Fluent CFD Research Articles

Numerical simulation of R134a evaporation in a cold water production system

Abstract In this paper, we introduce a numerical model designed to analyze the evaporation process of R134a refrigerant within a cold water production system. Using the ANSYS Fluent CFD software, our simulation solves the Navier–Stokes equation, thus offering insights into the system’s flow dynamics. Our investigation underscores the efficacy of CFD as a reliable tool for modeling and forecasting flow behaviors within complex systems. Specifically, we delved into the impact of varying the empirical coefficient in the Lee model. Our results indicate that augmenting the coefficient value amplifies the R134a flow rate at the evaporator outlet. Notably, a coefficient value of 0.25 closely matches the experimental flow rate. Furthermore, we analyzed the ascending velocity of R134a vapor, achieving a robust agreement between our numerical simulations and experimental observations. This study underscores the potential of numerical modeling in enhancing our understanding and prediction of refrigerant evaporation dynamics within cooling systems.

Numerical simulation and analysis of combustion chamber model design to investigate the effects of number of inlet and concentration of oxidizer mixture on combustion characteristics

In this research it is found that number of inlets had a significant impact on combustion characteristics specifically emission of CO and unburned hydrocarbons. After the selection of number of inlets MILD investigation had been done on the effect of concentration (γ) of CO2/O2 on the combustion characteristics. It is found that by increasing the number of inlets decrease the emission level and unburned hydro carbon in outlets. For concentration of oxidizer, we find a value between 0.80-0.85 will be efficient for combustion due to minimum emission levels and unburned hydrocarbons. The research has been carried out in Ansys CFD fluent-> Energico 18.2-> Chemkin->. The model for reaction solves in energico and chemkin to generate results for unburned hydrocarbons and emission of CO.

Aerodynamic Drag Reduction Using a Conduit in the Ahmed Body

In this study, the focal challenge is reducing drag around the Ahmed body, a critical concern in aerodynamics. The approach involves perforating a rectangular conduit inside the body, redirecting part of the airflow from the front to the rear end to minimize drag. Using Ansys Fluent CFD software and the SST k-w turbulence model, a numerical model for turbulent flow around a 3D body has been developed. Through a series of numerical simulations, variations in the conduit’s position relative to the lowest slanted edge of the body have been explored. At the optimal position with the lowest drag, an examination has been conducted on the narrowing of the conduit outlet dimensions. Results indicate that, with a suitable conduit position and an appropriate exit narrowing, a decrease in drag of up to 3% could be achieved. Ongoing work involves the examination of the conduit’s tilt at the outlet to determine the optimal arrangement for further drag reduction. This research offers practical insights for drag reduction and contributes to the broader field of aerodynamics.

Numerical Investigation on Photovoltaic Thermal Panel Using Various Nanofluids Concentrations

Increasing the efficiency of solar panels is crucial for effective use of renewables. The present numerical study deals with improving the performance of a PVT system with nanofluid using CFD FLUENT software. ZnO-water and SiO2-water nanofluids are investigated and correlation are established between the PVT efficiency and various nanofluid volumetric concentrations ranging from 1% to 10%. Validation of the present results is verified by comparison with experimental data. Comprehensive research is conducted to evaluate the correlation between the thermophysical properties of nanofluids such as density, thermal conductivity, specific heat capacity and dynamic viscosity. The results demonstrate that the overall efficiency of the ZnO-water nanofluid and -water nanofluid increases by 0.44% and 0.24%, respectively, as the volumetric concentration of the nanofluid rises from 1% to 10%. The ZnO-water nanofluid reveals enhanced thermal and electrical efficiency compared to the -water nanofluid due to its superior thermal conductivity and enhanced heat transfer capabilities along the absorber tube. The ZnO-water nanofluid exhibits a greater heat transfer coefficient, thereby facilitating the cooling mechanism of the PV panel and reducing the PV cell temperature, hence enhancing power generation.

Experimental and numerical investigation of the thermal - hydraulic performance of flow inside helical coil elliptic tubes

Helical coil tubes are essential in a variety of engineering applications due to their improved heat transfer and compact shape. The current study presents an experimental and numerical investigation of geometrical optimization for helical coil elliptic tubes. Four distinct coil pitch values are examined with a constant perimeter for all geometries and three aspect ratio values (1, 0.75, 0.5) utilizing water as the working fluid across varying the volume flow rates. The helical coil has the same surface area as the tube for each coil. The numerical simulation is conducted using the ANSYS FLUENT CFD software (Version 19.2). The experimental and numerical results indicate that the increase in heat transfer due to an increase in mass flow rate is significantly greater than the improvement gained by changing the aspect ratios. Increasing the volume flow rate to 3 L/min significantly improves the average heat transfer coefficient, with a 66.6 % increase found at a maximum coil pitch of 0.08 m and an aspect ratio of 0.5. Furthermore, a helical coil with an aspect ratio of one (circular cross-section) exhibits the best compromise between pressure drop penalty and heat transfer enhancement, resulting in the greatest hydraulic thermal performance parameter.

Separation efficiency of a wastewater bar screen based on a 3D computational fluid dynamics modeling

The wastewater screening process is a crucial step in the majority of wastewater treatment plants, frequently using mechanical bar screens as the first filtration step to remove heavy debris from the wastewater flow. In the present study, two 3D geometries of bar screens with different screen openings were presented to investigate the effect of the variation in screen spacing of bars on the separation efficiency of debris. Based on the Ansys Fluent CFD code within the Eulerian-Lagrangian approach, the particle trajectories were tracked, and the retention efficiency of these two bar screens was evaluated. The results show that a higher particle separation efficiency is favored for small bar spacing and coarse particle sizes. Actually, despite the impact of bar spacing on the separation efficiency of particles, the adequate choice of this parameter is related to particle properties and the fluid flow inlet velocity. These parameters also have a great influence on the separation efficiency of bar screens. The study can help for more structural improvements in the shape of the screening media, which leads to enhanced performance of wastewater screening facilities.

Physical mechanism for prolonged test duration in shock tubes

The main challenge in the operation of shock tubes is the very short test time. Hence, this work was carried out to optimize the ratio of driver section to driven section length and to investigate its effect on the test time in a shock tube. Three different cases were tested in this paper for driver to driven tube length ratio of 2, 1, and 0.5. The study was conducted numerically using ANSYS Fluent CFD solver and k-epsilon realizable turbulent model. The shock wave strength and speed were monitored at two different locations downstream the driven tube for diaphragm pressure ratio of 10. The numerical model was verified with experimental measurements in a shock tube apparatus at the College of Engineering, Universiti Tenaga Nasional, Malaysia (UNITEN). From the numerical and experimental data, the primary shock strength was very comparable, while using low pressure ratio of 10. Subsequently, higher pressure ratio of 20 and 30 were implemented and the results were compared to select the longest test time. A driver section to driven section ratio of 2 resulted in a longer test time of approximately of 20 ms. In addition, insignificant reduction in the test duration of about 5 % was observed after increasing the driver tube pressure to 30 kPa. In contrast, higher peak pressure was recorded for pressure ratio of 30 for all three cases.

The effect of lateral intake slope on sedimentation transport

Generally, The problem of sediments at the entrances to subsidiary channels is considered one of the most common problems for which water resources engineers seek to find appropriate solutions, as it causes significant damage to hydraulic installations, as the accumulation of these sediments in the canal rollers over time leads to the collapse of those channels, which results in many losses. In this study, a three-dimensional mathematical model was developed using the Ansys Fluent CFD program, and this model was matched with previous laboratory experiments, as this mathematical model showed clear accuracy and consistency. Work was done on changing the geometry of the sub-channel and studying the effect of changing the inclination of the sub-channel on reducing the amount of sediment entering the channel or not, since the channel used in this study is 2 m. Adjustments were made to the inclination of the canal in two different forms: The first is to make the first half (1 m) of the canal horizontal, and the inclination begins in the second half, at three different angles, namely 15, 30, and 45 degrees. The other form is to change the inclination along the total length of the sub-channel (2 m) with the same effect. Angles 15, 30 and 45. The results showed the ineffectiveness of changing the inclination of the sub-channel from the middle of the distance, while the results of changing the total inclination were different. It is possible that the slope angle of 45 is considered the best in terms of increasing the speed and clearly reducing the area of the separation zone and the erosion zone.

Numerical exploration of the impact of fluid type in a uniquely designed shell and spiral tube heat exchanger

Shell and spiral tube heat exchangers are widely favored in refrigeration and applications such as heat recovery systems, food processing, and heat storage. Researchers' primary focus is to discover a simple and cost-effective approach to improve the efficiency of heat exchangers. The research employed a specially designed shell and spiral tube heat exchanger to enhance efficiency. This research involved utilizing ANSYS FLUENT CFD software to analyze the thermodynamic efficiency and predict heat transfer in the specified converter. The analysis incorporated factors such as displacement velocity coefficient and friction coefficient. Researchers are focused on finding a simple and cost-effective approach to improve the efficiency of heat exchangers. Furthermore, the selection of nanohybrid fluids is a crucial factor influencing the thermohydraulic performance of shell and spiral tube heat exchangers. Among the three fluid nanohybrids chosen for simulation, the water nanohybrid exhibited superior temperature performance, surpassing all other liquids. Furthermore, the optimal thermal performance for the hybrid nanofluid was observed at φ1 = φ2 = 0.7.

Thermal and Hydrodynamic Measurements of a Novel Chaotic Micromixer to Enhance Mixing Performance

In this study, three-dimensional simulations were conducted on a new passive micromixer to assess the thermal and hydrodynamic behaviors of Newtonian and non-Newtonian fluids subjected to low generalized Reynolds numbers (0.1 to 50) and shear-thinning properties. To acquire a more profound comprehension of the qualitative and quantitative fluctuations in fluid fraction using the CFD Fluent Code, the mass mixing index, rheological behavior, performance index, mixing energy cost, mass fraction distributions, temperature contours, and pressure drop were compared to illustrate the importance of the mixer geometry in the context of two miscible fluids with varying inlet temperatures. The selected geometry is characterized by a robust chaotic flow that substantially enhances thermal and hydrodynamic performance across all Reynolds numbers. A mass mixing exceeding 72.5% is obtained when Re = 5, reaching 93.5% when Re = 50. Furthermore, the evolution of thermal mixing for all behavior indexes reaches a step of 98% with minimal pressure losses. This work enabled the demonstration of a chaotic geometry in a highly efficient mixing system, leading to enhanced thermal performance for both Newtonian and non-Newtonian fluids. The results of the hydrodynamic and thermal characterization of the mixing of shear-thinning fluids within the micromixers under investigation are conclusive.

Entropy generation analysis and thermal synergy efficiency in the T-shaped micro-kenics

In this work, three different twist angles of a micro helical insert in a T-shaped are studied numerically in order to evaluate the laminar steady flow behavior of Newtonian fluid in chaotic geometry. In the geometries under consideration, thermal mixing behavior is carried out using fluids having two distinct input temperatures. Under the influence of chaotic advection and low rates of Reynolds number, the second law of thermodynamics is controlled in terms of the entropy generation caused by hydrodynamic and thermal processes. The governing equations are numerically solved using the CFD Fluent code. Thus, the micromixer's configuration demonstrated a very significant improvement in mixing degree while minimizing friction and thermal irreversibilities. The synergy coefficient, which depicts the link between velocity and heat transfer in angle form, is analyzed and the results are provided.

Effects of geometry and flow rate on the mixing process in passive Y-micromixer

In this work, we look at the mixing capabilities of a static Y-micromixer, which achieves very good mixing quality when compared to other recently proposed micromixers in terms of mixing quality. We propose to change both the quantity and arrangement of element pairs. The 3D momentum equations, continuity equation, and species transport equations have all been solved numerically at moderate Reynolds numbers using the CFD Fluent tool. The lengthening of the Y-shape is determined by the quantity of pairings. A comprehensive analysis was conducted by varying the number and position of element pairs across a broad spectrum of Reynolds numbers, ranging from 1 to 400. The numerical simulations examined the acquired outcomes by displaying the contours of mass fraction, vorticity, mixing performance and pressure losses in various planes. The chosen geometry, consisting of 4 pairs of components, has exceptional mixing capabilities. The mixing index surpasses 47% at Re = 1 and achieves a maximum of 99% at Re = 400. Furthermore, it exhibits a reduced pressure drop in comparison to other recently examined geometries. Hence, the chosen micromixer demonstrates excellent mixing capabilities at moderate Reynolds numbers, rendering it suited for improving fluid mixing in diverse microfluidics systems.

Response to the design conditions of a tube-bundle thermal energy storage unit with paraffin-copper foam composite as a storage medium

Owing to its potential to limit the issues of intermittency and instability in solar energy by means of phase-change materials (PCMs), latent heat thermal energy storage (LHS) has met increasing attention and been widely employed in thermal-based systems. Most PCMs, however, inherently exhibit poor heat conductance leading to modest rate of charging. To master this drawback, highly conductive metal foams are utilized to upgrade the bulk heat conductance of a PCM resulting in an enhanced rate of heat transport; hence, accelerating the melting process. This enhancement way is employed to promote the response of a tube-bundle thermal energy storage unit configured of staggered tubes filled with high-porosity copper foam embedded in paraffin wax as a storage medium. To charge the thermal energy storage (TES) unit proposed, a relatively hot stream of water is allowed to flow across the bundled tubes through the voids in-between. To check how feasible the proposed design is, the tubes enclosing the TES medium and the water flow in the shell surrounding have been simulated by ANSYS Fluent CFD code. A variety of design factors has been examined to explore their influence on the charging performance attained including structural properties of the metal foam employed along with the configuration of the tube-bundle considered. The foam structural characteristics inspected are the porosity ∅∈(0.89∼0.97) and pore density ω∈(5∼80)PPI, while various tube-bundle configurations have been tested in terms of the packing density N∈(15∼65)TubesLines/meterwidth as well as the shape of PCM tubes used b/a∈(0.25∼1). Results indicate that for a certain tube-bundle configuration, the best response is acquired when denser foam with lower porosity is used, while the best performance can only be achieved with higher porosity due to the better TES capacity offered. For certain foam structural properties of (∅=0.93&ω=80PPI), it has been observed that increasing the packing density can save up to 56 % of the time taken for charging completion with up to 200 % increase in storage capacity leading to up to 48 % improvement in the system overall performance. It has also been found that using paraffin embedded with copper foam as a TES medium accelerates the melting process considerably and saves more than half the time taken to charge the corresponding TES unit based on pure paraffin. It is also worth mentioning that the currently suggested LHS unit is not only of simple configuration, but practically efficient as well, with outstanding gross performance OP∈(104∼105). Through a proper manipulation of design conditions, it has been found that the charging response can be notably improved leading to substantial promotion in the overall performance realized.

From simulation to reality: CFD-ML-driven structural optimization and experimental analysis of thermal plasma reactors

Thermal plasma reactors offer an environment of high temperature, enthalpy, and reactivity, making them highly efficient for solid waste treatment and promising for clean energy production from municipal and industrial waste. Optimal geometrical parameters of the reactor can enhance waste treatment and reactor performance. This study presents a comprehensive analysis of 11 key geometrical parameters of a thermal plasma reactor. Utilizing CFD Fluent software, numerical simulations were conducted to generate a dataset. Subsequently, a predictive model focusing on the average temperature in the core melt zone was trained using six Machine Learning (ML) algorithms. The Particle Swarm Optimisation (PSO) algorithm optimized the hyperparameters of the Gradient Booster Regression (GBR) model, which was combined with a Genetic Algorithm (GA) to identify the reactor's optimal geometrical parameters. A DC arc plasma torch-solid waste thermal plasma reactor treatment system was established on this basis. The study also explored the effects of gasification coefficient, reaction temperature, and thermal plasma jet mode on system performance. Findings indicate that the PSO-GBR model achieved the highest prediction accuracy, with the temperature in the core reaction zone reaching 3621 K. The deviation between numerical simulations and machine learning predictions was a mere 1.3%. Enhancing syngas yield and energy efficiency is achievable by controlling reaction temperature and increasing the gasification coefficient. A laminar plasma jet mode, at equal power, provides a more effective reaction environment. The accuracy and reliability of the machine learning-driven regression model and optimization results are significant in guiding the optimal design of plasma reactors and advancing waste-to-energy conversion processes.

CFD simulation of solid/liquid phase change in commercial PCMs using the slPCMlib library

Modelling the solidification and melting behavior of phase change materials (PCMs) can present several challenges, including non-isothermal phase change, multi-step transitions, complex enthalpy-temperature relations and convective heat transfer. To tackle these challenges, this study proposes a novel numerical method based on real experimental data for modelling complex phase change behavior of commercial PCMs in Ansys Fluent CFD software. The phase transition of PCMs is simulated with the apparent heat capacity (AHC) method, which is implemented as a User-Defined Function (UDF). Heat convection is simulated with the Boussinesq approximation. The method is validated by comparing to the Ansys Fluent built-in Solidification and Melting (S&M) model for the case of piecewise constant heat capacity. The results show that AHC method provides excellent agreement with S&M model for a piecewise constant heat capacity model. In addition, the AHC method solves convergence problems even for narrow phase change temperature ranges when a smooth heat capacity function is assumed. Finally, the AHC model is also tested on a set of commercial PCMs exhibiting complex phase change behavior. Temperature dependent specific heat capacities are determined from heat capacity data provided by PCM manufacturing companies and are imported as cubic Hermite spline functions from the solid-liquid phase change material library slPCMlib available at https://slpcmlib.ait.ac.at/. From the presented case study and tested PCMs it can be concluded that the AHC method is numerically robust when used with sufficiently smooth heat capacity functions, and it can be recommended for the analysis of heat transfer with PCMs showing a complex phase change behavior.

Wind Velocity Effect on the Aerodynamic and Acoustic Behavior of a Vertical Axis Wind Turbine

In this work we present a numerical study on the effect of wind velocity on the aerodynamic and acoustic behavior of a Savonius-type vertical axis wind turbine (VAWT). The study focuses on the prediction of the torque coefficient for different flow velocities and rotational velocities of the wind turbine. We also present the triggering of the wake zone near the wind turbine blades to see the dynamic effect on the behavior of the wind turbine. The study of the numerical simulation is carried out using a fluent CFD calculation code using the finite volume method for the discretization of the differential equations. The equations governing the flow are solved by the SIMPLE algorithm using two K-epsilon turbulence models.

Impact Tip Speed Ratio in Performance Analysis for Horizontal Axis Wind Turbine (HAWT) with Optimal Twist and Tapered (OPT) Blade Shape

Performance for Horizontal Axial Wind Turbine (HAWT) is influenced by the difference in tip speed ratio (TSR) and mesh distribution. The objective of this article is to study the optimal performance of wind turbines when subjected to different mesh resolution, TSR and wind speed velocity.Therefore, it is important to study the effects of different mesh resolutions in terms of wind turbine performance. To achieve that, a 0.65m optimal twist and tapered (OPT) blade is used with various inlet velocities and TSR. This study uses the k-ꞷ shear-stress transport (SST) based Reynold-Average Navier Stokes (RANS) approach in commercial ANSYS Fluent CFD software. This simulation was performed using the Moving Ratio Frame (MRF) method. To find the optimum grid resolution, a Grid Independence Test (GIT) was conducted comparing the coefficient of power (Cp). From the RESULT, TSR 6 shows the best HAWT performance when Cp for inlet velocity 8 m/s is 0.2608.

КОМП'ЮТЕРНЕ МОДЕЛЮВАННЯ НЕСТАЦІОНАРНОГО ПРОЦЕСУ РОЗВИТКУ НАДЗВУКОВОГО ПЕРЕРОЗШИРЕНОГО СТРУМЕНЮ

Questions of numerical simulation of non-stationary process of the development of a supersonic overexpanded jet are considered. Unsteady Reynolds-averaged Navier-Stokes equations (URANS) of compressible flows, written in an arbitrary coordinate system, along with the Spalart-Allmaras one-equation differential turbulence model are applied. The calculations of non-stationary formation of an air cold supersonic jet during the blowing through a conical Laval nozzle (simulation of engine start-up) were made. The physical features of the shock and acoustic waves generation and propagation are discussed. In the stationary phase an overexpanded free supersonic turbulent jet is formed, which includes a Mach disc in its structure. The obtained results were compared with experimental data and calculations by other authors based on the ANSYS Fluent and FloEFD CFD tools.

Numerical simulation of a membrane desorber with the H2O-LiBr working mixture for absorption cooling systems

In absorption cooling systems, the refrigerant fluid is separated from the working-fluid mixture inside a component called “desorber”. Conventional desorbers operate by boiling separation; however, membrane modules are a potential alternative to replace them since they can operate below the working mixture boiling point and at atmospheric pressure conditions. The present paper presents a numerical simulation of a membrane desorber that uses the air gap membrane distillation configuration. The numerical analysis was carried out by means of ANSYS FLUENT CFD code using a 3D model. Temperature, concentration, and velocity contours were numerically obtained assuming H2O-LiBr solution at 41 % w/w, mass flow of 0.03 kg/s, temperature of 363.15 K, and cooling water at 303.15 K and 0.04 kg/s. The maximum error in simulated temperature was 11.9 % compared to the experimental data. According to the results, a solution temperature difference between the bulk and the membrane interphase up to 288.15 K was calculated. In addition, stagnated areas inside the solution channel cause velocity differences of up to 5 magnitude orders compared to the middle point in the solution channel. Since a maldistribution flow causes a “jet” inside the solution channel, and a non-homogeneous concentration distribution on the membrane interphase; as a result, a concentration difference up to 1.35 % between a point located at the border membrane interphase compared to a point located at the middle was observed. Therefore, the desorption rate can be improved with geometric modifications in the membrane desorber device.

Flow Patterns in Two Nanorefrigerants R600a/CuO and R410A/CuO During the Boiling Process

The present study aims to know the flow patterns in two nanorefrigerants R600a / CuO and R410A / CuO throughout the forced boiling process in horizontal square pipes. Those are obtained using the thermophysical properties of the refrigerants R600a and R410A in state liquid and vapor, as well as the properties of the CuO nanoparticles. The analysis was carried out using two methods: analytical and numerical. The analytical method was established by formulas and correlations through scientific articles and books to find an improvement in the two-phase heat transfer, under the conditions at an inlet temperature of 8 ° C and with a quality range of 0 to 1. This allowed to verify that by adding nanoparticles to the refrigerant, the transition between the flow regimes increases progressively, while the quality of the vapor decreases. For the numerical method, the different transition limits are specified in a simulation process in the Ansys Fluent CFD Software, under established design conditions, which consequently increases the general efficiency of any refrigeration system.