The possibility of achieving more efficient electricity generation by energy complexes on the basis of hydropower resources with predominantly using them in autonomous power supply systems is analyzed. The choice of daily amount of electricity production as a criterion for estimating the energy complex performance is substantiated. Methods for improving the generation efficiency are considered, such as daily load profile optimization, also when there is a buffer energy storage in the power system; combined generation of electricity; extremum seeking control of hydroelectric power units and maneuverable hydroelectric power units in the operation modes of micro pumped storage hydroelectric (microPSH) power plants, as well as electrochemical energy storage units, and their combinations. Special attention is paid to extremum seeking control implementation methods for various types of electric generators, which make it possible to increase the daily amount of electricity generated by both newly developed and existing complexes on the basis of hydropower resources without introducing significant changes in the design layout with taking into account stabilization of the autonomous electric network parameters. A new simpler and more accurate extremum seeking control method by monitoring mechanical rather than electrical parameters is proposed. To confirm the theoretical hypotheses on implementing extremum seeking control, field experiment data are given and analyzed, which testify that the proposed method is well grounded and highly efficient in nature. The costs of electricity in using different methods for storing it and for achieving better efficiency of its generation are compared, and versions of their combined use are considered. It has been confirmed that there is a significant potential for achieving more efficient electricity generation with the use of hydropower resources, and practical methods for achieving this aim are described.
In this work, a condition monitoring model of drum steam using Paraconsistent Annotated Logic (PAL) was investigated to provide the mathematical and logical foundation for the application of PAL to monitor condition of steam in boiler drum. Three methods are proposed in order to calculate evidence degrees from steam pressure and temperature and evaluate steam state in the drum. The Paraconsistent Analysis Node (PAN) takes evidence diagrams as input to analyze and process the inconsistency and uncertainty of signals corresponding to pressure and temperature. The PAN outputs the resultant real evidence degree, the Contradiction Degree and the Normalized contradiction degree. A network of paraconsistent analysis (PANnet) which is combined with these methods is also proposed in order to analyze and treat the contradiction. And based on this, the application of PAL for condition monitoring of drum steam, one of the local systems of the Fault Detection and Diagnosis (FDD) for Thermal Power Plants (TPPs), is demonstrated. For two faults, the fault detection times are reduced by 60 and 64
A vapor generator is among the most complex and thermally stressed component of the thermal cycle circuit of a power unit operating according to the organic Rankine cycle (ORC). As a rule, the ORC unit vapor generators intended for recovering the waste heat in industrial processes are “connected” to the source via an intermediate thermal oil loop. With such an arrangement, thermal oil, which has the maximum possible temperature, enters sequentially first the vapor generator’s evaporating and then heating part, in which it transfers heat to the power unit’s low-boiling working fluid (LBWF). The study addresses matters concerned with designing the evaporator, in the tubes of which the LBWF is heated to the saturation temperature at a specified pressure, boils, and is superheated prior to be supplied to a turbine (an expansion engine). Oil coolers of stationary power units operating on steam as working fluid are considered as prototypes for design implementation of the ORC unit evaporator: vertical shell and tube devices, including those with smooth tubes, with “disc–ring” type partitions with nonsealed and sealed process gaps, as well as with low knurled fins on tubes, with “disc–ring” type partitions, and sealed process gaps. The article presents the results of a review of experimental data and applicability analysis of existing models for calculating the heat transfer coefficient and critical heat flux for LBWF boiling in tubes, which can be recommended for including them into the device thermal-hydraulic design calculation. The procedure for calculating the pentane evaporator for a thermal capacity of 1440 kW for a 500 kWe ORC unit has been tested. A “field of solutions” has been obtained for the layout versions of the evaporator heat transfer surface composed of tubes made of carbon steel, stainless steel, brass, and copper, having an outer diameter of 10, 12, 14, 16, and 18 mm and wall thickness from 0.5 to 2.5 mm, as well as finned tubes the finning ratio of which was varied from 2.2 to 2.4. By applying correlation analysis methods, a data array on the optimal layout versions of the heat transfer surface for devices of all designs considered has been set up. Recommendations on selecting the design version of a pentane evaporator as part of an ORC unit have been compiled.
The development of tip clearance control and monitoring systems in gas turbines has led to a trend toward eliminating shrouds on rotor blades in a number of high-power stationary gas turbines, such as the SGT5-4000F, SGT-8000H, and others. Eliminating shrouds opens the possibility of optimizing turbine parameters, increases the degree of freedom in selecting the number of blades in the rotor, allows the reduction of rotor blades weight and, consequently, reduces the contour load on clearance above the unshrouded rotor blade (RB), which is not always possible, especially in aircraft turbines. To reduce inductive tip losses, several patents propose forming the tip area portion of the rotor blade with a slight curvature of the blade toward the suction surface in the circumferential direction. This minimizes the pressure difference between the pressure and suction surfaces near the blade tip. However, no quantitative estimates of this effect are provided. To obtain quantitative estimates of the impact of blade curvature at the tip area a computational study of the flow structure and energy loss level in the considered region was conducted using state-of-the-art CFD approaches for solving the 3D Navier-Stokes equations in a steady-state RANS formulation. In the first stage of the study, calculations were performed using the proprietary (in-house code) 3D NS software package. However, in the absence of experimental data the validation, justification and visualization of proprietary the numerical results obtained using the 3D NS program, computational studies of the flow in a rotor blade row with an open tip clearance were also conducted with the commercial software packages ANSYS FLUENT and ANSYS CFX. The computational study of the flow structure demonstrated a positive effect of this measure, resulting from a significant reduction in vortex formation zones due to flow in the tip clearance and, consequently, a reduction in losses when the rotor blade tip is tilted toward the suction surface.
In this study, the thermal conductivity of paraffin matrix was improved by adding functional graphene. Composite phase change materials (PCMs) based on paraffin and acid-treated graphene were prepared and tested at various treatment temperatures (90, 120, and 150°C) with varying mass fractions of the filler. Preliminary acid treatment of graphene reduced the interfacial thermal resistance and improved the dispersion stability of the filler in the matrix due to the introduction of functional groups onto its surface. The following key characteristics were determined for the obtained samples: dispersion stability of graphene, micromorphological structure, and chemical compatibility of the components. Fourier-transform infrared spectroscopy results showed that graphene treated with acid at 120°C exhibited more pronounced absorption peaks, indicating a higher content of O–H, C=O, and C–O bonds compared to graphene treated at other temperatures. Thermal conductivity measurements of the composite PCM samples at various temperatures revealed that at 60°C, the maximum increase in thermal conductivity (23.2
