Design, manufacture, and analysis of metal foam electrical resistance heater

This paper presents a novel concept using the radial heating element made from porous Fe–Cr–Al metal foam in an air heater. Electrical resistance heating has been used extensively to convert the electrical energy into thermal energy. An analytic heat transfer model is first developed to estimate dimensions of the heating element. Four prototype Fe–Cr–Al metal foam electrical heaters with different levels of porosity and density are built. A more detailed computational fluid dynamics modeling of prototype heaters to include the temperature loss to the surroundings is developed. Experiments are conducted to evaluate the effects of airflow rates and electrical current and measure the change of air inlet and outlet temperatures. The experimental temperature measurements show reasonably good agreement with modeling predictions. Finally, improvements to the initial concept are discussed.     

Fully automated measurement setup for non-destructive characterization of thermoelectric materials near room temperature

A measurement setup is presented that allows for a complete and non-destructive material characterization of electrochemically deposited thermoelectric material. All electrical (Seebeck coefficient α, electrical conductivity σ), thermal (thermal conductivity λ), and thermoelectric (figure of merit ZT) material parameters are determined within a single measurement run. The setup is capable of characterizing individual electrochemically deposited Bi(2+x)Te(3-x) pillars of various size and thickness down to a few 10 μm, embedded in a polymer matrix with a maximum measurement area of 1 × 1 cm(2). The temperature range is limited to an application specific window near room temperature of 10?°C to 70?°C. A maximum thermal flux of 1 W∕cm(2) can be applied to the device under test (DUT) by the Peltier element driven heat source and sink. The setup has a highly symmetric design and DUTs can be mounted and dismounted within few seconds. A novel in situ recalibration method for a simple, quick and more accurate calibration of all sensors has been developed. Thermal losses within the setup are analysed and are mathematically considered for each measurement. All random and systematic errors are encountered for by a MATLAB routine, calculating all the target parameters and their uncertainties. The setup provides a measurement accuracy of ±2.34 μV∕K for α, ±810.16 S∕m for σ, ±0.13 W∕mK for λ, and ±0.0075 for ZT at a mean temperature of 42.5?°C for the specifically designed test samples with a pillar diameter of 696 μm and thickness of 134 μm, embedded in a polyethylene terephthalate polymer matrix.     

高密度聚氨酯泡沫塑料天线罩的研制

硬质聚氨酯泡沫塑料具有质轻、绝缘、隔热、透波的特点.文中介绍了具有优良介电性能、高密度聚氨酯泡沫塑料天线罩的研制情况.通过进行聚氨酯发泡料配方试验、耐候涂料选择、天线罩成型工艺研究,研制出结构强度高、介电性能优异、耐候性好的天线罩,满足产品使用要求.     

Viscous pressure bulging of aluminium alloy sheet at warm temperatures

Improving the formability of aluminium alloy sheet metal by using warm or elevated temperature has become a valid approach. In this paper, viscous pressure bulging (VPB) at warm temperature is proposed. The coupled thermo-mechanical finite element method and experimental method were used to investigate the VPB of aluminium alloy AA3003 at warm temperature. The temperature distributions of sheet metal and viscous medium were analyzed for non-isothermal VPB. The influence of forming temperature on thickness distribution, forming load and failure location of sheet metal were investigated. Research results show the temperature gradient field in sheet metal forms when the initial temperature of viscous medium is lower than that of sheet metal. The formability and failure location of sheet metal changes with initial temperature of viscous medium.     

A continuum plasticity model for the constitutive and indentation behaviour of foamed metals

A yield surface is proposed that can be fitted to the plastic flow properties of a broad class of solids exhibiting plastic compressibility and different yield points in tension and compression. The yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fitted to three experimental results: (1) the compressive stress–strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial stress compression test. The model is implemented using finite elements and used to study the effects of plastic compressibility on two problems: the compression of a doubly notched specimen and indentation by a spherical indenter. The model is then fitted to the properties of a typical closed cell aluminum foam and used to study indentation into a dense aluminum face sheet on a foam foundation. The dependence of the indentation load–displacement curve on the relevant material and geometric parameters is determined, and a single load–displacement relation is presented which approximates the behaviour of a wide range of practical designs. These results can be used to design against indentation failure of sandwich panels.     

FE modeling of warm flanging process of large T-pipe from thick-wall cylinder

The large T-branch pipe made from the thick-wall cylinder is an important part in power, petroleum, and chemical equipment. The warm flanging process is used to manufacture the high-performance large T-branch pipe from thick-wall cylinder. The warm flanging process has a bulk-forming characteristic with heterogeneous temperature field and represents very different from the sheet flanging process. The finite element method is adopted to study the warm flanging process of large T-branch pipe due to complex local heating and local deformation. A viscoplastic FE model was built to simulate the whole process in the same process, including heating, forming, cooling, and relevant elastic springback. Only one set of mesh was used to ensure the connection of heating and forming, which was never proposed in the warm flanging process before. The experiment was conducted to verify the proposed model by comparing the geometry and defects. Accordingly, two kinds of typical defects, buckling and wrinkling, were found in both of the simulation and experiment results. And, the reasons of defects were investigated with the stress and metal flow analysis. The short lower die leads to the buckling. Due to the ellipse outer edge, the uneven rebound makes wrinkling at the ends of the process. Three relevant improved methods, lengthening the lower die, increasing the fillet of the upper die, and increasing the radius of the upper die, were proposed and studied to decline the defects.     

A numerical investigation to the strategies of the localised heating for micro-part stamping

Local heating renders attractive characteristics for achieving high efficiency of metal forming. With reference to micro-part stamping, two localised-heating methods, electrical heating and laser-heating, are investigated with FE simulation. Results show that electrical heating would result in an advantageous distribution of the temperature in a steel work-material. A desired temperature distribution may also be achievable for a copper work-material, if a high-powered laser beam is used. Both electrical heating and laser-heating enable reduction of the stamping force and increase of the aspect ratio that is achievable by stamping. The simulation also demonstrates that both electrical heating and laser-heating are able to result in the desired temperature-distributions at sufficiently high heating-rates and that the methods are easy to be implemented. The comparison further shows that electrical heating is more favourable for engineering applications.     

Thermal conductivity measurement and interface thermal resistance estimation using SiO2 thin film

In this paper, we describe an easy-to-use method to measure the thermal conductivity of thin films based on an electrical heating/sensing mechanism and a steady-state technique. The method used relative commonly used instruments, and without any signal processing circuit, is easy to be used in such thin-film thermal conductivity measurement. The SiO2 thin-film samples, prepared by thermal oxidation, plasma enhanced chemical vapor deposition (PECVD), and E-beam evaporator, were deposited on a silicon substrate. The apparent thermal conductivity, the intrinsic thermal conductivity of SiO2 films, and the total interface thermal resistance of the heater/SiO2/silicon system were evaluated. Our data showed agreement with those data obtained from previous literatures and from the 3 omega method. Furthermore, by using a sandwiched structure, the interface thermal resistance of Cr/PECVD SiO2 and PECVD SiO2/silicon were also separately evaluated in this work. The data showed that the interface thermal resistance of Cr/PECVD SiO2 (metal/dielectric) is about one order of magnitude larger than that of PECVD SiO2/silicon (dielectric/dielectric).     

等离子数字化熔射成形SOFC核心部件PEN及复阻抗分析

采用等离子熔射与机器人数字化成形技术相结合的方法制备SOFC瓦楞式核心部件PEN。基于交流复阻抗技术对制备的复合电极的电导率进行分析，并与流延法和等离子熔射结合制备的试样对比；采用经典的Arrhenius公式对试样电导率与温度的关系进行定量分析。结果表明，两种工艺制备的试样的电导率均随温度的升高而增大，呈现出明显的NTC效应；与流延和等离子熔射复合的方法相比，等离子数字化熔射成形工艺因为其连续喷涂成形的特点，可以大幅度降低界面接触电阻，提高试样的电导率。     

COUPLED ELECTRICAL-THERMALMECHANICAL ANALYSIS FOR ELECTRICAL/LASER HEATING ASSISTED BLANKING

A coupled electrical-thermal-mechanical analysis is conducted for electrical/laser heating assisted blanking. Two novel localized-heating methods, electrical heating and laser-heating, recently proposed for small-part blanking, are investigated with FE simulations. Results show that electrical heating would result in an advantageous distribution of temperature in a 316 stainless steel work-material. A desired temperature distribution may also be achievable for a copper work-material, if laser beam is used. Both electrical heating and laser-heating enable to reduce the blanking force and increase the aspect ratio achievable by blanking. The simulation also demonstrates that both electrical heating and laser-heating can result in desired temperature-distributions at sufficiently high heating-rates, ease of implementation and application. Comparatively, electrical heating could generate more favorable temperature distribution for small-part blanking.     

工业电导信号测量仪的研制

提出了一种基于新的激励模式的电导信号测量仪.该装置采用双极性脉冲电压源作为激励源,与交流激励的电导测试系统相比,削弱了介质电极化现象,简化了电路设计,并提高了数据的采集速度和精度.同时还专门设计了具有防腐、避免电化学反应及带有温度补偿的专用电导测量探头.经测试,该系统测量准确、抗干扰能力强,满足了工业流程中溶液电导特性的实时测量要求.     

High-speed thermo-microscope for imaging thermal desorption phenomena

In this work, we describe a thermo-microscope imaging system that can be used to visualize atmospheric pressure thermal desorption phenomena at high heating rates and frame rates. This versatile and portable instrument is useful for studying events during rapid heating of organic particles on the microscopic scale. The system consists of a zoom lens coupled to a high-speed video camera that is focused on the surface of an aluminum nitride heating element. We leverage high-speed videography with oblique incidence microscopy along with forward and back-scattered illumination to capture vivid images of thermal desorption events during rapid heating of chemical compounds. In a typical experiment, particles of the material of interest are rapidly heated beyond their boiling point while the camera captures images at several thousand frames∕s. A data acquisition system, along with an embedded thermocouple and infrared pyrometer are used to measure the temperature of the heater surface. We demonstrate that, while a typical thermocouple lacks the response time to accurately measure temperature ramps that approach 150 °C∕s, it is possible to calibrate the system by using a combination of infrared pyrometry, melting point standards, and a thermocouple. Several examples of high explosives undergoing rapid thermal desorption are also presented.     

Experimental study of cure process of foam rubber: observation of cell structure

Experimental study has been made during cure process of SBR/NR foam rubber. Rubber sample with 30 mm thick, made up by stacking thin rubber sheets in layers, was packed in a metal mold, and peroxide cure was performed by transient heat conduction. Rubber heating time was changed in several steps in order to study the effects of the cure time on the blowing characteristics. Also swelling test was conducted in order to study the relation between the cell structure and the crosslink density. Typical temperature field of one-dimensional, transient heat conduction was observed, and results of the observation studies showed that the cell structure changed depending on both the position from the heating surface and the heating time, and two extreme cell structure, open-cell foam, and closed-cell foam, was clearly observed. Image analyses of the cell structure showed that the porosity distribution increased with the increase of the distance from the heating surface, and the porosity was lower for longer heating time at a same position. Average area of the foam almost took similar results for the result of the porosity, and these various quantities were correlated to the crosslink density.     

High temperature Z-meter setup for characterizing thermoelectric material under large temperature gradient

To properly estimate a thermoelectric material's performance, one should be able to characterize a single thermoelectric (TE) element with a large temperature gradient. In this work, we present an experimental setup including a Z-meter that can heat the sample to a very high temperature of 1200 °C in vacuum. The Z-meter can simultaneously measure all three thermoelectric parameters (Seebeck coefficient, thermal conductivity, and electrical conductivity), as well as measure the generated power and the efficiency for a single TE leg. Furthermore, this measurement of power conversion efficiency is used to generate a measure of the material's ZT. An in situ metallurgical bond was used to achieve low thermal (0.05 Kcm(2)∕W) and electrical (3 mΩ) contact parasitics. An integrated strain gauge ensures reproducible thermal contact. At high temperature (>600 K), radiative heat transfer is modeled and the instrument is optimized to suppress the systematic error to below 7%. The TE parameters and ZT for a bulk-sample (Bi(2)Te(3)) and a thin-film sample (ErAs:InGaAlAs) with a large temperature gradient (ΔT ～ 200 K) have been measured and are within 3%-7% of the independently measured values.     

A novel approach for temperature control in ISF supported by laser and resistance heating

Aeronautical applications often require small batches of large-scale sheet metal parts made from titanium and its alloys. Due to the low formability of titanium at room temperature, warm forming processes are necessary. Incremental sheet metal forming (ISF) is suitable for production of prototypes and small batches as well as large-scale parts. A short review of the experimental work done by international scientists in the field of warm ISF including stationary and moved temperature sensors will be presented mostly applied from the backside of the sheet metal. The present paper shows a new approach for a tool setup including a thermocouple inside of the tool. Hence, the sensor for temperature measurement was moved with the forming zone. Furthermore, a suitable closed loop control including a PID controller will be presented. The characteristics of the controller will be discussed. By means of two different warm ISF processes (ISF with resistance heating and laser-assisted ISF), the applicability of the developed setup will be analysed and evaluated. It will be shown that the experimental setup is capable to ensure minimal temperatures needed to ensure adequate formability of Ti grade 5.     

Fabricating a micromould insert using a novel process

A new method of fabricating micromould inserts that is compatible with semiconductor manufacturing is proposed. Diffusion of phosphorous at a high temperature is first used to increase the electric conductivity of the surface of the silicon wafer to generate a silicon-based seed layer for electroforming. If the process temperature and the duration of doping with phosphorous are controlled, then the electric conductivity of this novel silicon-based seed layer can be expected to equal that of a metal seed layer. Then, a structure layer of amorphous silicon is successfully formed onto the silicon-based seed layer, by plasma enhanced chemical vapor deposition (PECVD). The structure layer has none of the defects that would be present if a metal seed layer were used to replace the silicon-based seed layer. Finally, a silicon-based master microstructure was created by using ICP-RIE to etch the structure layer. The silicon-based master has been demonstrated to be useable in successfully fabricating, by electroforming, a metal micromould insert with a large area and high aspect ratio.     

Broad-band and high-temperature ultrasonic transducer fabricated using a Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO3 single crystal∕epoxy 1-3 composite

In this paper, 1-3 composites based on Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO(3) (PIMNT) single crystal and high-temperature epoxy were fabricated with various volume fractions of PIMNT single crystal ranging from 0.4 to 0.9. The electrical properties were studied as functions of PIMNT volume fraction and temperature, and it revealed that the nature of ultrahigh electromechanical coupling coefficient (0.82-0.93) and low acoustic impedance (17-19 MRayl) of the composites can be retained within a wide temperature range from room temperature to 185?°C. Single element ultrasonic transducer using the PIMNT 1-3 composite was fabricated and characterized as a function of temperature. It was found that the transducer can still work normally at high temperatures, such as 165?°C, possessing a bandwidth of 95% and insertion loss of -27 dB.     

Towards a better comprehension of plasma formation and heating in high performances electron cyclotron resonance ion sources (invited)

Further improvements of electron cyclotron resonance ion sources (ECRIS) output currents and average charge state require a deep understanding of electron and ion dynamics in the plasma. This paper will discuss the most recent advances about modeling of non-classical evidences like the sensitivity of electron energy distribution function to the magnetic field detuning, the influence of plasma turbulences on electron heating and ion confinement, the coupling between electron and ion dynamics. All these issues have in common the non-homogeneous distribution of the plasma inside the source: the abrupt density drop at the resonance layer regulates the heating regimes (from collective to turbulent), the beam formation mechanism and emittance. Possible means to boost the performances of future ECRIS will be proposed. In particular, the use of Bernstein waves, in preliminary experiments performed at Laboratori Nazionali del Sud (LNS) on MDIS (microwave discharge ion sources)-type sources, has permitted to sustain largely overdense plasmas enhancing the warm electron temperature, which will make possible in principle the construction of sources for high intensity multicharged ions beams with simplified magnetic structures.     

Thermal characteristics of graphite foam thermosyphon for electronics cooling

Graphite foams consist of a network of interconnected graphite ligaments and are beginning to be applied to thermal management of electronics. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a specific thermal conductivity about five times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. For the purpose of graphite foam thermosyphon design in electronics cooling, various effects such as graphite foam geometry, sub-cooling, working fluid effect, and liquid level were investigated in this study. The best thermal performance was achieved with the large graphite foam, working fluid with the lowest boiling point, a liquid level with the exact height of the graphite foam, and at the lowest sub-cooling temperature.     

A high-vacuum deposition system for in situ and real-time electrical characterization of organic thin-film transistors

We present a home-built high-vacuum system for performing organic semiconductor thin-film growth and its electrical characterization during deposition (real-time) or after deposition (in situ). Since the environment conditions remain unchanged during the deposition and electrical characterization process, a direct correlation between growth mode and electrical properties of thin film can be obtained. Deposition rate and substrate temperature can be systematically set in the range 0.1-10 ML∕min and RT-150 °C, respectively. The sample-holder configuration allows the simultaneous electrical monitoring of up to five organic thin-film transistors (OTFTs). The OTFTs parameters such as charge carrier mobility μ, threshold voltage V(TH), and the on-off ratio I(on)∕I(off) are studied as a function of the semiconductor thickness, with a submonolayer accuracy. Design, operation, and performance of the setup are detailed. As an example, the in situ and real-time electrical characterization of pentacene TFTs is reported.