In this study, the authors proposed a new facility configuration to achieve a uniform thermal neutron flux distribution in the liver. They showed that a phi(max)/phi(min) ratio of 1.4 could be obtained without the need for organ rotation. Flux distributions and dose volume histograms were reported for different graphite configurations.

Thermal management of multi‐chip module and printed circuit board using FEM and genetic algorithms

PurposeTo determine the optimal chip/component placement for multi‐chip module (MCM) and printed circuit board (PCB) under thermal constraint.Design/methodology/approachThe placement of power dissipating chips/component is carried out using genetic algorithms (GA) in order to achieve uniform thermal distribution on MCM and PCB. The thermal distribution on the MCM and PCB are predicted using 2D‐finite element method (FEM) analysis. Different number of chip/component and FEM meshing size is used to investigate the placement of chips/components.FindingsThe optimal placement of chip/component using GA is compared well to other placement techniques. The coarse meshing for FEM employed here is found adequate to carry out optimal placement of components by GA.Research limitations/implicationsThe analysis is valid for constant properties of MCM or PCB and steady state conditions. The chip/component size is limited to a single standard size.Practical implicationsThe method is very useful for practical design of chip/component placement on MCM/PCB under thermal consideration.Originality/valueFEM analyses of MCM and PCB can be easily implemented in the optimization procedure for obtaining the optimal chip/component placement based on thermal constraints.

Micro gas sensor array with neural network for recognizing combustible leakage gases

A micro gas sensor array, consisting of four porous tin oxide thin films added with noble metal catalysts on a micro-hotplate, was designed and fabricated. The micro-hotplate was designed to obtain a uniform thermal distribution along with a low-power consumption and fast thermal response. The sensing properties of the sensors toward certain combustible gases, i.e., propane, butane, LPG, and carbon monoxide, were evaluated. A multilayer neural network was then used to classify the gas species. The results demonstrated that the proposed micro sensor array, plus multilayer neural network employing a backpropagation learning algorithm, was very effective in recognizing specific kinds and concentration levels of combustible gas below their respective threshold limit values.

Thermoelastic-Plastic Stress Analysis in a Thermoplastic Composite Disc

In this study, an elastic-plastic stress analysis is carried out on a steel fiber-reinforced thermoplastic composite disc under uniform thermal distribution. The composite disc is reinforced by steel fibers curvilinearly. Its mechanical properties are obtained by strain gauges and Instron test machine. The modulus of elasticity in the tangential direction is measured by fitting a solid disc to the composite disc, exactly. However, other material properties are found approximately. The material is assumed to be non work hardening. Stresses are determined for uniform temperature distribution. The magnitude of the tangential stress component in polar coordinates is the highest at the inner points of the disc. Plastic solution is performed numerically. Plastic region begins at the inner surface of the disc. The residual stress component of the tangential stress is the highest at the inner surface of the disc.

Investigation Of Thermal Distribution In TheProcess Chamber With The Effects Of Shape AndWall Insulation

Uniform thermal distribution has a critical effect on prototyping accuracy in rapid prototyping and rapid manufacturing. Any uneven thermal distribution in the work bed of the prototyping machine process chamber will result in product distortion. In order to get the best thermal distribution on the work bed, what kind of machine process chamber (PC) shape do we need to design? Do we need to insulate the process chamber wall? What are the effects of process chamber shape and wall insulation for a free convection flow pattern inside the process chamber? What’s the relationship between the thermal distribution and convection flow? In this study we have utilized CFD to develop fundamental understanding of thermal distribution and characteristic in the process chamber with the effects of different PC shape and different PC wall insulation. Numerical study in four configurations of PC shape and six configurations of PC wall insulation with different radiant heater duty cycles are presented in this paper.

Thermal and Geometrically Nonlinear Stress Analyses of an Adhesively Bonded Composite Tee Joint with Double Support

Carbon fiber reinforced plastics (CFRP) can be successfully joined to metal or composite structural components using the adhesive bonding technique [Semerdjiev, S. (1970). Metal to Metal Adhesive Bonding, Business Books Ltd., London.]. The stress and deformation fields occurring in the adhesive joints due to the thermal loads as well as the structural loads play an important role on the joint strength since the thermal and mechanical properties of the adhesive and adherends are different. Previous thermal stress analyses of the adhesive single-lap joints with simple geometries assumed a uniform temperature distribution through the adhesive joint, consequently predicted uniform thermal strain and stress distributions. In this study, the thermal stress analysis of an adhesively bonded tee joint with double support made of unidirectional CFRP was carried out for variable thermal loading conditions along its outer boundaries and different plate edge conditions. The large displacement and rotation effects were considered using the small strain-large displacement theory. The stress fields in the adhesive layer and the composite members of two tee joints bonded to a rigid base and a flexible plate were investigated. In the thermal analysis, a reference uniform temperature was attributed to all joint members for its stress free state, and air streams with different temperature and velocity were specified along the outer surfaces of the adhesive joint. In addition, the air streams were specified in the vertical or horizontal directions to the composite plates and adhesive layer. The consideration of convective and conductive heat transfer showed that nonuniform temperature distributions occurred in the adhesive tee joints. High heat fluxes took place along the free surfaces of the adhesive fillets at the free ends of the adhesive layers. Geometrical nonlinear stress analyses of two tee joints were carried out using the calculated temperature fields for two different plate edge conditions. Since the adhesive joints consist of materials with different thermal and structural properties, the thermal strains become incompatible along the adhesive layer–plate interfaces. Consequently, the stress concentrations occurred inside the adhesive fillets around the adhesive free ends, and in the regions near the adhesive layer–composite plate interfaces. The adhesive fillets, middle region of the horizontal plate, the elbow sections of the left and right supports appeared as most critical regions of the tee joints. In addition, the support length did not have similar effect of reducing the normal and shear stresses at these critical adhesive and adherend locations.

Thermal non-linear elastic stress analysis of an adhesively bonded T-joint

Adhesive joints consist of adherends and an adhesive layer having different thermal and mechanical properties. When they are exposed to uniform thermal loads the mechanical-thermal mismatches of the adherends and adhesive layer result in uniform but different thermal strain distributions in the adhesive and adherends. The thermal stresses arise near and along the adherend-adhesive interfaces. The present thermal stress analyses of adhesively bonded joints assume a uniform temperature distribution or a constant temperature imposed along the outer boundaries of adhesive lap joints. This paper outlines the thermal analysis and geometrically non-linear stress analysis of adhesive joints subjected to different plate edge conditions and varying thermal boundary conditions causing large displacements and rotations. In addition, the geometrically non-linear thermal stress analysis of an adhesively bonded T-joint with single support plus angled reinforcement was carried out using the incremental finite element method, which was subjected to variable thermal boundary conditions, i.e. air streams with different temperatures and velocities parallel and perpendicular to its outer surfaces. The steady state heat transfer analysis showed that the temperature distribution through the joint members was non-uniform and high heat fluxes occurred inside the adhesive fillets at the adhesive free ends. Based on the geometrically non-linear stress analysis of the T-joint bonded to both rigid and flexible bases for different plate edge conditions, stress concentrations were observed at the free ends of adhesive-adherend interfaces and inside the adhesive fillets around the adhesive free ends, and the horizontal and vertical plates also experienced considerable stress distributions along outer surfaces. In addition, the effect of support length on the peak thermal adhesive stresses was found to be dependent on the plate edge conditions, when a support length allowing moderate adhesive stresses was present.

SnO/sub 2/ gas sensing array for combustible and explosive gas leakage recognition

A gas-sensing array with ten different SnO/sub 2/ sensors was fabricated on a substrate for the purpose of recognizing various kinds and quantities of indoor combustible gas leakages, such as methane, propane, butane, LPG, and carbon monoxide, within their respective threshold limit value (TLV) and lower explosion limit (LEL) range. Nano-sized sensing materials with high surface areas were prepared by coprecipitating SnCl/sub 4/ with Ca and Pt, while the sensing patterns of the SnO/sub 2/-based sensors were differentiated by utilizing different additives. The sensors in the sensor array were designed to produce a uniform thermal distribution along with a high and differentiated sensitivity and reproducibility for low concentrations below 100 ppm. Using the sensing signals of the array, an electronic nose system was then applied to classify and identify simple/mixed explosive gas leakages. A gas pattern recognizer was implemented using a neuro-fuzzy network and multi-layer neural network, including an error-back-propagation learning algorithm. Simulation and experimental results confirmed that the proposed gas recognition system was effective in identifying explosive and hazardous gas leakages. The electronic nose in conjunction with a neuro-fuzzy network was also implemented using a digital signal processor (DSP).