Thermal Engineering最新文献

A software system for estimating the performance of a steam turbine condenser has been developed on the basis of its mathematical model, which takes into account the condenser interaction with the main ejector. The software system performs a number of key functions for diagnostics of condensing installations; in particular, it ranks the factors causing a growth of pressure in the condenser in comparison with its standard value in their significance and determines the decrease of electric power output resulting from deviation of each of the factors from their standard values. A distinctive feature of the developed software system is that it takes into account the interaction between the condensers and main ejectors in a wide range of steam loads and air in-leakages in the vacuum system, and the effect of this interaction on the turbine unit technical and economic indicators. It has been determined that, according to the results of the accomplished comparison between the predicted and standard data (i.e., verification), the accuracy of computation according to the mathematical models is more than sufficient for settling matters concerned with operational diagnostics of the condensing installation considered. By using the software system, one can analyze the steam turbine unit condenser performance, reveal the main factors causing degradation of its performance indicators, and make provisions for the measures on removing the revealed drawbacks and adjusting the most efficient condenser operation modes. By using the software system, it is also possible to construct the condenser standard and actual characteristics in the entire really permissible range of influencing parameters, diagnose the condenser heat transfer surface condition for any steam turbine units at combined heat and power plants (CHPPs) when specifying the necessary and sufficient input data on the design parameters of condensers and ejectors, and after carrying out the verification.

Units implementing the organic Rankine cycle (ORC) can utilize dozens of low-boiling substances, also called freons or refrigerants, as the working fluid. However, the classic solution for this cycle is the application of pentane and, therefore, this technology is sometimes called pentanoic. One of the main elements of the ORC unit circuit is the condenser, which is often a shell-and-tube heat exchanger cooled with circulating water. In spite of wide application of such apparatuses in steam turbine units, the elaboration of their design on the basis of the pentane technology is a challenging problem. For a prototype of this apparatuses, the KTR shell-and-tube condenser, which was previously often employed in refrigeration units with R12 refrigerant, is adopted in this work. Since chlorofluorocarbons and hydrochlorofluorocarbons have been phased out, equipment items intended for their application are also no longer manufactured by industry, which resulted in a shortage of information on their design and peculiarities of their design process. Hence, the authors carried out a search for and analysis of information about such apparatuses and developed and verified a procedure of design calculation of this equipment. In addition, models for calculating the heat-transfer coefficient during pentane condensation on tube bundles with rolled fins were reviewed, and these models were verified against experimental data on the condensation of propane, one of the closest homologues of pentane. The model proposed by A. Briggs and J.W. Rose has been found to yield the highest accuracy in engineering calculations of pentane condensers. Other models are also examined, which describe the effects of vapor shear and inundation of the lower tubes in the bundle on the heat-transfer coefficient during pentane condensation. It has been demonstrated that considering these effects during condensation of pentane and its homologues in the examined apparatus is impractical. The results of the design calculation of shell-and-tube condensers of pentane with a capacity of 173- and 2280-kW are presented. Recommendations for further optimization calculations are formulated.

A kinetic model is presented describing the formation of lead oxide vapor in the volume of a vapor bubble in the lead melt with its subsequent dissolution in the lead melt and crystallization in the bubble. The model is implemented in the approximation of homogeneous distribution of reagents and oxidation reaction products in the bubble volume. It is shown that vapor bubbles in the lead melt volume may be considered as chemical “microreactors” producing lead oxide vapor and nanoparticles in the bubble volume. The paper presents the results of calculation by a homogeneous model of the lead oxide vapor concentration in the bubble volume as a function of time and of the conditions for the possible formation of a soluble oxide shell on the bubble surface. The model includes mechanisms controlling lead evaporation and oxidation of lead vapor as it interacts with water vapor in the bubble volume and crystallization of lead vapor on the bubble inside surface with formation of a solid phase shell. Partial transformation of vapor bubbles into gas–vapor bubbles with an oxide shell could potentially affect their further behavior in the lead coolant. However, subsequent transport of the bubbles in the coolant circuit will lead to the dissolution of the oxide shell in the sections with the coolant at a higher temperature that will neutralize this negative effect. Moreover, formation of an oxide shell around the vapor bubbles can cause temporary trapping of hydrogen in the bubble volume.

Due to the continuous growth of municipal solid waste (MSW) volumes, their disposal with minimal negative impact on the environment is becoming a very urgent task. Thermal recycling of MSW is one of the most effective methods of their disposal because it allows not only to significantly reduce the volume of waste but also to obtain thermal and electrical energy. However, this process is accompanied by the formation of nitrogen oxides (NO_x), which contribute to the formation of smog and acid rain and negatively affect the environmental situation and public health. Therefore, the reduction of NO_x emissions is an important task for enterprises burning MSW with the release of electricity and heat to consumers. The article discusses selective noncatalytic reduction (SNCR) technologies used to reduce NO_x emissions at factories in Moscow oblast. The rationale for key technical decisions is presented, including the choice of reducing agent (urea), transport agent (air), and the reagent-injection system through nozzles arranged in three tiers. The results of calculations of the trajectories of the urea–air mixture jets in the cross-flow of flue gases are presented, confirming the effectiveness of the proposed configuration of the reducing agent supply system. It is shown that the use of air as a transporting agent in combination with the adopted nozzle placement scheme ensures uniform distribution of the reagent in the high-temperature zone, which increases the efficiency of NO_x reduction. The obtained results of the calculation studies can be used for further optimization of the SNCR system operation as well as for conducting operational tests at facilities engaged in MSW utilization.

A study of film-boiling processes of liquid subcooled to saturation state was conducted using numerical modeling based on the Volume of Fluid (VOF) method and the Lee model for describing heat and mass transfer at the interphase surface. During film boiling, a stable vapor film is formed between the wall and the liquid, eliminating their direct contact, which leads to low heat-transfer intensity. Under conditions of subcooling of the liquid to the saturation state, the intensity of film boiling increases significantly. Despite a thorough understanding of the heat and mass transfer mechanisms involved in this phenomenon, the development of new, more accurate models remains an active area of research. The efforts of researchers are driven by the need to accurately describe the cooling dynamics of high-temperature bodies and predict the onset conditions for high-intensity boiling regimes. Physical models explaining the emergence of these modes are still at the development stage. To verify and clarify them, there is insufficient information about the local characteristics of the vapor film and the features of free convective flow in subcooled liquid. The use of the VOF method allows for detailed tracking of changes in the interphase surface directly during the numerical simulation process. The article presents the results of modeling film boiling of water on the surface of a cylinder with a diameter of 2 mm with superheating of the wall up to 400 K and subcooling of the liquid up to 20 K. The discrepancy between the obtained simulation data and the experimental results published in literary sources does not exceed 10%. Information is provided on the distribution of film thickness, heat flux on the wall, and the interphase surface. According to the simulation, even with slight subcooling, the vapor is not “evacuated” from the vapor cavity, while evaporation is observed on one part of the interphase surface, and condensation on the other. The results of modeling taking into account buoyancy forces, associated with temperature nonuniformity in a subcooled liquid, and without taking them into account practically coincide, which indicates that the natural convection flow is formed mainly due to mass forces caused by difference in phase densities. The obtained data can be useful for creating more accurate empirical models describing the process of stable film boiling in subcooled liquid. All calculations were performed using the ANES CFD code developed at the Department of Engineering Thermal Physics of the National Research University MPEI.

One of the requirements that have to be met is substantiating the safety of newly designed and constructed lead cooled reactors is to evaluate the consequences from possible escape of fission products from nuclear fuel into the coolant during an accident in which part of fuel pins lose their leak tightness. Hence, it is of relevance to develop a model and a computation module based on this model for simulating the interaction of volatile fission products dissolved in the lead melt (iodine and cesium isotopes, and other radionuclides) with the bubbles of gaseous fission products (xenon and krypton isotopes). The consideration of this process is very important in substantiating the safety of lead cooled reactors, because the interaction of volatile fission products dissolved in the lead melt with the bubbles of gaseous fission products has an effect on the content of dissolved radionuclides in the lead melt and on the release of radionuclides into the gas space above the lead melt. The subsequent migration of radionuclides in the reactor gas circuit results in that the activity of radionuclides becomes redistributed in the circuit. It also facilitates the release of activity, as a consequence of loss of leak tightness of the circuit components, into the reactor rooms and the ventilation system. In addition, the bubbles of gaseous fission products in the lead melt interact with the hydrogen isotopes dissolved in the melt (protium and tritium) and facilitate their escape into the reactor gas circuit. The article presents the results from the development of the model and corresponding software unit, and its incorporation into the AEROSOL/LM module, which is part of the EUCLID/V2 integrated code, for calculating the behavior of inert radioactive gas bubbles, including the interaction of bubbles with the radionuclides dissolved in lead melt and the release of bubbles into the reactor gas space. To check how correctly the models are implemented in the code by means of software, the article presents data on the verification of the developed module based on the results of solving test problems.

To date, in the regulatory and technical documents containing requirements for the quality of fire-resistant fluids, there is no unified concept of the rejection indicators of oil, upon reaching the limit values of which the use of the oil is prohibited. In this regard, difficulties arise in making decisions about extending the service life of fire-resistant fluids. Some facilities use oils with an acid number of 3 mg KOH/g and higher, which significantly reduces the reliability of the oil-filled equipment of the power plant, up to the development of emergency situations. The article examines in detail the processes of destruction of fire-resistant fluids based on triaryl phosphates and the conditions for phosphating metals. The results are presented from studies of the surfaces of steel plates after conducting an analysis to determine the corrosion properties of oils in accordance with FR.1.31.2010.08899 Methodology for Measuring the Anticorrosion Characteristics of Samples of Mineral and Fire-Resistant (type OMTI) Turbine Oils (certificate of certification no. MVI 60-09 dated November 17, 2009). It has been shown that, when using oils with a maximum acid number, a film consisting of iron phosphates is formed on the surface of steel coupons, with the simultaneous occurrence of a polycondensation process of oil-decomposition products. Taken together, this leads to an incorrect definition of such an oil quality criterion as corrosion on steel plates. The results of studies of deposits taken from various units of the turbo unit lubrication system are presented, indicating an inevitable decrease in the reliability of the oil system when using oil with a high acid number.

Surface film condensation processes occur in many technical devices. For designing of industrial condensers, empirical methods are usually used, which, however, are insensitive to some factors affecting the intensity of these processes, which limits the range of their application for design. Using existing methods, it is possible for one to calculate the heat-transfer surface area required to maintain the required heat rate, but it is not possible to specify tube arrangement in the condenser, which determines the flow of the vapor-liquid mixture in the intertube space and, ultimately, the efficiency of the device. To design more efficient condensers, it is necessary to improve the methods, including those based on data obtained using modern methods of numerical modeling of heat and mass transfer processes. One of the promising methods for calculating surface condensation processes in tube bundles is the Volume of Fluid (VOF) method, supplemented by models for taking into account heat and mass transfer at the interphase surface. The VOF method has been implemented in some commercial codes, but the settings of the code parameters and the choice of a suitable mesh and turbulence model for calculating the condensation processes of moving vapor are not at all obvious. Previously, the authors of this work proposed and implemented a modified model of W.H. Lee in the in-house CFD code ANES and the commercial CFD code ANSYS Fluent for calculating heat and mass transfer processes at the interphase surface using the VOF method. The model was verified on typical problems and limited data for tube bundles. In this paper, condensation and turbulent vapor flow models are implemented in the open-source CFD code OpenFOAM. The models were validated on Stefan problems and condensation of moving and stationary vapor of various heat carriers, and cross-verification between OpenFOAM, ANES, and ANSYS Fluent codes was carried out.

In India, solar energy, especially concentrated solar power (CSP), offers a promising path toward the production of clean, renewable energy. The government’s ambitions for increasing the capacity of solar electricity and the abundance of solar resources have brought CSP into further spotlight. Notwithstanding its potential, CSP has encountered noteworthy obstacles impeding its extensive use. These difficulties include the absence of trustworthy data, the limitations of domestic production capacity, and the rivalry posed by photovoltaic (PV) technology. India boasts over 300 clear sky days a year with solar radiation of 1700–1900 kW h per kilowatt peak, making it a country with significant potential for producing electricity from solar power systems per watt. The Indian government has set goals to generate an additional 104 GW of solar electricity by 2025 and 448 GW by 2030. In this review, we try to offer a thorough evaluation of the present status of the CSP in India and discuss the obstacle and future potential of the same. This review aims to provide insightful information for researchers, policymakers, industry stakeholders, and practitioners in the renewable energy field.

Climate change with Egypt’s increasingly hot weather and its plans towards energy transition, addressing an approach for clean heating, ventilation, and air condition solutions is becoming requisite. This paper examines the potential of utilizing solar absorption cooling systems in institutional buildings by presenting a case study of a proposed solar absorption cooling system for a library building with an area of 4402 m², located at the British University in Egypt. The proposed solution is to replace 30% of the existing conventional air conditioning units with a hot-water driven single-effect absorption chiller powered by solar thermal vacuum tube solar collectors, coupled with a stratified hot water storage tank. The potential area of the solar collectors was calculated to be 856 m². A detailed analysis was done using TRNSYS (Transient Simulation System Software) as a simulation tool, to find that the optimum stratified hot water storage tank size is to be 10 m³; with a specific volume per solar collectors’ area of 0.01 m³/m². The proposed system covers the cooling demand of the library building for 8 to 9 months of the year without an auxiliary heater and saves almost 95% of the electrical energy consumed by the replaced conventional air conditioning system.