To investigate the wall-approaching film formation (WAFF) mechanism of water injected during the compression process of single screw compressor, then to realize reasonable control of water injection parameters, a numerical simulation of water and steam two-phase flow inside the compression chamber during the compression process was carried out. The WAFF characteristics of water injected inside the compression chamber and the influence laws of the key parameters such as water injection angle (IA), injection velocity (IV), injection mass flow rate (IMFR), screw rotor rotational speed (SRRS) and injection hole spatial position (IHSP) on the WAFF characteristics were analyzed. The results show that the water injected into the chamber forms a water film by approaching the wall. With the increase of IA and IV, the effective water film average thickness (EWF-AT) and surface area (EWF-SA) show an increasing trend. In the process of IMFR growth, EWF-AT and EWF-SA exhibit maximum values. Considering the goal of minimizing the injection power consumption, the IA of 70 degrees, IV of 30 m.s(-1) and IMFR of 0.3 kg.s(-1) were determined as the optimal water injection parameters. Selecting the appropriate IMFR, SRRS and IHSP will effectively increase EWF-AT and EWF-SA, then to prevent leakage.
Carbon dioxide capture and storage is an important technological pathway to achieve climate change response goals based on ensuring energy security,and is an important strategic choice for achieving carbon reduction in the power as well as industrial sectors.However,high energy consumption and accompanying issues are key to the limit the development of carbon capture and storage at scale.In this paper,the load-cycling performance and exergy distribution of coal-fired power plants integrated with full flue gas carbon capture systems are investigated,and the variable working conditions performance of two turbine configurations of low carbon emission coal-fired units is compared.The results show that the energy consumption of the carbon capture system is 3.9 GJ·t-1 CO2 for full flue gas carbon capture,and the large irreversibility of the absorption and desorption processes leads to low efficiency of the absorber and stripper.After integrating the carbon capture system into the coal-fired power station,the efficiency of the configuration with the heat recovery turbine exhaust system is 1.5％higher than that with the medium-pressure cylinder exhaust,and the efficiency of the unit with the heat recovery turbine exhaust system.
Under the influence of secondary flow, the film cooling deviates from the flow direction on the turbine blade, which directly results in undesirable uneven film coverage. On the pressure side, the film appears divergent, while on the suction side, it is bunched. To solve this problem, a kind of subregional compound angle is proposed, in which the angle in the spanwise direction is different in different regions depending on the strength and direction of the secondary flow. Four rows of film holes with five kinds of subregional compound angles are provided on the pressure side, while two rows of film holes with different subregional compound angles are provided on the suction side. The Reynolds Average Navier-Stokes (RANS) method of the SST k-omega turbulence model is chosen to solve the above blade arrangement. The results show that a significant improvement can be achieved by the introducing subregional compound injection of the film coolant compared to the case of simple injection. In compound injection, the injectant maintains sufficient momentum to prevent the coolant from being swept away by the secondary flow. This was found to be largely the case for most holes on the pressure side, and some holes on the suction side. However, for holes near the downstream section of the suction surface of the blade, where the passage vortex is strongest, no value is found for the compound angle that could redirect the coolant along the blade profile without radial deviation. In some cases, excessive values of the compound angle led to jet liftoff rather than spreading the film along the surface.
Recently, artificial neural networks (ANNs) have been frequently embedded in computational fluid dynamics (CFD) solvers as surrogate tools for solving chemical reaction kinetics, thereby accelerating the computation of chemical reaction source terms. Compared with other chemical acceleration methods, such as mechanism reduction and tabulation, ANNs have the potential to simultaneously save computational cost and preserve mechanisms' high fidelity. However, conventional data-driven ANNs highly rely on the training data for solving combustion reaction kinetics, and non-physical prediction errors can hardly be avoided. This paper proposes a physics-informed neural network for solving combustion reaction kinetics (CRK-PINN), which regularizes the ANN through physical principles, including the laws of mass action, Arrhenius, enthalpy conservation, element conservation, and mole fraction conservation. In the absence of training data, CRK-PINN can independently solve chemical reaction kinetics, reconstruct the combustion process, and infer intermediate species and temperature. Under the supervision of training data and physical principles, CRK-PINN significantly suppresses the non-physical errors of data-driven ANNs and presents lower data dependence. This is demonstrated by the 0-D autoignition prediction and direct numerical simulation (DNS) of laminar and turbulent flames. Compared with the direct integration method, CRK-PINN results in an acceleration of 6.0 similar to 14.6 times for solving a 10- species 21-step H2-Air chemical mechanism. This further leads to a 2.3 similar to 4.9 times speedup for simulations of reacting flows with satisfactory accuracy based on the OpenFOAM toolbox. Novelty and significance statement We propose a novel Combustion Reaction Kinetics Physics-Informed Neural Network (CRK-PINN) for solving detailed combustion reaction kinetics with features of multiscale and high stiffness. Soft constraints of physical losses have been developed in PINNs to solve ordinary differential equations (ODEs). Data preprocessing methods such as logarithm and normalization are commonly used to alleviate the multiscale issue. However, these techniques have not been effectively integrated to properly address detailed combustion reaction kinetics. Our CRK-PINN incorporates logarithmic-normalized combustion reaction kinetics ODEs and several conservation equations as physical constraints into a neural network, highlighting both technical challenges and our novelty. By incorporating comprehensive physical constraints, CRK-PINN can independently solves detailed combustion reaction kinetics without relying on training data. Compared with data-driven ANNs, CRK-PINN offers a surrogate model with improved physical completeness, error reduction, and low data dependence. Compared with the direct integration method, CRK-PINN provides satisfactory accuracy and evident computational acceleration.
Two-phase flow in non-circular cross-section flow channels such as micro-heat sinks and micro-channel heat exchangers has received extensive attention due to its heat-enhancing properties. In this paper, under the boundary of constant heat flux, an experimental investigation of the heat transfer properties of gas–liquid two-phase flow in horizontal channels with cross-sections of 4 × 4 mm and 8 × 3 mm is carried out using air and water as working fluids. The effects of different inlet gas and liquid inlet Reynolds numbers on the wall temperature and Nusselt number are discussed. The results show that the effects of the liquid Reynolds number and the gas phase Reynolds number on the heat transfer coefficient of the square tube and the rectangular tube are different. Under the same gas–liquid Reynolds number, the Nusselt number of the gas–liquid two-phase flow in the square-section tube can be increased by 3.2 times compared with that in the single-phase flow, while the Nusselt number of the gas–liquid two-phase flow in the rectangular tubes can be increased by 1.87 times. The results of this paper provide a reference for the design of microchannel heat exchangers and the establishment of mathematical models for Taylor flow heat transfer in rectangular and square tubes.
The structure of casing treatment has a significant influence on the stability expansion effect. The ending position of the rotatable ring is one of the important structural parameters in the controllable speed casing. The impact of ending position of the rotatable ring rotating at the same speed as the rotor on the stability expansion and stability expansion mechanism was studied in this paper. The results show that, when the ending position of rotatable ring expands downstream in the range of 20% to 60% axial chord length, because of the improvement in the tip leakage vortex trajectory and main flow/leakage flow interface, the stability expansion effect rises gradually. The further downstream expansion of ending position from 60% axial chord length, however, has a slight impact on tip flow, bringing out a steady stability expansion effect around 52.5%. The best stability expansion effect of ending position occurs at 60% axial chord length where the stable operating margin increases by 53.5%.
Energy storage is important for the application of the discontinuous and unstable renewable energy. The CaO/Ca (OH)2 thermochemical system of high energy density and little heat lose is promising for thermal energy storage, yet the heat and mass transfer processes related to dehydration reaction needs further improvement and the regulation manner related to the hydration reaction needs further investigation. In this work, a hybrid indirectdirect reactor of the CaO/Ca(OH)2 system is proposed with the physicochemical model developed to study the dehydration and hydration processes under different operating and structural conditions, and five indicators are defined to evaluate the overall reaction performance. During the dehydration process, the reactant is indirectly heated by the electrical heater at the reactor outside wall and the reaction proceeds in radial direction which is mainly limited by the poor heat transfer, leading to low energy storage efficiency of 6.1 %. The increase of reactant thermal conductivity and application of high-thermal-conductivity porous channel greatly enhance the heat transfer leading to significant reduction of reaction time and increase of energy storage efficiency up to 25.63 %. During the hydration process, the gas mixture directly contacts and reacts with solid reactant and the reaction proceeds in axial direction with reaction region of "U" shape which is mainly restricted by the reaction equilibrium. The thermal power density and reaction temperature of the hydration process can be regulated by the inlet mass flow rate and the inlet steam mass fraction respectively. The increase of inlet mass flow rate and inlet steam mass fraction leads to higher heat exchange efficiency at the same reaction extent and shorter hydration reaction time. The present study demonstrates the superiority of the indirect-direct type reactor and the performance of which can be further improved by optimizing the geometrical and operating conditions.
As a photoresponsive molecule, azobenzene molecule can realize optically-controlled phase change through the regulation of molecular structure, and store photothermal solar energy and phase change heat simultaneously, expected to achieve long-term heat storage and optically-controlled heat release of phase change materials (PCMs). In this paper, the photo-triggered controllable phase change behavior of two different grafting groups (AZO-A-14, AZO-O-14) photoswitch molecules mixed with straight-chain alkane, fatty alcohol and fatty acid PCMs at different ratios was investigated. The results show that the photoswitch molecules are more suitable for the phase change temperature control of fatty alcohol or fatty acid PCMs, and this is true for different con-centrations. Using a photoswitch with similar polarity to the substrate, the trans-photoswitch that are not fully isomerized as well as cis-photoswitch can be well dispersed in PCMs, thus hindering their nucleation. In addition, the total enthalpies of the two photoswitch molecules are 233.45 J/g and 229.21 J/g, and the enthalpies of the optically-controlled PCMs ranged from 176.15 J/g to 229.06 J/g. For fatty acid, the doped photoswitch mole-cules can significantly improve the total energy storage density, and considering the energy storage density and temperature difference of the optically-controlled phase change, the combination of alcohol and ether-grafted optically-controlled PCMs is the best choice. This study provides ideas for the improvement, development and application of optically-controlled PCMs in the future.
The current demand-based defrosting initiation strategies of air source heat pumps (ASHPs) faces difficulty in achieving a balance between cost and robustness. Therefore, an efficient and innovative demand-based defrosting initiation strategy is proposed in this paper, based on the learned the degradation of heating capacity (DHC) method using data-driven model. Firstly, the DHC method is developed using the initially installed sensors without additional sensors to identify the frosty state. Subsequently, the fully connected neural network (FNN) model is established for predicting frosty state using field measured data from the ASHP system. Finally, the effectiveness of the defrosting initiation strategy is further validated through practical testing. The results demonstrate that the DHC method provides a reliable database for training the FNN model, resulting in an impressive accuracy of 91.43% for predicting the frosty state in the testing set. By adopting the innovative demand-based defrosting initiation strategies, the defrosting frequency, heating loss, and power consumption are respectively decreased by 66.3%, 2.1%, and 6.0% with the SCOP enhanced by 8.6% during a heating season. The promising results highlight that the proposed strategy effectively reduces costs while ensuring the efficiency of demand-based control.
Fuel cells can be made to operate under a variety of conditions by implementing adjustable ejectors in their anode gas circulation systems. Based on a quasi-two-dimensional model and considering factors such as friction and variable area effects, a theoretical model of ejectors with needles was established to predict their primary and secondary flow rates. Theoretical calculations were used to analyze the variations in internal parameters and flow losses along the ejector, explain the reasons and laws behind the effect of needle position on ejector performance, and explore the control mechanism of different needle shapes on ejector flow rates. Finally, flow control experiments were conducted on three types of adjustable needle shapes-oblique straight, quadratic, and parabolic-to validate the precision of the adjustable ejector theoretical model and the controls of different shapes on the ejector flow rates. The research indicates that the relative errors of the quasi-two-dimensional model in predicting primary and secondary flow rates are within +/- 5 % and + 20 % to-5%, respectively. Both the primary and secondary flow rates were impacted by the needle position variation, though the impact on the secondary flow was weaker. The parabolic shape was optimal for the linear control of primary flow rates, followed by the oblique straight shape. The quadratic shape was the weakest, although the quadratic-shaped needle had a wider range of flow rate control. Modeling and experimental research on the adjustable ejector contributes to understanding the influence of the needle on the ejector performance under different working conditions, broadening the application range of the ejector, and providing a basis for flow control in the fuel cell system.
Ultrasonic techniques have been widely used to determine the volume fractions of liquid components in oil–water two-phase flow. The two major ultrasonic interactions amenable to volume fraction estimation are the sound speed and attenuation. Instead of using these two linear ultrasound parameters, this study explores the use of ultrasound nonlinear parameter to measure the volume fraction of oil–water two-phase flow. Based on the theoretical modeling of ultrasound nonlinear propagation and nonlinearity measurement principle using finite amplitude insertion substitution (FAIS), we established a relationship between volume fraction and the amplitude of the second harmonic components in the received ultrasound waveform. With the use of high-intensity ultrasonic excitation, two-end calibration, and second harmonic amplitude extraction, the volume fraction of water can be calculated. The performance of the proposed method is validated by the numerical simulations and experimental studies in a lab-scale flow loop. Good qualitative agreement between the model and results shows that the nonlinear ultrasonic measurement technique has good quantitative accuracy and high measurement sensitivity, which make it well suited for industrial applications.
High-precision numerical simulation of aero-engine combustors requires a suitable evaporation model. At present, quantitative research on the effects of the evaporation model on two-phase turbulence combustion simulation is insufficient. Ethanol has a higher latent heat of evaporation than other fuels like acetone and aero kerosene, thus it is especially sensitive to the evaporation model. This paper uses LES to simulate turbulence in an aero-engine combustor, and TPDF to describe the interaction between turbulence and chemical reactions. Numerical simulation results of the Abramzon-Sirignano (A-S), Spalding, and thick exchange layer (NC-TEL) evaporation models for high-Reynolds number ethanol combustion in two-phase turbulent jet flames are analyzed and compared with experimental data. Results suggest that per unit time, the A-S evaporation model has the largest evaporation mass, followed by the NC-TEL evaporation model, while the Spalding evaporation model has the smallest evaporation mass. Through quantitative analysis of the different evaporation models' influence on temperature, mixture fraction, and liquid phase distribution, it is found that the A-S evaporation model fits the experimental data better in the central region of jet flame but has worse performance in the other flame regions. The simulation result of the Spalding model is good in the X/D = 10 section, and that of the NC-TEL model shows the best result at X/D > 10 sections and in the outer regions of the jet flame. The maximum difference between the NC-TEL model results and the experimental data was 21.856 % in liquid phase velocity. Hence, the NC-TEL model has the best simulation performance.
With the advantages of low heat storage temperature, high heat storage density, and a low price, Na3PO4 has been proposed as a thermochemical heat storage candidate material for use in solar low-temperature heat storage engineering applications. However, the application of pure Na3PO4 is limited due to its propensity for agglomeration. In this study, activated carbon-based Na3PO4 (R-AC@Na3PO4) composites with mass fractions of 30%, 50%, and 80% were synthesized by melt impregnation method using activated carbon as the porous matrix. The morphology and structure of the composites were characterized, and their heat storage performances were investigated. The hydration experiments were carried out in a constant temperature and humidity chamber and dehydration experiments were carried out in thermogravimetric analysis and differential scanning calorimetry simultaneously. The results showed that at 30 °C, 60% relative humidity, the hydration equilibrium time for the composites were only 30%-40% of the pure material. Meanwhile, at a mass fraction of 80%, material's volumetric heat storage can reach 1793 J·cm-3 without agglomeration, and the performance was stable after 20 cyclic tests. This study provides a reference for the research and development of low-temperature thermochemical heat storage materials and offers more possibilities for R-AC@Na3PO4 composites in future engineering applications.
Nuclear energy can offer clean, efficient, and large-scale hydrogen production, and a polygeneration system can meet multi-level energy demands. In this study, a novel polygeneration system coupled with a very high-temperature gas-cooled reactor is proposed for realizing the cascade utilization of energy. High-grade heat is used for the high-temperature processes of hydrogen production, and low-grade heat is used for the low-temperature processes of hydrogen production, electricity generation, and process heat extraction. The system can output hydrogen, electricity, and high-temperature steam simultaneously. Process simulation of iodine-sulfur cycle is performed to obtain heat duty of each component in hydrogen production process. Energy and exergy analyses are used to analyze thermodynamic performance of the system. The power ratio (PR) of electricity generation to hydrogen production and the share of the main steam extracted for heat supply (aSTSR) are two important parameters for determining energy distribution of the system, and the overall energy and exergy efficiencies of the system reach 51.27% and 66.96%, respectively, when PR =1 and aSTSR = 0.15. The sulfuric-acid concentration tower has the largest exergy loss coefficient of 8.89%, followed by steam generator of 7.04%. These are crucial components for improving thermodynamic performance of the system. (c) 2022 Elsevier Ltd. All rights reserved.
>Heat-driven thermoacoustic refrigeration has drawn extensive concern in the past decades due to its advantages of high reliability and external heat-driven mechanism. In such a system, heat can be firstly converted into acoustic power and then the acoustical power drives a refrigerator to generate cooling effect without any
本研究以煤基活性炭产品为原料,尿素作为氮源,通过浸渍、高温活化的方法进行改性,开发了一款可用于煤制氢/重整制氢中温变换气中CO2脱除的煤基富氮活性炭,并对其进行结构及性能表征.其中性能最优样品U-80C-N-550,其表面氮含量为9.92％,N/O比1.22,水接触角为137.92°±1.24°.在测试条件为99.99％CO2气氛,200℃温度,1 MPa压力下,CO2吸附容量可以达到1.27 mmol/g,且在进行40次吸附解吸循环过程中CO2吸附量基本保持不变,循环稳定性好.结果表明,不同条件下制备的富氮活性炭样品表面含氮基团含量及种类不同,因此通过改变吸附剂制备工艺条件,可适当调控活性炭表面含氮基团的种类及含量,从而提高其CO2吸附性能的同时增强其疏水性,得到了适合于含水蒸气富氢气体中脱除CO2的吸附剂.
为准确获得ECMO氧合器内血液流动细节,本文以交错排布的120根中空纤维束构成的简化氧合器为对象,采用基于沉浸边界法(IB)的自编程序对二维稳态血液层流进行数值模拟.结果表明,中空纤维束区域血液运动黏度变动范围在3.37～7.04×10-6 m2/s,模拟时需要考虑血液的流变特性.通过对比IB自编程序与商业CFD软件Fluent的计算结果可知,最大壁面切应力和压降的最大相对误差分别为3.38％和2.9％,验证了IB自编程序计算氧合器微间隙流道内血液流动的准确性.与基于多孔介质假设的一维半经验公式相比,IB自编程序能够反映沿程粘性损失和惯性损失的变化,并可依据切应力累积值、溶血指数、血细胞停留时间三个指标对氧合器血液损伤风险进行综合评估.研究结果可为ECMO的性能预测、临床运行参数调节提供科学依据.
气膜冷却是燃机高温透平叶片的关键冷却技术,准确高效地预测气膜冷却的温度场对于冷却设计具有重要意义.本文针对圆孔射流密度比(DR)为1、速度比(VR)为0.46的工况,基于大涡模拟(LES)的流场数据,单独求解采用不同标通量模型的时均标量输运方程,对比分析了各个模型的预测效果及其参数影响.评估的标通量模型包括梯度扩散模型(GDH)、广义梯度扩散模型(GGDH)和高阶广义梯度扩散模型(HOGGDH).结果显示,GDH对射流核心的流向扩散预测较弱,对于温度场的分离再附特征也不能准确捕捉.GGDH和HOGGDH模型能够较好地预测下游扩散,对分离再附现象也有较好的反映.本文进一步指出,GGDH和HOGGDH模型引入雷诺应力从而隐含了垂直于标量梯度的输运模式,使其对温度场的预测更为准确.
具有高温室效应值的制冷剂面临淘汰,废弃制冷剂需要进行销毁处理.然而目前常用的销毁技术存在高能耗、产物有害等问题,因此需要寻找更为节能环保的降解技术.本文提出了一种新的制冷剂光热协同催化的降解方案,并对代表性制冷剂R134a进行了实验研究,探究了催化剂、温度、光强、反应组分等不同条件对降解反应的影响,并对其降解机理进行了推测.在本文实验条件下,R134a矿化率基本达到100％.
螺旋管式换热器换热系数高且结构紧凑,被用于高温气冷堆蒸汽发生器及中间换热器.这类换热器壳侧为有壁面包围的横掠管束流动,而壁面的存在会对横掠管束流动产生一定影响.本文中采用分裂式热膜测量了不同管距管径比(P/D)和不同雷诺数(Re)下横掠顺排管束流动管间和管后的速度分布.讨论了流动充分发展区域P/D、Re对管间和管后时均速度分布的影响.然后分析了P/D、Re对管间和管后雷诺正应力分布的影响.选取Re=35875的结果,从频谱角度分析了产生不同雷诺正应力分布的原因,并比较了P/D对管间速度频谱的影响.
