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In this paper, the pulsating combustion of a premixed propane-butane fuel with air in a vortex combustion chamber is considered. The conclusion of the refined frequency equation is made. The characteristic of the mixture supply system is given.

It is noted that digital artificial agricultural ecosystems imply the use of digital control systems of abiotic factors, with appropriate software and algorithms. The algorithm through thermoregulation ensures the highest flow of moisture and nutrients through the plant. The leaf temperature corresponds to the maximum rate of photosynthesis. It is shown that CO2 assimilation and thermoregulation are related, as water vapor and carbon dioxide pass through the same stomatal openings. The aim of the research is to establish, for selected samples of vegetable crops, the level of CO2 concentrations at which the biomass growth of these crops is maximal, as well as the degree of thermoregulation heat reduction for average CO2 concentrations of 1000 ppm and higher. A specially designed stand was used for the studies. The following crops were used for studies of the influence of CO2 concentration on the thermoregulation heat: from vegetables the cucumber cultivar “Courage” and from green spices the cultivar “Coriander”, and for studies of the influence of CO2 concentration on productivity - salad cultivar “Gambrel”. The samples were planted in four cubes of mineral wool, in each of which five plants were placed. Variable concentration was provided by a system of carbon dioxide supply from a cylinder with a reducer, a hose and an electromagnetic valve. It was experimentally proven that the increasing of the CO2 concentration leads to an increase in the weight of green mass, and this increase has an extreme at the concentration of 2944 ppm (for the lettuce culture), with a slight decrease in thermoregulation temperature (for cucumber by 1.4 °C, and for coriander by 0.47 °C). Such a decrease will not lead to a significant deterioration of thermoregulation processes and may not be taken into account in the operation of digital control of them.

The performance of sintered permanent magnets with nucleation-type coercivity mechanism is largely governed by the magnetic state of thin surface layers of constituent grains, and a deeper insight into magnetization–demagnetization processes occurring in the shell part of the grains is very important for further improvement of hard magnetic materials. In this work, we used Nd2Fe14B and SmCo5 single crystals as model objects. By applying magneto-optical Kerr microscopy and conventional magnetometry, we compare the magnetization–demagnetization processes occurring in the thin surface layer and in the volume of both single crystals. We show that upon magnetization along the c-axis, the volume of the single crystals saturates in the field, rigorously determined by demagnetization factor of the bulk sample, whereas in the surface layer a magnetic domain structure exists up to 1.88 T in Nd2Fe14B and 1.19 T in SmCo5 regardless of their bulk demagnetization factors. This means that the surface layer with orientation perpendicular to c-axis magnetizes as a thin magnetic film and has an effective demagnetization factor N eff ∼ 1. We also show that this effect can be reproduced in the framework of conventional finite element method modeling but the analytical solution of this problem still needs to be found. We believe that our findings can be useful for understanding of the formation of a high coercive state in nucleation-type permanent magnets, where the phenomenological concept of the large effective demagnetization factor N eff plays an important role.

The draft tube of the hydraulic turbine serves to recover the kinetic energy of the water flow that leaves the runner. The amount of this energy depends on the turbine type, its specific speed and flow capacity. For high specific speed turbines, influence of the draft tube on the turbine efficiency is more essential. The height of the elbow-type draft tube has a considerable influence on its performance. Statistics show that increasing the height of the draft tube leads to a considerable increase of the turbine efficiency, but it also increases the scope and cost of civil works. The present paper presents the solution of the multi-objective optimization problem directed to minimization of the height of the toroidal elbow-type draft tube and maximization of the overall efficiency of the turbine. During optimization, 11-19 parameters that determine the shape and dimensions of the draft tube were subject to variation. In optimization, efficiency was maximized in two operating points: best efficiency point and full-load point. Cavitation qualities were defined as constraints. In order to correctly assess the turbine efficiency and cavitation, the computational domain included one channel of the distributor, one channel of the runner and draft tube; whereas losses in the spiral case and stay ring were determined using empiric formulae. Within the optimization the flow analysis was performed using 3D steady-state Reynolds averaged Navier Stokes equations closed by the k-ε turbulence model. On solid walls the method of wall functions was used. The turbine head, being the difference of specific energies in the inlet and outlet cross sections, was pre-set as a constant value, while the discharge was determined in the course of solution of the problem. A multi-objective genetic algorithm was used to solve the optimization problem. For the draft tube shapes obtained in the course of optimization, their performance characteristics and flow character were compared by means of CFD. It was found that it is possible to significantly reduce the height of the classical toroidal draft tubes without considerably affecting their performance characteristics.