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Traditional research of environmental impact of natural draft cooling tower in nuclear power plant is based on diffusion model or tunnel experiment, and with the development of modern mainframe computers and turbulence models, it is possible to use CFD method to simulate plume drift. The CFD software, due to its powerful computing ability, can simulate and display the plume drift more accurately. This paper presents an effective way of generating terrain grids which can be used in StarCD, a CFD software. The SRTM terrain data is obtained from internet and IDW interpolation method is used in the co-ordinates translation process. A powerful program named GridInter is developed using Fortran90 to convert terrain data to StarCD vertex file, terrain grids generation process in StarCD including nuclear power plant building grids combination is also introduced, this model can be directly used in the numerical simulation of plume dispersion. [ABSTRACT FROM AUTHOR]

This paper mainly uses ANSYS-FLUENT 19.2 software to simulate the movement of the air-flow in a three-separation combined classifier. The simulation results indicate that the air-flow is uniformly distributed in the V-classifier under the action of dispersion plates and baffles. As the air-flow enters the rotor channel, the tangential velocity of the air-flow increases uniformly and remains stable in the axial direction, providing a stable centrifugal force field for particle classification. From the analysis of the flow field and particle trajectories, the separation interface between the upward path for particles and the downward path for coarse particles is relatively clear. The experimental results with sodium bicarbonate show that the V-classifier has a good pre-classification effect. The rotor cage speeds of 300 rpm and 500 rpm are the best working conditions for the coarse powder and fine powder collection, respectively. This study not only provides a new strategy for the design and development of air classifier, but also provides theoretical guidance for its application in industrial production. [ABSTRACT FROM AUTHOR]

Billet reheating is an important part of the steel production process. Since the production process will adopt different tube billet arrangement strategies, and the condition of the furnace hearth will also change due to long-term operation and accumulation of iron oxide scales, these factors will inevitably affect heating efficiency and temperature distribution uniformity of the tube billet, thereby affecting the quality of the final product. In this study, a physical and mathematical model was established for a 48 m diameter rotary hearth furnace of the seamless steel pipe production-line and typical 300 mm diameter tube billets of different lengths. Commercial FLUENT code was used to carry out CFD numerical simulation research on the influence of the aforementioned factors. Optimizing and adjusting strategies under different arrangement strategies were proposed, and the influence of furnace hearth condition change on heating effect was studied. The methods and simulation approach of this paper also have guidance for the billet heating control in similar continuous heating furnaces. [ABSTRACT FROM AUTHOR]

Data-driven approaches have achieved remarkable success in different applications, however, their use in solving PDE has only recently emerged. Herein, we present the potential fluid method, which uses existing data to nest physical meanings into mathematical iterative processes. Potential fluid method is suitable for PDE, such as CFD problems, including Burgers' equation. Potential fluid method can iteratively determine the steady-state space distribution of PDE. For mathematical reasons, we compare the potential fluid method with the finite difference method and give a detailed explanation. [ABSTRACT FROM AUTHOR]

Transformers are one of the most capital investments in the solar power generation. Their safe and stable operations in the electrical networks are important. The main failure factor of transformers is the high temperature generated by the losses during operation, which increases the probability of insulation damage that significantly affects the useful life of transformer. Considering the importance of oil temperature and its effects on the life of the transformer, a numerical method is developed in this paper to optimize the cooling system of the transformer. In this regard, genetic algorithm is used as an optimization method to minimize the total cost of the cooling system while maintaining the required thermal conditions of the transformer. A comprehensive parametric study is carried out among the effective cooling geometry parameters using 3-D electromagnetic and thermal models of the photovoltaic transformer to evaluate and analyze the temperature distribution. The accuracy and feasibility of the proposed method is established by comparing the numerical results with those obtained from the experimental test. The results of the proposed method are found to be in a good agreement with the experimental and simulation results. [ABSTRACT FROM AUTHOR]

This paper addresses the non-equilibrium condensation (NEC) in supersonic steam ejector under the assumptions of no slip velocity between the droplets and vapor phase and homogenous nucleation. The experimental data carried out by Moore has been used to verify the numerical results. It is illustrated that the maximum value of the flow mach number of the NEC model is lower than that of the equilibrium condensation model, and NEC model increases the ejector's entrainment ratio in comparison equilibrium condesation model. When using the NEC model, the nucleation characteristics such as subcooling degree, nucleation rate could be obtained in ejector flow field. [ABSTRACT FROM AUTHOR]

This paper focuses on the CFD studies on one of the commonly used drying processes for different applications. First, a brief information about drying is given with determining important properties that effect drying characteristics. Next, basic principles of CFD modelling are explained while capabilities of computational processing are presented. A detailed literature survey about CFD studies in convective drying process is then conducted. Finally, some sound concluding remarks are listed. It may be concluded that the CFD is a powerful and flexible tool that can be adopted to many different physical situations including complex scenarios, results of CFD simulations represent good predictions for fluid-flow, heat and mass transfer of various drying methods and those numerical studies can be used for validation and controlling of applicability of new drying systems. [ABSTRACT FROM AUTHOR]

This paper involves an exhaust gas waste heat recovery system for vehicles, which uses thermoelectric modules and a heat exchanger to produce electric power. Based on summarizing the latest research of vehicle exhaust thermoelectric generator, it presents two new fin structures for the cylindrical heat exchanger in a thermoelectric generator system. It mainly studies the thermal performance of two kinds of 3-D cylindrical heat exchanger models including spiral-fin heat exchanger with variable pitch in a CFD simulation environment. In terms of interface temperature and thermal uniformity and based on an evaluation method of the temperature uniformity for the heat exchangers, the thermal characteristics of heat exchangers with different pitch angle of the twisted fins, pitch of spiral fin, fin thickness, and fin height are discussed. Two new fin structures are feasible to enhance the heat transfer performance of heat exchanger. [ABSTRACT FROM AUTHOR]

In this paper, influence of magnetic field on turbulence characteristics of twodimensional flow is investigated. The present study has been undertaken to understand the effects of a magnetic field on mean velocities and turbulence parameters in turbulent 2-D channel flow. Several cases are considered. First laminar flow in a channel and MHD laminar channel flow are analyzed in order to validate model of magnetic field influence on electrically conducting fluid flow. Main part of the paper is focused on MHD turbulence suppression for 2-D turbulent flow in a channel and around the flat plate. The simulations are performed using ANSYS CFX software. Simulations results are obtained with BSL Reynolds stress model for turbulent and MHD turbulent flow around flat plate. The nature of the flow has been examined through distribution of mean velocities, turbulent fluctuations, vorticity, Reynolds stresses and turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

This review paper provides data about research activities at the School of the turbulent swirling flow at the Faculty of Mechanical Engineering, University of Belgrade, conducted in the period 1941 up to date. An overview is provided of the main directions in this research area. First papers dealt with the turbulent swirling flow in hydraulic turbines to be continued by the experimental and analytical approaches on the axial fans pressure side. The complexity of 3-D, non-homogeneous, anisotropic turbulent velocity fields required complex experimental and theoretical approach, associated with the complex numerical procedures. Analytical approaches, complex statistical analyses and experimental methods and afterwards CFD employed in the research are presented in this paper. The 150 scientific papers, numerous diploma works, several master of science (magister) theses, six Ph. D. theses and two in progress, 40 researchers, national and international projects are the facts about the School. Scientific references are chronologically presented. Numerous abstracts from scientific conferences, presentations, projects with industry and lectures are not given here. [ABSTRACT FROM AUTHOR]

Due to the rapid progress in computer hardware and software, CFD became a powerful and effective tool for implementation turbulence modeling in defined combustion mathematical models in the complex boiler geometries. In this paper the commercial CFD package, ANSYS FLUENT was used to model fluid flow through the boiler, in order to define velocity field and predict pressure drop. Mathematical modeling was carried out with application of Standard, RNG, and Realizable k-ε turbulence model using the constants presented in literature. Three boilers geometry were examined with application of three different turbulence models with variants, which means consideration of 7 turbulence model arrangements in FLUENT. The obtained model results are presented and compared with data collected from experimental tests. All experimental tests were performed according to procedures defined in the standard SRPS EN 303-5 and obtained results are presented in this paper for all three examined geometries. This approach was used for improving construction of boiler fired by solid fuel with heat output up to 35 kW and for selection of the most convenient construction. [ABSTRACT FROM AUTHOR]

In order to accelerate the numerical simulation and optimization of gas turbine-related configurations, a source based computational fluid dynamics (SCFD) approach is developed for flow and heat transfer simulations. Different sources depending on the fluid porosity at each grid node in the computational domain are introduced to the continuity, momentum, energy and turbulence model equations, so that both the fluid and solid regions can be solved as one region. In the present paper, test cases including a ribbed channel and a winglet shrouded turbine cascade with tip injection are investigated using the SCFD and CFD with body-fitted meshes. Impacts of grid clustering and turbulence model equation sources on the SCFD precision are examined. Numerical results show that the SCFD predicts consistent aerothermal performance with the fluid dynamics with body-fitted meshes and experiments. The validated SCFD scheme is then employed in a response surface optimization of tip jet holes on the winglet shroud tip. A jet arrangement with the minimum energy loss and injection mass-flow rate is obtained, indicating that source based predictions can be applied to the preliminary aero-thermal design of turbine blades. [ABSTRACT FROM AUTHOR]

This paper is presented in order to elucidate some numerical investigations re-lated to a partially premixed gasoline fuelled engine by means of three dimen-sional computational fluid dynamics code. Comparing with the diesel fuel, gaso-line has lower soot emission because of its higher ignition delay. The application of double injection strategy reduces the maximum heat release rate and leads to the reduction of NOx emission. For validation of the model, the results for the mean in-cylinder pressure, heat release rate, NOx and soot emissions are com-pared with the corresponding experimental data and show good levels of agree-ment. The effects of injection characteristics such as, injection duration, spray angle, nozzle hole diameter, injected fuel temperature and exhaust gas recircula-tion rate on combustion process and emission formation are investigated yielding the determination of the optimal point thereafter. The results indicated that opti-mization of injection characteristics leads to simultaneous reduction of NOx and soot emissions with negligible change in indicated mean effective pressure. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics is a numerical tool that is highly accurate to simulate a very large number of applications and processes. The CFD analysis has emerged as a viable technique to provide effective and efficient design solutions. In this paper, a CFD analysis for improving temperature distribution in a chili dryer is presented. The CFD technique is used to simulate the temperature distribution inside the chamber. For this purpose, the continuity, momentum and energy equations are considered. The results obtained by CFD analysis based on a specific geometry are presented in order to improve the temperature distribution. In addition, these results were verified experimentally. The distribution of temperatures showed small differences around 4 K during the warming up period. The simulation and experimental results can be useful for further designs of chili dryers with different specific geometries. [ABSTRACT FROM AUTHOR]

In this paper, numerical solutions for the generalized Rosenau-KdV equation are considered via the energy and momentum conservative non-linear implicit finite difference scheme. Unique existence of the conservative properties of the solutions for the difference scheme is shown. Numerical results demonstrate that the scheme is efficient and reliable. [ABSTRACT FROM AUTHOR]

The paper discusses the temperature changes in mechanical jet tabs in a system of rocket motor thrust vector control, estimated by the simulation and experimental tests methodology. The heat transfer calculation is based on complex computational fluid dynamics simulations of both the nozzle and external tab flows, as the comprehensive integral flow zones with high flow parameters gradients. Due to a complexity of the model for flow calculations, the experimental estimation of the calculated results is carried out. The temperature is measured by jet tabs embedded thermocouples, and conducted through the rocket motor static tests. A good agreement of the calculated and measured results is achieved. The main aim of the developed method is to establish an approved calculation tool for designing new thurst vector control systems in order to avoid disadvantages due to overheating. [ABSTRACT FROM AUTHOR]

With increasing inlet temperature of gas turbines, turbine blades need to be effectively protected by using cooling technologies. However, the deposition from the fuel impurities and dust particles in the air is often found inside film holes, which results in partial hole blockage. In this paper, the deposition geometry is simplified as a rectangular channel, and the effect of three blockage ratios is investigated by using the computational fluid dynamics. In addition, water droplets are also released from the coolant inlet to provide a comparison of the results with and without mist injection. It is found that the lateral film cooling effectiveness is reduced with increasing blockage ratio. For all the cases with the blowing ratio 0.6, 1% mist injection provides an improvement of the cooling performance by approximately 10%. [ABSTRACT FROM AUTHOR]

Turbine blades operate under a harsh environmental condition, and the inlet temperature of gas turbines is increasing with requirement of high engine efficiency. Some cooling schemes are adopted to prevent these blades from the thermal erosion of the hot mainstream. Film cooling technology is used widely and effectively in gas turbines. The coolant air is suppressed to the wall by the mainstream after jetting out of the film hole. A new hole configuration is first proposed to improve the film cooling characteristics in this paper. Comparison between a conventional cylindrical hole and a new combined hole is conducted by CFD, and effects of various blowing ratios and droplet sizes are also investigated. Results show that the combined hole configuration provides a wider coverage than that in the cylindrical hole configuration case at high blowing ratios (M = 1.0 and M = 1.5). In addition, the film cooling with mist injection also provides a significant enhancement on cooling performance especially for the combined hole case with a small droplet size (10-5 m). [ABSTRACT FROM AUTHOR]

This paper, dealing with the problems of mathematical description of the tunnel fire development process with the use of experimental data, outlines the procedure of correction of the existing and obtaining of an improved CFD model package. The improved CFD model was developed on the basis of detailed analysis and comparison of experimental and numerical results, through consideration of the physical structure of all processes affecting combustion. During the analysis it was noticed that the existing CFD model in the part covering combustion based on the so-called steady laminar flamelet model, treats the combustion process almost as a direct correlation between the processes of mixing gasses and heat release rate. This potential deficiency has been overcome by correction of the model in the section defining boundary condition for the burning surface and by establishing a direct correlation between the measured value of the fuel mass change rate and the amount of heat released from burning surface. In this way a modification of complex stoichiometric combustion processes was avoided, while providing the model that better describes and predicts the course of events in this type of complex, anisotropic and turbulent flow of gases in the tunnel. [ABSTRACT FROM AUTHOR]

The aim of the research described in this paper, is to make a virtual thermal manikin that would be simple, but also robust and reliable. The virtual thermal manikin was made in order to investigate thermal conditions inside vehicle cabins. The main parameters of the presented numerical model that were investigated in this paper are mesh characteristics and turbulence models. Heat fluxes on the manikin's body segments obtained from the simulations were compared with published results, from three different experiments done on physical thermal manikins. The presented virtual thermal manikin, meshed with surface elements of 0.035 m in nominal size (around 13,600 surface elements) and in conjunction with the two-layer RANS Realizable k-e turbulence model, had generally good agreement with experimental data in both forced and natural flow conditions. [ABSTRACT FROM AUTHOR]

As the global demand for energy grows, numerous studies in the field of energy efficiency are stimulated, and one of them is certainly the use of pumps in turbine operating mode. In order to reduce time necessary to determine pump characteristic in turbine operating mode problem was studied by computational fluid dynamics approach. The paper describes various problems faced during modeling (pump and turbine mode) and the approaches used to resolve the problems. Since in the majority of applications, the turbine is a pump running in reverse, many attempts have been made to predict the turbine performance from the known pump performance, but only for best efficiency point. This approach does not provide reliable data for the design of the system with maximum energy efficiency and does not allow the determination of the head for a wide range of flow rates. This paper presents an example of centrifugal norm pump operating in both (pump and turbine) regime and comparison of experimentally obtained results and computational fluid dynamics simulations. [ABSTRACT FROM AUTHOR]

Combustion in a large-bore natural gas fuelled diesel engine operating under homogeneous charge compression ignition mode at various operating conditions is investigated in the present paper. Computational fluid dynamics model with integrated chemistry solver is utilized and methane is used as surrogate of natural gas fuel. Detailed chemical kinetics mechanism is used for simulation of methane combustion. The model results are validated using experimental data by Aceves, et al., conducted on the single cylinder Volvo TD100 engine operating at homogeneous charge compression ignition conditions. After verification of model predictions using in-cylinder pressure histories, the effect of varying equivalence ratio and engine speed on combustion parameters of the engine is studied. Results indicate that increasing engine speed provides shorter time for combustion at the same equivalence ratio such that at higher engine speeds, with constant equivalence ratio, combustion misfires. At lower engine speed, ignition delay is shortened and combustion advances. It was observed that increasing the equivalence ratio retards the combustion due to compressive heating effect in one of the test cases at lower initial pressure. Peak pressure magnitude is increased at higher equivalence ratios due to higher energy input. [ABSTRACT FROM AUTHOR]

Simulations for both multiphase flows and supersonic single phased flows are well known, however the combination is a less investigated area of research, as the two basic approaches of computational fluid dynamics, the pressure and the density based approach, each describe one of the phases in a better way than the other one. In this paper, we systematically investigate the solver quality of the open source computational fluid dynamics code OpenFOAM in handling transonic flow phenomena that typically occur inside the breaking chamber of high voltage circuit breakers, during contact separation. The solver quality is then compared with that of chosen commercial computational fluid dynamics tools. The main advantage of OpenFOAM is that, contrary to most of the commercial simulation tools, it is license fee free and allows access to the source code. This means that complicated multi physics phenomena inside the arcing chamber can be directly modeled into the code by users, which opens an opportunity to remove limitations of commercial computational fluid dynamics tools. Particularly, the shock capturing capability of OpenFOAM will be evaluated for the transonic internal flow which typically occurs in high voltage circuit breakers. Overall, OpenFOAM shows acceptable shock capturing capabilities in the performed verification and validation studies, with the solver quality comparable to some of the tested commercial computational fluid dynamics tools. There is still room for further solver quality improvements in OpenFOAM by implementing better shock capturing schemes such as a density- based flux-difference-splitting scheme or by writing better physical modeling of the shock/boundary layer interaction into the open architecture of OpenFOAM. [ABSTRACT FROM AUTHOR]

The numerical investigation on the wet steam flow in the last two stages of a 1000 MW fossil-fired low pressure steam turbine is presented in this paper. The non-equilibrium model via the classical nucleation theory is employed to simulate the condensing flow of the wet steam. The characteristics of the flow filed from design condition to low volume flow condition are calculated and the static performance of last stage moving blade is also obtained. The development of the back- flow phenomenon is clearly captured through the analysis of the velocity triangle. [ABSTRACT FROM AUTHOR]

In this paper, both the steady-state and transient-state of the films flow are investigated by CFD. The journal bearing dynamic characteristics such as the load capacity, damping and stiffness coefficients for several eccentricity, and length over diameter ratio (L/D) are obtained and compared with each other in different working conditions. Furthermore, the variation of various research parameters with eccentricity and L/D are also illustrated in detail. [ABSTRACT FROM AUTHOR]

This paper describes a numerical analysis of a heat transfer enhancement technique that introduces fractal-shaped design for impingement cooling. Based on the gas turbine combustion chamber cooling, a fractal-shaped nozzle is designed for the constant flow area in a single impingement cooling model. The incompressible Reynolds-averaged Navier-Stokes equations are applied to the system using CFD software. The numerical results are compared with the experiment results for array impingement cooling [ABSTRACT FROM AUTHOR]

This paper presents modification of the existing guided missile which was done by replacing the existing front part with the new five, while the rear part of the missile with rocket motor and missile thrust vector control system remains the same. The shape of all improved front parts is completely different from the original one. Modification was performed based on required aerodynamic coefficients for the existing guided missile. The preliminary aerodynamic configurations of the improved missile front parts were designed based on theoretical and computational fluid dynamics simulations. All aerodynamic configurations were tested in the T-35 wind tunnel at the Military Technical Institute in order to determine the final geometry of the new front parts. The 3-D Reynolds averaged Navier-Stokes numerical simulations were carried out to predict the aerodynamic loads of the missile based on the finite volume method. Experimental results of the axial force, normal force, and pitching moment coefficients are presented. The computational results of the aerodynamic loads of a guided missile model are also given, and agreed well with. [ABSTRACT FROM AUTHOR]

In the present paper, the combustion process and emission formation in the Lister 8.1 in-direct injection diesel engine have been investigated using a computational fluid dynamics code. The utilized model includes detailed spray atomization, mixture formation and distribution model which enable modeling the combustion process in spray/wall and spray/swirl interactions along with flow configurations. The analysis considers both part load and full load states. The global properties are presented separately resolved for the swirl chamber (pre-chamber) and the main chamber. The results of model verify the fact that the equal amount of the fuel is burned in the main and pre-chamber at full load state while at part load the majority of the fuel is burned in the main chamber. Also, it is shown that the adherence of fuel spray on the pre-chamber walls is due to formation of a stagnation zone which prevents quick spray evaporation and plays an important role in the increase of soot mass fractions at this zone at full load conditions. The simulation results, such as the mean in-cylinder pressure, heat release rate and exhaust emissions are compared with the experimental data and show good agreement. This work also demonstrates the usefulness of multi-dimensional modeling for complex chamber geometries, such as in in-direct injection diesel engines, to gain more insight into the flow field, combustion process, and emission formation. [ABSTRACT FROM AUTHOR]

Nowadays, computational fluid dynamics codes are prevalently used to simulate the gas dynamics in many fluid piping systems such as steam and gas turbines, inlet and exhaust in internal combustion engines. In this paper, a computational fluid dynamics software is used to obtain the total energy losses in adiabatic compressible flow at compact exhaust manifold junction. A steady-state one-dimensional adiabatic compressible flow with friction model has been applied to subtract the straight pipe friction losses from the total energy losses. The total pressure loss coefficient has been related to the extrapolated Mach number in the common branch and to the mass flow rate ratio between branches at different flow configurations, in both combining and dividing flows. The study indicate that the numerical results were generally in good agreement with those of expe-rimental data from the literature and will be applied as a boundary condition in one-dimensional global simulation models of fluid systems in which these com-ponents are present. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical simulation of air flow around the arrays of flat plate collectors and determination of the flow field, which should provide a basis for estimating a convective heat losses, a parameter which influences their working characteristics. Heat losses are the result of the reflection on the glass, conductive losses at the collector's absorber plate, radiation of the absorber plate and convective losses on the glass. Wind velocity in the vicinity of the absorber plate depends on its position in the arrays of collectors. Results obtained in the numerical simulation of flow around collectors were used as boundary conditions in modeling of thermal-hydraulic processes inside the solar collector. A method for coupling thermal-hydraulic processes inside the collector with heat transfer from plate to tube bundle was developed, in order to find out the distribution of the temperature of the absorber plate and the efficiency of the flat plate collectors. Analyses of flow around arrays of collectors are preformed with RNG k-ϵ model. Three values for free-stream velocity were analysed, i. e. 1 m/s, 5 m/s, and 10 m/s, as well as two values for the angle between the ground and the collector (20° and 40°). Heat transfer coefficient was determined from the theory of boundary layer. Heat transfer inside the plate cavity was analyzed assuming constant intensity of radiation. [ABSTRACT FROM AUTHOR]

Electronic chips are arranged in various manners according to design conditions and constraints, and thus the influence of chip arrangement on the entire thermal performance should be understood ahead of design and manufacture of electronic cooling systems. In this paper, a minichannel heat sink is considered for electronic cooling, and three kinds of chip arrangement are designed and studied: diagonal arrangement (Case 1), parallel arrangement (Case 2), and stacked arrangement (Case 3). The single-phase laminar liquid flow and conjugated heat transfer of the minichannel heat sinks are investigated through computational fluid dynamics technique for dealing with the normal-scale Navier-Stokes equations and energy equations. Numerically predicted results are qualified by comparing the previous experimental data and by a grid-independent test. Temperature distributions on the chip surfaces are presented and the thermal performance in terms of total thermal resistance is also compared. It is found with diagonal arrangement (Case 1) the minichannel heat sink provides the best thermal performance. [ABSTRACT FROM AUTHOR]

In this paper we present numerical study, using software named Calculation FDS, of thermal plume that evolve from the source at the entrance of a vertical channel. In the literature, there are researchers who are interested in the interaction of plume with confined medium. These studies are based on the determination of the global structure of plume confined. It is found that this plume consists of three distinct zones. First zone near source (instability zone), followed by a second zone, the plume development, and third zone which is the zone of turbulence, Comparing the overall structure of the plume confined to that of the free plume, one can identify the presence of a third zone (zone of instability). The aim is firstly to determine the height of the instability zone located above of source, and secondly, to make a spectral study frequencies exhaust. Thus, effects of geometrical parameters on frequencies of these escapements and height an instability zone can be shown. The final aim is to establish correlations between the dimensionless Strouhal and Grashof numbers. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including heat transfer, thermal process in internal combustion engines and computational fluid dynamics.

The aim of this paper is to examine whether the use of baffles in a combustion chamber, one of the well-known low-cost methods for the boiler performance improvement, can be enhanced. Modern day tools like computational fluid dynamics were not present at the time when these measures were invented, developed, and successfully applied. The objective of this study is to determine the influence of location and length of a baffle in a furnace, for different mass flows, on gas residence time. The numerical simulations have been performed of a simple Scandinavian stove like furnace. The isothermal model is used, while air is used as a medium and turbulence is modeled by realizable k-e model. The Lagrange particle tracking is used for the residence time distribution determination. The statistical analysis yielded the average residence time. The results of the computational fluid dynamics studies show that influence of baffle positions, dimension, and flow rates can decrease residence time even 17% but also increase it up to 13%. Vertical position of the baffle is the most important factor, followed by the length of the baffle, while the least important showed to be the mass flow. [ABSTRACT FROM AUTHOR]

In this paper Lattice Boltzmann simulation of turbulent natural convection withlarge eddy simulations in tall enclosures which is filled by air with Pr = 0.71has been studied. Calculations were performed for high Rayleigh numbers (Ra = 107-109) and aspect ratios change between 0.5 and 2 (0.5 < AR < 2). The present results are validated by finds of an experimental research at Ra = 1.58·109. Effects of the aspect ratios in different Rayleigh numbers are displayed on streamlines, isotherm counters, vertical velocity and temperature at the middle of the cavity, local Nusselt number and average Nusselt number. The average Nusselt number increases with the augmentation of Rayleigh numbers. The increment of the aspect ratio causes heat transfer to decline in different Rayleigh numbers. [ABSTRACT FROM AUTHOR]

Biomass energy is one of the most accessible and readily available carbon-neutral energy options as a RES. It is regarded as a viable alternative fuel for coal combustion, particularly for biomass co-firing with pulverized coal, with numerous applications. The CFD can provide reasonably accurate solutions to complex thermo-chemical-fluid interactions, which is useful for understanding the design or retrofit of boilers and can save time, money, and effort. In this study, a CFD simulation of a 300 MW pulverized coal boiler with biomass co-firing was performed to investigate the impact of biomass co-firing with coal, considering the biomass co-firing ratio, mixing effect, and feeding temperature. The results show that the flow field in the furnace does not change significantly under different biomass blending ratio. Biomass co-firing can reduce peak temperatures in the furnace and make the temperature distribution more uniform. The concentration of unburned carbon in the furnace decreases as the biomass blending ratio increases. Furthermore, biomass blending has a significant impact on nitrogen oxide reduction, with NOx emissions reduced by 20% and 28%, respectively, when the biomass blending ratio is 15% and 30%. The change of parameters inside the furnace caused by the reduction of biomass powder feeding temperature about 80 K is not significant. On the other hand, co-firing biomass with coal, reduces the risk of biomass spontaneous combustion while maintaining the furnace combustion stability and boiler combustion efficiency. The optimum ratio of biomass co-firing ration is deduced in this study is up to 20%. [ABSTRACT FROM AUTHOR]

With the rapid development of information technology equipment and its use in the teaching and learning activities, the working environment (especially indoor air quality) in which students and pupils spend a great deal of time in educational institutions has been changing. Therefore, special attention must be paid to indoor air quality and comfort. It is of great importance to maintain indoor air quality in an object, such as information technology classrooms, where a large number of students spend long periods of time. Poor indoor environment can negatively affect scholarly performances and cause discomfort and poor work performance. The problem of indoor air quality in educational institutions can be more serious than in other types of objects, because of the higher concentration of students and information technology equipment. This paper analyzes the changes in air quality in an information technology classrooms, when occupied with students, for the period from March to April. The changes of indoor air temperature, relative humidity, and carbon dioxide concentration are monitored in the classroom, as well as outdoor temperature and relative humidity. Several cases are studied: the classroom with closed windows and doors (closed classroom), the classroom with natural ventilation, the classroom cooled with a split system (cooled classroom). Responses of students are followed for each case. The analysis is performed based on the measurement results and numerical simulations using the computational fluid dynamics package, and measures are proposed to improve the indoor air quality in the considered classroom. [ABSTRACT FROM AUTHOR]

Thermodynamic optimization of thermal devices requires information about the influence of operational and structural parameters on its behaviour. The interconnections among parameters can be estimated by tools such as CFD, experimental statistic of the deviceetc. Despite precise and comprehensive results obtained by CFD, the time of computations is relatively long. This disadvantage often cannot be accepted in case of optimization as well as online control of thermal devices. As opposed to CFD the neural network or regression is characterized by short computational time, but does not take into account any physical phenomena occurring in the considered process. The CFD model of heat exchanger was built using commercial package Fluent/Ansys. The empirical model of heat exchanger has been assessed by regression and neural networks based on the set of pseudo-measurements generated by the exact CFD model. In the paper, the usage of the developed empirical model of heat exchanger for the minimisation of TEC is presented. The optimisationconcerns operational parameters of heat exchanger. The TEC expresses the cumulative exergy consumption of non-renewable resources. The minimization of the TEC is based on the objective function formulated by Szargut. However, the authors extended the classical TEC by the introduction of the exergy bonus theory proposed by Valero. The TEC objective function fulfils the rules of life cycle analysis because it contains the investment expenditures (measured by the cumulative exergy consumption of non-renewable natural resources), the operation of devices and the final effects of decommissioning the installation. [ABSTRACT FROM AUTHOR]

In this paper, turbulent swirling flow in circular pipe is numerically investigated using OpenFOAM, an open-source computational fluid dynamics software. Flow is computed as 2-D axisymmetric, with various turbulent models, but with main accent on computations with Reynolds stress transport models. Two Reynolds stress models were used in computations: Launder-Gibson and Speziale-Sarkar-Gatski models. Previous author's experimental results are used as a validation tool for numerical computations. It was shown that standard two-equation models can not predict the flow in right manner, while the Reynolds stress models give good prediction of mean velocities. As a part of research Speziale-Sarkar-Gatski model is implemented in OpenFOAM code. [ABSTRACT FROM AUTHOR]

This paper presents a review of particle deposition research in film-cooled gas turbines based on the recent open literature. Factors affecting deposition capture efficiency and film cooling effectiveness are analyzed. Experimental studies are summarized into two discussions in actual and virtual deposition environments. For investigation in virtual deposition environments, available and reasonable results are obtained by comparison of the Stokes numbers. Recent advances in particle deposition modeling for computational fluid dynamics are also reviewed. Various turbulence models for numerical simulations are investigated, and solutions for treatment of the particle sticking probability are described. In addition, analysis of injecting mist into the coolant flow is conducted to investigate gas-liquid two-phase flow in gas turbines. The conclusion remains that considerable research is yet necessary to fully understand the roles of both deposition and multiphase flow in gas turbines. [ABSTRACT FROM AUTHOR]

Lately, experimental methods and numerical simulations are equally employed for the purpose of developing incineration bubbling fluidized bed (BFB) facilities. The paper presents the results of the 2-D CFD model of liquid fuel combustion in BFB, applied for numerical simulation of a fluidized bed furnace. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The proposed numerical model comprises energy equations for all three phases (gas, inert fluidized particles, and liquid fuel), as well as the transport equations of chemical components that are participating in the reactions of combustion and devolatilization. The model equations are solved applying a commercial CFD package, whereby the user submodels were developed for heterogenic fluidized bed combustion of liquid fuels and for interphase drag forces for all three phases. The results of temperature field calculation were compared with the experiments, carried out in-house, on a BFB pilot facility. The numerical experiments, based on the proposed mathematical model, have been used for the purposes of analyzing the impacts of various fuel flow rates, and fluidization numbers, on the combustion efficiency and on the temperature fields in the combustion zone. [ABSTRACT FROM AUTHOR]

In this paper the steady-state analysis has been carried out on single phase natural circulation loop with water and water based Al2O3 (Al2O3-water) nanofluid at 1%, 3%, 5%, and 6% particle volume concentrations. For this study, a 3-D geometry of natural circulation loop is developed and simulated by using the software, ANSYS (FLUENT) 14.5. Based on the Stokes number, mixture model is adopted to simulate the nanofluid based natural circulation loop. For the simulations, the imposed thermal boundary conditions are: constant heat input over the range of 200-1000 W with step size of 200 W at the heat source and isothermal wall temperature of 293 K at the heat sink. Adiabatic boundary condition is imposed to the riser and down-comer. The heat transfer characteristics and fluid-flow behavior of the loop fluid in natural circulation loop for different heat inputs and particle concentrations are presented. The result shows that the mass-flow rate of loop fluid in natural circulation loop is enhanced by 26% and effectiveness of the natural circulation loop is improved by 15% with Al2O3-water nanofluid when compared with water. All the simulation results are validated with the open literature in terms of Reynolds number and modified Grashof number. These comparisons confidently say that the present 3-D numerical model could be useful to estimate the performance of natural circulation loop. [ABSTRACT FROM AUTHOR]

Numerical flow simulations have been carried out in order to analyze the possibilities of numerical prediction of a steady-state incompressible air flow through a conical diffuser named Azad diffuser. The spreading angle of this diffuser is 8° and it has cylindrical parts of the constant diameter in the inlet and outlet flow zones. Numerical analysis has been performed by the use of the standard k-ε turbulence model. The simulations have been performed using the Ansys CFX and the OpenFOAM software for cases of 2-D and 3-D computational domains. In both cases a fully developed turbulent flow at the inlet section of diffuser is present. The numerical flow simulation in a 2-D computational domain has been performed under the assumption of an axisymmetric flow in the diffuser. Numerically obtained results have been compared with experimental data. Results obtained with these two softwares have also been mutually compared. At the end the results obtained by CFD for the cases of 2-D and 3-D computational domains have been mutually compared, and the advantages and disadvantages of performing numerical simulations under the assumption of an axisymmetric flow in the diffuser have been analyzed. [ABSTRACT FROM AUTHOR]

The aim of the paper is to present a three dimensional transient cooling analysis of an automobile cabin with a virtual manikin under solar radiation. In the numerical simulations the velocity and the temperature distributions in the automobile cabin as well as around the human body surfaces were computed during transient cooling period. The surface-to-surface radiation model was used for calculations of radiation heat transfer between the interior surfaces of the automobile cabin and a solar load model that can be used to calculate radiation effects from the Sun's rays that enter from the glazing surfaces of the cabin was used for solar radiation effects. Inhomogeneous air flow and non-uniform temperature distributions were obtained in the automobile cabin and, especially in ten minutes of cooling period, high temperature gradients were computed and measured and high temperature values were obtained for the surfaces which were more affected from the sunlight. Validations of the numerical results were performed by comparing numerical data with the experimental data presented in this study. It is shown that the numerical results were in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The main objective of the paper is to present the results of the computational fluid dynamics simulation of a direct injection single cylinder engine using diesel, biodiesel, or different mixture proportions of diesel and biodiesel and compare the results to a test bed measurement in the same functioning point. The engine used for verifying the results of the simulation is a single cylinder research engine from AVL with an open engine control unit, so that the injection timings and quantities can be controlled and analyzed. In Romania, until the year 2020 all the fuel stations are obliged to have mixtures of at least 10% biodiesel in diesel. The main advantages using mixtures of biofuels in diesel are: the fact that biodiesel is not harmful to the environment; in order to use biodiesel in your engine no modifications are required; the price of biodiesel is smaller than diesel and also if we compare biodiesel production to the classic petroleum based diesel production, it is more energy efficient; biodiesel assures more lubrication to the engine so the life of the engine is increased; biodiesel is a sustainable fuel; using biodiesel helps maintain the environment and it keeps the people more healthy. [ABSTRACT FROM AUTHOR]

In this paper some results concerning the evolution of 3-D fluid flow pattern through all four strokes in combustion chambers with entirely different bowl in piston geometry layouts ranging from "omega" to "simple cylinder" were presented. All combustion chambers i. e. those with "omega" bowls, with different profiles, and those with "cylinder" bowls, with different squish area ranging from 44% to 62%, were with flat head, vertical valves, and identical elevation of intake and exhaust ports. A bunch of results emerged by dint of multidimensional modeling of non reactive fluid flow in arbitrary geometry with moving objects and boundaries. The fluid flow pattern during induction and compression in all cases was extremely complicated and entirely 3-D. It should be noted that significant differences due to geometry of the bowl were encountered only in the vicinity of top dead centre. Namely, in the case of "omega" bowl all three types of organized macro flows were observed while in the case of "cylinder" bowl no circumferential velocity was registered at all. On the contrary, in the case of "cylinder" bowl some interesting results concerning reverse tumble and its center of rotation shifting from exhaust valve zone to intake valve zone during induction stroke and vice-verse from intake valve zone to exhaust valve zone during compression were observed while in the case of "omega" bowl no such a displacement was legible. During expansion the fluid flow pattern is fully controlled by piston motion and during exhaust it is mainly 1-D, except in the close proximity of exhaust valve. For that reason it is not affected by the geometry of the bowl. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical flow simulation in ventilation mill of Kostolac B power plant, where louvers and centrifugal separator with adjustable blade angle are used. Numerical simulations of multiphase flow were performed using the Euler Euler and Euler-Lagrange approach of ANSYS FLUENT software package. The results of numerical simulations are compared with measurements in the mill for both types of separators. Due to very complex geometry and large number of the grid cells, convergent solution with the Eulerian model could not be obtained. For this reason the mixture model was employed resulting in very good agreement with measurements, concerning the gas mixture distribution and velocity at the main and secondary burners. There was large difference between the numerical results and measurements for the pulverized coal distribution at the burners. Taking into consideration that we analyzed dilute mixture with very low volume fraction of the coal, the only choice was the Euler Lagrange approach, i. e. discrete phase model limited to volume fraction of the discrete phase less than 10-12%. Obtained distributions of the coal at the burners agree well for both types of separators. [ABSTRACT FROM AUTHOR]

In this paper the lattice Boltzmann method and field synergy principle are applied to simulate two-dimensional incompressible steady channel flow under low Reynolds number, and analyze the local influence on velocity field and temperature field caused by inserting cylinder obstacles of different cross-section. Furthermore, field synergy principle of elliptic flow type is applied to demonstrate that the increased interruption within the fluid increases the synergistic level between the velocity field and temperature gradient field. As the intersection angle between the velocity vector and the temperature gradient vector decreases by inserting cylinder obstacles to fluid field, the results of heat transfer will improve significantly. [ABSTRACT FROM AUTHOR]

In this paper CFD was used for simulation of the indoor climate in a part of a low energy building. The focus of the work was on investigating the computational set up, such as grid size and boundary conditions in order to solve the indoor climate problems in an accurate way. Future work is to model a complete building, with reasonable calculation time and accuracy. A limited number of grid elements and knowledge of boundary settings are therefore essential. An accurate grid edge size of around 0.1 m was enough to predict the climate according to a grid independency study. Different turbulence models were compared with only small differences in the indoor air velocities and temperatures. The models show that radiation between building surfaces has a large impact on the temperature field inside the building, with the largest differences at the floor level. Simplifying the simulations by modelling the radiator as a surface in the outer wall of the room is appropriate for the calculations. The overall indoor climate is finally compared between three different cases for the outdoor air temperature. The results show a good indoor climate for a low energy building all around the year. [ABSTRACT FROM AUTHOR]

The objective of this research work is to improve the in-cylinder air flowfor facilitate better mixing and ultimately achieve complete combustion. From the literature it is revealed that the bowl shape of the piston has influence on creating effective swirl, tumble, and cross tumble motions during intake and initial stages of compression stroke. Different types of combustion chambers have been designed by keeping the same bowl volume to maintain the constant compression ratio and to ensure that the improvement is only due to geometric parameters such as bulge diameter, lip distance, and bowl to bore diameter ratio. Simulation work is carried out using ANSYS Fluent 14.5 computational fluid dynamics tool. The influence of these parameters on in-cylinder flow was also studied in this paper. The values of swirl, tumble, and cross tumble were calculated. Further to ensure the results of theoretical simulation a modified re-entrant combustion chamber was fabricated and the experimental work has been carried out in Kirloskar TAFI single cylinder, 4-stroke, compression ignition engine for diesel and jatropha methyl ester blend 20%. The experimental results were compared with the conventional chamber. It is found that the modified re-entrant chamber improves the brake thermal efficiency and reduced HC, CO, and smoke emissions of diesel and jatropha methyl ester blend 20%for all the tested conditions when compared to the conventional chamber. [ABSTRACT FROM AUTHOR]