Analysis of numerical instability of centrifugal pumps operational characteristics

In recent years, computational fluid dynamics has been increasingly used in the development of various types of rotating machines. In the case of water turbines and pumps, a large number of researches have been published recently, related to the use of different numerical methods for prediction of efficiency, cavitation characteristics and different dynamic phenomena. For basic analysis an accurate result near the optimal operating regime is sufficient, but for detailed analysis the numerical analyses in the wider field of operating conditions are necessary. Thus, we encounter some otherwise known physical phenomena that occur in the part load and full load regime. In these areas, due to the nature of the flow, various non-stationary phenomena occur that are dominant for such operating regimes. In this paper, the problems that arises if we consider only stationary results and some recommendations to avoid later problems in the operation of centrifugal pumps are presented.

Superlubric Polycrystalline Graphene Interfaces

The effect of corrugated grain boundaries on the frictional properties of extended graphitic contacts incorporating a polycrystalline surface are investigated. The friction is found to be dominated by shear induced buckling and unbuckling of corrugated grain boundary dislocations, leading to a nonmonotonic behavior of friction with normal load and temperature. The underlying mechanism involves two competing effects, where an increase of dislocation buckling probability is accompanied by a decrease of the dissipated energy per buckling event. These effects are well captured by a phenomenological two-state model, that allows for characterizing the tribological properties of any large-scale polycrystalline layered interface, while circumventing the need for demanding atomistic simulations. The resulting negative differential friction coefficients obtained in the high-load regime can reduce the expected linear scaling of grain-boundary friction with surface area and restore structural superlubricity at increasing length-scales.

Graph-analytical method of load mode analysis of ferromagnetic current stabilizer

In this paper we consider the application of graph-analytical method for the analysis of the load regime of ferromagnetic current stabilizer. It is proved that under active load the current of the ferromagnetic stabilizer and magnetic flux are related by the ellipse equation where the axes coincide with the axes of coordinate system. The advantage of the proposed method is that it is possible to use an experimentally obtained characteristic.

Simulation of Optimizing the Partial Load Performance of a Gas Turbine Combined Cycle Using Exhaust Heat Recuperation and Inlet Bleed Heating

This paper proposes a novel method to extend the operating range and improve the partial load efficiency of the gas turbine combined cycle (GTCC). The combination of exhaust heat recuperation and inlet bleed heating (IBH) was evaluated through a cycle simulation. The degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency. The recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. Both IBH and recuperation were effective in extending the operating range. The turndown ratio was predicted to decrease by approximately 10%p. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

Simulation of Optimizing the Partial Load Performance of a Gas Turbine Combined Cycle Using Exhaust Heat Recuperation and Inlet Bleed Heating

Extending the operating range and improving the partial load efficiency of the gas turbine combined cycle (GTCC) is becoming increasingly important. This paper proposes a novel method to achieve the two goals simultaneously. To fulfill the research objective, the combination of exhaust heat recuperation and inlet bleed heating (IBH) was adopted and evaluated. A cycle simulation was conducted to confirm whether the research goal could be achieved. A recuperator was installed between the compressor and combustor of the gas turbine, and the degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency compared to the conventional GTCC plant. In contrast to the conventional GTCC plant, the recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. The simulation showed that both IBH and recuperation are effective in extending the operating range. The predicted reduction in the turndown ratio was approximately 10%p. The partial load efficiency improvement by the recuperation was sensible. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

Creatinine is a biochemical marker for assessing how untrained people adapt to fitness training loads

Background To study the peculiarities of changes in creatinine concentration in blood serum of untrained men during the prolonged usage of training loads different in volume and intensity, and to determine the value of this biochemical marker for the assessment of adaptive body changes during fitness training. Methods We examined 50 untrained men aged 18–20 years who had no contraindications for practicing fitness. Taking into account the aim of the research, we divided these people into two groups: group A and group B. The research participants used training load regimes different in volume and intensity: representatives of group Aused low intensity training load regime (Ra = 0.53) and representatives of group B used high intensity training load regime (Ra = 0.72). To assess the adaptive body changes in the examined contingent, we used the anthropometry method (circumference body size) and bioimpedansometry (body composition indicators). We also determined the features of adaptation-compensatory body reactions to different training loads by means of biochemical control of creatinine concentration in blood serum. Results The obtained results showed a significant increase in basal level of creatinine concentration in blood serum (by 17.6%) of group B representatives fixed after 3 months of practicing fitness in high intensity training load regime (Ra = 0.72). This group representative also revealed the most pronounced manifestation of adaptive body changes confirmed by the results of the maximal muscle strength growth (1RM) and circumference body size, which was almost 2.5 times higher than the results of group A representatives for the same period of time. The parameters indicating the load volume in a set (Wn) were almost 62.0 % higher in group A representatives in comparison with group B during all stages of control. Nonetheless, the highest creatinine concentration in blood serum (by 11.1 % (p < 0.05) was fixed in group A representatives in response to training load after 3 months of practicing. This fact testifies to the important role of the creatine phosphokinase mechanism of energy supply of muscular activity in the conditions of high volume and low intensity training load regime (Ra = 0.53). Conclusion The analysis of the results obtained during a series of experimental studies indicates the need and feasibility of using the indicator of basal level of creatinine concentration in blood during fitness training, especially in the conditions of high intensity and low volume training load regime (Ra = 0.72), as an informative marker for assessing the process of long-term adaptation.