Gepulstes Heißdraht‐Vakuummeter mit Pirani‐Sensor. Pulsed hot filament vacuum gauge with Pirani sensor

The hot filament gauge according to Pirani is usually operated in the stationary mode in which the applied electrical heating power equals the total heat losses. The heat loss by the thermal conductivity of the gas increases with increasing pressure which allows to derive the measuring signal for the pressure. However, at pressures above some 100 mbar the thermal conductivity starts to saturate which results in a strong decrease of the measuring accuracy of the hot wire gauge. A few years ago, a proposal was published to make use of the heat capacity of the gas which is proportional to pressure. Subject of the present paper is a decisive investigation of the dynamical behaviour of the Pirani sensor. For this purpose, both the heating and cooling processes of the wire were measured. As follows from the experimental data and theoretical estimations, a considerable amount of energy is stored in the gas at atmospheric pressure, i.e. much more than in the wire, but this energy content has only a small effect on heating and cooling rates. Reasons for this behaviour are the strong heat losses by the thermal conductivity of the gas, the rather weak thermal coupling between the wire and surrounding as well as the smallness of the average temperature increase of the gas. Furthermore, an intermittent operation of the Pirani sensor was tested in which the voltage applied to the wire gradually increases. Advantages of this operation mode are a significant improvement of the measuring characteristics above 100 mbar and a substantial reduction of the power consumption.     

Dynamical behaviour of the Pirani sensor

The conventional Pirani gauge has poor performance at atmospheric pressures since here the stationary thermal conductivity of gases saturates. In contrast, the heat capacity of the gas does not saturate. It is accessible by a pulsed operation of the wire. The present paper gives an investigation of the Pirani gauge signal for the non-stationary heating and cooling processes. As follows from the experimental data and theoretical estimates, at atmospheric pressure a substantial amount of energy is stored in the gas, much more than in the wire. However, the energy of the gas has only a rather small effect on heating and cooling rates. The reasons for this behaviour are the strong heat losses due to the thermal conductivity of the gas, the rather weak thermal coupling between the wire and surrounding gas as well as the smallness of the average temperature elevation of the gas over ambient. Nevertheless, the effect of the heat capacity of the gas on the rates is sufficiently strong to provide a usable measuring signal. The pulsed operation of the wire and the recording of the time-dependent signal can be accomplished by a smart controller. Such an instrument would provide a substantially improved performance of the Pirani sensor at pressures above 100 mbar.     

Physikalische Grundlagen des Wärmeleitungs-Vakuummeters

In the common design of a thermal conductivity vacuum gauge according to Pirani, a thin wire is heated by an electric current and the heat loss from the wire by the heat transfer of the surrounding gas is used to derive the gas pressure. Other mechanisms of heat loss are the thermal conductivity of the wire, which transports heat to its cold ends, and the thermal radiation. In the present paper the various mechanisms of heat loss in an axially symmetric setup are investigated in detail and described by analytical formulae. Operation of the sensor by a regulated power supply allows to keep the electrical resistance of the wire and thus the mean wire temperature constant. However, changes in gas pressure affect the temperature profile along the wire and, concomitantly, the heat transfer by the wire towards its ends and the loss by thermal radiation. Experimental data of the heating power vs. pressure obtained with nitrogen and hydrogen in a typical setup are presented and compared with calculated values.     

Self‐Regulated Smectic Emulsion with Switchable Lasing Application

A structurally reversible smectic liquid crystal (LC) emulsion made of semifluorinated rod‐type molecules in silicon oil, which is controlled by simple heating and cooling, is presented. Without adding any kind of additives, such as surfactants, polymers or emulsifiers, and without using any special tools, such as microfluidics or gas bubbling, the LC molecules spontaneously form monodisperse spherical and myelin‐like structures upon cooling from the isotropic temperature. The LC emulsion can easily trap guest materials, providing a platform for repeatable and reliable switchable emulsification. For example, this interesting system enables the realization of an on–off lasing system by confining fluorescent dyes in the LC droplets.     

Entwicklung des dynamischen Abschreckens in Hochdruck‐Gasabschreckanlagen

Development of dynamic quenching in high pressure gas quenching cells A new quenching sensor was developed for measuring the quenching conditions in high‐pressure gas quenching cells. This QC³‐Sensor (Quench Control in Cold Chambers) measures the cooling curve in a pre‐heated sensor‐head. The sensor can be used for process‐monitoring, process‐control and process‐steering. This quenching sensor was successfully tested for the precise initiation of “dynamic quenching”. The newly developed dynamic quenching consists of a gas‐quench with varying quenching intensity. It was shown on simple rings and on gear wheels made of the steel grade 16MnCr5 that the dynamic quenching has the potential to reduce heat treatment distortions. Especially the spread of the geometry‐changes can be reduced significantly, if the quenching intensity is lowered during quenching.     

NiTi形状记忆合金基本驱动特性

研究了预应变ＮｉＴｉ形状记忆合金的基本驱动特性，结果表明，加热和冷却过程回复力存在滞后行为；卸载过程中应力与应变具有与加热、冷却过程相关的非线性关系；卸尖力随卸载应变速率增加而降低，此外研究了预应变ＮｉＴｉ合金丝产生回复力后对外应力的响应行为。     

Virtuelles Werkstoff‐ und Prozessdesign funktionaler Schichten

Virtual Material‐ and Processdesign of Functional Coatings Thermally sprayed and plasma transferred arc clad coatings are often used to improve the surface properties of mechanical parts with regard to an improved wear and corrosion behavior. New coating processes and applications can be developed, if it is possible to control the coating microstructure by a defined management of the process parameters. Simulation can be used to get a detailed understanding of the process‐material interaction for a defined controlling of the process parameters with less experimental effort. This allows a systematic variation of the coating structure and to calculate the parameter set which represents the best compromise between a high deposition rate and low residual stresses in the coating. In order to model thermal spraying, the following sub‐processes are considered: gas flow, material supply, heating and accelerating of particles, particle impact on the substrate, coating formation, solidification and formation of residual stresses. The results presented in this paper will demonstrate the influence of the process parameters on particle properties and subsequently on the splat formation, the coating formation and the coating microstructure. Controlling different process parameters like material injection conditions and substrate properties, the heating, cooling and solidification behavior of the particles and the coating structure can be influenced significantly.     

Programmable selectivity for GC with series-coupled columns using pulsed heating of the second column

A series-coupled ensemble of a nonpolar dimethyl polysiloxane column and a polar trifluoropropylmethyl polysiloxane column with independent at-column heating is used to obtain pulsed heating of the second column. For mixture component bands that are separated by the first column but coelute from the column ensemble, a temperature pulse is initiated after the first of the two components has crossed the column junction point and is in the second column, while the other component is still in the first column. This accelerates the band for the first component. If the second column cools sufficiently prior to the second component band crossing the junction, the second band experiences less acceleration, and increased separation is observed for the corresponding peaks in the ensemble chromatogram. High-speed at-column heating is obtained by wrapping the fused-silica capillary column with resistance heater wire and sensor wire. Rapid heating for a temperature pulse is obtained with a short-duration linear heating ramp of 1000 degrees C/min. During a pulse, the second-column temperature increases by 20-100 degrees C in a few seconds. Using a cold gas environment, cooling to a quiescent temperature of 30 degrees C can be obtained in approximately 25 s. The effects of temperature pulse initiation time and amplitude on ensemble peak separation and resolution are described. A series of appropriately timed temperature pulses is used to separate three coeluting pairs of components in a 13-component mixture.     

Application of ZnO single-crystal wire grown by the thermal evaporation method as a chemical gas sensor for hydrogen sulfide

A zinc oxide single-crystal wire was synthesized for application as a gas-sensing material for hydrogen sulfide, and its gas-sensing properties were investigated in this study. The gas sensor consisted of a ZnO thin film as the buffer layer and a ZnO single-crystal wire. The ZnO thin film was deposited over a patterning silicon substrate with a gold electrode by the CFR method. The ZnO single-crystal wire was synthesized over the ZnO thin film using zinc and activated carbon as the precursor for the thermal evaporation method at 800 degrees C. The electrical properties of the gas sensors that were prepared for the growth of ZnO single-crystal wire varied with the amount of zinc contained in the precursor. The charged current on the gas sensors increased with the increasing amount of zinc in the precursor. It was concluded that the charged current on the gas sensors was related to ZnO single-crystal wire growth on the silicon substrate area between the two electrodes. The charged current on the gas sensor was enhanced when the ZnO single-crystal wire was exposed to a H2S stream. The experimental results obtained in this study confirmed that a ZnO single-crystal wire can be used as a gas sensor for H2S.     

Development of a virtual variable-speed compressor power sensor for variable refrigerant flow air conditioning system

This paper proposed a universal virtual variable-speed compressor power (VVCP) sensor for VRF system based on 20-coefficient model. Compressor power can be obtained by the VVCP sensor using three input parameters (frequency, condensing temperature and evaporation temperature) which are measured by system itself. The performance of the proposed VVCP sensor is evaluated using experiments data. Experimental conditions include cooling, heating and non-standard refrigerant charge levels. The result shows that the mean square percentage errors (MSPE) are 9.9% under cooling conditions and 7.96% under heating conditions. The MSPE are 9.88% at steady state and 9.75% at dynamic state when the VVCP sensor is applied under nine different refrigerant charge levels. It demonstrated that the proposed VVCP sensor can obtain compressor power under cooling, heating and non-standard refrigerant charge levels, which could be applied to do operational monitoring and fault detection and diagnosis for VRF system at low cost.     

Thermochromism from Ultrathin Colloidal Sb2Se3 Nanowires Undergoing Reversible Growth and Dissolution in an Amine–Thiol Mixture

Liquid‐based thermochromics can be incorporated into an arbitrarily shaped container and provide a visual map of the temperature changes within its volume. However, photochemical degradation, narrow temperature range of operation, and the need for stringent encapsulation processes are challenges that can limit their widespread use. Here, a unique solution‐based thermochromic comprising ultrathin colloidal Sb₂Se₃ nanowires in an amine–thiol mixture is introduced. The nanowires undergo reversible growth and dissolution with repeated cycles of heating and cooling between 20 and 160 °C, exhibiting intense and contrasting color changes during these processes. Furthermore, the transition temperature in which a change in color first appears can be continuously tuned over a range larger than 100 °C by introducing controlled amounts of Sn²⁺. The colloidal nanowire dispersion in the amine–thiol mixture retains its thermochromic properties over hundreds of temperature cycles, continuous heating at 80 °C over months, and shelf life of up to 2 years in an open container under ambient conditions. To illustrate its utility as a robust liquid thermochromic, the nanowire solution is coated onto standard filter paper and its uses as a rewritable surface by thermal scribing, as well as an inexpensive means of visualizing the temperature distribution of an anisotropically heated block are demonstrated.     

Temperature‐Controlled High‐Speed AFM: Real‐Time Observation of Ripple Phase Transitions

With nanometer lateral and Angstrom vertical resolution, atomic force microscopy (AFM) has contributed unique data improving the understanding of lipid bilayers. Lipid bilayers are found in several different temperature‐dependent states, termed phases; the main phases are solid and fluid phases. The transition temperature between solid and fluid phases is lipid composition specific. Under certain conditions some lipid bilayers adopt a so‐called ripple phase, a structure where solid and fluid phase domains alternate with constant periodicity. Because of its narrow regime of existence and heterogeneity ripple phase and its transition dynamics remain poorly understood. Here, a temperature control device to high‐speed atomic force microscopy (HS‐AFM) to observe dynamics of phase transition from ripple phase to fluid phase reversibly in real time is developed and integrated. Based on HS‐AFM imaging, the phase transition processes from ripple phase to fluid phase and from ripple phase to metastable ripple phase to fluid phase could be reversibly, phenomenologically, and quantitatively studied. The results here show phase transition hysteresis in fast cooling and heating processes, while both melting and condensation occur at 24.15 °C in quasi‐steady state situation. A second metastable ripple phase with larger periodicity is formed at the ripple phase to fluid phase transition when the buffer contains Ca²⁺. The presented temperature‐controlled HS‐AFM is a new unique experimental system to observe dynamics of temperature‐sensitive processes at the nanoscopic level.     

Supercritical Fluid–Liquid–Solid (SFLS) Synthesis of Si and Ge Nanowires Seeded by Colloidal Metal Nanocrystals

Semiconductor nanowires, 5 to 20 nm in diameter and micrometers in length, appear to be promising candidates for a variety of new technologies, including computing, memory, and sensor applications. Suitable for these applications, silicon (Si) and germanium (Ge) nanowires ranging from 4 to 30 nm in diameter and micrometers in length can be produced in high temperature supercritical fluids by thermally degrading organosilane or organogermane precursors in the presence of organic‐monolayer‐protected gold nanocrystals. Although gas phase vapor–liquid–solid (VLS) methods can be used to produce a variety of different nanowire materials, high temperature supercritical fluids provide wire size control through nanocrystal size selection prior to synthesis, and high product yields due to the high precursor solubility.     

Shape‐Memory Topographies on Nickel–Titanium Alloys Trained by Embossing and Pulse Electrochemical Machining

The two‐way shape‐memory effect (TWSME) in Nickel–titanium (NiTi) alloys is of interest for applications in aerospace, biomedicine, and microengineering due to its reversible shape recovery. In this study, the authors demonstrate two approaches to obtain switchable surface structures using the TWSME. Samples are structured using two surface geometries by either cold embossing, or pulse electrochemical machining (PECM). After planarization, a change from optically smooth to structured and vice versa is observed. The switch is induced through heating and cooling the sample above and below the phase transformation temperature. The protrusions reflect the pattern applied by the two processes. Both methods are promising for preparation of switchable metallic surfaces on larger areas.     

Fabrication of Flexible MoS2 Thin‐Film Transistor Arrays for Practical Gas‐Sensing Applications

By combining two kinds of solution‐processable two‐dimensional materials, a flexible transistor array is fabricated in which MoS₂ thin film is used as the active channel and reduced graphene oxide (rGO) film is used as the drain and source electrodes. The simple device configuration and the 1.5 mm‐long MoS₂ channel ensure highly reproducible device fabrication and operation. This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility. Compared to using rGO thin film as the active channel, this new gas sensor exhibits much higher sensitivity. Moreover, functionalization of the MoS₂ thin film with Pt nanoparticles further increases the sensitivity by up to ～3 times. The successful incorporation of a MoS₂ thin‐film into the electronic sensor promises its potential application in various electronic devices.     

Mit Wärme Kälte erzeugen

A steam jet cooling plant Steam jet cooling plants with water as a medium to be cooled are preferably used to chill down to 0°C and below. Since most industrial enterprises have steam and cooling water supply nets already, steam jet cooling plants can be installed there quite easily. They are characterised by ‐ low investment costs, ‐ robust and simple construction, ‐ immediate response to changes of the required cooling capacity, ‐ very low maintenance and spare parts costs. Under certain conditions even hot water or waste steam (low‐pressure, vacuum or wet steam) can be used as a motive medium. A surplus of steam, perhaps, which occurs during the summer may be used for cooling purposes, easily. Below a steam jet cooling plant for a district cooling system is described which has been installed with the company Energieversorgung Gera GmbH (Gera, Germany). Since then, it has been worked successfully. The maximum chilling capacity is 600 kW (12°C/6°C).     

Surface Aspects in Fatigue of Shape Memory Alloys (SMA)

The present paper briefly reviews the role of surfaces in fatigue of shape memory alloys (SMAs). When polished and defect free austenitic surfaces are cooled to lower temperatures, the martensitic transformation creates a pattern of surface upheavals; and an inverse pattern forms when polished and defect free martensite is heated. In full transformation cycles (heating followed by cooling or cooling followed by heating) high quality surfaces can only be re‐established if no fatigue occurs. After multiple cycling intrusions and extrusions can be detected which represent fatigue damage accumulation. Cracks can grow from extrusions and intrusions. We also show that fatigue cracking can start from surface defects which are for example introduced by wire drawing. We then briefly discuss surface treatments which are intended to improve fatigue resistance of shape memory alloys. These may consist in the modification of the SMA microstructure in the surface region (by deformation or diffusion treatments). They can also involve coating procedures where other elements are deposited on the SMA surface. However, SMA performance and the intensity of exploitable SM effects are usually reduced by surface treatments.     

Realization of Nanolene: A Planar Array of Perfectly Aligned,Air‐Suspended Nanowires

Air suspension and alignment are fundamental requirements to make the best use of nanowires' unique properties; however, satisfying both requirements is very challenging due to the mechanical instability of air‐suspended nanowires. Here, a perfectly aligned air‐suspended nanowire array called “nanolene” is demonstrated, which has a high mechanical stability owing to a C‐channel‐shaped cross‐section of the nanowires. The excellent mechanical stability is provided through geometrical modeling and finite element method simulations. The C‐channel cross‐section can be realized by top‐down fabrication procedures, resulting in reliable demonstrations of the nanolenes with various materials and geometric parameters. The fabrication process provides large‐area uniformity; therefore, nanolene can be considered as a 2D planar platform for 1D nanowire arrays. Thanks to the high mechanical stability of the proposed nanolene, perfectly aligned air‐suspended nanowire arrays with an unprecedented length of 1 mm (aspect ratio ≈5100) are demonstrated. Since the nanolene can be used in an energy‐efficient nanoheater, two energy‐stringent sensors, namely, an air‐flow sensor and a carbon monoxide gas sensor, are demonstrated. In particular, the gas sensor achieves sub‐10 mW operations, which is a requirement for application in mobile phones. The proposed nanolene will pave the way to accelerate nanowire research and industrialization by providing reliable, high‐performance nanowire devices.     

Extraordinarily Stretchable All‐Carbon Collaborative Nanoarchitectures for Epidermal Sensors

Multifunctional microelectronic components featuring large stretchability, high sensitivity, high signal‐to‐noise ratio (SNR), and broad sensing range have attracted a huge surge of interest with the fast developing epidermal electronic systems. Here, the epidermal sensors based on all‐carbon collaborative percolation network are demonstrated, which consist 3D graphene foam and carbon nanotubes (CNTs) obtained by two‐step chemical vapor deposition processes. The nanoscaled CNT networks largely enhance the stretchability and SNR of the 3D microarchitectural graphene foams, endowing the strain sensor with a gauge factor as high as 35, a wide reliable sensing range up to 85%, and excellent cyclic stability (>5000 cycles). The flexible and reversible strain sensor can be easily mounted on human skin as a wearable electronic device for real‐time and high accuracy detecting of electrophysiological stimuli and even for acoustic vibration recognition. The rationally designed all‐carbon nanoarchitectures are scalable, low cost, and promising in practical applications requiring extraordinary stretchability and ultrahigh SNRs.     

冷热水联供机组性能实验研究

建立了燃气内燃机驱动的冷热水联供系统,测量了空调名义工况条件下机组的制冷和供热性能,并实验研究了内燃机的转速对机组制冷和供热的影响特性。实验结果表明系统在空调名义工况条件下的制冷量467．1kW,供热量为148．7kW,一次能源利用率达1．9,与常规电制冷＋锅炉供热相比能源节约率达37．8％。在实验测试的内燃机转速范围内制冷系统的制冷量和余热回收供热量随内燃机转速的降低而降低,但制冷系统和冷热水联供系统能源利用率均随内燃机转速的降低而升高,表明机组在部分负荷运行时,应优先调节内燃机的转速,从而确保系统具有较高的能源利用率。该联供系统有效回收利用了内燃机的余热,提高了能源利用率,商业化前景较好。