CFD Techniques Research Articles

Optimal Design of Perforated Diversion Wall Based on Comprehensive Evaluation Indicator and Response Surface Method: A Case Study

To investigate the impact of parameters of diversion wall holes on the flow state in the forebay of a combined sluice-pumping station project and optimize the relevant parameters, a total of 50 numerical simulations based on the CFD technique were performed, adopting the design of orthogonal experiments with 25 schemes under self-draining conditions and pumping conditions, respectively. For synthesizing flow state evaluation indicators under self-draining and pumping conditions, the variation coefficient method was used, and the results were analyzed through the response surface method. Thus, the relationship between the parameters of the diversion wall holes and the comprehensive evaluation indicator was established. The steepest ascent method was used to obtain the optimal parameters, and the results showed that the optimized holes can balance the flow state under self-draining and pumping conditions in the combined sluice-pumping station project. Compared to the case with the diversion wall unperforated, the uniformity of axial velocity distribution in the 6# inlet channel and 7# sluice chamber increased by 6.6% and 5.2%, respectively, and the maximum transverse velocity decreased from 0.32 m/s to 0.21 m/s, with a fall of 34.4%. This study provides reference and technical support for the hydraulic characteristic analysis, optimization design and rectifying measures selection of the combined sluice-pumping station project.

Mathematical procedure for predicting tube metal temperature in the radiant superheaters of a tangentially and front fired utility boilers

The superheaters can be indicated as one of the most critical components of the utility boilers experiencing highest temperatures. The local overheating of the heat exchangers material is a significant operational issue. The current and future market conditions implicate new unfavourable regimes of boiler operating conditions bringing the need for prediction capability of tube wall temperature in either design or retrofit process. There is a need to obtain a realistic metal temperature distribution based on uneven heat flux absorbed and complex steam flow. The current paper demonstrates a computational methodology of predicting tube metal temperature of radiant superheaters platens. It couples a full scale 3-D boiler simulations based on CFD technique on the combustion side with an in-house 1-D heated pipe flow model of the steam side. The methodology was applied to two different boilers with different firing strategy (front fired and tangentially fired) to demonstrate the model flexibility. The model is capable of identifying the exact location of specific platen in which the metal maximum temperature occurs. A validation study was conducted by utilising the available measurements. The computations are in qualitative and quantitative agreement with measurement. The modelling approach can be easily extended to boilers utilising all types of fuels as well as heat recovery steam generators.

Numerical Simulation in the Wind Action Analyses in Logistic Sheds with a Bridge Vent

Using Ansys Fluid Flow software, a numerical investigation was to study the wind distribution around logistic sheds with a bridge vent. Then, were considered several wind directions - direct approaching, oblique, oblique opposing, lateral, and opposing - and neighborhood conditions. The Shear Stress Transport turbulence model and rectangular mesh were employed. The application validation of the CFD technique occurred in the logistic shed without a bridge vent, and the results showed good concordance with the literature. Results analyzed areas characterized by suction and overpressure, as well as the attachment points and the recirculation zones in the flow visualization.

Numerical investigation on the effect of slit thickness and outlet angle of the bladeless fan for flow optimization using CFD techniques

The effect of outlet thickness and outlet angle of the bladeless fan have been an alysed numerically on the aerodynamic performance of the bladeless fan. Five different aerofoil profiles have been considered for the present work is Eppler 479, Eppler169, Eppler 473, S1046 and S1048. The bladeless fan arrangement has been achieved by converting the aerodynamic models listed above. The ANSYS ICEM CFD 16.0 have been used to discretize the enclosure and bladeless fan through finite volume approach. The mesh model is then imported into ANSYS CFX 16.0 pre-processor for applying the required boundary conditions. The governing equations namely continuity and momentum are used to solve the flow physics through and across the bladeless fan and SST k-? turbulence model has been used to predict the turbulence in the bladeless fan. The effect of outlet thicknesses and outlet angles have been varied for all the five aerofoil configurations mentioned and the volumetric flow at inlet have been adjusted from 5 LPS to 80 LPS. Outlet thickness is varied from 0.8, 1.0, 1.3, 1.5 and 2 mm and the slit angle is varied from 20 degrees to 80 degrees in step of 10 degrees. The results predicted that Eppler 473 aerofoil profile showed better performance when the thickness of slit and outlet angle has been fixed constant as 1 mm and 70 degree respectively. Also, the maximum discharge flow ratio is recorded for an inlet volumetric flow rate of 80 LPS and it is found to be 34.37. The present numerical study substantiated that outlet thickness plays a dominant role on the bladeless fan’s aerodynamic performance compared to outlet angle and aerodynamic shape considered in this numerical analysis. The contours of velocity, streamline and pressure of the bladeless fan have been discussed.

Revisit flame modulation towards low-NOx and uniform thermal field in heating flue of a coke oven

To alleviate the environmental issues from the coal coking process, many efforts have been conducted on air staging and flue gas recirculation to dilute oxygen content with only a modest success of a NO discharge between 500 and 1000 ppm. In this work, we have attempted to modulate the structure of the fuel inlet to dilute the fuel content for a further mitigation of NOx emission. By using the CFD technique, three key structural parameters were used to demonstrate the effect on NOx formation and thermal uniformity in the heating flue. A three-dimensional CFD model was established based on an industrial scale coke oven battery of 7.63 m in height, and its reliability was verified by validating the calculation against practical data collected on-site. Comparative simulations were carried out in terms of flue gas flow pattern, temperature profile, fuel species and NO concentration distribution. The results show that the benchmark battery has probably selected appropriate parameters for the internal recirculation, but falls short with respects to the size of fuel inlet and the space between the fuel and air inlets. Compared to the basic design, the modified one presents a 57.3% reduction in NO formation, and an improved vertical temperature uniformity.

Numerical investigation on the effect of slit thickness and outlet angle of the bladeless fan for flow optimization using CFD techniques

The effect of outlet thickness and outlet angle of the bladeless fan have been an alysed numerically on the aerodynamic performance of the bladeless fan. Five different aerofoil profiles have been considered for the present work is Eppler 479, Eppler169, Eppler 473, S1046 and S1048. The bladeless fan arrangement has been achieved by converting the aerodynamic models listed above. The ANSYS ICEM CFD 16.0 have been used to discretize the enclosure and bladeless fan through finite volume approach. The mesh model is then imported into ANSYS CFX 16.0 pre-processor for applying the required boundary conditions. The governing equations namely continuity and momentum are used to solve the flow physics through and across the bladeless fan and SST k-? turbulence model has been used to predict the turbulence in the bladeless fan. The effect of outlet thicknesses and outlet angles have been varied for all the five aerofoil configurations mentioned and the volumetric flow at inlet have been adjusted from 5 LPS to 80 LPS. Outlet thickness is varied from 0.8, 1.0, 1.3, 1.5 and 2 mm and the slit angle is varied from 20 degrees to 80 degrees in step of 10 degrees. The results predicted that Eppler 473 aerofoil profile showed better performance when the thickness of slit and outlet angle has been fixed constant as 1 mm and 70 degree respectively. Also, the maximum discharge flow ratio is recorded for an inlet volumetric flow rate of 80 LPS and it is found to be 34.37. The present numerical study substantiated that outlet thickness plays a dominant role on the bladeless fan’s aerodynamic performance compared to outlet angle and aerodynamic shape considered in this numerical analysis. The contours of velocity, streamline and pressure of the bladeless fan have been discussed.

STUDY ON COOLING OF HIGH PERFORMANCE SIC FEATURES

High-performance electronic parts are vital features in almost all modern motorized machines. These silicon components are significantly minimised, especially in transportation branch. Concentration of performance requires perfect cooling conditions. A fluid flow cooling by an active cooling circuit with heat sinks is a commonly used principle. Sufficient cooling and uniform temperature field on heat transfer area are crucial parameters for the sustainable function of Silicon-Carbide components. Producer of electric vehicles induces research in the field of coolers due to the requirements of installed SiC features. This study uses advanced CFD methods to analyse the current state of commonly manufactured heat exchangers and provides new approaches by CFD optimisation in combination with 3D printed replacement parts. Approach based on 3D print also allows design inspiration in natural principles. Biomimetic inspiration shows a wide range of thousands of years lasting optimisation made by nature. Research in this field can help us with the evolution of enhanced heat transfer surfaces. Developed coolers were examined by CFD techniques. Simulations of heat transfer are verified by laboratory measurement of prototype heatsinks. These techniques are presented on the unique design of a heat sink which was simulated, manufactured, and measured. The study shows CFD approaches, describes details of prototype measurement, and also deals with negative issues of metal 3D print.

Evaluation of thermal hydraulic flow and enhancement of heat performance in different 3D dimpled tube configurations according to design of experiment analysis

ABSTRACT The existing numerical research is concentrated on studying pressure drop, various velocity components, and heat performance behavior of heat exchanger pipe fitted with dimple on the inner pipe wall. Three-dimensional computational calculations using the CFD technique are conducted to study the influence of four geometrical parameters, including the distance between dimples, number of dimples, dimple diameter, and dimple pitch on the enhancement of thermo-hydraulic heat transfer. Also, the effects of the following parameters are optimized using the design of experiments (DOE) approaches combined with both Taguchi and Response Surface Methods. The results revealed different patterns of flow field and heat performance due to the use of dimples on the inner pipe surface. Moreover, utilized dimples can rise heat performance due to the interactions between the dimpled wall surfaces and swirling flow; hence, that can rise in area of heat transfer. Detailed flow analysis between dimples and pipe wall is demonstrated to describe the mechanisms of heat performance and pressure drop change. The orthogonal experiment outcomes revealed that the optimal design of the dimpled pipe has improved by about 35.75% and 36.1%. The numerical outcomes indicate that high value for the overall evaluation factor (PEF) is higher than 1. Based on the above findings, it can be found that hydrodynamic analysis flow, enhancement of heat transfer performance, and dimple optimization are required for different design applications.

High Power Output Augmented Vertical Axis Wind Turbine

Nowadays, wind energy is one of the most cost-effective and environmentally friendly energies in high demand due to shortages in fossil fuels and the necessity to reduce global carbon footprint. One of the main goals of wind turbine development is to increase the power output of the turbine either by increasing the turbine blade swept area or increasing the velocity of the wind. In this article, a proprietary augmentation system was introduced to increase the power output of vertical axis wind turbines (VAWT) by increasing the free stream velocity to more than two folds. The system comprises two identical airfoiled casings within which the turbine/turbines are seated. The results showed that the velocity slightly increases when decreasing the gap between the casing. It was also found that changing the angle of attack of the housing has more impact on the augmented airspeed. CFD technique was used to assess the velocity and flow of air around the system.

EVALUATING MATHEMATICAL HEAT TRANSFER EFFECTIVENESS EQUATIONS USING CFD TECHNIQUES FOR A FINNED DOUBLE PIPE HEAT EXCHANGER

EVALUATING MATHEMATICAL HEAT TRANSFER EFFECTIVENESS EQUATIONS USING CFD TECHNIQUES FOR A FINNED DOUBLE PIPE HEAT EXCHANGER

Entropy analysis and thermal energy storage performance of PCM in honeycomb structure: Effects of materials and dimensions

This manuscript focuses on comprehensive investigation of entropy analysis and improve energy storage of phase change material (PCM) using a honeycomb material. In the last decade, the honeycomb structure has quickly emerged as a major tool for improving heat transfer rate, particularly for the back of solar radiation PV panels. The aim of this study was to investigate the effect of honeycomb cell wall thickness (0.2 - 2 mm), cell diameter (2 - 16 mm), and honeycomb material types (cellulose, graphite, polyethylene, stainless steel, magnesium alloy, aluminum, and copper) on heat transfer rate of paraffin. These parameters have significant impact on paraffin's energy storage. The variables were optimized numerically using the CFD techniques according to phase change behavior, kinetic energy storage, and total energy storage of composite/paraffin. The results showed that the embedded metal cage had no effect on the total heat storage capacity of paraffin (27.89 W) for 0.33 mm wall thickness of honeycomb. The other optimal geometrical specifications of a honeycomb were determined to be 10mm cell diameter, and stainless-steel material. The ideal honeycomb cell has a uniform distribution of temperature and phase change in all cells at the same time. The entropy study confirmed that the phase transition of PCM with stainless steel honeycomb fins happened homogeneously and promptly. Furthermore, the heat transfer can be improved with changing the geometry of honeycomb structure, and addition fins inside cell.

Experimental and Numerical Investigations of Underground Coal Gasification (UCG) Using Half-teardrop Shape Cavity

In this work, the process of Underground Coal Gasification (UCG) was studied experimentally and numerically. The typical cavity of UCG was a half-teardrop shape. The coal samples were collected from Mae Moh coal mine, Thailand. The coal type is mainly lignite. To generate the gasification process, the coal sample was heated in the half-teardrop cavity by injecting partial oxidant, which is air, according to the Equivalent Ratio (ER) of 0.1, 0.2, 0.3, 0.5, and 0.7. The properties of the product gas were measured using a syngas analyser. CFD technique, ANSYS (Fluent), was used to simulate flow characteristics and gasification process in the cavity. The experimental results show that the low heating value (LHV) of syngas peaks at 0.92 MJ/m3 when ER = 0.1, and LHV decreases monotonically as ER increases. The CFD results show that the area of high temperature in the UCG cavity is larger when the ER was greater.

Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle

A model of a submerged angular cavitation nozzle is established, which consists of a contraction part, parallel middle part, and expansion part. Based on the CFD technique, a numerical simulation of the flow field of the submerged cavitation nozzle is carried out, in which a multiphase mixture model, cavitation model, and renormalization group (RNG) k-ε turbulence model are applied. Considering the influence of mixture density on cavitation, the effects of the inlet contraction part, parallel middle part, and outlet expansion part on the velocity and vapor volume fraction are studied. The numerical simulation results show that the mixture density is essential in the cavitation jet. When the nozzle diameter d is fixed, the designed angular cavitation nozzle with contraction angle α = 13.5°, parallel middle part length Ld = 3d, expansion part length Le = 4d, and expansion angle β = 60° can effectively bring out cavitation. A cavitation cloud is produced near the rigid wall of the outlet expansion section and diffuses in a vortex ring shape. Optimizing the nozzle structure can improve the cavitation effect of the nozzle. The feasibility of this model is verified by relevant experimental data.

Numerical simulation of pulverized coal combustion in a rotary kiln under O2/CO2 atmosphere

The cement industry is the second largest source of global man-made CO2 emissions after the power industry, and the adoption of O2/CO2 combustion technology for cement kilns is of great significance in reducing CO2 emissions. In this paper, the effects of pulverized coal mixed air combustion and pulverized coal mixed O2/CO2 combustion on the velocity field, temperature field, CO2 and NOx concentration distribution in rotary kiln were investigated by CFD technique. The results showed that there is no difference in the velocity distribution between the two atmospheres, and the speed difference between the primary and secondary air creates a re-circulation zone near the burner. The O2/CO2 atmosphere combustion decreased the maximum temperature, but improved the uniformity of the temperature field. The pulverized coal burnout rate under O2/CO2 atmosphere decreased by 3.55% compared to O2/N2 atmosphere. The mole fraction of CO2 at the rotary kiln outlet is 0.08 and 0.93 for O2/N2 and O2/CO2 combustion atmospheres, respectively. It is easier to achieve CO2 aggregation and capture under O2/CO2 atmosphere than under O2/N2. The NOx concentration at O2/CO2 is approximately one half of that at O2/N2, which can save the investment on denitrification equipment. The simulation results reasonably agree with the measured data. The findings of this work will provide a reference for the generalization and application of the O2/CO2 flue gas cycle calcinating cement technology.

ANALYSIS OF SHELL AND TUBE HEAT EXCHANGER USING CFD”

Our paper's main goal is to design the Heat Exchanger by adjusting many variables to improve its performance and efficiency, to find the best solutions, and to prepare it for use in challenging and dangerous situations. The heat exchanger, which involves both fluid flow and heat transfer, is simulated using the CFD technique. Through this procedure, we discover the pressure distributions, velocity vectors, and temperature gradients. This analysis demonstrates that the temperature values between the simulated and experimental values differ.

Experimental and CFD Analysis on the Effect of Various Cold Orifice Diameters and Inlet Pressure of a Vortex Tube

An experimental investigation was conducted to investigate the effects of different cold orifice diameters and operating pressures of the vortex tube. A vortex tube test rig was employed to conduct the experiments for various cold orifice diameters and operating pressures. Cold orifice diameters range from 1 mm to 6 mm, whereas the pressure condition ranges from 2 to 5 bar. The vortex generators were made up of brass material having six inlet nozzles. It was found that the temperature separation of the vortex tube significantly depends on the cold orifice diameter of the vortex tube and operating pressure. The study demonstrates the deviation of cold temperature separation with respect to the cold orifice diameters and inlet pressure for different cold mass fractions. In addition, present experimental results are used to determine the optimum cold orifice diameter, which is 5 mm at 5 bar inlet pressure. The percentage improvement in average cold temperature separation for 5 mm cold orifice diameter is 66.18% compared to rest of the cold orifice diameters at an inlet pressure of 5 bar. The maximum cooling power separation is 0.08 kW at 0.3 cold mass fraction and inlet pressure of 5 bar. The CFD technique was approached to discuss the complex fluid flow inside the tube at various radial distances. A three-dimensional numerical study was done and validated with the present experimental work. It was found that the numerical results are in good agreement with the present experimental data.

Computational fluid dynamics (CFD) analysis of centrifugal pumps

Centrifugal pumps are mostly used in different fields like industries, agriculture and domestic applications. Objective of this paper is to give a critical review of CFD analysis of centrifugal pump along with future scope for further improvement of flow efficiency. Computational Fluid Dynamics is the most used tool for simulation and analysis. 3-D numerical CFD tool is used for simulation of the flow field characteristics inside the pump machinery. CFD for centrifugal pump is used to solve numerical simulation problems working as a tool for getting performance prediction of modelled design at different conditions, and can derive information and study of pump performance on the system, Study of pressure contours, velocity contours, flow streamlines, cavitation analysis, analysis of interaction effects in different components, prediction of axial thrust etc., is also be studied by CFD techniques. Simulation makes it possible to visualize the flow condition inside a centrifugal pump. The present paper describes the head, power, efficiency and to evaluate the pump performance using the ANSYS CFX-14, a computational fluid dynamics simulation tool.

Neighborhood, Topography, and Wind Direction Effects on Wind Pressure Distribution on the Low-rise Building Roof

Low-rise buildings are the majority of the houses that are constructed all over the world. Experiments of the wind loads acting on these buildings provide vital information to design secure structures and adverse weather conditions resistants, considering the basic parameters as roof slopes and the wind direction. This study estimated the distribution of wind pressures around the contour of buildings with gable roofs, considering diverse neighborhood conditions, namely the number and geometric configuration of buildings on the ground, in conjunction with the different angles of wind incidence and topography. The simulations took place with Ansys Workbench software, and the RNG K-Epsilon turbulence model and tetrahedral mesh were employed. The application validation of the CFD technique occurred in the double-sloped pitched roof structure. The results showed good concordance with the literature. The pressure coefficients were analyzed, as well, in the flow visualization, highlighting the attachment points and the recirculation zones.

CFD Modeling and Simulation of a Tiny House in Extreme Weather Conditions

The subject of this research is the use of CFD techniques to identify the impact of using shutters in case of tiny house. Low temperatures and the aim to use as less energy amount as possible need solution. The composites shells allow designing efficient shutters that is isolating in an important manner windows. The CFD software allows to identify the air currents and the areas where heat is lost due to the extreme weather conditions.

Low-head high specific speed Kaplan turbine for small hydropower – design, CFD loss analysis and basic, cavitation and runaway investigations: A case study

In an era of growing energy demand, it is necessary to reach for lower water potentials to be used by a hydro unit. Due to low damming, a hydro unit must be designed to allow the flow of as much water as possible with maximum efficiency. This ensures optimal use of hydropower and minimization of turbine size. Therefore, this paper presents the construction of a model Kaplan turbine (runner diameter of 300 mm) with a high specific speed, designed to work under ultra-low and low heads up to 3 m.Adjustable guide vanes and runner blades were designed by means of an inverse problem method using a two-dimensional axisymmetric model. In the case of the adjustable guide vane, two shapes have been designed. The first has a classical shape and the second has a non-classical shape. The influence of both guide vanes on the turbine operation was analysed using the CFD technique. As a result, the turbine with a non-classical shape blade has a higher hydraulic efficiency and the efficiency curve is flatter. As part of these calculations, many variants of turbine settings were analysed (192 cases), namely 4 angles of classical guide vanes, 4 angles of non-classical guide vanes, and 4 angles of runner as well as 2 angles of a conical draft tube and 3 rotational speeds. The energy losses occurring in the flow elements of the turbine and their mutual contribution are presented in this paper.Model experimental tests of the turbine were carried out on the test stand with a wide range of settings of the guide vanes (the tests used a guide vane with a non-classical shape), the runner and its rotational speed. The research is aimed at determining the basic parameters of efficiency, the effect of cavitation and the runaway speed. Cavitation and runaway characteristics as well as the results of the resistance torque (friction losses) and its share in the total moment are presented.As a result of design, analytical, and experimental works the low-head high specific speed model Kaplan turbine was obtained and diagnosed. The realization of large flows, combined with the high efficiency of the machine is always a difficult task. The paper briefly describes the shapes of the designed guide vanes and runner blade obtained by the inverse problem method. However, more emphasis has been focused on the presentation of model tests that are rare for this type of machine. Therefore, the measurement uncertainty, measuring devices and the course of the conducted basic performance, cavitation and runaway tests are described in detail. Additionally, for the selected cases, a visualization of the flow with forced cavitation in the runner during cavitation tests is also presented.