Commercial Computational Fluid Dynamics Code Research Articles

Effects of convergent–divergent vortex finders on the performance of cyclone separators using computational fluid dynamics simulations

This study investigates the effect of convergent–divergent vortex finders on the performance of cyclone separators, which is measured in terms of pressure drop and collection efficiency. Six cyclone models (two with uniform diameter and four with convergent–divergent vortex finders) were numerically simulated. The numerical simulations have been carried out using the commercial computational fluid dynamics code (CFD) Fluent v15. The simulation procedure has been validated using experimental data from the published literature where a good agreement between the numerical results and the experimental data is seen. A grid independence test has been carried out by using two levels of grids for correctness of our simulation. The Reynolds averaged Navier–Stokes (RANS) and continuity equations have been solved for the flow simulation. The Reynolds stress model is used for modeling the stress tensor and closing the RANS equations. The results show that a convergent–divergent vortex finder is capable of producing better performance (pressure drop and collection efficiency) than the uniform diameter cyclones. Only one performance parameter can be improved in uniform diameter cyclones. In comparison to the standard uniform vortex finder cyclones, the convergent–divergent vortex finder improves the pressure drop by 6% and also reduces the cut-size to 1.4 from 1.6 µm. It is further seen that decreasing the throat area or increasing only the lower diameter of the vortex finder causes the performance to degrade. This study proves that convergent–divergent instead of uniform diameter vortex finders can be used in gas cyclones for obtaining a better performance with the same geometry.

Viscous equilibrium analysis of heat transfer on blunted cone at hypersonic flow

High speed flow requires consideration of some complex phenomena such as chemical reactions. In fact, as flow velocity increase, high temperature of hypersonic velocity excites molecules to react and causes dissociation and ionization. Accurate analysis of existing schemes by considering appropriate models and equations is crucial for investigation of hypersonic flow with chemical reactions. The main objective of this investigation is to study the aerodynamic characteristics of hypersonic flow undergoes equilibrium chemical reaction by means of commercial computational fluid dynamic CFD code. Although current available software contains air species exist at high temperature, lacks adequate thermodynamics and transport relations which should be consider for equilibrium flow such as compressibility factor and equilibrium constant. Therefore, an external code is needed to calculate all thermodynamics and transport properties of dissociated air in equilibrium condition at various temperature and pressure accurately. Numerical computations achieved for both laminar and turbulent flow at two different angles of attack around blunted cone. Both perfect gas and equilibrium air results are presented and compared with available experimental data. Good agreement between equilibrium results and the experimental data confirming the capability of the present scheme for predicting the behavior of air in chemical equilibrium especially the heat transfer on the surface and perfect gas limitation.

Fill Factor Effects in Highly-Viscous Non-Isothermal Rubber Mixing Simulations

Abstract A finite volume technique in a commercial computational fluid dynamics (CFD) code is employed in this study to simulate transient, incompressible, non-Newtonian and non-isothermal rubber mixing. The simulation processes are conducted in a two-dimensional(2D) domain, where a mixing chamber partially-filled with rubber is equipped with a pair of two-wing non-intermeshing counter-rotating rotors. The main objective is to assess the effect of different fill factors of rubber on dispersive and distributive mixing characteristics by simulating 15 revolutions of the rotors rotating at 20 min−1. 50%, 60%, 70%, 75%, 80% and 90% are the six different fill factors chosen for the study. An Eulerian multiphase method has been applied to solve for the two different phases, rubber and air. The non-Newtonian property of rubber is handled using the shear rate dependent Carreau-Yasuda model, along with an Arrhenius function to include the temperature dependency. In addition to the governing equations related to the conservation of mass, momentum and energy, the volume of fluid (VOF) method is chosen to track the interface between air and rubber. With regard to the results, flow patterns, thermal distributions, viscosity behavior and volume fraction are analyzed for the different fill factors. In addition, dispersive and distributive mixing behavior is also assessed in detail using Lagrangian statistics, such as mixing index, cumulative distribution of maximum shear stress, cluster distribution index (CDI), scale of segregation (SOS) and length of stretch (LOS), calculated from massless particles. Both the Eulerian and Lagrangian results showed that fill factors between 70% and 80% presented the most reasonable and efficient mixing scenario, and also exhibited the best dispersive and distributive mixing characteristics combined.

Numerical and Experimental Study of Flow Characteristics in Solar Collector Manifolds

The flow through a forced circulation Z-type flat plate solar collector was investigated by means of combined experimental measurements and numerical simulations. The efficient operation of such collectors depends on the uniformity of the flow rate distribution among their riser tubes, while low pumping power demand is also sought. Mass flow rate measurements in the riser tubes were performed, utilizing a specially adapted ultrasound instrument for various values of total flow rates in the collector. By means of a commercial Computational Fluid Dynamics (CFD) code, laminar and turbulent flow models in different computational grids were tested and validated against the experiments. Appropriate metrics were introduced to quantify flow rate distribution non-uniformity among the risers, and pressure drop through the manifold was calculated. Parametric studies for flow conditions outside the experimental window were performed utilizing the CFD method in order to assess the effect of the Reynolds number in the flow distribution among the riser tubes. Furthermore, aiming to enhance flow rate uniformity, a methodology based on modifying the diameter of each riser tube was applied and successfully demonstrated. The proposed method can be employed in large solar collector arrays, either as stand-alone systems or as belonging to hybrid alternative sources of energy (ASE) systems, aiming to optimize their overall efficiency.

Verification and Validation of OpenFOAM for High-Lift Aircraft Flows

This paper presents a detailed investigation into the performance of the open-source finite volume computational fluid dynamics (CFD) code OpenFOAM for complex high-lift aircraft flows. A range of cases are investigated, including a zero-pressure gradient flat plate, a NACA0012 airfoil at varying angles of attack, a DSMA661 airfoil, a NASA High-Lift Common Research Model, and a Japan Aerospace Exploration Agency (JAXA) standard model (JSM) high-lift aircraft model. The final three cases were computed as part of the third AIAA High Lift Prediction Workshop. For all of these, the same mesh and turbulence model is used to benchmark against the commercial CFD code STAR–CCM+. The paper shows that OpenFOAM using the Spalart–Allmaras model matches the lift and drag coefficient within 3% of the commercial code for all the test cases simulated. For the JSM high-lift aircraft for which experimental data is available, both codes show good agreement at prestall angles of attack but fail to capture the location of separation at poststall angles, even though the global lift appears to be well predicted. Although OpenFOAM demonstrated comparable accuracy to a range of CFD codes for these aforementioned test cases, further work is required to improve the robustness and stability of OpenFOAM for these types of flows.

Wall roughness modification of a standard Lagrangian model for the prediction of saltation velocities in gas-solid flows

The reduction of harmful emissions is an important issue in coal fired power stations and a technique used to reduce the emissions of oxides of Sulphur and Nitrogen is low NOx burners. A requirement for effective operation is to supply the burners with a uniform stream of pulverised fuel (PF) without incurring particle settling.A valuable tool in analysing multiphase flows in PF systems are numerical models in the form of Computational Fluid Dynamics (CFD) simulations. Various models can be used to simulate the transportation of particles, the closer the model is to the physics of reality, the more computationally expensive it is. Commercial CFD codes have proven to be valuable in the analysis of multiphase flows. This study evaluates a numerical technique that can offer results that reasonably predict the onset of settling at the most economic computational cost.Numerical models were compared to literature to evaluate ability of the Lagrangian model to predict the onset of settling. The standard Lagrangian model predicted excessive settling of the particle phase because the effects of wall roughness and inter-particle collisions were not accounted for. A wall roughness modification enhanced the particle distribution in the pipe and predicted better pressure drops.

Hydraulic analysis of EU-DEMO divertor plasma facing components cooling circuit under nominal operating scenarios

Within the framework of the Work Package DIV 1 – “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the steady state thermal-hydraulic behaviour of the DEMO divertor cassette cooling circuit, focussing the attention on its Plasma Facing Components (PFCs). The research campaign has been carried out following a theoretical-computational approach based on the Finite Volume Method and adopting the commercial Computational Fluid-Dynamic code ANSYS-CFX.A realistic model of the PFCs cooling circuit has been analysed, specifically embedding each Plasma Facing Unit (PFU) cooling channel with the foreseen swirl tape turbulence promoter, hence resulting in a finite volume model much more detailed than those assessed in previous analyses. Its thermal-hydraulic performances have been numerically evaluated under nominal steady state conditions, also comparing the obtained results with the corresponding outcomes of analogous analyses carried out for a simplified PFCs configuration, without swirl tapes. Moreover, the main thermal-hydraulic parameters have been evaluated in order to check whether the considered PFCs cooling circuit might fulfil the total pressure drop requirement (Δp <1.4 MPa), providing a uniform cooling of the Vertical Target PFU channels with a viable CHF margin (>1.4).The PFCs cooling circuit thermal-hydraulic behaviour has been additionally assessed at alternative operative conditions, issued to check the viability of a coolant velocity reduction, in order to minimize corrosion and vibrations inside the PFU channels.Models, loads and boundary conditions assumed for the analyses are herewith reported and critically discussed, together with the main results obtained.

Systematic study on propulsive performance of tandem hydrofoils for a wave glider

This paper presents the propulsive performance optimization of tandem hydrofoils equipped in a wave glider in head sea conditions with the aid of computational fluid dynamic (CFD) method by using a commercial CFD code, STAR-CCM+.Firstly, this work performs a systematic study on a single 2D hydrofoil to study the effect of varying the pivot position and the torsional spring stiffness to seek for the optimum propulsive performance within a range of velocity. Secondly, parametric studies on the propulsive performance of 2D and 3D six tandem hydrofoils are conducted by varying the oscillation amplitude and the torsional spring stiffness. The result reportsThe results show that the torsional springs play a critical role in propulsive performance, comparing to the pivot position. The propulsive performance of the middle hydrofoil is greater than the others in the fore and after positions. When 2D and 3D six tandem hydrofoils achieve the optimum propulsive performance, the frequency ratio is chosen to be around 25 (torsional spring stiffness (kS=0.8N⋅m/rad)) and 17 (torsional spring stiffness (kS=11.8N⋅m/rad)), respectively. Comparing to previous study, the propulsive performance of each hydrofoil in six tandem hydrofoil configuration is greatly improved and none of hydrofoil produce negative thrust.

Preliminary design and performance analysis of a positive displacement hydraulic turbine

Positive displacement turbines (PDT) find their use in applications with low flowrate, high head and having lower specific speed requirement, which is below the operational range of the conventional turbines. In the present work, an initial PDT was designed using the governing equations of fluid flow to extract the unused energy from the hot water transportation pipelines. The turbine was of lobe type with two rotors each having four lobes. The tip clearance, side clearance and other leakage losses were considered while designing using fundamental principles coupled with the empirical co-relations from the literature. The initial design’s performance analysis had been carried out numerically using commercial computational fluid dynamics (CFD) code ANSYS CFX. The objective of the present study was to reveal the performance of the preliminary design for the given conditions and examine the causes of pulsations in torque, pressure and flow rate from the fluid flow characteristics.

A CFD‐Based Mixing Model for Vegetated Flows

AbstractThis paper provides a computational fluid dynamics (CFD)‐based modeling framework for predicting flow field, turbulence, and mixing characteristics within vegetated environments such as ponds and wetlands. The framework has been implemented within a commercial CFD code—ANSYS Fluent 19—via a set of user‐defined functions. Following the approach outlined by King et al. (2012, https://doi.org/10.1017/jfm.2012.113), the standard k‐ε turbulence closure model has been modified to capture the energy transfer at the vegetation/clear flow shear interface and within the vegetation. The implementation assumes that vegetation is vertical, but nonorthogonal flow in the horizontal plane is accounted for. Values for the drag coefficient and the mixing coefficients are estimated based on the vegetation stem diameter and density. Following Tanino and Nepf (2008, https://doi.org/10.1017/S0022112008000505), a switch has been incorporated to account for the fact that the relevant length scale changes from stem diameter to stem spacing as stem density increases. A set of model parameters is proposed, based on a reevaluation of previously published laboratory data and theoretical analysis. Five different experimental data sets are used to demonstrate that the model is able to predict mixing within fully vegetated systems and due to both vertical and horizontal shear layers. The framework was developed to provide a practical prediction tool for engineering purposes, in particular for the estimation of residence time distributions in real partially vegetated stormwater management ponds. Its implementation here within a commercial CFD package potentially facilitates application to complex pond geometries, including patches of different types of vegetation with different bulk stem diameter and density characteristics.

Aerodynamic Analysis and Parametric Study of the Blended-Wing-Body-Type Business Jet

The market demand on business jets is growing fast. The Blended-Wing-Body (BWB) configuration is adapted to design high-efficient green business jet. Conceptual study of the BWB-type transonic business jet is carried out. The BWB-type business jet expected to provide a better cabin space and aerodynamic performance to compare with the conventional business jet. An aerodynamic analysis of the BWB-type transonic business jet is performed to understand the flow field around the aircraft at a high subsonic flight speed. The commercial CFD (Computational Fluid Dynamics) code, ANSYS Fluent, is used for aerodynamic analysis. A parametric study is carried out to analyze the relation between the design parameters and aerodynamic characteristics. The commercial PIDO (Process Integration and Design Optimization) tool, PIAnO, is used to perform a parametric study. As a result of parametric study, the sensitivity of the design parameters is analyzed and a proportion of aerodynamic influence of each design parameter is presented. One of the sample design configurations for detailed aerodynamic analysis is selected. As a result of the aerodynamic analysis, aerodynamic coefficients and pressure coefficient distribution around the BWB-type business jet are presented. Increase of AOA and Mach number produces stronger shock and drag coefficient is increased due to wave drag.

CFD study of blockage ratio and boundary proximity effects on the performance of a tidal turbine

The effects of blockage ratio and boundary proximity on tidal turbine performance are quantified in this study using computational fluid dynamics (CFD). Reynold averaged Navier–Stokes (RANS) equations are solved using the commercial CFD code ANSYS CFX. Steady-state analyses are performed using a rotating frame of reference technique, and a shear stress transport turbulence model is used. Results from the numerical model are validated with experimental data. RANS CFD simulations are performed over tip speed ratios (TSRs) from 1 to 9. The simulation-based performance curve approximately match the experimental performance curve, with errors ranging from 4 to 9%. Blockage ratios from 0.02 to 0.19 are evaluated for a constant depth of two rotor diameters to study the effect of blockage on turbine performance. Results show that shaft power increased by 13 and 47% for TSRs of 5.11 and 9.05, respectively, when the blockage ratio increased from 0.02 to 0.19. Additionally, for these TSRs and blockage ratios the turbine thrust increased by 7 and 10%. The presence of a boundary layer resulted in a calculated thrust increases between 1.6 and 2.3% and power between 2.7 and 3.5% for the entire range of evaluated blockage ratios.

Pressure Study on Pipe Transportation Associated with Cemented Coal Gangue Fly-Ash Backfill Slurry

Cemented coal gangue-fly ash backfill (CGFB) slurry has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the characteristics of CGFB slurry fluidity in its pipe transportation. A general description about the components of the CGFB is provided involving the percentage of composition, particle size distribution (PSD) and rheological performance. The CGFB flow characteristics of the slurry pipeline were simulated in a straight pipe and 90° elbow pipe, respectively, combined with the pressure loss and conveying velocity distribution. With the help of the commercial computational fluid dynamic (CFD) code FLUENT, the modeling was conducted with various slurry feeding velocities. These results showed the local resistance loss in a bending pipe is significantly higher than the resistance in a straight pipe under the same conditions associated with CGFB transportation. The velocity distribution of the slurry solid particles in the slurry’s movement forward is more decentralized as the hydraulic inlet velocity increases. Based on these simulation data, a correlation was developed to predict the resistance loss of the CGFB slurry as a function of the hydraulic inlet velocity, pipe diameter and CGFB slurry rheological characteristics.

Numerical simulation of hydrodynamic cavitation in acetic acid solutions with different concentrations

To investigate cavitation phenomenon in acetic acid solution, numerical simulation was performed using the commercial computational fluid dynamics code of ANSYS Fluent. A comparison for acetic acid solutions of different concentrations flowing in a Venturi tube was implemented, focusing on the effect of the solution concentration on cavitation. Distributions of velocity, static pressure as well as the volume fraction of cavitation in the Venturi tube were analyzed. Flow and cavitation characteristics were explained. The results show that the non-uniformity of pressure distribution is enhanced with the increase of the solution concentration. Cavitation in the Venturi tube is featured by cavitation clouds. As the solution concentration rises, the length of the cavitation cloud decreases, and the cavitation intensity decays continuously. The results of this study can contribute to raise the effectivity and environmental efficiency of cleaning applications of acetic acid solutions.

Void fraction distribution in a bisectional bubble column reactor

This article presents the distribution of the local void fraction (α) in a mock‐up bisectional bubble column with a diameter of 0.63 m. Owing to the lack of such data in the literature, α was investigated experimentally using a microresistivity (R) probe and a phase discrimination procedure based on the probe signal. The two‐phase mixture that consisted of air and tap water was measured at 342 nodes in the vertical half‐section plane of the column. Relatively small differences between the volume‐integrated local values of α and the measured total gas holdups showed reasonably good agreement under all conditions. Experimental data were used for validation of a bubble column numerical model for a low hydrodynamic regime with commercial computational fluid dynamics (CFD) code. The difference between the CFD calculated total gas holdup and the experimentally measured mean value is 8.8%, while some differences in the local void fraction distributions were found in the lower part of the column. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1186–1197, 2019

Particle classification and drag coefficients of irregularly-shaped combustion residues with various size and shape

In a vast number of industrial applications, particle-laden flows consist of irregularly-shaped particles with various sizes and shapes and thus, the drag coefficient is strongly affected and different for each particle. The key issue is to incorporate these characteristics within numerical calculations. Therefore, a sample-set of irregularly-shaped combustion residues or rather clinker flakes, with sizes between 50μm and 250μm was experimentally and numerically investigated. Particle geometry, terminal velocity measurements and drag analysis were carried out within the present work. Areflected-light microscope and an optical particle analyzer were used for geometry analysis. Terminal velocities were measured in a water filled glass column with a commercially available digital camera with a recording rate of 1000 frames per second and a frame-by-frame tracking method. At first a simple particle classification method based on this geometrical analysis and terminal velocity measurements in a static fluid was introduced. As a result, several particle groups were defined based on the obtained data. As a second step, this data were used as input parameters for two simple drag models from literature. The required particle shape parameters were determined by velocity recalculations and data fitting. Furthermore, the applicability of these drag models in combination with the experimentally determined particle shape descriptors was evaluated within a simple test rig, where freely falling particles are exposed to a lateral compressed airflow. The particles would be deflected and settle at different positions at the bottom of the test rig. Numerical calculations of the test rig were performed using a commercial Computational Fluid Dynamics (CFD) code and a numerically efficient Euler-Lagrangian approach in order to predict the accurate motion of particles. The particle mass dispersion at the bottom of the test rig was compared to numerical results. It was shown that the used drag models in combination with the experimentally determined particle shape descriptors improved the prediction of particle drag coefficients and trajectories significantly without an increase of computational cost and time.

Numerical simulations of cross wind effects on cyclist aerodynamic resistance

Introduction : In outdoor cycling, cross wind can affect the race strategy and the final results. Ad-hoc strategies, like echelons and Belgian tourniquet formations, are indeed adopted by cyclists to reduce wind effects and aerodynamic drag. Forces and moments generated by cross winds have been often studied for isolated wheels [1,2] and for an entire isolated cyclist [3-5]. However, to the best of our knowledge, the impact of cross wind on a couple of cyclists has not yet been investigated. In this study, Computational Fluid Dynamics (CFD) simulations are used to evaluate the effect of cross wind on the aerodynamic resistance of a couple of cyclists in two different configurations: (1) when the trailing cyclist is placed in line with the leading cyclist (Fig. 1a) and (2) when both cyclists are staggered (Fig. 1b). To compare the results, additional simulations have been performed for a single cyclist. Moreover, the impact of the upstream turbulence intensity is investigated. CFD simulation: The cyclist geometry used in these simulations has been obtained by means of high resolution 3D laser scanning of elite cyclists. Further information is provided in Refs. (Defraeye, Blocken, Koninckx, Hespel, & Carmeliet, 2010) and (Blocken, Defraeye, Koninckx, Carmeliet, & Hespel, 2013). The computational grids consist of prismatic cells in the boundary layer region near the cyclist body while tetrahedral cells are adopted in the rest of the domain using proper growth factors. The total number of cells is about 8.3 M and 14.0 M, for the single and drafting cyclists, respectively. The simulations are performed using the commercial CFD code ANSYS/Fluent 15.0. The 3D steady Reynolds- Averaged Navier-Stokes (RANS) equations are solved in combination with the standard k- Iµ turbulence model with low Reynolds number modelling based on the one-equation Wolfshtein model. This choice was made since a good agreement with wind tunnel tests was achieved in a previous validation study for the case of zero yaw angle (Blocken, Defraeye, Koninckx, Carmeliet, & Hespel, 2013). The distance from the centre point of the wall adjacent cells to the cyclist body is about 30 I¼m corresponding to an average y* value of about 1. The simulations are performed for yaw angles between 0° and 45° in 5° intervals. Results: the results show that the drag of the leading cyclist is affected by the position of the trailing cyclist only at low yaw angles ( I¸ < 15 degrees). In this case, the drag area coefficient, C d A, is reduced by about 2.5% (not shown in the figures). The drag of the trailing cyclist however is highly influenced by his position with respect to that of the leading cyclist (Fig. 2). When the yaw angle is less than 15° the in line configuration is still advantageous while for larger angles the staggered configuration shows the best behavior both in terms of drag area coefficient and side force area coefficient, C s A. In the case of a single cyclist, a reduction of the drag area is obtained as the yaw angle increases. Conversely the side force area coefficient is increasing almost linearly with larger yaw angles. However the dimensional drag is almost constant until an angle of around 25°, while after it slightly increases. In future studies other configurations will be analyzed and bicycles will be included in the models.

Computational analysis of solid particle-erosion produced by bottom ash slurry in 90° elbow

Present work is devoted to investigation of the slurry erosion wear in a 90° elbow by using commercial Computational fluid dynamics (CFD) code FLUENT. Discrete phase erosion wear model was used to predict erosion in 90° elbow by solving the governing equations through Euler-Lagrange scheme. Particle tracking was considered by using standard k-ε turbulence scheme for the flow of bottom ash slurry. Erosion wear in elbow was investigated along with velocity distribution and turbulence intensity. The radius-to-diameter (r/D) ratio was taken as 1.5. Results show that erosion rate increases with increase in velocity. Present numerical simulation model holds close agreement with previous studies. Distorted patterns appeared at low velocities. The V-shape pattern appeared on the outer wall of elbow at high velocities. The low velocity region occurs around circumference of elbow wall at outer wall of elbow due to stimulation of the drag forces near the wall region.

Computational Fluid Dynamics Prediction of the Dynamic Behavior of Autonomous Underwater Vehicles

Prediction of the dynamic behavior of autonomous underwater vehicles (AUVs) is the basis for developing the control system and optimizing the hydrodynamic shape of AUVs. A fast and efficient prediction method of dynamic behavior of AUVs was developed with the secondary programming of a commercial computational fluid dynamics (CFD) code of FLUENT. In the proposed CFD method, mass properties of the AUV and thrust of the propeller were coupled to the 6-degree-of-freedom (DOF) dynamic equations of AUV in the form of user defined functions. A subregional unstructured mixed meshing strategy combining static meshes and dynamic meshes was proposed to improve the computational efficiency and to realize the 6-DOF movement of AUV. The proposed CFD prediction method can predict not only the dynamic behavior of the AUV, but also its surrounding flow field. Dynamic behavior of a seafloor mapping AUV in straight running and turn running were predicted using the developed CFD strategy. Comparison between the prediction results from the CFD method and those from the sea trials proved the proposed method to be accurate and effective. Some measures were put forward to improve motion performance of the vehicle according to the prediction results.

Thermal-hydraulic analysis of the First Wall of a CO2 cooled pebble bed breeding blanket for the EU-DEMO

The Demonstration Fusion Reactor in Europe (EU-DEMO) is considered to be the last step before building a commercial fusion power plant. Up to now, He has been chosen as gas coolant for three of the four candidate breeding blankets proposed for the EU-DEMO, being the Helium Cooled Pebble Bed (HCPB) among them. The choice of He coolant is supported, among other features, by its superior heat transfer capabilities, its transparency to neutrons and chemical inertness. However, the use of this coolant in DEMO poses some feasibility questions, like the large coolant inventory, resulting in possible safety issues, as well as the large circulating power. On the other side, CO2 has been the fluid coolant choice in the nuclear fission industry for gas-cooled reactors since the 1950s. The key advantage of this gas is its larger density, which results in more compact components, lower coolant inventories, lower circulating powers and thus better plant thermal efficiency. This, coupled also with a relatively high molecular stability at moderate temperatures (up to 600 °C), its larger availability and lower price make CO2 an attractive coolant for a pebble bed breeding blanket, as an alternative to He.As a Plasma Facing Component, the First wall (FW) is one of the components under the most challenging environment. Currently, the FW region at the upper port inboard location is expected to suffer the most critical heat flux loads. Indeed, a peak charged particle heat flux 0.99 MW/m2 together with a radiation heat flux of 0.18 MW/m2 is foreseen at this location. This paper reports the thermal-hydraulic analyses carried out to find the practical heat flux limits by using CO2 as coolant. The analyses have been performed by using the commercial computational fluid dynamics (CFD) code ANSYS CFX. Different augmented technical wall roughness areas have been considered, for a best heat transfer-to-pressure drop ratio. Sensitivity analyses have been performed as well for higher peak particle heat fluxes, evidencing that a CO2-cooled FW can dissipate peak heat fluxes up to 1.8 MW/m2 keeping the circulator power in a reasonable range.