Investigating the effect of submerged impingement jet on heat transfer in water-alcohol mixtures

This paper presents new results of experiments on spherical sample cooling with submerged impingement jet in subcooled water-alcohol mixtures. The influence of the ethanol concentration on the occurrence of intensive boiling regime is detected. Experiments are carried out on a stainless-steel sample in a water-ethanol mixture, in a wide range of concentrations and temperatures. The result includes an increase of the heat transfer intensity at exposure of the submerged impingement jet. The intensive boiling regime is detected with a higher ethanol content compared to experiments in a calm liquid.

The effect of reversion of Strain Induced Martensite (SIM) and grain refinement on the Intergranular Corrosion of High Mn steel

The surface phase constituent of high-manganese austenitic stainless steel after cold work (15%, 30%, and 50%) and thermal aging at 900°C for 30 min. and 6 hrs, was characterized using X-Ray diffraction spectrum. The microstructural analysis was conducted using an optical microscope, a scanning electron microscope, and the electron back scattered diffraction technique. The double-loop electrochemical potentiokinetic reactivation test was used to measure the Intergranular corrosion resistance (degrees of sensitization). The results showed that fine-recovered grains of austenite and strain-induced martensite together formed the surface of high-manganese steel after cold work. Because of the formation of strain-induced martensite in the cold work samples, their Intergranular corrosion were much higher than that of the as-received sample. Besides, the degree of sensitization of 15% cold work was higher (i.e., more intergranular corrosion) compared to the degrees of sensitization of 30% and 50% cold work. On the contrary, the intergranular corrosion of high-manganese austenitic stainless steel sample subjected to cold work was eliminated during thermal aging at 900°C for six hours because of the reversion of strain-induced martensite and fine-reverted austenite grains. Owing to this grain refinement of austenite, faster diffusion rate of Cr at higher temperature and cold work helped healing of Cr-depletion zone in a shorter time. In other words, because the results showed that on 50% cold work and thermal aging at 900°C for six hours, the high-manganese austenitic stainless steel does not become susceptible to intergranular corrosion. Hence, it could be beneficial to investigate the intergranular corrosion of high-manganese austenitic stainless steel.

Electrochemical Corrosion Behavior of Laser Welded 2205 Duplex Stainless-Steel in Artificial Seawater Environment under Different Acidity and Alkalinity Conditions

The electrochemical corrosion behavior of laser welded 2205 duplex stainless-steel in artificial seawater environment (3.5% NaCl solutions) with different acidity and alkalinity conditions (different pH values) was investigated using different techniques. Namely, capacitance measurements (Mott–Schottky approach), electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The formation of pitting corrosion on the exposure surfaces of the tested duplex stainless-steel samples was investigated and confirmed by characterizing the surface morphology using field emission scanning electron microscope (FE-SEM). Based on the obtained results, a proportional relation has been found between pH value of the solution medium and the generated film resistance due to the processes of charge transfer, which directly affecting the pitting formation and its specifications. Since the film layer composition created on the duplex stainless-steel surface is changes depending on the pH value, it was found that different bilayer structure type was generated according to the acidity or alkalinity level. The presented bilayer is almost composed from metal oxides, such as iron oxide and chromium oxide, as confirmed by Raman Spectroscopy technique. As the pits size and its quantity increased with decreasing pH value, it can be concluded that the corrosion resistance property of the laser welded 2205 duplex stainless-steel sample is improved on the alkalinity direction of the solution. Vice versa, higher acidic solution has more ability for corrosion.

Evaluation of the uncertainty associated with sample holders in NAA measurements in LAN/IPEN

In IPEN’s Neutron Activation Laboratory (LAN/IPEN), thin stainless steel sample holders are used for gamma spectrometry in NAA measurements. This material is very practical, but its chemical composition may be troublesome, as it presents large amounts of elements with intermediate atomic number, with attenuation factors for low-energy gamma-rays that must not be neglected. In this study, count rates obtained using different sample holders were compared. To accomplish that, an Am-241 source, with 59-keV gamma emission, was used so that low-energy gamma attenuation differences can be determined. Moreover, in order to study the energy dependence of these differences, a Ho-166m source was also used. From these results, it was possible to analyze the experimental error associated to the variations between sample holders, with the aim of introducing an addictive term to the uncertainty analysis of comparative Neutron Activation Analysis results.

Effect of Agitation, Temperature, and Quenching Medium on Cooling Curve and cooling rate for Steels

The control of quenching process has been investigated in this study by developing a quench system design to simulate the quenching process and measure the time – temperature history inside the sample during the cooling stage. The main purpose of this quench system is to evaluate the quench power of different quenchant at different conditions (type, temperature and agitation).A stainless steel sample was used with a suitable measurement as a probe in designing this quench system.The performance of two of quenchants (water and brine) with different conditions was investigated, and the designed probe was used to illustrate the effect of quenching parameters (quenchant type, temperature and its agitation) on cooling curves and cooling rate.The quenching system has proven its ability to work effectively and the results showed that heat transfer properties were significantly affected by quenchant parameters.

Tribological Behavior of the 316L Stainless Steel with Heterogeneous Lamella Structure

In this paper, the tribological behavior of 316L stainless steel with heterogeneous lamella structure (HLS), prepared through 85% cold rolling technology and subsequent annealing treatment (750 °C, 10 min), were conducted on a ball-on-disc tribometer under different normal loads in dry ambient air conditions. The morphologies, structures, and compositions of the raw and worn surfaces were analyzed by 3D surface profilometer, XRD, SEM, EDS and TEM. Based on this, the results showed that the HLS 316L stainless steel samples exhibited lower and more steady friction coefficients than coarse-grained samples, especially under higher loads, which can be attributed to the existence of numerous oxidative particles across sliding interfaces. However, the wear resistance of HLS 316L stainless steel sample was a little weakened compared to that of the coarse-grained sample under a normal load of 5 N. When the load increases up to 15 N, an obviously decreased wear resistance was found for the HLS of the 316L stainless steel sample, which was 50% lower than that of coarse-grained sample. This can be ascribed to the more severe oxidative and abrasive wear performance of HLS 316L stainless steel sample under dry sliding conditions.

Electrochemical polishing of selected stainless steels

The AISI 316Ti (EN 1.4571) austenitic stainless steel sample (50 × 30 × 1,5 mm) was used for the study. The main elements forming the steel are: chromium (16-18%), molybdenum (2.0-3.0%), nickel (10.0-14.0%), titanium (max 0.7%), and iron as the rest of the steel composition. The electrolytic polishing operations were performed at the current density of 50 A/dm2. The main elements of the electropolishing setup were a processing cell, a DC power supply RNG-3010, the electrodes and connecting wiring. The studies were carried out in the electrolyte of initial temperature of 50±5 °C. For the studies, as the electrolyte a mixture of two acids, i.e. H3PO4:H2SO4 equal to 60%:40%, was used. For surface characterization the 3D roughness parameters(Sa=0.744 μm, Sq=0.984; Sp=2.32, Sv=3.5, St=5.88; Ssk=–0.898; Sku=2.97) regarding ISO25178 were used.

MOBILE ACCUMULATORS FOR DISCRETE SYSTEMS HEAT-COLD SUPPLIES. Part 2.

The purpose of this article is selection and substantiate the construct materials for a mobile battery of thermal energy. To evaluate the impact of chemical corrosion on the structural materials of the tank-battery, and researching the strength of the tank-battery during transportation and determination the feasibility of introducing and effectiveness of investments in environmental measures on the example of the implementation of the discrete heating / cooling systems. A comparison has been made of the technical characteristics chosen for our studies of heat storage material - bischofite and sodium acetate trihydrate, which showed that both substances have certain advantages and limitations in their application. An experiment was carried out to determine the stability of the material for corrosion, after the 10 cycles of heating-cooling, the metal parts that were deposited in the bischofite solution remained virtually unchanged, no corrosion marks were observed. While specimens that were in the melt of sodium triacetate have obvious corrosion marks (except for a stainless steel sample). Particularly noticeable corrosion of samples that were on the verge of air and sodium triacetate. Thus, it has been confirmed that the use of hydrated salt melts requires additional measures to protect against corrosion of metals, and the use of polymer materials is limited by the temperature of their application. Calculations of the strength of the tank-accumulator at static and dynamic loads with the account of transportation are carried out. Taking into account the obtained results of Mises stress, the tensile stresses in the cut and stresses of bolted joints during rolling during transport under conditions of use of steel constructions are higher. In the course of determining the feasibility of implementing the project, it was tested and proposed to supplement the methods of calculating the investment of energy saving measures and projects by a fundamentally new method of strategic rapid analysis "3E". This method allows you to get a graphical representation of the result of the analysis and with a high degree of probability to determine the strategy of financing the implementation projects. The analysis is based on three main criteria, namely: energy, environmental and economic. These weighting criteria consist of a number of values that are necessary to obtain a likely return on the payback of the implementation project. The results of express analysis are clearly represented in the form of the area of permissible values on the triangular diagram, which we are invited to call the "3E triangle" in the initial words of words: Energy, Ecology and Economics. An economic analysis has also been conducted, which showed that the estimated payback period of the project is less than five years, and the volume of annual revenue from the sale of thermal energy and cold is 1470000 UAH. Thus, the project is attractive for investment.