Steam Generator Design Research Articles

Numerical study on flow instability in parallel helical tubes under ocean conditions

The superimposed coupling of flow oscillations generated by transient external forces under ocean conditions and flow oscillations in parallel helical tubes during two-phase flow instability may lead to more complex flow oscillation phenomena in parallel helical tubes. However, there is still a lack of understanding regarding the effect of ocean conditions on the two-phase flow instability within parallel helical tubes. The two-phase flow instability in parallel helical tubes under ocean conditions is numerically investigated in the present study. The effects of ocean conditions on the flow behavior and instability threshold in parallel helical tubes are studied with mass flux 200 kg/m2s and inlet subcooling within 5–70 °C. The results show that the mass flow rate decreases as the inclination angle increases. A larger rolling amplitude or shorter period increases the flow and temperature oscillation amplitude. Two characteristic frequencies are found in the natural circulation flow instability under the rolling motion. As the rolling amplitude increases, the compound flow oscillation amplitude is larger and more chaotic with a certain phase shift. The effect of stationary inclining on the flow instability threshold is rather significant than rolling effect. The results of the present study can serve as a significant reference for the operation and design of the helical-coiled once-through steam generator under ocean conditions.

Frictional pressure drop correlation of steam-water two-phase flow in helically coiled tubes

Helically coiled tubes are utilized as the heat transfer tubes for High-Temperature Gas-cooled Reactor (HTGR) steam generators due to their compactness, thermal expansion accommodation and high heat transfer coefficient. A clear understanding of the pressure drop characteristics is important for the design and operation of steam generators. In this study, experiments were conducted to investigate the frictional pressure drop characteristics in helically coiled tube with a very large curvature ratio of 0.109. The experiments were carried out in a steam quality range of 0.1–0.9, system pressure range of 3.5–7 MPa, mass flux range of 320–1100 kg/m2s. The results indicate that the frictional pressure drop increased with the increase of mass flux, decreased with the increase of system pressure. It first increased with the increase of steam quality, and reached a maximum value at a steam quality of approximately 0.8, then decreased until steam quality reached unity. Based on the present work and existing experimental database, 25 existing correlations are evaluated and none of them could satisfactorily fit all the data. Therefore, a new correlation based on the Martinelli and Nelson correlation was proposed. Compared with existing correlations, it has a broader range of applicability (operating pressure from 0.75 to 8 MPa, mass flux from 200 to 1100 kg/(m2·s), steam quality from 0.03 to 0.99, and curvature ratio from 0 to 0.109.), and higher accuracy (weighted mean MAPE of 8.92 % and arithmetic mean MAPE of 8.81 %). It also has better compatibility with straight tubes.

Degradation of remaining mechanical properties of bainitic 2.25Cr1Mo steel during creep

In this work, the microstructure and remaining mechanical properties of bainitic 2.25Cr1Mo steel plate used in steam generator of sodium cooled fast reactor during creep were systematically examined. Creep tests at 530 °C with a rupture time up to 18800 h reveals that the creep stress correlates linearly with the Larson-Miller parameter (PLM), while the creep plasticity is rather independent on PLM. The remaining strength parameters, such as yield strength (RP0.2), ultimate tensile strength (Rm) and hardness (H), are found to linearly decrease with PLM, while the remaining plasticity is seen to increase. It suggests that the application of creep stress to the steel accelerates the softening of the material. During the creep process, the dislocation density in bainitic matrix decreases, while the number density of carbides increases, sacrificing the solution strengthening and leading to a continual reduction in the lattice parameter. Although abundant fine carbides precipitate after creep rupture, the remaining strength is however reduced. Instead, the weakening effect due to reduction in dislocation and solute content overwhelms the strengthening of precipitation, resulting in a degradation of the remaining strength. The obtained remaining mechanical properties are attempted to be applied in the design and operation assessment of steam generator.

Single-phase heat transfer prediction in helical coiled tubes in turbulent regime

The accurate estimation of thermal–hydraulic parameters is crucial for the design of Small Modular Reactor steam generators, particularly in the case of complex geometries such as helical coiled tubes (HCTs). Reliable design tools are therefore essential for successful design. In this study, we compiled a database of 706 experiments to evaluate the predictive performance of commonly used correlations for heat transfer estimation in turbulent regime HCTs. Despite ranking the correlations according to their predictive performance, none of the existing correlations were able to accurately predict the broad range of experimental data. Therefore, a new correlation called FAMA was derived, which is simple to use, robust and significantly more accurate than any other correlation. Based on the Colburn Analogy, the FAMA correlation achieved a mean absolute difference of 6.21% compared to the experimental database, which represents a 25.7% improvement over the best existing correlation. Furthermore, the FAMA correlation exhibits good asymptotic behavior in straight tubes and is recommended for single-phase flow in HCTs for turbulent Reynolds numbers up to 135,000, curvatures from 0.00963 to 0.2035, and torsions up to 0.81. The Schmidt́s criterion is adopted for determining the critical Reynolds number. Due to its superior performance and wide range of applicability, the FAMA correlation is recommended for modeling and studying helically coiled steam generators as found in novel integral reactors.

Design optimization for pressurized water reactor using improved quantum fish swarm algorithm and intuitionistic linguistic decision-making

Nuclear power has garnered significant attention as a clean energy resource in expediting carbon peaking and achieving carbon neutrality. It contributes to sustainable economic growth while addressing national energy security concerns. As one of the most crucial components, pressurized water reactors require improvements in several key aspects, including strengthening the natural circulation capacity, increasing the reactor power, and reducing the reactor volume. However, the volume of pressurized water reactors is usually positively correlated with their power. Increasing the reactor power results in an expansion of its volume, which poses challenges for the reactor layout and also requires additional investment. Hence, in order to reduce the reactor volume while meeting its performance requirements, this study introduces a novel design optimization approach utilizing an improved quantum fish swarm algorithm and intuitionistic linguistic decision-making. Firstly, a nonlinear mathematical model for volume optimization of the steam generator (SG) and pressurizer (PR) is constructed. Then, the improved quantum fish swarm algorithm is proposed to obtain volume optimization alternatives for the SG and PR. Quantum computation strategies are introduced to enhance the global optimization ability and population diversity. Additionally, the vision range and step size of the quantum fish swarm are adjusted adaptively to improve the optimization precision. To further accelerate the algorithm convergence, the prospect-elimination strategy is built. Last but not least, the intuitionistic linguistic decision-making is presented to gain the optimal design alternative by taking four characteristics into account, namely, the fuzziness and hesitancy of evaluation information, the consensus reaching process, the bounded rationality of decision-making behaviors, and the complementarity, independence and redundancy among nuclear evaluation criteria. A case study on the SG and PR design optimization is implemented to demonstrate the reliability and reasonability of the proposed approach.

Analysis of startup process of small modular reactor with OTSGs

The ACP100 adopts the design of Once-Through steam generators(OTSGs). During the startup process, it involves the complicated heat transfer phenomenon which changes from single phase flow heat transfer to two phase flow heat transfer on the secondary side of OTSGs. In order to avoid the OTSGs operating in the operating interval where flow instability will occur, the coolant temperature of primary side and the feedwater flow rate of secondary side are all strictly required in the two phase flow operating interval of OTSGs. Besides, the regulation and fluctuation of the reactor nuclear power during the startup process influenced the stability of OTSGs operation, which makes the development and the validation startup strategy more important. The OTSGs simulation model of Babcock & Wilcox company design has been developed with APROS, the simulation result shows that it has good accordance with the operation parameters in literature. This model can capture the two phase flow heat transfer phenomenon on the secondary side of OTSGs. On this basis, the ACP100 startup numerical model has been developed also with APROS. The key parameters influenced the OTSGs operation during the whole startup process has been acquired in simulation. The recommendation for improving OTSGs operation stability during ACP100 startup process has been given.

Interfacial engineering of MXene-based composite aerogel for high-performance, multifunctional solar steam generator

MXene, an emerging two-dimensional material, has shown its evident application prospects in solar-driven interfacial water evaporation due to excellent photothermal conversion capability. However, MXene still suffers from a few undesirable characteristics in this scenario, including weak stability, self-stacking, and suboptimal optical absorption. To address these issues, in this paper, we fabricated a MXene-based composite aerogel, featuring with interconnected porous structure, broad and high solar absorption, good wettability and photothermal capacity. As our judicious structural and compositional design for the aerogel decreased the evaporation enthalpy of water, the solar steam generator based on the aerogel exhibited an outstanding water evaporation rate as high as 2.31 kg m−2 h−1 under one sun irradiation (and the corresponding solar-to-vapor conversion efficiency reached 90.8 %). Additionally, the aerogel was also designed with an excellent adsorption capacity for removal of heavy metal ions from water as well as a good antibacterial ability, which should be helpful in dealing with the complex working environments for solar steam generators. This work may shed light on the design and development of multifunctional solar steam generators toward practical and sustainable applications.

Design optimization of compact gas turbine and steam combined cycles for combined heat and power production in a FPSO system–A case study

This case study aims to cover a wide range of relevant aspects related to combined cycle design, mechanical integrity and operational reliability for cogeneration of heat and power in FPSO systems. The methods consist of combined optimization of combined cycle thermodynamic design and geometry of steam generator; vibration analysis for flow induced vibrations; and thermal stress estimation of casings during cold start-stop scenarios. Challenges and opportunities for reliable water treatment systems are explored. The results show that small tubes, a compact tube bundle and a low condensation temperature reduces the once-trough steam generator (OTSG) weight. The vibrations numerical simulations in this work support the standard recommendations of using 35 times tube OD as upper limit for the unsupported tube length, which could be used as a reasonable design criterion. Thermal stresses analysis indicates that the design of beam arrangement, location, and stiffness of beams has a major impact on thermal stresses, and can be optimized to different plate thicknesses in order to avoid fatigue damage. Focus should be on reducing leaks of deaerator, steam turbine and condenser. It is recommended to add Na sensors after condenser and investigating the use of Electrodeionization (EDI) technology for make-up water production from seawater.

Enhancing hydraulic stability in once-through steam generators of small nuclear power plants: A novel approach using throttling baffles and feed pipes.

Given the increasing global interest in small nuclear power plants (SNPPs), the proposed research aims to investigate the design of once-through steam generators (OTSGs) used in SNPPs, with a particular focus on ensuring hydraulic stability in the heat exchange tubes. The study will examine the theoretical issues of ensuring stability and propose a new approach that includes the installation of throttling baffles and feed pipes to achieve hydraulic stability in OTSGs. The research will use a 45 MW capacity OTSG as an example, based on the design of the ship nuclear power plant KLT-40S, whose heat exchange surface (HES) is a set of coaxial cylindrical coils, similar to 60% of SNPPs with pressurized water reactors (PWRs). The rest of the SGs have either straight or U-shaped vertical heat exchange tubes (HET). The study will also explore the results of calculating the additional hydraulic resistance in front of the heat exchange tubes and propose a new method for clarifying the existing inequality used to ensure stability. Ultimately, the goal of this research is to provide a novel design for OTSGs based on throttling baffles and feed pipes to ensure hydraulic stability in SNPPs and provide new insights and methods for research in this field.

DESIGN OF HELICAL TYPE STEAM GENERATOR FOR EXPERIMENTAL POWER REACTOR

Reaktor Daya Eksperimental (RDE) is a high-temperature gas-cooled reactor (HTGR) for electricity generation, heat generation, and hydrogen production by Batan. Empirical and numerical calculations are needed to strengthen the existing design. The numerical method by computational fluid dynamic (CFD) analyzes temperature distribution and pressure drop along the pipe. The Batan RDE steam generator design has a seven-layer helical pipe model, while this research uses a one-layer helix pipe. In empirical calculations, the heat transfer region has three sections; single-phase liquid, two-phase, and single-phase vapor heat transfer. In numerical calculations, apply the assumption of constant heat flux and constant working fluid properties. The results of empiric calculations data showed that the helical pipe height was 3.98 m, shorter than the Batan design, which is 4.97 m. This considerable difference due to empirical calculations did not cover the safety factor. The results of numerical calculations show that in the single-phase, empiric calculation data were acceptable since the different values of numerical calculations for empiric calculations data were below 10%. Meanwhile, the case of the two-phase numerical calculations is not satisfactory and needs further research to obtain optimal results.

Cavity-shaped direct solar steam generator employing conical helical tube for high-temperature application: Model development, experimental testing and numerical analysis

Concentrating solar thermal technologies are drawing more attention since it can substantially contribute to a carbon-neutral society. The solar receivers are essential in this technology to convert solar energy efficiently into thermal energy. Moreover, high-temperature steam generation is the promising application for concentrated solar power plants or industirial processes. Therefore, the direct solar steam generator has been gaining more attention due to its advantages of low operation and maintenance costs. Most solar steam generator designs consist of a tube with helical configuration because of its high heat exchange performance and compactness. However, only few studies address solar steam generators with conical helical tubes. Thus, both experimental and simulation data of this design are scarce. This paper shows the successful development and experimental testing of a solar steam generator with a conical helical tube. The experimental results proved that the developed solar steam generator can produce high-temperature steam of 600 °C at an inlet pressure and mass flow rate of 150–200 kPa and 2.5 kg/h, respectively. The overall calculated energy efficiency (thermal and optical efficiency) was 60–62%. In addition, a coupled 1D-3D numerical model was implemented to analyze the solar steam generator’s performance. The model consists of a 3D cavity heat transfer model and a 1D two-phase fluid flow model. The numerical analysis demonstrated the ideal generator’s performance (energy efficiency of 68–69%) and the great impact of convection in the heat losses (50% of the total energy losses). Although more research of the convection is required, the presented results provide a basis for designing further, upscaled solar steam generators employing conical helical tubes.

Effects of Pipe Inclination on Global Two-Phase Flow Parameters

Inclined two-phase flow geometries can be found in advanced nuclear reactor systems, such as the helical coil steam generators being considered for use in current integral steam generator designs. While this geometry includes inclination and centrifugal effects coupled together on two-phase flow, there have been limited studies to separate these effects to develop robust models. The majority of two-phase flow research is conducted on vertical channels, with recent work being conducted in a horizontal orientation and limited work in inclined pipes. In the current work, experiments are conducted in an adiabatic two-phase flow test facility to investigate the inclination effect on an air-water flow in straight pipes near atmospheric pressure. The pipe is made of clear acrylic with an inner diameter of 25.4 mm. The inclination of the flow loop can be adjusted in increments of 0.1 deg. Measurement capabilities are included to obtain local two-phase flow parameters such as void fraction, interfacial area concentration, bubble velocity, and Sauter-mean diameter using a local multisensor conductivity probe, local two-phase flow static pressure and pressure drop using a pressure transducer, and flow visualization using a high-speed video camera system. The experimental studies performed in the current work demonstrate how changes in inclination angle can affect the gas distribution flow regime transition and two-phase frictional pressure drop. Based on these experimental results, existing correlations for frictional pressure drop are evaluated, and the modified Lockhart-Martinelli correlation is found to predict the two-phase frictional pressure drop for inclined two-phase flows. This method agrees with experimental data within 7% on average.

Design of heat recovery steam generator (HRSG) and selection of gas turbine based on energy, exergy, exergoeconomic, and exergo-environmental prospects

The full repowering of an existing fossil fuel steam power plant is investigated. This study aims to introduce and examine the most important parameters, i.e., the design of the heat recovery steam generator (HRSG) and selection of the gas turbine (GT). The repowered cycle is studied in perspectives of energy, exergy, economic, and environmental views. Considering the pressure levels of the HRSG and the number of HRSGs in the new cycle, six different cases are evaluated. The produced power of the original units is 200 MW. The results of this study show that using two 180 MW GT and two HRSGs results the maximum possible thermal efficiency. By using a high-capacity GT (380 MW), the maximum efficiency will be obtained in case of using one HRSG. Moreover, in all cases, the CO2 production rate is reduced. Introducing new nondimensional parameters named x, y, and α, the balance of the axial force of the steam turbine shaft and the capacity of cooling system are considered. The effect of various parameters on these three parameters are analyzed.

A three-region movable-boundary helical coil once-through steam generator model for dynamic simulation and controller design

A simple but accurate mathematical model is crucial for dynamic simulations and controller design of helical coil once-through steam generator (OTSG). This paper presents a three-region movable boundary dynamic model of the helical coil OTSG. Based on the secondary side fluid conditions, the OTSG is divided into subcooled region (two control volumes), two-phase region (two control volumes) and superheated region (three control volumes) with movable boiling boundaries between each region. The nonlinear dynamic model is derived based on mass, energy and momentum conservation equations. And the linear model is obtained by using the transfer function and state space transformation, which is a 37-order model of five input and three output. Validations are made under full-power steady-state condition and four transient conditions. Results show good agreements among the nonlinear model, linear model and the RELAP5 model, with acceptable errors. This model can be applied to dynamic simulations and controller design of helical coil OTSG with constant primary-side flow rate.

A deep-learning reduced-order model for thermal hydraulic characteristics rapid estimation of steam generators

Model reduction is a method that maps full-order conservation equations into lower-order subspaces or establish a data-driven surrogate model to reduce the complexity of the entire physical system, which has been widely applied in various fields in recent years. Compared with computational fluid dynamics (CFD) simulations, reduced-order model (ROM) can quickly and instantly obtain simulation results at low cost, which provides an economical alternative approach for the research and design process which need large number of repetitive simulations. In this paper, a deep-learning ROM was developed based on the proper orthogonal decomposition (POD) and machine learning (ML) method. The rapid estimation of two significant thermal hydraulic parameters in steam generator (SG), including the void fraction and temperature, was carried out by ROM. By POD mode analysis, the order for void fraction and temperature field was reduced by 88.3% and 96.7%, respectively. An artificial neural network was trained to reflect the implicit nonlinear mapping relationship between the CFD inputs and feature coefficients. The ROM was validated by comparing the predicted results with refined CFD results. The maximum absolute errors of void fraction and temperature are 0.1 and 0.03 K with speedup on the order of 104, indicating that the developed ROM can quickly and accurately estimate the thermal hydraulic characteristics of SG under different operating conditions. This work may provide a novel approach for the parameter sensitivity analysis and optimization design of SG and give valuable reference for the digital twin and the real-time online monitoring of the SG.

Experimental study and analysis of design parameters for analysis of fluidelastic instability for steam generator tubing

In this paper, the evaluation method of fluidelastic instability (FEI) of newly designed steam generator tubing in pressurized water reactor (PWR) nuclear power plants is discussed. To obtain the parameters for prediction of the critical velocity of FEI for steam generator tubes, experimental research is carried out, and the design parameters are determined. Using CFD numerical simulation, the tube array scale of the model experiment is determined, and the experimental device is designed. In this paper, 7 groups of experiments with void fractions of 0% (water), 10%, 20%, 50%, 75%, 85% and 95% were carried out. The critical damping ration, fundamental frequency and critical velocity of FEI of tubes in flowing water were measured. Through calculation, the total mass and instability constant of the immersed tube are obtained. The critical damping ration measured in the experiment mainly included two-phase damping and viscous damping, which changed with the change in void fraction from 1.56% to 4.34%. This value can be used in the steam generator design described in this paper and is conservative. By introducing the multiplier of frequency and square root of total mass per unit length, it is found that the difference between the experimental results and the calculated results is less than 1%, which proves the rationality and feasibility of the calculation method of frequency and total mass per unit length in engineering design. Through calculation, the instability constant is greater than 4 when the void fraction is less than 75%, less than 4 when the void fraction exceeds 75% and only 3.04 when the void fraction is 95%.

Numerical Study on the Effect of Deposit Layer on the Minimum Wall Thickness of Boiler Water Tube under Different Operating Conditions

Water wall tube temperature is a major parameter in the steam generator design which has a significant role in keeping the steam generator available. Thus, knowing the tube average temperature in different operating conditions is very important to avoid the causes of tube failures. High temperatures are a major cause of various types of failures, such as overheating, hydrogen damage, thermal stress, etc. Furthermore, deposits on the inner tube wall contribute to such failure by changing the thermal resistance of the tube wall, which causes a significant increase in the tube wall’s average temperature, consequently lowering the allowable stress. Therefore, the model was created by using ANSYS FLUENT (Canonsburg, PA, USA) to determine the wall average water tube wall temperature considering the deposit layer thickness (magnetite). Furthermore, this model was verified. It was found that increasing tube thickness can increase the average tube temperature but combining it with increasing deposit thickness leads to higher temperatures. In other words, the effect of the deposit on the tube with higher thickness is higher than on the tube with lower thickness. By discussing the minimum thickness of the water wall tube, the suitable selection of the tube thickness and courses of action concerning the operating conditions that minimize the potential overheating of water tubes in the furnace section of the boiler can be determined.

Multi-objective optimization of helical coil steam generator in high temperature gas reactors with genetic algorithm and response surface method

High temperature gas reactors (HTGRs) have broad prospects in industry. The helical coil steam generator, which plays an important role in energy conversion in HTGRs, is widely adopted due to its high thermal efficiency. However, the design and performance analysis for helical coil steam generators is a definitely tough job induced by its complex structure and operation conditions. In this paper, an innovative multi-objective optimization process was proposed to manage the key parameter design of steam generators in HTGRs. Firstly, the system response of steam generators is investigated. The sensitivity of geometric parameters on the steam generator thermal performance is obtained through the response surface methodology (RSM). Finally, the geometric parameters of steam generators are optimized using the genetic algorithm with the goal of a higher heat transfer coefficient and a lower tube side pressure drop. Compared with the original design pressure drop (1.19 MPa) and heat transfer coefficient (1.007 kW∙m−2∙K−1, the optimal solution obtained by multi-objective genetic algorithm (MOGA) decreases the pressure drop by 50.76% and improves the overall heat transfer coefficient by 15.00%. It shows that MOGA performs well in heat transfer optimization of steam generators in HTGRs.

Efficient Solar‐Powered Interfacial Evaporation, Water Remediation, and Waste Conversion Based on a Tumbler‐Inspired, All‐Cellulose, and Monolithic Design

AbstractThe 3D steam generator with cold evaporation surface (CES) provides a means for high‐efficiency interfacial steam generation due to the low heat loss and continuous ambient energy input. However, the poor floating stability of CES steam generators when suffering wave slamming has limited their practical application in open water. Herein, a cellulose‐based monolithic aerogel integrated with three structural elements is developed inspired by tumblers, which can synchronously achieve outstanding antioverturning stability in waves and a high evaporation rate (4.21 kg m−2 h−1). A single‐stage solar water purification device is constructed based on the photothermal aerogel, which attains an ultra‐high daily water yield of ≈32.6 L m−2 and surpasses a large amount of single‐stage solar stills. The steam generator can also be used to purify wastewater containing Co2+ via adsorption. Gratifyingly, the Co3O4/C catalyst obtained from the pyrolysis of aerogels loaded with Co2+ exhibits good catalytic activity for carbon monoxide oxidation, demonstrating the potential for waste conversion. This work provides new insights into the design of solar steam generators used in open water, and offers a promising way for the disposal and utilization of contaminated steam generators after wastewater purification.

Numerical study on the enhanced heat transfer characteristics of steam generator with axial economizer

The heat transfer enhancement of heat exchangers is vital to improve energy utilization efficiency in industrial fields. The axial economizer used in steam generator is a typical enhanced heat transfer device. In this paper, the mechanism of heat transfer enhancement in steam generator with axial economizer was studied and the key thermal hydraulic parameters in steam generator were analyzed. The effects of divider plate heights and flow distribution on the heat transfer characteristics were also investigated. Results show that the axial economizer can effectively increase the heat exchange up by 2% and the steam production up by 3%. Within a certain range (0–2.2 m), the increase of divider plate height is beneficial for heat transfer enhancement. The flow distribution on the hot and cold sides would affect the heat transfer obviously. The influence of flow distribution on the heat transfer in steam generator is mainly concentrated in the cold side region. The conclusions can provide references for the design and operation of a new steam generator with the axial economizer, and are also meaningful for the enhancing heat transfer research in other industrial fields involving shell-and-tube heat exchangers.