(Cr1‐x,Alx)N ein Review über ein vielseitig einsetzbares Schichtsystem

(Cr_1‐x,Al_x)N a review about a multi‐purpose coating system Nitride based coatings claimed a big market share for PVD‐coatings. Especially in the field for high temperature die casting and cutting operations chromium based coatings are well used. These coatings are also used in low temperature processes for the coating of machine parts. In the beginning of the nineties first examinations are done on the ternary system Chromium‐Aluminium‐Nitride. This system shows an excellent corrosion behaviour against many different liquids, but gains also a high hardness for a good wear behaviour. By changing the AlN to CrN content and the coating design CrAlN opens up a wide range for different coating applications. A major step for machine parts was the reducing of coating process temperature beneath 200 °C. This was only possible by using pulsed power supplies. CrAlN shows a very good performance on the fast growing market of coated machine parts e.g. on spindle bearings.     

电除尘器智能管理软件的开发研究

文章以火电厂静电除尘器集散控制系统为研究对象,开发电除尘器智能管理软件.实现对电除尘器的实时监控;建立专家知识库,通过调用知识库内容对电除尘器进行故障在线判断;以烟气出口粉尘浊度值为依据,进行闭环控制,实现能量管理;根据煤种以及锅炉燃烧和运行工况对电除尘器进行效率预测.     

Propane heat pump with low refrigerant charge: design and laboratory tests

Independently of the choice of refrigerant, environmental and or safety issues can be minimised by reducing the amount of refrigerant charge per heat pump or refrigeration system. In the investigation reported here, a laboratory test rig was built, simulating a water-to-water heat pump with a heating capacity of 5 kW. The system was designed to minimize the charge of refrigerant mainly by use of mini-channel aluminium heat exchangers. It was shown that the system could be run with 200 g of propane at typical Swedish operating conditions without reduction of the COP compared to a traditional design. Additional charge reduction is possible by selecting proper compressor lubrication oils or by using a compressor with less lubrication oil.     

A note on the Chen correlation of saturated flow boiling heat transfer

The Chen (Ind. Eng. Chem. Process Des. Dev., 1966, 5(3): 322–329) correlation of saturated flow boiling heat transfer is one of the most influential flow boiling heat transfer correlations. It adopted the additive concept and incorporated the Reynolds number factor F and the suppression factor S. Chen presented F and S as the best-fit curves without any parametric equation. However, the parametric equations of F and S were widely used in citing the Chen work, among which some were not accurate, and some had typos in the original sources and then used by others. The objective of this paper is to point out the incorrect and inaccurate equations in the literature. For this purpose, the existing expressions of F and S in the available literature are presented and compared with the Chen best-fit curves. The work provides a reference for the correct use of the Chen correlation.     

Flow boiling heat transfer of carbon dioxide with PAG-type lubricating oil in pre-dryout region inside horizontal tube

A flow boiling heat transfer model for horizontal tubes is proposed for CO₂ with entrained polyalkylene glycol (PAG) type lubricating oil in the pre-dryout region. A general power law-type model with a power number of 3 is used together with the average thermodynamic properties of the CO₂–oil mixture. A convective enhancement factor (F) is recommended according to the relationship between the Lockhart–Martinelli parameter and the ratio α_tp/α_l, which was obtained based on previous experimental results for CO₂ and oil. A new suppression factor (S) is introduced that comprises a suppression term for forced convection and oil concentration term for bubble generation. A comparison of six correlations showed that the proposed correlation can depict the influence of the mass and heat fluxes on both nucleate and convection boiling reasonably well.     

Optimal design of a light commercial freezer through the analysis of the combined effects of capillary tube diameter and refrigerant charge on the performance

In this work, a discussion on a methodology to optimize the performance of a commercial freezer by using a simulation tool is presented. In order to provide a practical tool for deciding the best combination of refrigerant charge and capillary tube diameter, the results of the numerical studies are shown in the form of two-dimensional maps. The usefulness of this type of representation lies in the possibility of selecting the best operating point of the system, taking into account not only the efficiency or the power consumption but also the technical constrictions imposed by parameters such as the suction line temperature, the condenser subcooling, the evaporator superheat, and the run-time ratio. The discussion leads to the conclusion that the useful performance map is drastically reduced when all the operation requirements must be satisfied. Once the system design had been optimized, an additional numerical study, aimed at identifying the influence of the external conditions on the system behavior, was performed. The results show that the performance reduction can be effectively minimized modifying the refrigerant charge.     

Fatigue performance of friction stir welded Al2024 alloy in a different corrosive environment

The study examines the corrosion fatigue behavior of friction stir welded Al2024 alloy in the corrosive medium. The fatigue tests are conducted at a stress ratio of -1 in the different corrosive medium. The decrease in the fatigue life of welded joints in the corrosive environment is attributed to an increase in the crack initiation susceptibility in the presence of corrosive media. The fractured surfaces are investigated using the scanning electron microscopy (SEM). The formation of the corrosive compounds was studied using x-ray diffractometry.     

Herstellung einer komplexen Titan‐Knochenschraube aus Metallpulverspritzguss

Complex titanium bone screw fabricated by metal injection moulding M etal I njection M oulding (MIM) is a recently developed powder metal forming technology which is ideally suited to manufacture small geometrically complex parts from alloy powders. This innovative technology was used to fabricate a complex bone screw using metal powder of the biological inert Ti Al6 Nb7 alloy. This article presents the MIM‐technical boundary conditions to produce the screw and results of mechanical and chemical screw tests which qualify this injection moulded part as an advanced implant.     

Scherfließen und Wandgleiten von Massen für den Pulverspritzguss

This contribution presents coupling of laws for shear flow and wall slipping by the shear stress at the slipping interface. It includes the special case of Coulombian friction postulated by Uhland as well as the assumption of a constant sliding velocity along the flow channel according to Mooney. As an example, Ostwald and de Waele's law of shear thinning flow is combined with a shear stress of sliding depending on internal pressure by a power law. Examined feedstocks for metal injection molding showed a rheological behavior according to the model presented.