PTC发热器件的老化问题

本文针对翅片式PTC发热器件的功率衰退──老化问题，从PTC片子的生产工艺，居里温度点，电板材料及粘接工艺几个方面论述了出现老化的原因，并从生产角度提出了改进的措施。

提高电热设备效率的措施

编辑同志：请问提高电热设备效率的措施有哪些？（河南省杞县陈家辉）陈家辉同志：①严格控制使片j，尽量以一次能源直接加热；②采用高效电热器件，提高电热转换效率；③搞好电热设备保温，提高热效率；④采用自动控制，使电热设备在最佳状态运行；

沥青加热新工艺及节能技术

介绍了沥青加热新工艺,加热源采用最高温度小于350°的电热器件,直接插人锅内的沥青加热,输送沥青管道改为自然重力管道输送,管道保温工艺改为电加热保温方式,加热控制利用微机集散自动控制以实现最小能耗。改造后的沥青加热新工艺全年可收益52.31万元。

方形落地式变频空气调节器凝露原因分析及改善

凝露问题是空调质量问题之一,严重影响用户的生活和工作环境。本文基于热力学分析凝露的成因,针对变频空调提出改善措施,可通过增加电控逻辑及电热器件改善凝露问题。

管道防冻电伴热设计思路及选型方案

随着时代进步，科技发展，越来越多的高新技术产品被广泛的应用到各个行业的各个领域中，“自控温电伴热带”产品，作为当今世界上先进的智能型电热器件，已经被广泛的应用在众多行业，如环保、石油、建筑、化工、钢铁、冷冻等等的各个领域，为管道、罐体、设备等的伴热保温问题提供了良好的解决方案。

看点

“中国好技术” 近日，北方稀土新型镧铁硼系贮氢合金、铬酸镧陶瓷电热器件等7个项目获得“中国好技术”称号。据了解，“中国好技术”评选活动由中国生产力促进中心会同国家相关机构和企业共同发起和举办，活动共征集科技创新和可产品化技术成果790项，经过40多位知名专家的两轮严格评审，最终遴选出154项先进适用、贴近民生的“中国好技术”成果。

Characterization of Oxide Charge During Hot-Carrier Degradation of Ultrathin Gate pMOSFETs--Investigated by Charge Pumping Technique

The generation of oxide charge for 4nm pMOSFETs under hot-carrier stress is investigated by the charge pumping measurements.Firstly,the direct experimental evidences of logarithmic time dependence of hole trapping is observed for pMOSFETs with different channel lengths under hot-carrier stress.Thus,the relationships of oxide charge generation,including electron trapping and hole trapping effects,with different stress voltages and channel lengths are analyzed.It is also found that there is a two-step process in the generation of oxide charge for pMOSFETs.For a short stress time,electron trapping is predominant,whereas for a long stress time,hole trapping dominates the generation of oxide charge.

An integrated thermoelectric-assisted photoelectrochemical system to boost water splitting

Common solar-driven photoelectrochemical(PEC) cells for water splitting were designed by using semiconducting photoactive materials as working photoelectrodes to capture sunlight. Due to the thermodynamic requirement of 1.23 eV and kinetic energy loss of about 0.6 eV, a photo-voltage of 1.8 V produced by PEC cells is generally required for spontaneous water splitting. Therefore, the minimum bandgap of1.8 eV is demanded for photoactive materials in single-photoelectrode PEC cells, and the bandgap of about 1 eV for back photoactive materials is appropriate in tandem PEC cells. All these PEC cells cannot effectively utilize the infrared light from 1250 to 2500 nm. In order to realize the full spectrum utilization of solar light, here, we develop a solar-driven PEC water splitting system integrated with a thermoelectric device. The key feature of this system is that the thermoelectric device produces a voltage as an additional bias for the PEC system by using the temperature difference between the incident infrared-light heated aqueous electrolyte in the PEC cell as the hot source and unirradiated external water as the cold source. Compared to a reference PEC system without the thermoelectric device, this system has a significantly improved overall water splitting activity of 1.6 times and may provide a strategy for accelerating the application of full spectrum solar light-driven PEC cells for hydrogen production.

Low carrier concentration leads to high in-plane thermoelectric performance in n-type SnS crystals

As a simple binary compound, p-type SnS shows great competitiveness in thermoelectrics due to the certain appealing carrier and phonon transport behaviors, coupled with its cost-effectiveness, earth-abundance and environmental compatibility. To promote the application of low-cost thermoelectric devices, we synthesized n-type SnS crystals through bromine doping. Herein, we report a high in-plane power factor of ~28 μW cm^(-1)K^(-2), and attribute it to an outstanding in-plane carrier mobility in the crystal form and the large Seebeck coefficient benefitting from the low carrier concentration. The calculations of elastic properties show that the low lattice thermal conductivity in SnS is closely related to its strong anharmonicity. Combining the excellent electrical transport properties with low thermal conductivity, a final ZT of ~0.4 is attained at 300 K, projecting a conversion efficiency of ~5% at 873 K along the in-plane direction.

Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology

During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cool- ing techniques for electronic and microelectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection,liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.

Hierarchically porous composite fabrics with ultrahigh metal–organic framework loading for zero-energy-consumption heat dissipation

The long-term safe operation of high-power equipment and integrated electronic devices requires efficient thermal management,which in turn increases the energy consumption further.Hence,the sustainable development of our society needs advanced thermal management with low,even zero,energy consumption.Harvesting water from the atmosphere,followed by moisture desorption to dissipate heat,is an efficient and feasible approach for zero-energy-consumption thermal management.However,current methods are limited by the low absorbance of water,low water vapor transmission rate(WVTR)and low stability,thus resulting in low thermal management capability.In this study,we report an innovative electrospinning method to process hierarchically porous metal–organic framework(MOF)composite fabrics with high-efficiency and zero-energy-consumption thermal management.The composite fabrics are highly loaded with MOF(75 wt%)and their WVTR value can be up to 3138 g m^(-2) d^(-1).The composite fabrics also exhibit stable microstructure and performance.Under a conventional environment(30℃,60%relative humidity),the composite fabrics adsorb water vapor for regeneration within 1.5 h to a saturated value Wsat of 0.614 g g^(-1),and a corresponding equivalent enthalpy of 1705.6 J g^(-1).In the thermal management tests,the composite fabrics show a strong cooling capability and significantly improve the performance of thermoelectric devices,portable storage devices and wireless chargers.These results suggest that hierarchically porous MOF composite fabrics are highly promising for thermal management of intermittent-operation electronic devices.

Excellent thermoelectric performance of boron-doped n-type Mg_(3)Sb_(2)-based materials via the manipulation of grain boundary scattering and control of Mg content

Thermoelectric devices require thermoelectric materials with high figure-of-merit(ZT)values in the operating temperature range.In recent years,the Zintl phase compound,n-Mg_(3)Sb_(2),has received much attention owing to its rich chemistry and structural complexity.However,it hardly achieves high ZT values throughout the medium temperature range.Herein,by increasing the sintering temperature as much as possible,we successfully increased the average grain size of the compound by 15 times,and the grain boundary scattering was manipulated to obtain high carrier mobility of up to 180 cm^(2)V^(-1)s^(-1).Simultaneously,we optimized the Mg content for ultralow lattice thermal conductivity.We first doped the Mg_(3)Sb_(2)-based materials with boron for higher sintering temperature,good thermal stability,and higher hardness.The synergistic optimization of electrical and thermal transport resulted in excellent ZT values(0.62 at 300 K,1.81 at 773 K)and an average ZT of 1.4(from300 to 773 K),which are higher than the state-of-the-art values for n-type thermoelectric materials,demonstrating a high potential in device applications.

Characterization of the thermal conductivity of La0.95r0.05CoO3 thermoelectric oxide nanofibers

Thermoelectric oxide nanofibers prepared by electrospinning are expected to have reduced thermal conductivity when compared to bulk samples. Measurements of nanofibers＇ thermal conductivity is challenging since it involves sophisticated sample preparation methods. In this work, we present a novel method suitable for measurements of thermal conductivity of a single nanofiber. A microelectro- mechanical （MEMS） device has been designed and fabricated to perform thermal conductivity measurements on a single nanofiber. A special Si template was designed to collect and transfer individual nanofibers onto a MEMS device. Pt was deposited by a focused ion beam to reduce the effective length of a prepared nanofiber. La0.95r0.05CoO3 nanofibers with diameters of 140 run and 290 run were studied and characterized using this approach at room temperature. Measured thermal conductivities yielded values of 0.7W-m 1-K-1 and 2.1 W.m-I＇K-1, respectively. Our measurements in La0.95r0.05CoO3 nanofibers confirmed that a decrease of linear dimensions has a profound effect on its thermal conductivity.

Numerical Study of Natural Convection on Horizontal Strips Embedded in an Vertical Adiabatic Substrate

A full solution of two-dimensional Navier-Stokes and energy equation was conducted numerically to analyze the natural convection of the horizontal strip with an adiabatic substrate. The main features of such convection are: (i) the leading and trailing edge effect, (ii) the non-boundary layer effect, and (iii) the side edge effect. The results are compared with the boundary layer theory and experimental data.

Dual effect of NH4F additive in the hydrothermal deposition of antimony selenosulfide thin film for high-performance solar cells

Hydrothermal deposition of antimony selenosulfide(Sb_(2)(S,Se_(3)))has enabled solar cell applications to surpass the 10%efficiency threshold.This deposition process involves the reaction of three precursor materials:Sb,S,and Se.However,this process generates an unfavourable gradient of Se and S anions in the Sb_(2)(S,Se)_(3)film,which limits further efficiency improvements.Herein,we demonstrate how NH_(4)F can be used as an additive to regulate the band gradient of the Sb_(2)(S,Se)_(3)and modify the surface of the CdS electron-transporting layer.On the one hand,NH_(4)F inhibits the decomposition of Na_(2)S_(2)O_(3)and selenourea,which optimizes the deposition process and allows for adjustment of the Se/S ratio and their distribution in the Sb_(2)(S,Se)_(3)film.On the other hand,hydrolysis of NH_(4)F induces dissolution and redeposition of CdS,thereby effectively improving the morphology and crystallinity of the CdS substrate.Finally,the dual effect of NH_(4)F enables improved surface morphology and energy alignment of the Sb_(2)(S,Se)_(3)film,thus yielding a maximum efficiency of 10.28%,a 12%improvement over the control device.This study demonstrates an effective strategy for simultaneously modifying a sulfide-based substrate and regulating the element distribution during the deposition of a metal chalcogenide film for optoelectronic device applications.

Experimental study on high-power LEDs integrated with micro heat pipe

Micro heat pipe(MHP) is applied to implement the efficient heat transfer of light emitting diode(LED) device.The fabrication of MHP is based on micro-electro-mechanical-system(MEMS) technique,15 micro grooves were etched on one side of silicon(Si) substrate,which was then packaged with aluminum heat sink to form an MHP.On the other side of Si substrate,three LED chips were fixed by die bonding.Then experiments were performed to study the thermal performance of this LED device.The results show that the LED device with higher filling ratio is better when the input power is 1.0 W; with the increase of input power,the optimum filling ratio changes from 30% to 48%,and the time reaching stable state is reduced; when the input power is equal to 2.5 W,only the LED device with filling ratio of 48% can work normally.So integrating MHP into high-power LED device can implement the effective control of junction temperature.

Forced Convective Air Cooling from Electronic Component Arrays in a Parallel Plate Channel

This paper discusses air forced convection heat transfer from inline protruding elements arranged in eight rows. The streamwise and spanwise spacings between elements were varied using a splitter plate that can be positioned at three different modular configurations. A set of empirical formulas waspresented to correlate the experimental data for the design of air cooling systems. Arrays of components with one odd-size module have been tested also. Experimental results show that blocks near the entrance and behind the odd-size module have improved performance compared with uniform arrangements. Accordingly, temperature sensitive components are suggested to be arranged in these locations.

Thermoelectric transport across graphene/hexagonal boron nitride/graphene heterostructures

We report thermoelectric transport measurements across a graphene/hexagonal boron nitride （h-BN）/graphene heterostructure device. Using an AC lock-in technique, we are able to separate the thermoelectric contribution to the I-V characteristics of these important device structures. The temperature gradient is measured optically using Raman spectroscopy, which enables us to explore thermoelectric transport produced at material interfaces, across length scales of just 1-2 nm. Based on the observed thermoelectric voltage （AV） and tem- perature gradient （AT）, a Seebeck coefficient of -99.3 μV/K is ascertained for the heterostructure device. The obtained Seebeck coefficient can be useful for understanding the thermoelectric component in the cross-plane I-V behaviors of emerging 2D heterostructure devices. These results provide an approach to probing thermoelectric energy conversion in two-dimensional layered heterostructures.

A preliminary experimental validation of superposition strategy in thermal management of integrated circuit with multiple hot-spots

Thermal management is a key issue in the integrated circuit(IC)design.In this paper,the superposition strategy was experimentally validated using a modeling IC device,which was fabricated by laboratory-level microfabrication technique.Metal thin film resistors on the top of dielectric layer were used to analogize the multiple hot-spots in the modeling IC device.The measured temperature rise with multiple hot-spots agrees well with the predictions given by the superposition calculations.With the help of the superposition strategy,thermal management of IC device can be significantly simplified by decomposing the system into sub-systems and optimizing each part individually.The influence coefficients in the superposition strategy extracted from the experimental measurement offer the IC designers a useful engineering tool to facility the thermal optimization and evaluate the thermal performance of IC devices.