A simple and technologically feasible method for liquid boiling heat transfer enhancement has experimentally been studied. Central to the proposed method is setting up conditions under which the working fluid boiling temperature is reached at a lower temperature to which a copper heat transfer surface is heated. The experiments were carried out under the liquid bulk boiling conditions at atmospheric pressure on a flat copper surface, above which round brass plates were placed at an adjusted height. The maximum heat flux value made 500 kW/m2. Various plate location options were considered to determine the optimal conditions under which the maximal heat transfer coefficient is reached. Boiling curves for all of the studied options were obtained, heat transfer coefficients were calculated, and their comparative analysis was carried out. It has been found that the brass plate optimal placement height and diameter have an essential influence on the process performance. According to the experiment results, the option involving the use of several plates turned to be the most optimal one: the heat transfer coefficient increased by up to 80
One specific feature connected with using the Rankine cycle with low boiling working fluids (LBWF) is the need to significantly heat the fluid before supplying it to the evaporator. Quite little attention is paid in the scientific literature to arrangement of this process and design of the appropriate device. This is despite the fact that the fraction of heat transferred in it from the heat source to the LBWF in liquid state is commensurable with that in the boiling process in the evaporator (which is considered to be the main one) and may even exceed it. The article considers development of the heater design for a capacity of 1340 kW as part of a power unit for an electrical capacity of 500 kW, which uses pentane as working fluid. The following oil coolers of stationary power installations operating on steam are considered as prototypes for the heater: vertical shell-and-tube apparatuses with smooth tubes, with disc–ring type partitions with nonsealed and sealed process clearances; with low knurled fins on the tubes, with disc–ring type partitions and sealed process clearances, and with longitudinally finned tubes as part of tube-in-tube elements. The results of design calculations for a liquid pentane heater of all designs considered are given. The flowrate of pentane heated in the apparatus from 72 to 149°С was equal to 6.05 kg/s. For apparatuses with smooth tubes and disc–ring type partitions, the calculation was carried out for tubes with the outer diameter equal to 12, 14, 16, and 18 mm, and wall thickness from 0.5 to 3 mm, made of four materials: copper, brass, carbon steel, and stainless steel. For apparatuses containing tubes with low knurled finning, the possibility of using the same tubes as in the prototype (the oil cooler), as well as GEWA-K tubes produced by Wieland-Werke AG company (Ulm, Germany) made of copper and steel, was studied. The article presents the results of a comparative analysis of the overall mass and dimensions for the obtained design versions, and of the thermal-hydraulic indicators of the processes that take place in them. Recommendations on selecting the design version of the pentane heater as part of the power unit considered have been formulated.
The prospective contribution the carbon capture, utilization and storage (CCUS) technologies can make in achieving the climatic neutrality of the global economy is studied. The current state of and possibilities for diffusion of the CCUS technologies across the world is examined. It is shown that the modern global development rates of these new technologies correspond to the parameters characterizing the advancement of their historical analogs—nuclear power, renewable energy sources, and environment protection technologies. Two dynamic development scenarios (historical and intense ones) of CCUS capacities for the period up to 2200 with the cumulative absorption equal to 250 and 520 billion t CO2, respectively, by 2100 are proposed. Based on new in-depth assessments of the absorption capacity potential of the Earth’s forests, a scenario of the carbon sink into the global biota is developed, which ensures a cumulative absorption of up to 70 billion t CO2 by 2100 and up to 100 billion t CO2 by 2200. It is shown that, given the existing limitations on the biotic sink, neither the historical nor the intensive scenario of reducing the anthropogenic greenhouse gas emissions is able to achieve the climatic neutrality of the global economy (by 2200 and 2100, respectively) unless the CCUS technologies are used. For both scenarios, it is necessary to set up CCUS systems for a total capacity at a level of 8–10 billion t CO2/year; however, according to the intensive scenario, this level has to be reached already in 2070 (with subsequently decreasing the annual absorption), whereas in the historical scenario, a smoother growth to the end of the current century is assumed. The model assessments of the global climatic system response to the proposed anthropogenic impact scenarios show that in the case of their having been implemented, these scenarios are able to cap the average global temperature rise by 1.5–2.0°С, but they are not able to prevent the planet from remaining in the zone of dangerous overheating for a long (more than one and a half century) period of time.
The high voltage electric heater is being often used in helping to manage load fluctuations in renewable energy utilization. Its value lies in its ability to rapidly convert electricity into heat without transformers using directly the high voltage power available on the distribution grid. However, the former 10 kV electric heater, where the insulation tube is not installed, is limited in use because it exhibits unstable phenomena including electrical shock. For stable operation, we proposed a 10 kV electrical heater equipped with ceramic insulated tubes, unlike the previous types, and determined its geometric size and operating parameters through numerical and experimental analysis of coupled heat, hydraulic, and electric fields in the water heating process. A mathematical model was introduced to describe coupled thermal, hydraulic and electrical fields. This model was calculated with ANSYS Fluent in range of velocity 0.2–1.0 m/s and temperature 20–60°C. The calculated thermal power was compared with the real thermal power of the 10 kV electric heater operating under identical conditions. It is found that the predicted thermal power is acceptable and the insulation tube is appropriate with the geometrical size (diameter 0.17 m, height 0.5 m). This study makes possible to determine operation parameters and geometrical sizes of high voltage electric heaters with various capacities in the design stage.
In this study, amine-functionalized graphene NH_2-G is used as a nanomaterial to improve the thermal performance of paraffin wax (PW). PW is used as a phase change material (PCM). Reinforcement of graphene at volume percentages of 0.20 and 0.40 NH_2-G is a very effective and useful nanomaterial to enhance the thermal performance of PW, which makes it a perfect choice for various types of thermal energy storage (TES) applications.
The key performance indicators of three five-stage low-pressure cylinder (LPC) versions having identical first stages and identical rotors are compared using a virtual test bench in the rated mode of their operation. The versions of the LPC-1 with semibowed guide vanes and the LPC-2 with integral guide vanes of the four last stages were also studied in a wide range of operation modes by varying the backpressure downstream of the compartment from 0.0035 to 0.0245 MPa. In addition, the LPC-3 with radial guide vanes of all stages was virtually studied only in the nominal mode of operation. A computer program for 2D verification gas dynamic calculation of the LPC flow path was used as the virtual test bench. In order to obtain stable results of complex calculations, this program was incorporated into the core of the main software implementing the nonlinear computer optimization method, which is a combination of the relaxation method (the alternating-variable descent method, the Gauss–Seidel method) and direct version ordering method according to the performance criterion (the direct search method). The tests performed have shown that in the nominal operation mode, the LPC-3 is inferior to the LPC-2 and LPC-1 in the power output and economic efficiency. In a wide variation range of operating parameters, up to the last stage windage modes, the LPC-2 is more preferred than the LPC-1 in power (by up to 1.8 MW) and efficiency (by up to 1.6
The article analyzes the existing experimental data on critical heat flux in the fuel assemblies (FAs) of VVER reactors when used without heat and mass transfer intensifier grids. The data obtained on thermophysical facilities at eight different companies in Russia and around the world are considered; the total number of experimental models makes 80 ones. The article presents an analysis of experimental data distribution with respect to various characteristics of FA models, including the number of fuel rods, heated length, and existence of a radial or an axial power distribution profile. The article also compares the experimental data with the calculation results obtained using the certified subchannel thermal-hydraulic code SC-INT and the design formula of OKB GIDROPRESS implemented in its composition for determining the critical heat flux (CHF). An analysis of almost 5000 points was carried out, from which a conclusion has been drawn that the data obtained on different thermophysical facilities feature a high degree of scatter: the resulting values of arithmetic mean and rms deviations of the CHF values calculated using the SC-INT code from the experimental data make 4.4 and 23.5
Nowadays, new technical solutions allowing NPPs to operate in daily load following modes are systematically put in use in the nuclear power industry. To minimize the number of switching operations in the course of maneuvering, it is necessary to consider the systems that have an effect on the stability of power unit operation in changing the base operation mode without switchovers to standby lines. The article presents a comprehensive analysis of various process circuit arrangements of the intermediate separation and steam reheating (ISSR) system for nuclear power plant steam turbine units (STUs). The aim of the study is to select a rational configuration of the separated moisture draining arrangement that would ensure high power performance and operational reliability indicators. The study methodology involves consideration of moisture separation arrangements in the domestically produced STUs of NPPs, comparative modeling, and heat balance calculations of STUs equipped with a modernized system for draining separated moisture from the moisture separator-reheater separated moisture drain tank for estimating the STU performance efficiency. It has been found in the course of the study that the separated moisture drain system configurations were already modernized at existing power plants. As a result, it has been determined that the process arrangement with a united separated moisture drain tank features better efficiency in stationary operation modes. For making its operation more stable in transient modes, in particular, to prevent separated moisture from flashing and prevent cavitation from occurring in the pumps when the load is reduced, a set of technical solutions has been proposed and substantiated. They include installing a drain cooler in the low pressure heater (LPH-4) and setting up a forced separated moisture cooling system by means of condensate injection. It is shown that the adopted solutions have turned to be very efficient to ensure stable and cavitation-free operation of pump equipment.
Various modifications of the Stodola formula have hitherto been used for calculating the leak through a seal. The parameters appearing in the Stodola formula are easily determined in a calculation or a simple experiment. However, for evaluating the flowrate coefficient appearing in the Stodola formula, a special experiment has to be carried out for each throttle type. It is also necessary to calculate the straightness ratio, which takes into account incomplete velocity deceleration. For determining the flowrate coefficient and straightness ratio, specialists of the MPEI Department for Steam and Gas Turbines proposed—as far back as the 1950s—simple relationships, which are still used nowadays without any updating. The problem of more accurately assessing the leaks through seals still remains of issue. An important feature of the dependences for the stiffness of aerodynamic overshroud force nonconservative components on the tip clearance obtained at the NRU MPEI is that there is a maximum in the area of its relatively small values (0.5–0.7 mm). In addition, it has been found that the nonconservative component of the aerodynamic force that emerges in overshroud tip clearances is almost inversely proportional to the flowrate through these seals. Thus, to ensure acceptable leak flowrate through these seals under the conditions of a tradeoff between minimizing the clearance for reducing the leak and increasing the clearance to avoid self-exited vibration from occurring, it is necessary to improve the leak determination accuracy. The aim of the study was to evaluate the accuracy of the methods applied for calculating the flowrate coefficient and straightness ratio. To this end, a special model has been designed and produced, which makes it possible to study geometrically similar straight-flow seals and seals with complete deceleration of velocity in the chamber. It has been shown that, whatever the convenience of using the dimensionless ratio of tip clearance to the fin end thickness for determining the flowrate coefficient, one should not overestimate its versatility, and that the currently used flowrate coefficient dependence on the dimensionless ratio needs updating.
The article presents the results of a study of combusting brown coal (BC), anthracite (A), and their mixtures taken in the ratios (BC : A) equal to 7 : 3, 1 : 1, and 3 : 7 in terms of organic mass in water–oxygen fluid at the pressure р ≤ 25 MPa, which was carried out for the first time. The experiments were carried out with coals heated in the Н2О/О2 fluid medium at a rate of 1°С/min to 550°С and in pumping the fluid through the bed of coal mixture (BC : A = 7 : 3) and heating the reactor at a rate of 1.5°С/min to 420°С. It is shown that the coals and their mixtures are oxidized in the autoclave regime according to the thermal explosion mechanism. This facilitates almost complete combustion of organic carbon for a few tens of seconds at relatively low temperature (below 700°C). The ignition temperature and combustion dynamics of mixtures with predomination of one of coals (BC or A) in the autoclave regime are similar to the combustion characteristics of this coal; the combustion of coals with the equal content of BC and A proceeds in two stages. It has been found that in pumping the Н2О/О2 fluid through a bed of coal mixture, their intense combustion at 230−300°С is accompanied by the generation of combustible components and their entrainment by steam flow. The organic carbon combustion rate under these conditions is governed by the oxygen flowrate supplied into the reactor. The obtained study results can become a basis for the development of promising technologies for combustion of coals and coal enrichment waste in high pressure steam to yield a high-enthalpy heat carrier.
In recent years, specialists have paid significant attention to development of heat transfer enhancement methods that make it possible to reduce energy consumption and increase the heat transfer coefficient. Application of such methods is of special importance if there are high local heat fluxes and compact sizes of heat transfer devices. The use of local heating makes it possible to decrease energy consumption and enhhance the transfer processes. However, many mechanisms of heat transfer and ways for improving it still remain insufficiently understood. In the present study, the effect the laser heating power and its modulation frequency (local heating) have on heat transfer in a 1.4–5.1 mm thick liquid layer was considered. In carrying out the study, the particle image velocimetry (PIV) and particle tracking velocimetry (PTV) methods were applied for measuring velocity fields, and infrared recording was used for analyzing the temperatre fields. In the laser power modulation mode (0.05–1 Hz), high heat transfer intensity is retained when the average power is decreased by 40
The article presents the basic statements of the hypothesis put forward on the factors causing the occurrence of intense heat transfer regime during film boiling of subcooled liquid. A new relationship for the temperature difference corresponding to the moment at which transition to fast cooling regime occurs is derived. This relationship takes into account the thermophysical properties of cooled surface and roughness scale on it, the thermophysical properties of cooling liquid and its subcooling. The model has been verified against experimental data under the conditions of free bulk motion of liquid. Unlike our previously published model versions, the liquid subcooling is now taken into account in a more natural way, namely, by the cooling liquid properties and its flow dynamics rather than by introducing empirical corrections. Separate attention is paid to experimental data on cooling metal bodies with the known surface irregularity scale, because the developed relationship depends quite strongly on it. For verification purposes, we collected experimental data on the cooling of spherical and cylindrical samples made of stainless steel, nickel, and copper with various coatings (chromium carbide, gold, and silver), carbon steel, titanium, and FeCrAl and zirconium alloy in water, ethanol, and water–ethanol mixtures with different concentrations. Additional experiments on cooling a copper ball with nickel coating in subcooled water were carried out. For verifying the model, we used experimental data of other researchers on cooling in subcooled water of heated bodies made of zirconium, stainless steel, Inconel, and Zircalloy. The calculation carried out using the newly developed mode has demonstrated good agreement between the obtained results and predominant amount of experimental data.
Triethylene glycol (TEG) dehydration is a commonly used method for natural gas dehydration. However, the sulfur-containing exhaust gases generated during dehydration are challenging to eliminate. Therefore, developing an effective method for removing sulfur-containing tail gas is essential. This paper analyzes the characteristics of various waste gas desulfurization technologies, proposes a combined approach of alkaline absorption followed by combustion for tail gas treatment, and proposes a new type of burner structure that enhances both the gas intake method and the structure of the burning furnace. By numerical methods, the internal flow field and combustion characteristics of the combustor are investigated, the Realizable k–ω turbulence model and eddy-breakup combustion model are employed in the computational model to predict species composition, flow field, and temperature. The simulation results show that this scheme can better remove the sulfur-containing components in the exhaust gas. The H_2S concentration is reduced from 0.2630 to 0.0009
Thermal power facilities generate substantial quantities of solid waste during water purification and fuel burning processes, presenting significant challenges for environmental management and resource conservation. This investigation examines and characterizes solid wastes produced by an Egyptian thermal power installation, with focus on water treatment sludge containing aluminum compounds, spent granular activated carbon (GAC), depleted ion-exchange resins (IERs) of various classifications, and combustion residues. Currently, these materials are predominantly sent to landfills without utilization, representing a missed opportunity for resource recovery. This work presents waste generation patterns at an Egyptian thermal power facility and provides comprehensive characterization of these materials. Management approaches were evaluated to improve treatment efficiency, enhance recycling potential, and minimize waste generation, while exploring applications of these materials as suitable starting materials for manufacturing valuable products. The investigation tested environmentally responsible methodologies for waste valorization, including aluminum extraction from treatment sludge and potential reapplication of spent filtration carbon and ion exchange materials. These materials, previously utilized for water purification, have diminished in operational effectiveness over time. However, material analysis confirms retention of favorable porous structure characteristics, indicating potential for reuse. The water treatment operations integral to thermal power generation yield several waste streams with notable potential for CO2 sequestration applications. Our findings demonstrate that Egyptian heavy fuel oil combustion residues present the highest environmental hazard due to elevated concentrations of potentially toxic metals, while simultaneously offering a unique source of valuable vanadium, nickel, and zinc, suggesting economic viability for metal recovery processes. The proposed resource recovery approaches provide pathways to improve environmental performance and operational efficiency in power generation through effective waste management practices and resource conservation.
With the aim to develop petroleum sludge thermal recycling technologies, the parameters characterizing the combustion of these sludges in mixtures with spent oils, diesel fuel, and methanol are studied. In combusting petroleum sludge without additions, sulfur and nitrogen oxide emissions are recorded in amounts four times higher than those produced in combusting diesel fuel. If petroleum waste is mixed with spent oils, the specific concentrations of SO2 and NO (recalculated for the heating value and mass of fuel combusted) decrease by 20–29 and 7–10
Approaches used to compare the possibilities and economic efficiency of ion exchange and reverse osmosis separation technologies in obtaining demineralized water are considered. The article shows the way in which the economic equilibrium point position on the feed water total dissolved solids (TDS) scale may change depending on the choice of technical solutions in implementing ion exchange and reverse osmosis, on the ratio between the tariffs for electricity and costs of chemicals used for regenerating ion exchange resins, on the technology for water pretreatment before the main demineralization stage, on the water treatment plant capacity, and also on other factors influencing the operating costs (OPEX). It is demonstrated that under the conditions in Russia, namely, at a relatively low cost of electricity and rather costly chemicals, the most economically efficient and technologically sustainable water treatment plant layout used to obtain demineralized water with the residual electrical conductivity equal to 0.1 µS/cm from surface sources in a very wide TDS range is a combination of one pass RO with separate Н‒ОН ion exchange implemented according to the UPCORE countercurrent regeneration process. The spectrum of technical solutions that shall mandatorily be compared at the stage of water treatment plant design feasibility study has been determined, and it is emphasized that the choice of the optimal process of water demineralization can only be made provided that all factors and conditions of implementing a particular project are subjected to a competent and comprehensive analysis. The data presented testify that attempts of water demineralization based on the sole membrane separation methods (so called Integrated Membrane Technologies—IMT) may result in degraded economic efficiency of water treatment plants.
The article presents a mathematical model of a vertical cylindrical reactor heated by flue gases for pyrolysis of spent tire chips. The tire chips layer was modeled by spheres of the same diameter with simple cubic packing; the model took into account the dependence of layer porosity and permeability on the section height coordinate and raw material conversion degree. For describing the kinetics characterizing the thermal decomposition process of rubbers included in the tire composition, we used a model with one global kinetic step and the reaction products generation selectivity condition, which depends only on temperature. The system of 2D unsteady differential equations of heat and mass transfer and kinetics was solved numerically based on the Thomas algorithm for tridiagonal matrices. The article presents the results of mathematical model verification against the data of thermogravimetric analysis and experiments on laboratory facilities, which confirm the model adequacy. The article also presents the results of calculating the pyrolysis process characteristics (the mass of raw material processed and the yield of main products – pyrolysis gas, liquid fraction, and carbon residue) and comparative efficiency of the reactors of two types: a fixed bed reactor (FBR) and a move bed reactor (MBR), the bed is which is moved by periodically unloading a part of carbon residue in the reactor lower part and synchronously charging tire chips into the reactor upper part. The reactor autothermal operation conditions have been determined. The energy flows have been analyzed, and the parameters of reactor optimal operation conditions have been determined.
The article presents an integrated procedure for 3D designing of turbomachinery stages, which combines the use of a blade passage shape parametric description and neural networks. The procedure has at its heart a blade parametric model on the basis of Bezier curves, which employs eight to ten controlling parameters (thickness, edge radiuses, inlet/outlet angles, etc.), due to which it becomes possible to produce smooth profiles and reduce the problem dimensionality. By using such approach, a fully connected neural network for predicting the profile loss coefficient in nozzle vane cascades has been developed. The network architecture includes three hidden layers with Swish activation functions and Dropout regularization. The network was trained on a dataset of 2D CFD computations covering a wide range of geometric parameters, Mach numbers (0.6–0.95), and Reynolds numbers (1.6 × 105–1.1 × 106). The trained model’s median prediction error amounted to less than 0.24
The article presents the results of studying the biomass gasification process in a spouted bed at a temperature of 750‒950°C under atmospheric pressure, and with varying steam flowrate. The characteristics of producer gas and solid residue are determined. The quasi-stationary gasification process energy efficiency in using the gas obtained is quantified. The total H2 and CO concentration in the producer gas mixture reached 57 vol
Boiling heat transfer (BHT) is impacted by a variety of parameters. Surface characteristics such as roughness and material are some of them which have significant effect on the flow boiling (FB). The surface material’s impacts on subcooled flow boiling heat transfer (SFB-HT) in a channel at various velocities and roughness are experimentally investigated for water-alumina nanofluid (concentration: 0.1 vol
