Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Maciej B. Lachowicz"

Analysis of the causes of corrosion on bearing steel transported by sea DOI:10.15199/28.2018.4.3

  In order to prevent corrosion damage of cargo subject to corrosion during transport, it is subjected to temporary protection. This protection consists of weakening the aggressiveness of the environment, mainly by lowering the relative humidity, using volatile inhibitors or preserving the surface with the use of lubricants and oils. The immersion method is usually used for protection with preservatives, in which the object is placed in a special tub filled with the preservative. In the case of maintenance of large elements, the spray method is used more often. Filiform corrosion is a special type of local corrosion, in which corrosion changes are characterized by a specific form of dissemination in the form of thin, shallow and non-crosslinking corrosion threads of considerable length. It is classified as a type of atmospheric corrosion and also referred to as underfilm corrosion or filamentary corrosion. This type of corrosion attacks metals coated with organic coating, mainly aluminium and magnesium alloys. However, there have also been cases in which steel has been subject to this type of corrosion [1÷3]. Threads formed from corrosion products have an active head on their front which is a cell that wanders on the surface of the metal and a long trailing tail formed behind the head and filled with dry, porous corrosion products [4]. Oxygen is easily transported through the filament tail [5]. The thread has a red colour, characteristic for Fe2O3, while the active head is green or blue, which is related to the presence of ferrous ions. The width of typical threads ranges from 0.5 to 1.5 mm [6]. The thread length is several times the diameter [7]. If corrosion develops under favourable conditions, then the thread dimensions are similar. Changes in atmospheric conditions (temperature, humidity, protective layer thickness) lead to the existence of corrosion macro and micro threads [7]. It was found that the width of threads increa[...]

Role of microstructure in corrosion of microchannel heat exchangers DOI:10.15199/28.2018.3.1

  Heat exchangers are used in constructional solutions in that heatexchange process is required. Construction of a heat exchanger is crucial for its effectiveness. The heat exchanger in a personal car is mounted before the radiator in front of the car. Heat from a refrigerant is transferred through walls of flat tubing with microchannels to fins and then to ambient air. Condenser is responsible for removing heat from gaseous refrigerant under high pressure and at high temperature. By removing heat, the refrigerant becomes liquid (Fig. 1). Volume of emitted exhaust gas is significantly influenced by load of the engine that drives the air-conditioning compressor and thus by amount of the refrigerant used in the air-conditioning system. The Montreal and Kyoto Protocols enforce also use of smaller amounts of refrigerants with high Global Warming Potential index (GWP for R134a = 1430). For this reason, condensers become much more efficient than they were a dozen years ago. Currently, automotive A/C systems use mainly high-performance multiflow subcool condensers (Fig. 2). Construction of a condenser is based on aluminium flat tubing with microchannels. A system of lamellae is arranged between microchannels, creating a network of tiny channels for air flow. The lamellae are brazed under controlled atmosphere (CAB technology) to flat condenser tubes (Fig. 3). This type of joints used in place of mechanical joints are popular not only with regard to lower production costs, but also to better meeting the requirements of safety and recycling [1]. Lamellae are usually made of an alloy series 3000, most often the grades 3003, 3103 and 3203. For brazing, alloys series 4000 are used, mainly the grades 4343, 4145, 4047 and 4045 [1÷4]. In the case of this solution, there is no risk of galvanic corrosion that occurs in shell-and-tube structures. However, this does not mean that they are completely free from corrosion risk. The issues related to[...]

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