Numerical Study of Powder Flow Nozzle for Laser-Assisted Metal Deposition

Metal additive manufacturing has received much attention in the past few decades, and it offers a variety of technologies for three-dimensional object production. One of such technologies, allowing large-sized object production, is laser-assisted metal deposition, the limits of which are determined by the capabilities of the positioning system. The already-existing nozzles have either a relatively low build rate or a poor resolution. The goal of this work is to develop a new nozzle with a centered particle beam at high velocity for the laser-assisted metal additive manufacturing technologies. Scientific challenges are addressed with regards to the fluid dynamics, the particle-substrate contact, and tracking of the thermodynamic state during contact. In this paper, two nozzles based on the de Laval geometry with Witoszynski and Bicubic curves of convergence zone were designed; the results showed that the average flow velocity in a Bicubic outlet curve nozzle is around 615 m/s and in Witoszynski this is 435 m/s. Investigation of particle beam formation for the Bicubic curve geometry revealed that small particles have the highest velocity and the lowest total force at the nozzle outlet. Fine particles have a shorter response time, and therefore, a smaller dispersion area. The elasto-plastic particle-surface contact showed that particles of diameter limited up to 3 μm are able to reach experimentally obtained critical velocity without additional heating. For particle sizes above 10 μm, additional heating is needed for deposition. The maximum coefficient of restitution (COR) is achieved with a particle size of 30 μm; smaller particles are characterized by the values of COR, which are lower due to a relatively high velocity. Particles larger than 30 μm are scalable, characterized by a small change in velocity and a rise in temperature as their mass increases.

RATIONAL FOR REHEATING IN THE AUTOMATED LINE FOR RING BLANKS PRODUCTION

Features and requirements to the use of reheating of ring blanks in the conditions of production on the automated line are considered. An assessment is given for a technological temperature state of ring blanks at various stages of production under conditions of the automated line. For assessment of rational for reheating at production of ring blanks, a classification of ring manufacturing technology is proposed with the production of a pressed non-core blank in an open die, with the production of a pressed profile blank in a closed die, with the production of a pressed profile blank in a stamp with reverse extrusion. The technology of ring rolling with the production of a pressed non-core blank in an open die is the most economical and does not require the use of reheating in the manufacture of rings made of medium-alloy steels. The technology of ring rolling of a profile blank obtained in a closed die does not require the use of additional heating after pressing, in the case of manufacturing rings with a simplified profile on the outer or inner diameters of the ring. In the manufacture of rings with a more complex profile on the outer and inner diameters of the ring, as well as rings made of high-alloy steels, the final decision on the need for additional heating is made depending on the temperature of the end of intensive plastic deformation for the selected steel grade of the ring. The technology of ring rolling with the production of a pressed profile blank in a die with reverse extrusion requires the use of reheating after the pressing operation before the ring rolling operation, and is recommended for the manufacture of rings from medium- and high-alloy steels with a complex profile section on the outer and inner diameters, wall thicknesses, with a ratio of wall thickness to outer diameter D within h / D = 0.011...0.016 and with a ratio of wall thickness to ring height L within h / L = 0.020...0.041. The proposed recommendations are intended for use in the development of technological support for the operation of the automated ring-rolling complex at OJSC “BELAZ”.

Estimation of the efficiency of combining a npp with a hydrogen facility under conditions of safe use of hydrogen in a steam turbine cycle

THE PURPOSE. System efficiency and competitiveness assess of a new scheme for combining a nuclear power plant with a hydrogen complex based on additional heating of feed water and superheating of live steam in front of the high-pressure cylinder of a steam turbine. METHODS. Basic laws of thermodynamics were applied when developing and substantiating a new scheme for combining a nuclear power plants (NPP) with a hydrogen facility; theoretical regularities were applied of heat engineering; basic regularity were applied of fatigue wear of power equipment and assessment of its working resourse; basic regularities were applied for the assessment of operating costs and net present value (NPV). RESULTS. A new scheme is presented of the combination of a nuclear power plant with a hydrogen facility and a description of its operating principle on the example of a two-circuit nuclear power plant with a VVER-1000 reactor and a C-1000-60 / 1500 turbine. The data are presented on an increase in the productivity of steam generators at nuclear power plants with additional heating of feed water in the range of 235-250 ° C from its nominal value of 230 ° C. The temperature was estimated of live steam superheat depending on the temperature of the additional heating of the feed water. The results are presented of the calculation of the generated peak power by the power unit and the efficiency of conversion of the night off-peak power of the NPP into peak power, as well as the efficiency of the power unit of the NPP depending on the temperature of additional heating of the feed water. Main regularities are given for taking into account the fatigue wear of the main equipment of the hydrogen facility, including the rotor of the NPP turbine in the conditions of the stress-cyclic operation. The results are presented of assessing the cost of peak electricity NPP in combination with a hydrogen facility in comparison with a pumped storage power plant (PSPP) both for the current period and for the future until 2035. CONCLUSION. Hydrogen facility efficiency and competitiveness depends significantly on the intensity of the use of the main equipment in the conditions of the intense-cyclic operation. The hydrogen facility will competitiveness noticeably increase in comparison with the PSPP in the future. Efficiency of the NPP power unit and NPV is highest when the feed water is heated to 235 ° C and superheating of live steam in front of the high-pressure cylinder of the C-1000-60/1500 turbine up to 470°C.The hydrogen facility competes with the PSPP with her specific capital investment at the level of 660 USD / kW, provided that the boosting capabilities of the turbine are used with live steam overheating at 300 ° C and additional heating of feed water to 235°C on the current period. The PSPP does not compete with the hydrogen facility both for the current period and in the future with her specific capital investment of $ 1,500 / kW and above.

Design of the Heat Pipe Helium Greenhouse for the Effective Use of the Soil Heat

This scientific work presents the results of scientific research on the use and accumulation of solar energy for heat supply of a solar greenhouse. For a real assessment of the problem, the following information can be cited as an example: in a greenhouse with a total area of 234 m2 covered with polyethylene film must be installed, on the average, with 6-8 furnaces to provide a certain amount of warm air. One furnace consumes about 2448 m3/h of natural gas for four months, and during this time 8.6 kg of carbon dioxide (CO2) is emitted from one furnace. As a result, taking into account the payment for the consumption of natural gas, the problem of the cost of the obtained products, energy conservation, and also environmental protection is very urgent. To solve this problem, a solar greenhouse with an additional heating chamber was constructed at the research site of the State Energy Institute of Turkmenistan. In this structure, excess of solar and heat energy of the soil was accumulated in mountain stones, and carbon dioxide that emits soil (horse manure was used as a soil) was used to feed the Chlorella vulgaris suspension grown in the photobioreactor, which in its turn had a beneficial effect on its cultivation. To transfer heated air from the additional heating chamber to the solar greenhouse and the accumulated thermal energy of the soil, polyethylene pipes with holes were used. Due to the use of the heat capacity of the materials (rock stones), a two-layer coating of the structure, compaction of the northern side with wool and accumulated heat energy, it was possible to achieve a positive temperature in the solar greenhouse in the minus environmental values. The technologies and processes considered in this research are mainly renewable energies and technical (chemical reactions) solutions such as photovoltaic (PV) modules, phase exchange material (PCM), underground heat storage technologies, energy efficient heat pumps and facade materials for the better heat insulation. The obtained results of the research work can be applied in solar greenhouses, the construction of which is planned in the areas remote from the central power supply network, since heat supply is carried out using solar energy and electric lighting is implemented due to the solar panels with a built-in LED lamp. It should be borne in mind that the intensity of solar radiation on the territory of Turkmenistan fluctuates in the range of 700-800 W/m2, which indicates the huge possibilities of using solar energy.

Comparison of evaporator stations with and without pre-evaporator

Two sugar factories with a processing capacity of 6000 t/d of beet and falling film type evaporators in all effects but differing in the lay-out of the evaporator station were compared. A five-effect station with serial juice flow from effect 1 to 5 was compared with a five-effect station, where the thin juice is fed into the 4th effect (pre-evaporator), and then after additional heating to the 1st effect. For the two sugar factories identical process parameters and identical technological equipment were assumed. It was found that the use of a pre-evaporator gives significant operating benefits to the operating of the evaporation station, which may support decision of its application despite the higher installation costs compared to the station without pre-evaporator.