Fluent Model Research Articles

A biparametric analysis on the steady performance of bidirectional pumping hydrodynamic-static hybrid dry gas seal

Purpose The purpose of this paper is to obtain the matching relationship between spiral groove, equalizing groove and operation parameters through the biparametric analysis for the bidirectional pumping hydrodynamic-static hybrid dry gas seal (BP-HHDGS). Design/methodology/approach The large eddy simulation (LES) model in Fluent is used to simulate the flow field of BP-HHDGS, and the biparameter variables method is chosen to analyze the effects of different parameters on the performance of BP-HHDGS. Findings BP-HHDGS has a greater opening force than hydrostatic dry gas seal (HDGS); the vortex is formed after lubricating gas is exhausted from the throttle. Increasing the depth of the equalizing groove and spiral groove has a synergistic enhancement effect on the opening force and leakage of BP-HHDGS. There is a matching relationship between spiral angle and rotational speed. The preferred parameter ranges in current conditions are found as follows: spiral angle αa = 15°–24°; groove-dam ratio λ = 0.4–0.7; equalizing groove depth hj > 35 µm; spiral groove depth hg = 5-10 µm. Originality/value The high starting capacity of HDGS is given to the hydrodynamic type seal, and thus the application promotion of HDGS in high-speed working condition is realized at the same time. This work also provides precise and quick theoretical guidance for the selection and design of hydrodynamic-static dry gas seal and further promotion.

Analysis of Atomization Performance of Linear Laval Nozzle under Varied Water Pressures Based on VOF and DPM Models

Particulate matter from coal and stone operations is a primary air pollution source. The traditional nozzle requires high-pressure conditions, and the atomization droplets are large and uneven. This paper aims to study a linear Laval nozzle and investigate the impact of water pressure on atomization performance. The volume of fluid (VOF) model and discrete phase model (DPM) of Fluent are used to simulate the internal and external fields of the nozzle and analyze the velocity, droplet size, and atomization angle. The results show that the optimized water pressure parameters are 0.1 MPa with an air pressure of 0.5 MPa. Droplets in the middle are smaller, while those on the sides are larger. Compared to traditional nozzles, the water pressure is reduced by over 90%, and the Sauter mean diameter (SMD) decreases by over 50%. Moreover, the theoretical spray angle increases by approximately 150%.

Study of heat transfer coefficients of multiple high-pressure fan-shaped water impinging on the lower surface of high-temperature steel billets

The lack of research on the boiling heat transfer coefficient on billet surfaces during the high-pressure fan-shaped water descaling process significantly affects the cooling, quality, and rolling efficiency of the billet surface. This paper utilizes the Eulerian multiphase flow model in Fluent 19.0 software to simulate the boiling heat transfer behavior of multiple high-pressure fan-shaped water jets impinging the surface of high-temperature steel billets during descaling. The study highlights the correlation between the boiling heat transfer coefficient and three key parameters: the Reynolds number, dimensionless target distance, and dimensionless temperature. The simulation’s accuracy was validated by comparing the simulation results against experimental data. Findings indicate that the boiling heat transfer coefficients were respectively higher in the stagnation area, the lower side of the overlap zone, and at the edges of the flow strands on the billet surface, reaching up to approximately 6000 W·m−2·K−1. Additionally, the heat transfer coefficients were higher in the downstream region compared to the upstream area. The boiling heat transfer coefficient increased by 13.7 % and 9.38 % as the Reynolds number increased from 278,031 to 340,486 and as the initial temperature increased from 1373.15 K to 1573.15 K, respectively. On the other hand, the boiling heat transfer coefficient decreased by 19.0 % when reducing the target distance from 20 de to 54 de. Finally, a function was established to describe the boiling heat transfer coefficient based on the Reynolds number, dimensionless target distance, and dimensionless temperature.

FLUENT: Towards a more flexible design and planning approach

The following paper introduces the FLUENT model, a contemporary university course planning approach built on the findings from a research which used the results of a survey, interviews to university key informants and a literature review based on the PRISMA methodology. FLUENT is an acronym that stands for Flexible Universal Education Model for a New Hybrid. Faced with the complexity of teaching and uncertainty in planning, the model aims to comprehensively address course planning intricacies. Unlike traditional models, FLUENT adopts a fully online perspective, acknowledging the potential of online education. It incorporates evidence-backed elements from course design, as for example emphasizing deep understanding, accurate planning, or crucial structuring elements. The structuring elements encompass time, space, technology, students' agency, and teachers' reflectivity. Additionally, FLUENT integrates principles of reversibility, addressing unforeseen circumstances, and recognizes students in both face-to-face and online environments. The model promotes flexibility, personalization, interaction, and collaboration, aligning with the pillars of future learning. FLUENT stands out by offering reversible design, considering diverse needs of students, and being adaptable to diverse institutional infrastructures. The model emphasizes learning paths, competencies, and aligning objectives, providing a comprehensive framework for course planning.

Soil Marginal Effect and LSTM Model in Chinese Solar Greenhouse.

The food crisis has increased demand for agricultural resources due to various factors such as extreme weather, energy crises, and conflicts. A solar greenhouse enables counter-seasonal winter cultivation due to its thermal insulation, thus alleviating the food crisis. The root temperature is of critical importance, although the mechanism of soil thermal environment change remains uncertain. This paper presents a comprehensive study of the soil thermal environment of a solar greenhouse in Jinzhong City, Shanxi Province, employing a variety of analytical techniques, including theoretical, experimental, and numerical simulation, and deep learning modelling. The results of this study demonstrate the following: During the overwintering period, the thermal environment of the solar greenhouse floor was divided into a low-temperature zone, a constant-temperature zone, and a high-temperature zone; the distance between the low-temperature boundary and the southern foot was 2.6 m. The lowest temperature in the low-temperature zone was 11.06 °C and the highest was 19.05 °C. The floor in the low-temperature zone had to be heated; the lowest value of the constant-temperature zone was 18.29 °C, without heating. The minimum distance between the area of high temperature and the southern foot of the solar greenhouse was 8 m and the lowest temperature reading was 19.29 °C. The indoor soil temperature tended to stabilise at a depth of 45 cm, and the lowest temperature reading at a horizontal distance of 1400 mm from the south foot was 19.5 °C. The Fluent and LSTM models fitted well and the models can be used to help control soil temperature during overwintering in extreme climates. The research can provide theoretical and data support for the crop areas and the heating of pipelines in the solar greenhouse.

Bayesian parameter estimation and evaluation of the K-ω shear stress transport model for plane impinging jets

Numerical simulations with semi-empirical turbulence models are commonly used to model impinging jets, often used for cooling solid surfaces. In this work, the constants in the k-ω shear stress transport model in ANSYS FLUENT are calibrated to experimental velocity and heat transfer data for a plane turbulent impinging air jet to determine if Kennedy-O’Hagan calibration (Kennedy and O’Hagan 2001 J. R. Stat. Soc. B 63 425–64) can improve predictions of near-surface velocities and surface Nusselt numbers for similar flows. Impinging jets have been proposed to cool the target plates of the divertor in future magnetic fusion energy reactors, where simulations are used to estimate divertor performance. The flat-plate divertor (Wang et al 2009 Fusion Sci. Technol. 56 1023–7) uses a plane jet of helium issuing from a B = 0.5 mm slot to cool a surface with radius of curvature of 44B at a distance 4B from the slot. Predictions from the calibrated numerical model are compared with independent experimental data at different flow conditions, as well as surface temperature data for a flat plate divertor test section. The contribution of this work is evaluation of the accuracy of a calibrated turbulence model for modest extrapolations in flow geometry and flow conditions for a plane impinging jet.

Numerical two-dimensional optimization of a cylindrical fuselage for bioinspired unmanned aerial vehicle based on non-dominated sorting genetic algorithm-II

To achieve an aerodynamically efficient design of fuselage for bioinspired unmanned aerial vehicles (UAV), the development of a systematic method is of paramount need. This work presents a multiobjective optimization study for shape parameterization of a 2D fuselage of foldable flapping wing UAV in low Reynolds number (2e05) flight conditions. The novelty of the research work lies in integrating S1223 airfoil characteristics for predicting the efficient shape design of the fuselage. This paper offers four sections; (i) the validation of the ANSYS Fluent model with experiment, (ii) the exploration of design variables using Design of Experiment (Sparse Grid Initialization), (iii) the implementation of response surface method (Genetic Aggregation) to know about dimensional sensitivity among independent and dependent variables and (iv) the application of multiobjective optimization method i.e. NSGA II to optimize the drag and lift coefficient. To identify the superiority, a comparative study between the original and optimized fuselage is presented considering many parameters like pressure contours, velocity contours, pressure coefficients, and streamlines representations. It is evident from various results that the 2D optimum shape significantly minimizes the drag coefficient and increases the lift coefficient. This work also makes room for 3D shape optimization, which helps in prototype fabrication for real-time flight conditions.

Applicability Study of Euler–Lagrange Integration Scheme in Constructing Small-Scale Atmospheric Dynamics Models

The atmospheric flow field and weather processes exhibit complex and variable characteristics at small scales, involving interactions between terrain features and atmospheric physics. To investigate the mechanisms of these process further, this study employs a Lagrangian particle motion model combined with a Euler background field approach to construct a small-scale atmospheric flow field model. The model streamlines the modeling process by combining the benefits of the Lagrangian dynamics model and the Eulerian integration scheme. To verify the effectiveness of the Euler–Lagrange hybrid model, experiments using the Fluent wind field model were conducted for comparison. The results show that both models have their advantages in handling terrain-induced wind fields. The Fluent model excels in simulating the general characteristics of wind fields under specific terrain, while the Euler–Lagrange hybrid model is better at capturing the upstream and downstream disturbances of the terrain on the atmospheric flow field. These findings provide powerful tools for in-depth diagnostic analysis of atmospheric flow simulation and convective precipitation processes. Notably, the Euler–Lagrange hybrid model demonstrates excellent computational efficiency, with an average computation time of approximately 2 s per time step in a Python environment, enabling rapid simulation of 40 time steps within approximately 90 s.

Computational fluid dynamics of flow boiling and conjugate heat transfer characteristics in a mini/micro-channel printed circuit steam generator

Numerical investigation of printed circuit heat exchanger PCHE was carried out for the water-steam system to optimize the design parameters for the possible use of PCHE as a steam generator in integral nuclear reactors- thus targeting efficient renewable energy by enhancing heat transfer. Heat fluxes, overall heat transfer coefficient (OHTC), and volume fraction of steam in a single channel of PCHE are reported for counter-current flow arrangement. The numerical model consisted of 1mm∗1.5mm single hot and cold channel. The heat transfer parameters were calculated using the Volume of Fluid (VOF) model in ANSYS Fluent with boundary conditions: top/bottom adiabatic; left/right periodic; mass flow inlet and pressure outlet. The effect of cold side degree of inlet subcooled (DISC) – varied from 100 to 0 K with a decrement of 20 K- and mass flux (200 to 500 kg/m2.s on OHTC, vapor fraction, pressure drop, and effectiveness was studied. For the fixed degree of subcooled, the OHTC and pressure drop increase as cold side mass flux increases. Similarly, for the fixed mass flux at varying DISC, the OHTC increases and pressure drop decreases for low mass fluxes up to 200 kg/m2.s because most of the channel remains in the nucleate boiling regime. However, with further increase in mass flux opposite trends in OHTC and pressure drop were observed due to single phased regime. The vapor fraction of steam increases with lower DISC at low mass fluxes and decreases with the increase in mass flux. The effectiveness decreases as the cold side inlet temperature approaches saturation temperature at 3 MPa.

Numerical modelling of thermal hysteresis in melting and solidification of phase change materials

This research focuses on exploring the impact of thermal hysteresis effects on the performance of Phase Change Materials (PCMs) used in thermal storage or buffering applications. Computational Fluid Dynamics modeling in ANSYS Fluent is employed to investigate thermal hysteresis phenomena during solid-liquid phase change. The traditional enthalpy-porosity method is extended by introducing an alternative relationship between the liquid fraction and PCM temperature, implemented in Fluent through User Defined Functions. The study demonstrates the developed model by simulating a rectangular PCM enclosure with a heated wall featuring a time-dependent temperature boundary condition. Considering convective heat transfer, a comparison is made between the newly developed hysteresis model and the default solidification-melting model of ANSYS Fluent. The new model facilitates numerical analysis of thermal hysteresis during partial and complete melting and solidification processes, enabling the study of hysteresis effects on the part-load operation of PCM systems.

Influence of building spatial patterns on wind environment and air pollution dispersion inside an industrial park based on CFD simulation.

The "spatial pattern-wind environment-air pollution" within building clusters is closely interconnected, where different spatial pattern parameters may have varying degrees of impact on the wind environment and pollutant dispersion. Due to the complex spatial structure within industrial parks, this complexity may lead to the accumulation and retention of air pollutants within the parks. Therefore, to alleviate the air pollution situation in industrial parks in China and achieve the circular transformation and construction of parks, this study takes Hefei Circular Economy Demonstration Park as the research object. The microscale Fluent model in computational fluid dynamics (CFD) is used to finely simulate the wind flow field and the diffusion process of pollutants within the park. The study analyzes the triad relationship and influence mechanism of "spatial pattern-wind environment-air pollution" within the park and studies the influence of different spatial pattern parameters on the migration and diffusion of pollutants. The results show a significant negative correlation between the content of pollutants and wind speed inside the industrial park. The better the wind conditions, the higher the air quality. The spatial morphology parameters of the building complex are the main influences on the condition of its internal wind environment. Building coverage ratio and degree of enclosure have a significant negative correlation with wind conditions. Maintaining them near 0.23 and 0.37, respectively, is favorable to the quality of the surrounding environment. Moreover, the average height of the building is positively correlated with the wind environment condition. The rate of transport and dissipation of pollutants gradually increases as the average building height reaches 16 m. Therefore, a reasonable building planning strategy and arrangement layout can effectively improve the wind environment condition inside the park, thus alleviating the pollutant retention situation. The obtained results serve as a theoretical foundation for optimizing morphological structure design within urban industrial parks.

Numerical Analysis of Three Vertical Axis Turbine Designs for Improved Water Energy Efficiency

A hydrokinetic turbine with a vertical axis is specifically designed to harvest the kinetic energy from moving water. In this study, three vertical axis water turbines, namely Gorlov, Darrieus, and Savonius turbines, were compared for their efficiency via numerical modeling for steady-state conditions via the ANSYS 2022 R2 Fluent model. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) was implemented with an SST k-ω turbulence model. The dynamic mesh technique, which allows modeling according to changes in angular velocity at each time step, was used to simulate flow around the turbines for six different velocities (from 0.5 to 3 m/s). The efficiency of the turbines was compared and the results were analyzed. The pressure, velocity, and turbulence kinetic energy distributions around the rotor were measured at different rotational angles and results indicated a wider operating range for the Darrieus and Gorlov turbines compared to the Savonius turbine. The highest power coefficient of 0.293 was achieved in the model featuring a Darrieus turbine, corresponding to a TSR value of 1.34, compared to 0.208 for the Gorlov and 0.257 for the Savonius turbine, at TSR values of 1.3 and 1.06, respectively. Numerical modeling results pointed to a significantly higher self-starting capacity for the Savonius turbine compared to the others.

CFD modeling of thermal processes in the firebox and heat load distribution on the screen surface firebox

Using ANSYS FLUENT numerical modeling and mathematical modeling, the main characteristics of combustion processes during the combustion of natural gas were determined. In this work, the combustion processes and NOx formation in the firebox were modeled at different loads of the GM- 50-14/250 boiler. The temperature distribution along the height of the firebox and the heat load on the screen panels were determined. The results of calculations by two types of models were compared with each other and with the data of measurements on the operating equipment. The environmental performance of the firebox, namely the formation of NOx at different heat loads, was determined. The maximum boiler capacity at which its operation meets European environmental standards was determined. The deviation of calculations on the formation of NOx in the GM-50-14/250 boiler at 40% of the rated power compared to the results of field tests using ANSYS FLUENT modeling was 8%, and using the mathematical model - 27%. When operating at rated power, the deviations of the results decreased to 2% and 8%, respectively. The deviation of the results of thermal calculations of the combustion in the firebox by different types of modeling in the active combustion zone and at the outlet of the firebox is up to 3% at different loads.

FLUENT model for simulating cyclic voltammetry in electrochemistry

FLUENT model for simulating cyclic voltammetry in electrochemistry

A ONE-WAY COUPLED APPROACH FOR MULTISCALE CHARACTERIZATION OF FILLING OF DUAL-SCALE FIBROUS REINFORCEMENTS CONSIDERING AIR COMPRESSIBILITY AND DISSOLUTION IN LUMPED FASHION

The filling characterization of dual-scale fibrous reinforcements is challenging due to the presence of subdomains with dissimilar permeabilities, existence of wicking effects, and combination of air compressibility and dissolution phenomena. These factors cause flow imbalances inside the representative unitary cell (RUC), which lead to void formation and influence the behavior of macroscopic field variables, affecting the parts manufacturing by liquid composite molding (LCM). Here, the filling characterization of woven fabrics used in LCM is done using one-way coupled simulations. Once RUC geometry is characterized by scanning-electron microscopy (SEM), and stereomicroscopy, standard thickness test, and resin viscosity are measured, the multiphase finite volume method-volume of fluid (FVM-VOF) model of ANSYS Fluent is used for the three-dimensional filling of the RUC, incorporating an experimentally calibrated air entrapment parameter (λ) to consider air compressibility and dissolution; then, a lumped function for the coupling term with macroscopic equations is obtained in terms of volume-averaged variables. This function is used in the equivalent Darcy macroscopic model, which is solved using a dual-reciprocity boundary element method (DR-BEM) algorithm. By considering a single value of λ during the simulation, neglecting wicking effects, and normalizing physical variables, unified injection pressure-independent results for the local tows saturation and normalized pressure fields at mesoscopic scale were obtained, as well as for global tows saturation and normalized pressure and fluid front profiles at macroscopic scale, thus simplifying the filling characterization of reinforcements. Numerical results are coherent with unidirectional injection experiments at both scales.

Numerical Simulation of Pyrethrin Aerosol Deposition

Highlights A steady state, laminar CFD model was developed to simulate the airflow inside an aerosol exposure chamber. The CFD model predicted the droplet tracks and deposition of various sizes of aerosol droplets. Larger aerosol droplets had higher deposition efficiency. A Higher flow rate, but still within the laminar flow regime, caused lower deposition efficiency for all droplet sizes. Abstract. Aerosol insecticides (e.g., pyrethrin) are widely used for the control of stored products insects inside food facilities. To optimize pyrethrin aerosol application, computational fluid dynamics (CFD) was used to predict airflow and aerosol transport inside a vertical flow aerosol exposure chamber operated under laminar flow conditions. A discrete phase model in ANSYS FLUENT 2021 R1 was developed, and simulations were conducted to track pyrethrin droplets of various diameters (0.1 to 20 µm) and determine their deposition onto Petri dishes located near the center of the chamber. The deposition efficiency of the different aerosol droplet sizes and the effect of two flow rates (5 × 10-4 m3 s-1 and 4 × 10-4 m3 s-1) on deposition efficiency were determined. The results showed that the predicted deposition of pyrethrin aerosol increased with increasing droplet size, largely due to inertial and gravitational effects. Deposition efficiencies decreased with the higher flow rate—with 0.1% to 96.6% predicted deposition efficiencies for the low flow rate and 0.1% to 93.8% for the high flow rate. Results of this study can be used to improve aerosol application methods for stored product insect control. Keywords: Aerosol deposition, Aerosol insecticide, Computational fluid dynamics, Confused flour beetle, Deposition efficiency, Discrete phase model, Numerical simulation, Particle tracking, Pyrethrins, Stored product insect.

Numerical investigation on flow characteristics of multi-stream supersonic nozzle with serpentine configuration

The serpentine configuration is utilized in the multi-stream supersonic nozzle of the Adaptive Cycle Engine to improve the stealth performance of next-generation fighters. Compared to single-stream conventional nozzles, the multi-stream supersonic nozzle involves a larger number of design parameters and exhibits a strong interaction between the multiple streams. The serpentine configuration introduces a complex influence on the flow characteristics of the multi-stream supersonic nozzle, which presents significant challenges in designing high-performance nozzles. It is crucial to understand and effectively manage the flow features to optimize the design of multi-stream supersonic nozzles with a serpentine configuration. As a result, the effects of the serpentine configuration and nozzle pressure ratio (NPR) on the flow characteristics of the multi-stream supersonic nozzle were investigated numerically in this paper. The numerical simulation employs the implicit density-based algorithm and Shear Stress Transport k-ω turbulent model of the commercial software ANSYS Fluent. The results show that the shock waves and contra-rotating vortices are generated by the nonuniform main stream and corner vortices from the serpentine configuration when the streams mix, which lead to the decline of the aerodynamic performance compared to the no serpentine case. The mass flow rate of the main stream and tertiary stream reduce by 1.4 % and 4.2 %, respectively, and the thrust performance reduces by 0.35 %. As the NPR rises, the tertiary streams are compressed by the main stream. The mass flow rate of the tertiary streams drop sharply with the contraction of the actual throat area. The flow condition of the tertiary streams convert from the over-expanded condition of convergent-divergent nozzle to the critical condition of convergent nozzle. Due to the enlargement of the actual exit area for the main stream, the maximal thrust performance is at NPR = 7.0 instead of the designed NPR.

An Investigation of the Thermal Performance of a Tropical Greenhouse Constructed With an Earth Air Heat Exchanger

Abstract To maintain optimum plant growth temperature (i.e., 25–35 °C), the thermal performance of an earth air tunnel heat exchanger (EATHE)-integrated single-span saw-tooth greenhouse (GH) was assessed in peak summer. With the side and roof vents opened, natural ventilation due to wind and stack effect controlled the air movement and temperature inside the GH. In this configuration, the average temperature inside the GH remained higher than the ambient temperature by 1.5 °C for the entire period of the experiment. For EATHE (installed at a depth of 3.2 m) assisted GH with polyethylene (PE) cover, the air from the EATHE outlet entered inside the GH at 33 °C, and the average temperature within the GH was maintained at 4 °C lower than the ambient temperature. When the shading net was installed over the PE cover with the EATHE, the transmitted radiations into the GH were reduced from the roof, and the inside temperature was maintained 7 °C below the average ambient temperature (i.e., 45 °C). The measured temperatures along the length of the EATHE were compared with the indigenously developed code named PEAT (performance analysis of earth–air tunnel) and found to be in good agreement within ±4.5% deviation. The temperature distribution inside the GH was predicted using a computational fluid dynamics (CFD) model in ansys fluent with ±5% deviation from experimental results. With parametric analysis from the PEAT code and CFD model, the desired depth of the EATHE and the mass flowrate of air required to bring down the GH indoor temperatures to the optimum plant growth range were determined.

Thermal gasification of biomass in fluidized bed

Chemicals, heat, and electricity can all be made with biomass, a renewable energy source. Biomass gasification is more environment friendly than biomass combustion because it produces less carbon dioxide (CO2) and other polluting gases (NOx and SO2). Present paper is focused on biomass gasification using fluidized bed. CFD analysis are performed in a cylindrical fluidized bed gasification chamber with a diameter of 6.6 cm and static bed height of 100 cm. The biomass inlet is located at a height of 0.73 cm with diameter of 0.75 cm; unstructured grid is chosen for the analysis. In this study 39,250 cells and 40,086 nodes are used to perform the simulations. CFD simulations are carried out to investigate the devolatization behavior of biomass. Fluent model of volatile material is modified according to the ultimate and proximate analysis of biomass. To know the effect on conversion efficiency of biomass a different equivalence ratio is considered as a process parameter in the range of 0.2 to 0.3. The stoichiometric ratio considered as 0.4 for biomass gasification. Mass fraction of species generated from partial combustion i.e. gasification.

Cause Analysis of Condensed Water Induced Bulging in High-Pressure Steam Tee Joints of a Pyrolyzer

High-pressure steam pipes inevitably suffered from the reciprocal interaction of high pressure and temperature during a long-period service, causing deformation and cracking. However, only limited studies about abnormal bulging caused by condensed water have been carried out. To study the relationship between bulging and condensed water, bulging tee joints belonging to high-pressure steam pipes were investigated with a macro visual inspection, chemical composition analysis, and metallographic microscopy. According to the analysis of the bulging samples, pearlite spheroidization was found in the abnormal bulging tee joint. The ANSYS FLUENT modeling indicated that the tube wall of bulging tees was continuously subjected to alternating stress, causing the cyclic transformation of the liquid–gas phase inside the tee joint. The results indicate that the stress produced by a condensed water droplet ranges from 532.8 MPa to 59 MPa, continuously exerting pressure on the tube wall of the tee joint. When combined with the variation in the temperature field, the temperature of the severe bulging tee joint and slight bulging tee joint alternates. Further modeling illustrates that the stress generated by the impact of condensed water droplets on the high-temperature tee joints causes a ratcheting effect, which is identified as the main factor contributing to the bulging of the tee joint. Deterioration of the microstructure is considered a secondary mechanism.