Non-uniform Heat Distribution Research Articles

Characterizing solid-state ignition of runaway chemical reactions in Ni-Al nanoscale multilayers under uniform heating

Nanoscale layers of nickel and aluminum can mix rapidly to produce runaway reactions. While self-propagating high temperature synthesis reactions have been observed for decades, the solid-state ignition of these reactions has been challenging to study. Particularly elusive is characterization of the low-temperature chemical mixing that occurs just prior to the ignition of the runaway reaction. Characterization can be challenging due to inhomogeneous microstructures, uncontrollable heat losses, and the nonuniform distribution of heat throughout the material prior to ignition. To reduce the impact of these variables, we heat multilayered Ni/Al foils in a highly uniform manner and report ignition temperatures as low as 245 °C for heating rates ranging from 2000 °C/s to 50 000 °C/s. Igniting in this way reveals that there are four stages before the reaction is complete: heating to an ignition temperature, low temperature solid-state mixing, a separate high temperature solid-state mixing, and liquid-state mixing. Multiple bilayer spacings, heating rates, and heating times are compared to show that the ignition temperature is a function of the bilayer spacing. A symmetric numerical diffusion model is used to show that there is very little chemical mixing in the first 10 ms of heating but significant mixing after 50 ms. These predictions suggest that ignition temperatures should increase for the slowest heating rates but this trend could not be identified clearly. The modeling was also used to examine the kinetic parameters governing the early stages of solid-state diffusion and suggest that grain boundary diffusion is dominant.

Generated forces and heat during the critical stages of friction stir welding and processing

The solid-state behavior of friction stir welding process results in violent mechanical forces that should be mitigated, if not eliminated. Plunging and dwell time are the two critical stages of this welding process in terms of the generated forces and the related heat. In this study, several combinations of pre-decided penetration speeds, rotational speeds, tool designs, and dwell time periods were used to investigate these two critical stages. Moreover, a coupled-field thermal-structural finite element model was developed to validate the experimental results and the induced stresses. The experimental results revealed the relatively large changes in force and temperature during the first two stages compared with those during the translational tool movement stage. An important procedure to mitigate the undesired forces was then suggested. The model prediction of temperature values and their distribution were in good agreement with the experimental prediction. Therefore, the thermal history of this non-uniform heat distribution was used to estimate the induced thermal stresses. Despite the 37% increase in these stresses when 40 s dwell time was used instead of 5 s, these stresses showed no effect on the axial force values because of the soft material incidence and stir effects.

Photo-thermal effect enhances the efficiency of radiotherapy using Arg-Gly-Asp peptides-conjugated gold nanorods that target αvβ3 in melanoma cancer cells.

BackgroundThermotherapy has been known to be one of the most effective adjuvants to radiotherapy (RT) in cancer treatment, but it is not widely implemented clinically due to some limitations, such as, inadequate temperature concentrations to the tumor tissue, nonspecific and non-uniform distribution of heat. So we constructed arginine-glycine-aspartate peptides-conjugated gold nanorods (RGD-GNRs) that target the alpha(v) beta(3) Integrin (αvβ3) and investigate whether the photo-thermal effect of RGD-GNRs by near infrared radiation (NIR) could enhance the efficiency of RT in melanoma cancer cells.ResultsRGD-GNRs could be seen both on the surface of the cell membranes and cytoplasm of A375 cells with high expression of αvβ3. After exposed to 808 nm NIR, RGD-GNRs with various concentrations could be rapidly heated up. Compared to other treatments, flow cytometric analysis indicated that RT + NIR + RGD-GNRs increased apoptosis (p < 0.001) and decreased the proportion of cells in the more radioresistant S phase (p = 0.014). Treated with NIR + RGD-GNRs, the radiosensitivity was also significantly enhanced (DMFSF2: 1.41).ConclusionResults of the current study showed the feasibility of using RGD-GNRs for synergetic RT with photo-thermal therapy. And it would greatly benefit the therapeutic effects of refractory or recurrent malignant cancers.

Microstructural and mechanical performance of aluminium to steel high power ultrasonic spot welding

Welding of Aluminium 6111-T4 to bare and two different zinc coated steels was successfully carried out using high power ultrasonic spot welding. The thermal behaviour and non-uniform heat distribution at the local weld area were investigated. The effect of heat generation on precipitates dissolution and natural aging of Al6111-T4 was studied. The maximum hardness in TMAZ was 10-15Hv higher than natural aging which is because of higher rate of precipitation due to reduction in grain/subgrain size. The performance of soft hot-dipped DX56-Z and hard galvannealed DX53-ZF zinc coated steels was discussed in terms of mechanical properties and joinability, in comparison with uncoated steel. The highest peak load (3.25kN) and fracture energy (∼5kNmm) was reached in the case of aluminium to hot dipped DX56-Z zinc coated steel joints owing to the maximum ductility. In contrast, in aluminium to galvannealed DX53-ZF zinc coated steel joints failure was promoted earlier with low mechanical properties of 2.6kN shear strength and 1.25kNmm fracture energy as a result of damage to the zinc layer. Formation of brittle Al–Fe intermetallic layer at the interface of aluminium to bare steel was the main effect of reduction in ∼3.0kN lap shear strength at the maxima. Surface damage due to sonotrode welding tip penetration was seen to be more severe in aluminium to bare DC04 steel compared to other weld combinations that resulted strength loss when the thickness of the weld nugget is reduced at the optimum condition.

Focusing Optimization for High-Power Continuous-Wave Second-Harmonic Generation in the Presence of Thermal Effects

We study thermal effects in high-power single-pass second-harmonic generation (SP-SHG) of continuous-wave (cw) green radiation in MgO:sPPLT and describe optimization of critical factors including the fundamental beam waist, position, and focusing parameter, for attainment of maximum SP-SHG efficiency. By developing a numerical model combining split-step Fourier and finite-element methods, we compute the relevant parameters for optimization of SP-SHG of a cw Yb-fiber laser at 1064 nm in a 30-mm-long crystal. Real experimental parameters and boundary conditions are used to simulate nonuniform heat distribution in the crystal under high-power operation and study its effects on SP-SHG optimization. The results indicate that for input powers exceeding a certain limit, the Boyd and Kleinman (BK) criteria for optimum focusing are no longer valid. By increasing the fundamental power to 50 W, we find that the optimum focusing parameter decreases by a factor of 4, from ξ =2.8 to 0.7. We also find that the maximum SP-SHG output power is always obtained for fundamental waist at the center of the crystal, and we present a general strategy for the choice of ξ at different fundamental powers. Using a top-sinked oven design, the BK focusing condition can be established even at high fundamental powers.

Study of Air-Flow and Temperature Distribution in a Small-Scale Dryer for Grains Drying

This paper describes the work performed on a small-scale dryer designed to allow agricultural product to be dried by farmers via usage of slanted plates for grains transportation. This work involves the prototype design, computational simulation using Comsol Multiphysics and study of the results. The computational simulation results are plotted in temperature contour-plots based on the prototype modelling and boundary conditions. The results illustrate the difference in opening and closing of grains inlet and also effects of the temperature distribution within the dryer. Air-flow relative humidity is also introduced to allow observation of the drying air-flow on the grains. The simulation results are shown and elaborated here. From the results, it is evident the grains can be dried as the injected heated air-flow is projected onto the plates. It can also be concluded here that farmers may need to close the grains inlet of the dryer to prevent heat loss and non-uniform distribution of heat.

Regular and chaotic oscillations of a Timoshenko beam subjected to mechanical and thermal loadings

Dynamics of a Timoshenko beam under an influence of mechanical and thermal loadings is analysed in this paper. Nonlinear geometrical terms and a nonuniform heat distribution are taken into account in the considered model. The mathematical model is represented by a set of partial differential equations (PDEs) which takes into account thermal and mechanical loadings. The problem is simplified to two PDEs and then reduced to ordinary differential equations (ODEs) by means of the Galerkin method taking into account three modes of a linear Timoshenko beam. Correctness of the analytical model is verified by a finite element method. Then, the nonlinear model is studied numerically by a continuation method or by a direct numerical integration of ODEs. An effect of the temperature distribution on the resonance near the first natural frequency and on stability of the solutions is presented. The increase of mechanical loading results in hardening of the resonance curve. Thermal loading may stabilise the beam dynamics when the temperature is decreased. The elevated temperature may transit dynamics from regular to chaotic oscillations.

Influence of Thermal Parameters on the Structure and Intensity of Vortex Motion of a Melt in DC Arc Furnaces

The vortex motion of a metal melt in a dc bottom-electrode arc furnace has been modeled numerically with allowance for different thermal parameters. The motion of the melt was described by magnetic hydrodynamic equations for a nonisothermal liquid. An algorithm of solution of the problem within the framework of standard packages of applied programs has been developed. It has been shown that a determining contribution to the vortex motion of the metal melt is made by the electromagnetic Lorentz force. It has been established that a significant influence is exerted by convective flows resulting from the nonuniform distribution of heat that is released in the electric-arc region. A nonuniform distribution of the Joule heat from the electric current flowing over the melt exerts a minor influence on the structure and intensity of the vortex melt motion.

Application of Packaging Technique in Fiber Bragg Grating Temperature Sensor for Measuring Localized and Nonuniform Temperature Distribution

The development of Fiber Bragg Grating (FBG) sensing technique has improved significantly especially in the sensor head design and real-time data acquisition technique. This paper presents the development of a simple and cost effective packaging technique that further enhances the performances of the FBG sensor. The packaged FBG sensor overcomes the nonuniform heat distribution of a bare FBG that causes eccentric response of FBG spectrum. Therefore, the packaged FBG sensor could be operated for a localized area with high temperature differential. The packaging also compensates the unwanted strain effect from the surrounding which makes temperature measurement become more accurate. The experimental works have been successfully carried out to demonstrate the system operation and the packaging functionalities. The temperature sensitivity coefficient of the bare FBG sensor measured in experiment is 10.05 pm/°C, while the packaged fiber sensor is 10.09 pm/°C, which are expected from the design.

Assessment of Residual Stresses and Distortion in Stainless Steel Weld Joints

Welding introduces significant residual stresses in the welded structure/component due to non-uniform heat distribution during heating and cooling cycle. To control, reduce, or beneficially redistribute the residual stresses in weld joints, the stress distribution needs to be known. In the present study, weld joints of 10 mm thick 316LN stainless steel were made by multi-pass TIG and A-TIG welding processes and their residual stresses distribution and distortion values were measured and compared. While V-groove edge preparation was required for making multi-pass TIG weld joint, square-edge preparation was sufficient for making single pass A-TIG weld joint. Ultrasonic nondestructive technique based on the critically refracted longitudinal waves (LCR waves) has been used for the quantitative surface/sub-surface residual stress measurements in the weld joints. Distortion measurements were carried out before and after welding using height gauge. Peak tensile residual stress and the angular distortion values were lower in the A-TIG weld joint compared to that of the multipass TIG weld joint.

Thermal mode-switching of a passively Q-switched microchip Nd:YAG laser

In the present article, the thermal distribution inside the gain medium of a passively Q-switched microchip laser is modeled and simulated for actual practical values associated with an available microchip laser constructed in our laboratory. The effects of the non-uniform heat distribution on the spectral properties of the output laser beam have been investigated and simulated with the variation of diode-pump power and pulse repetition rate. It is observed that the gain bandwidth as well as Optical Path Difference (OPD) values of the propagating pulses are significantly decreased, while the Nd:YAG chip is cooled down to a certain value. The validity of the utilized model is checked by setting and characterizing the spectral properties of a fabricated laboratory microchip laser under different heating conditions. It is verified that when the temperature of the gain material is changed by an electronically controlled Peltier device, the spectrum of the output laser beam can be switched between single- and dual-mode situations. This physical character has shown good agreement between the presented model and obtained experimental results.

应用均温板于非均匀热物理条件

均温板(Vapor Chamber)为一两相流热传组件，具有将热量均匀扩散传递的功能，非常适合应用在不均匀发热的热源条件上。本文主要即是探讨均温板应用于非均匀发热的电子组件，如CPU、GPU及LED等，其扩散传递热量的能力。首先利用本文所开发的计算程序VCEK_ML V1及BaseResistance_ML，先行估算均温板的扩散传递热量的能力，再使用窗口软件VCTM V1.0配合热性能实验，分析整个均温板模块在非均匀热源物理条件的热流现象，最后可藉由热显像仪的温度分布结果验证均温板扩散热量的传递能力。结果显示，均温板模块可有效改善非均匀热物理条件的热分布现象，比纯铜及纯铝板佳。 A vapor chamber is a two-phase heat transfer components with a function of spreading and transferring uniformly heat capacity so that it is ideal for use in non-uniform heating conditions. This article mainly researches in vapor chamber application on non-uniform heating electronic components, such as CPU, GPU, and LED, with its ability to spread and heat transfer. Firstly, the calculation program developed in this paper named as VCEK_ML V1 and BaseResistance_ML employ to estimating the ability for spreading and transferring heat amount of vapor chamber. Then the Windows software VCTM V1.0 with the thermal-performance experiment analyzes the thermal phenomena of the Vapor Chamber module in the thermo physical conditions of non-uniform heat source, and finally, a thermal imager can be employed and proved the heat spreading capability of vapor chamber through the temperature distributions. The results showed that, a vapor chamber module can effectively improve the thermo physical conditions of non-uniform heat distribution phenomenon, which is better than pure copper and pure aluminum plates.

Experimental investigation of non-uniform heating effect on flow boiling instabilities in a microchannel-based heat sink

Two-phase flow boiling in microchannels is one of the most promising cooling technologies for coping with high heat fluxes produced by the next generation of central processor units (CPUs). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with non-uniform heating, using water as the cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated. It was observed that boiling inside microchannels with axially non-uniform heating leads to high temperature non-uniformity in the transverse direction.

Impact of Occupant Modelling on the Prediction of Airflow around Occupants in a Ventilated Room

Localized ventilation systems typically create highly asymmetric or non-isothermal environments around occupants with significant vertical temperature gradient and highly non-uniform airflow regimes that could be directed toward a segment of the body. These effects may have pronounced impact on occupant’s thermal comfort. The airflow field and temperature distribution near the occupant can be determined either by performing full-scale measurements or by simulation methods. Usually, human subjects or manikins are used in field studies involving measurement techniques. However, as an alternative to full-scale measurement, Computational Fluid Dynamics (CFD) has been proven to be a practical and valuable tool for predicting the airflow field. At the same time, the accuracy of the predictions of the local airflow within the microclimate of the occupant is highly dependent on the proper modelling of the occupant itself. The human body not only has a complicated physical shape, but also has complex thermo-physiological properties. Modelling of all these aspects is a formidable challenge and an extremely time-consuming task. Therefore, various simplifications have been made in order to decrease the level of complexity so that the computation may be performed with the available computer resources.This paper reports the results of a detail numerical simulation to study the impact of occupant modelling on the airflow and temperature distribution and their influences on the occupant’s thermal comfort. First, the predictions made by the CFD model were compared with experimental data that were measured in a specially designed experimental chamber. Good agreement was observed. Four type of configuration were used to model the occupant: a conventional block form, three-node, six-node and finally eight-node configurations. Further simulations were carried out to investigate the assumption of uniform heat distribution. An assessment of uniform and non-uniform heat distribution scenarios for various occupant configurations and ventilation systems showed that the assumption of uniform heat distribution is valid for a wide range of operating conditions.

An assessment of claims of ‘excess heat’ in ‘cold fusion’ calorimetry

Claims of ‘excess heat’ from measurements of the heat of electrolysis at several watts of power are largely based on use of poorly characterized, isoperibol, heat-conduction calorimeters with single-point temperature sensors. This paper describes construction, testing, and calibration of a calorimeter of similar design. Heat-conduction calorimeters with single-point temperature sensing and inadequate mixing are subject to large systematic errors resulting from non-uniform heat distribution within the system. Confirmation of electric-heater calibration by a chemical reaction with a well-known enthalpy change is a minimum requirement to insure accuracy. Improper or incomplete calibration is a probable cause for many claims of ‘excess heat’ in ‘cold fusion’ experiments.

A Study on Thermal Performance of Heat Pipe for Optimum Placement of Satellite Equipment

A study on the operation of a heat pipe with two heat sources has been performed to optimize the heat distribution of satellite equipment. A numerical modeling is used to predict the temperature profile for the heat pipe assuming cylindrical two-dimensional laminar flow for the vapor, and the conduction heat transfer for the wall and wick. An experimental study using the copper-water heat pipe with the length of 0.45 m has been performed to evaluate the numerical model and to compare the temperature distribution at the outer wall for the non-uniform heat distribution. The results on temperature profiles for the heat input range from 29 W to 47 W on each heater are presented. Also the correlation between the heat input and the temperature increase is presented for the optimum distribution on two heaters. The result shows that the outer wall temperature can be controlled by redistribution of heat sources. It is also concluded that the heat source closer to the condenser can carry more heat while maintaining lower temperatures at the outer wall.

Optimization of radiation therapy, III: A method of assessing complication probabilities from dose-volume histograms

To predict the likelihood of success of a therapeutic strategy, one must be able to assess the effects of the treatment upon both diseased and healthy tissues. This paper proposes a method for determining the probability that a healthy organ that receives a non-uniform distribution of X-irradiation, heat, chemotherapy, or other agent will escape complications. Starting with any given dose distribution, a dose-cumulative-volume histogram for the organ is generated. This is then reduced by an interpolation scheme (involving the volume-weighting of complication probabilities) to a slightly different histogram that corresponds to the same overall likelihood of complications, but which contains one less step. The procedure is repeated, one step at a time, until there remains a final, single-step histogram, for which the complication probability can be determined. The formalism makes use of a complication response function C(D, V) which, for the given treatment schedule, represents the probability of complications arising when the fraction V of the organ receives dose D and the rest of the organ gets none. Although the data required to generate this function are sparse at present, it should be possible to obtain the necessary information from in vivo and clinical studies. Volume effects are taken explicitly into account in two ways: the precise shape of the patient's histogram is employed in the calculation, and the complication response function is a function of the volume.

Evaluation of Error Incurred in Determining Thermal Properties by Laser Flash

Abstract The problem inherent in the laser flash method is the involvement of comparatively large errors occasioned by the non-uniform radial distribution of the intensity of radiant heat emitted by the laser. This error due to non-uniform heating is evaluated in this paper from the theoretical analysis made of a case where radiant heat with parabolic intensity distribution impinges pulsewise on one surface of a disk. The result indicates that much of the existing data reported in literature from measurements by laser flash are not very reliable, and that serious error in determining thermal properties can only be avoided by imposing severe limitations on the dimensions of the specimen, or else the results obtained from pulsewise and non-uniform heating of the specimen are subject to correction to account for the non-uniform heat distribution.