Lateral Temperature Distribution Research Articles

Influences of Solution Flow and Lateral Temperature Distribution on Surface Morphology in Solution Growth of SiC

The influences of solution flow and lateral temperature distribution on the surface morphology of the 4H-SiC single crystal grown from solution was investigated. A flat surface region was enlarged by the seed-rotation rate. The solution flow simulation indicated that the higher rotation rate made the outward solution flow ordered beneath the solution surface. Such a solution flow was thought to be effective to enlarge the flat region of growth front. Furthermore, a full-flat surface was obtained with a hollow-type graphite rod at a seed-rotation rate of 60 min-1. The simulated results of temperature distribution showed the hollow-type graphite rod reduced the lateral temperature gradient at the SiC-solution interface. The ordered solution flow and the small temperature gradient at the growth front were found to be effective to make the growth front flat in the solution-growth method.

Towards full predictions of temperature dynamics in McNary Dam forebay using OpenFOAM

Hydroelectric facilities impact water temperature; low velocities in a reservoir increase residence time and enhance heat exchange in surface layers. In this study, an unsteady three-dimensional model was developed to predict the temperature dynamics in the McNary Dam forebay. The model is based on the open-source code OpenFOAM. RANS equations with the Boussinesq approximation were used to solve the flow field. A realizable κ-ε model that accounts for the production of wind turbulence was developed. Solar radiation and convective heat transfer at the free surface were included. The result of the model was compared with the field data collected on August 18, 2004. Changes in diurnal stratification were adequately predicted by the model. Observed vertical and lateral temperature distributions were accurately captured. Results indicate that the model can be used as a numerical tool to assess structural and operational alternatives to reduce the forebay temperature.

The thermal impact of aquifer thermal energy storage (ATES) systems: a case study in the Netherlands, combining monitoring and modeling

Results are presented of a comprehensive thermal impact study on an aquifer thermal energy storage (ATES) system in Bilthoven, the Netherlands. The study involved monitoring of the thermal impact and modeling of the three-dimensional temperature evolution of the storage aquifer and over- and underlying units. Special attention was paid to non-uniformity of the background temperature, which varies laterally and vertically in the aquifer. Two models were applied with different levels of detail regarding initial conditions and heterogeneity of hydraulic and thermal properties: a fine-scale heterogeneity model which construed the lateral and vertical temperature distribution more realistically, and a simplified model which represented the aquifer system with only a limited number of homogeneous layers. Fine-scale heterogeneity was shown to be important to accurately model the ATES-impacted vertical temperature distribution and the maximum and minimum temperatures in the storage aquifer, and the spatial extent of the thermal plumes. The fine-scale heterogeneity model resulted in larger thermally impacted areas and larger temperature anomalies than the simplified model. The models showed that scattered and scarce monitoring data of ATES-induced temperatures can be interpreted in a useful way by groundwater and heat transport modeling, resulting in a realistic assessment of the thermal impact.

The Study of Temperature Rise in a 90-Degree Sharp Bend Microchannel Flow Under Constant Wall Temperature Condition

AbstractThis study presents the fluid temperature measurement at a 90-degree sharp bend inside a microchannel using molecule-based temperature sensor technique. This technique provides both detailed and global information for temperature investigation in microfluidic research. Rhodamine B was selected as the molecule-based temperature probe in the experiment to provide non-invasive and straightforward measurements. To resolve the luminescence deviation in the microscale temperature measurements introduced by the corner structure, in-situ calibration method and pixel-by-pixel correction were applied during the data reduction. The temperature measurement was performed in a 200μm wide, 67μm deep and 2cm long PDMS microchannel with a 90-degree sharp bend at the center. The temperature profile was measured at a Reynolds number of 27.66 using Rhodamine B in DI water while the bottom of channel was heated at 50°C. As revealed by the molecule-based temperature sensor, the temperature variation along the central line increased 2°C while passing the corner. Additionally, the lateral temperature distributions upstream of the corner show the temperature increase near the outer side of microchannel and decreased near the inner side. The velocity profiles around the 90-degree sharp bend were acquired to analyze the flow after corner. Secondary flow structure after the corner was observed in the velocity profiles along the depth of the microchannel. This study analyzes the thermal flow fields in the microchannel with a 90-degree sharp bend and reveals that regardless of the low Reynolds number, the flow mixing after the corner resulted in the increase of temperature downstream of the bend.

Residual Stress Measurements of 4H-SiC Crystals Using X-Ray Diffraction

The room temperature residual stress of 4H-SiC wafers has been investigated using a precise X-ray diffraction method. A large strain was observed for the circumferential direction of wafers, more than ten times larger than those measured along the principal plane direction and the radial direction. Optimizing the lateral temperature distribution in growing crystals leads to reduction of residual stress of wafers with high crystal quality.

C111 ヒートポンプ給湯用プレート式凝縮器の熱交換特性(OS4 省エネルギー・コジェネ・ヒートポンプ(1))

This study deals with heat transfer characteristics in a blazing plate heat exchanger used as a condenser in heat pump hot water heater. In this report, experiments of single channel heat exchanger were carried out by using a pump driven two-phase flow loop. The test section has one path for each fluid, refrigerant and water. The effects of mass flow rate of refrigerant and water, wave height of plate, and setting arrangement, vertical with downward refrigerant flow or horizontal, were examined. HFC134a was used as the refrigerant. Superheated vapor was supplied to the condenser, and heated water. Water was flowing in the counter flow direction. The wall temperature distribution of the refrigerant path was measured by an infrared camera. As a result, it was shown that the lateral temperature distribution for the horizontal arrangement was affected by the wave pattern while that for the vertical arrangement was uniform.

Distributed electro-thermal RF-LDMOS model

To develop an accurate RF-LDMOS large signal model,temperature distribution across a multi-finger device was researched.Using the three dimensional image method,temperature distribution across a finger was easily calculated.Furtherly,for multiple fingers,lateral temperature distribution could be obtained under the superposition principle.A thermal matrix was used to describe the model and the thermal parameters were obtained by fitting with the calculation results.Compared with the traditional thermal model,this model can be used to characterize the heat transferring horizontally by using mutual thermal resistances between fingers and the average thermal resistance network is replaced by distributed thermal RC network to model the multi-fingers.The calculation results show that it can present the temperature distribution and predict the average thermal resistance of scaling devices more accurately.

Study on Temperature Stresses in Concrete Box Girders Due to Heat of Concrete Hydration

The temperature distribution and strains due to heat of hydration of cement in a concrete box girder were measured on site during construction of the Harbin Songpu Bridge. The lateral and vertical temperature distributions and stresses in webs and slabs were analyzed. The study of the measured results shows that there are large temperature differences in the box-girder sections, and both the lateral and vertical temperature distributions and stresses are nonlinear. In some parts of the sections, the tensile stresses are even greater than the characteristic value of concrete tensile strength.

The near-field thermal microwave radiation response of a biological object to the local change of the lateral temperature distribution

A layer-by-layer method is theoretically developed for reconstructing the temperature distribution inside a biological object from the measured outgoing thermal microwave radiation energy flux. The measurement is carried out along the plane parallel to the heated object surface in the surface’s near-field area. The equation of the inverse problem is obtained. The equation couples the 2D spatial Fourier-component of Poynting’s outgoing radiation vector with the similar Fourier-component of the lateral temperature distribution along elementary inner layers parallel to the object surface. The obtained equation is solved for the case of a 1D periodic or local depth-uniform lateral temperature distribution inside an object. The effective half-width of the spatial-harmonic spectrum for the outgoing thermal radiation energy flux is shown to be estimated by the double wave number inside the object. At the same time, the spatial half-width of a biological object’s thermal-radiation response to a local change in the lateral temperature distribution is estimated as a half of the wavelength inside the object. This result justifies the antenna size conventionally applied in biomedical research.

Uniformity of the wafer surface temperature during MOVPE growth of GaN-based laser diode structures on GaN and sapphire substrate

Wafer bowing has a strong impact on the wavelength homogeneity of InGaN based light emitters due to the strong temperature dependence of the In incorporation. Using in-situ curvature measurements and pyrometry we have studied the impact of growth conditions on the lateral and vertical temperature distribution across the wafer and on wafer bow on sapphire and GaN substrates. From the pyrometry signal at 950 nm the temperature of the substrate holder can be deduced. Using 400 nm pyrometry the surface temperature was determined for sufficiently thick GaN layers. While total flow and satellite rotation were found to have no impact, the total pressure affects the vertical temperature profile and thus the wafer bow. However, the effect is small and can only be used for fine tuning. To compensate for the strain of the AlGaN cladding layer in laser structures precurved GaN substrates are shown to be advantageous. Photoluminescence confirmed a spatially uniform surface temperature distribution during the deposition of the InGaN quantum well active region with a peak wavelength around 500 nm and a deviation as low as 3.5 nm on flat sapphire substrates and precurved GaN substrates.

Temperature analysis of AlGaN/GaN based devices using photoluminescence spectroscopy: Challenges and comparison to Raman thermography

Photoluminescence (PL) spectroscopy was used to determine lateral temperature distributions in AlGaN/GaN based devices. Results are compared to Raman thermography data and to thermal modeling to assess challenges in the determination of temperature in devices using PL analysis and corresponding solutions. In conjunction with Raman thermography, the vertical temperature distribution in the devices is determined and the thermal boundary resistance at the GaN/SiC interface extracted.

Advanced structures for heat transfer studies on diaphragms

Suspended diaphragm devices were designed for heat transfer studies of the diaphragm material and optionally added thin films. The diaphragm embeds a thin-film heating resistor and two thin-film thermistors to measure temperature drops along a rectangular diaphragm section. Custom design of interconnection limbs and thin-film devices enables a nearly uniform lateral temperature distribution and minor alteration of the temperature field by the thermistors. The device dimensions allow the simultaneous determination of thermal conductivity λ and emissivity ε from a single temperature transient experiment. For the stratified SiO2/SiNx diaphragm, λ=0.938W/Km and ε=32.8% was deduced. Applied to a 130 nm Cr film embedded between the dielectric layers, λCr=12.26W/Km was obtained. The embedded chromium layer changes the observed emissivity to 44.3%.

A Temperature-Gradient-Induced Failure Mechanism in Metallization Under Fast Thermal Cycling

In this paper, a novel mechanism is shown to cause the failure evolution in a metallization system under fast temperature cycle stress. The failure evolution is triggered by the lateral temperature distribution across the device, which causes an accumulating plastic deformation of the metallization. The root cause for the deformation emerges at the position of the maximum gradient in temperature.

Thermal thickness and evolution of Precambrian lithosphere: A global study

The thermal thickness of Precambrian lithosphere is modeled and compared with estimates from seismic tomography and xenolith data. We use the steady state thermal conductivity equation with the same geothermal constraints for all of the Precambrian cratons (except Antarctica) to calculate the temperature distribution in the stable continental lithosphere. The modeling is based on the global compilation of heat flow data by Pollack et al. [1993] and more recent data. The depth distribution of heat‐producing elements is estimated using regional models for ∼300 blocks with sizes varying from 1°×1° to about 5°×5° in latitude and longitude and is constrained by laboratory, seismic and petrologic data and, where applicable, empirical heat flow/heat production relationships. Maps of the lateral temperature distribution at depths 50, 100, and 150 km are presented for all continents except Antarctica. The thermal thickness of the lithosphere is calculated assuming a conductive layer overlying the mantle with an adiabat of 1300°C. The Archean and early Proterozoic lithosphere is found to have two typical thicknesses, 200–220 km and 300–350 km. In general, thin (∼220 km) roots are found for Archean and early Proterozoic cratons in the Southern Hemisphere (South Africa, Western Australia, South America, and India) and thicker (>300 km) roots are found in the Northern Hemisphere (Baltic Shield, Siberian Platform, West Africa, and possibly the Canadian Shield). We find that the thickness of continental lithosphere generally decreases with age from >200 km beneath Archean cratons to intermediate values of 200±50 km in early Proterozoic lithosphere, to about 140±50 km in middle and late Proterozoic cratons. Using known crustal thickness, our calculated geotherms, and assuming that isostatic balance is achieved at the base of the lithosphere, we find that Archean and early Proterozoic mantle lithosphere is 1.5% less dense (chemically depleted) than the underlying asthenosphere, while middle and late Proterozoic subcrustal lithosphere should be depleted by ∼0.6–0.7%. Our results suggest three contrasting stages of lithosphere formation at the following ages: >2.5 Ga, 2.5–1.8 Ga, and <1.8 Ga. Ages of komatiites, greenstone belts, and giant dike swarms broadly define similar stages and apparently reflect secular changes in mantle temperature and, possibly, convection patterns.

Fatigue Properties of BGA Solder Joints: A Comparison of Thermal and Power Cycle Tests

To meet the state‐of‐the‐art requirements of BGA assemblies necessitates direct coupling of field conditions, simulation tools for life‐time study and advanced experiments for the assessment of physical degradation. For conventionally soldered SMD components, transformations between test and field conditions are still not completely known. For new types of array components, the answers critically depend upon ‘Component age’ and change in fatigue mechanisms. The increasing complexity of microelectronic assemblies and the hidden joints of BGAs lead to an increase in reliability problems in this field. Therefore, to describe failure‐free times for different applications, fatigue relevant parameters of the ball solder joints need to be studied. With regard to the thermal coefficient of expansion, BGAs are mainly asymmetrical, consequently residual strains and stresses are generated in the solder joint array. The level of strains and stresses depends upon the global and local mismatch, the applied operating conditions and the temperature distribution in the ball solder joint array (chip location, ambient and operating temperature). For thermo‐mechanical cycling procedures, hold and ramp times at upper and lower temperatures (e.g., −20°C/+100°C) are used to initiate strains in materials and interfaces. BGAs and PCBs show comparable thermal levels with regards to the test procedures mentioned before, and the resulting stress conditions in the ball solder joints are a function of package size, DNP, etc. The test results with regard to the generation of cracks are not directly comparable to the fatigue behaviour under operating conditions. Therefore, different types of degradation tests were developed: thermo‐mechanical, mechanical, electrical and/or corrosive procedures. Depending upon the chip location in the BGA package (symmetrically: PBGA, TBGA, CBGA; asymmetrically :MCM‐BGA) frequencies, lateral and vertical temperature distribution under simulated power dissipations, and the internally generated heat will be used to induce stresses in the ball solder joints. For different values of power dissipation and ambient conditions, thermal measurements were performed, screening the top to the bottom side of the BGA and the array field. The resulting information is a precondition in order to define power cycle parameters. For different test procedures, locations of defects, crack initiation and growth in ball solder joints were studied by metallographic analysis. The practical measurements serve as analytical input to compare thermal and power cycle tests and they are a necessary step to perform a lifetime prediction.

Interferometric measurement of lateral temperature distribution during laser-assisted processing of thin films

An experimental method is proposed for the determination of temperature profiles during laser irradiation of supported thin films. The method is applied to the measurement of the evolution of the temperature profile during the oxidation of thin vanadium films on glass, induced by a CW argon ion laser beam. A temperature decrease in the centre of the laser beam due to negative feedback is detected. The advantages and limitations of the method are discussed.

Comprehensive modeling of diode arrays and broad-area devices with applications to lateral index tailoring

A numerical model for calculating the emission characteristics of diode laser arrays and broad-area devices operating well above threshold is discussed. This model uses the beam propagation technique for determining the field intensities for several lateral modes, while simultaneously and self-consistently solving for the two-dimensional current flow through the laser structure and the subsequent carrier diffusion in the active region. The active-region temperature distribution is also computed in a self-consistent manner, based on the flow of heat generated in the active region through the layered device structure to a constant-temperature heat sink. The model is applied by investigating the sensitivity of the lasing modes of a broad-area diode laser to variations in the lateral temperature distribution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Advancements in silicon web technology

Low defect density silicon web crystals up to 7 cm wide are produced from systems whose thermal environments are designed for low stress conditions using computer techniques. During growth, the average silicon melt temperature, the lateral melt temperature distribution and the melt level are each controlled by digital closed loop systems to maintain thermal steady state and to minimize the labor content of the process. Web solar cell efficiencies of 17.2% AM1 have been obtained in the laboratory while 15% efficiencies are common in pilot production.

Evaluation of Temperature Distribution of Melt in Silicon Ribbon Growth

An improved Edge-defined Film-fed Growth apparatus is used to grow wider silicon ribbon crystals. A rectangular graphite heater with a shape similar to the die top structure is used in order to increase the length of uniform temperature. A thermal radiation modifier prevents the growth of crystals with non-uniform thickness. The lateral temperature distribution at the die is quantitatively analyzed from the thickness of the grown crystal. The appropriate temperature distribution for growing wide ribbons is determined. As a result, growth of an 8.4 cm wide ribbon is achieved. The dependence of the crystal thickness and width on the growth rate and system temperature is also investigated.

Lateral Distribution of Pressure in Thin Strip Rolling

A method is presented for the determination of the lateral distribution of pressure in thin strip rolling. A simplified three-dimensional analysis of elastic deformation of the rolls is developed for use in the method. Pressure in the roll edge contact regions (in underface rolling), as well as in the roll-strip contact region, is considered. In the case of four-high, planetary, and Sendzimir-type mills, the lateral distribution of pressure between the work roll and backup rolls is also found. Calculated results indicate lateral pressure distributions which have peak values at each edge of the strip with a minimum at the center. The degree of this nonuniformity depends on roll geometry and configuration. Partition of the total rolling force between roll-strip contact and roll edge contact in underface rolling is also determined. Since interroll heat transfer is dependent on contact area, and hence, pressure, the results can also aid the determination of lateral temperature distributions in the rolls. In addition, the method is potentially useful for a study of the influence of roll geometry and configuration on strip shape.