Numerical simulation of aluminum holding furnace with fluid-solid coupled heat transfer

To predict three-dimensional temperature distribution of molten aluminum and its influencing factors inside an industrial aluminum holding furnace,a fluid-solid coupled method was presented.The fluid-solid coupled mathematics models of aluminum holding furnace in the premixed combustion processing were established based on mass conservation,moment conservation,momentum conservation,energy conservation and chemistry species conservation.Computational results agree well with the test data of the typical condition.The maximum combustion temperature is 1 850 K.The average temperature of the molten aluminum is 1 158 K,and the maximum temperature difference is about 240 K.The average temperature increases 0.3 ℃ while the temperature of combustion air increases 1 ℃.The optimal excess air ratio is 1.25-1.30.

Numerical Simulation and Experimental Study of Heat-fluid-solid Coupling of Double Flapper-nozzle Servo Valve

The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.

Numerical simulation of thermodynamics coupling in hot forming process of elliptical head used in power station

To reduce the time of getting an ideal elliptical heat used in power station through repairing and testing a die repeatedly according to experience,finite element software Deform-3D was used to research the simulation of deformation-heat transfer coupling in hot forming process of elliptical head with the size of Φ1200 mm ×100 mm. The variations of stress,stain,temperature,thickness and strain rate in forming process were gotten,and the forming quality was evaluated from roundness,thinning rate and thermal contraction. The results show that the maximum thinning rate of the elliptical head is 7. 31% ,it is close to the orthographic place; and the inner diam- eter obtained from simulation is 1200. 6 - 1202. 977 mm,it is in the range of inner diameter tolerance required; all the data fit well with the practical dimension data of processing head.

NUMERICAL SIMULATION OF CASTING PROCESS

In this paper, the development status of casting numerical simulation technology is introduced. In additional, mathematical model, solution method, initial condition, boundary condition and defect predicting scheme of foundry process are also analyzed, which include the mold filling process, solidification process and the process coupling fluid flow with heat transfer. Finally, a practical casting is taken out to show how to predict defects and optimize foundry process with numerical simulation technology.

Numerical simulation of temperature distribution of deep field in temperature mine

In order to study the temperature distribution of deep field,mathematical mod- els of temperature field in field and surrounding rock were built based on heat transfer and seepage theory.Combined test data with mathematical model,the temperature distribution under heat-transfer and underground-water coupling was studied by using Golden Soft- ware Surfer and Matlab.The results show that distribution law of most isothermal lines is very similar in deep field,and temperature gradient is equal in general.At the same time, temperature distribution is influenced by underground-water and fault.In surrounding rock, seepage changes symmetrical distribution of temperature field and vector,and the tem- perature field may divide into inward-diffusion area and outward-diffusion area.Peripheral temperature of working will approach to the temperature of airflow.In inward diffusion area the distribution of temperature and temperature vector is symmetric,and the direction of temperature vector point to the center of working.The action of airflow is stronger than seepage in inward diffusion area,however,the case opposite is true in outward diffusion area.

Controlling Roll Temperature by Fluid-Solid Coupled Heat Transfer

Currently, when magnesium alloy sheet is rolled, the method of controlling roll temperature is simple and inaccurate. Furthermore, roll temperature has a large influence on the quality of magnesium alloy sheet; therefore, a new model using circular fluid flow control roll temperature has been designed. A fluid heat transfer structure was designed, the heat transfer process model of the fluid heating roll was simplified, and the finite di erence method was used to cal?culate the heat transfer process. Fluent software was used to simulate the fluid?solid coupling heat transfer, and both the trend and regularity of the temperature field in the heat transfer process were identified. The results show that the heating e ciency was much higher than traditional heating methods(when the fluid heat of the roll and tempera?ture distribution of the roll surface was more uniform). Moreover, there was a bigger temperature di erence between the input and the output, and after using reverse flow the temperature di erence decreased. The axial and circum?ferential temperature distributions along the sheet were uniform. Both theoretical calculation results and numerical simulation results of the heat transfer between fluid and roll were compared. The error was 1.8%–12.3%, showing that the theoretical model can both forecast and regulate the temperature of the roll(for magnesium alloy sheets) in the rolling process.

Analysis of coupled flow-reaction with heat transfer in heap bioleaching processes

A mathematical model for heap bioleaching is developed to analyze heat transfer, oxygen flow, target ion distribution and oxidation leaching rate in the heap. The model equations are solved with Comsol Multiphysics software. Numerical simulation results show the following facts： Concentration of oxygen is relatively high along the boundary of the slope, and low in the center part where leaching rate is slow. Temper- ature is relatively low along the slope and reaches the highest along the bottom region near the slope, with difference being more than 6℃. Concentration of target mental ions is the highest in the bottom region near the slope. Oxidation leaching rate is relatively large in the bottom and slope part with a fast reaction rate, and small in the other part with low oxygen concentration.

Coupled Conductive-Convective-Radiative Heat Transfer in Hollow Blocks with Two Air Cells in the Vertical Direction Subjected to an Incident Solar Flux

This work presents the results of a set of steady-state numerical simulations about heat transfer in hollow blocks in the presence of coupled natural convection,conduction and radiation.Blocks with two air cells deep in the vertical direction and three identical cavities in the horizontal direction are considered(typically used for building ceilings).Moreover,their outside horizontal surface is subjected to an incident solar flux and outdoor environment temperature while the inside surface is exposed to typical indoor environment conditions.The flows are considered laminar and two-dimensional over the whole range of parameters examined.The conservation equations are solved by means of a finite difference method based on the control volumes approach,relying on the SIMPLE algorithm for what concerns the coupling of pressure and velocity.The effects of the number of cells in the horizontal direction and the thermal conductivity on the heat transfer through the alveolar structure have been investigated.The results show that the number of holes has a significant impact on the value of the overall heat flux through the considered structure.

Numerical Analysis on Thermal Function of Clothing with PCM Microcapsules

To study the influences of phase change material(PCM)microcapsules in clothing on human thermal responses,a mathematical model is developed.The improved Stolwijk’s model is used to simulate human thermo-regulatory process,and the coupled heat and moisture transfer including the moisture sorption/desorption of fibers and effects of phase transition temperature range on the phase change processes of the PCM is considered in clothing model.Meanwhile,the theoretical predictions are validated by experimental data.Then,the interactions between human body thermal responses and the heat and moisture transfer in clothing are discussed by comparing the prediction results with PCMs and without PCMs.Also the effects of fiber hygroscopicity on clothing and human thermal responses are compared.The conclusion shows that the clothing with PCMs microcapsules can delay the human temperature variations and decrease the sweat accumulation rate on the skin surface and heat loss during changing of ambient conditions,and fiber hygroscopicity reduces the effect of PCM microcapsules on delaying garment temperature variations very significantly.

Applications and verification of a computational energy dynamics model for mine climate simulations

A complete thermodynamic model is described for temperature and heat flow distribution simulation for ventilation networks in underground mines.The method is called the Computational Energy Dynamics(CED)model of the heat,mass,and energy transport.The Thermal and Humidity(TH)transport elements of the full model are described for advection,convection,and accumulation,encompassing heat capacity,radiation,latent heat for evaporation,and condensation in the airways,as well as variable heat conduction and accumulation in the rock strata.The thermal flywheel effect for time-dependent temperature field applications is included in the model solution.A CED model validation exercise is described,directly evaluating the iterated,minimized energy balance errors for the mechanical and thermal energy components for each network branch after a converged solution is determined.A simulation example relevant to mine safety and health is shown with the CED-TH model,demonstrating its capabilities in efficiency and accuracy in comparison with measurement results.

The fast method and convergence analysis of the fractional magnetohydrodynamic coupled flow and heat transfer model for the generalized second-grade fluid

In this paper,we first establish a new fractional magnetohydrodynamic(MHD)coupled flow and heat transfer model for a generalized second-grade fluid.This coupled model consists of a fractional momentum equation and a heat conduction equation with a generalized form of Fourier law.The second-order fractional backward difference formula is applied to the temporal discretization and the Legendre spectral method is used for the spatial discretization.The fully discrete scheme is proved to be stable and convergent with an accuracy of O(τ^(2)+N-r),whereτis the time step-size and N is the polynomial degree.To reduce the memory requirements and computational cost,a fast method is developed,which is based on a globally uniform approximation of the trapezoidal rule for integrals on the real line.The strict convergence of the numerical scheme with this fast method is proved.We present the results of several numerical experiments to verify the effectiveness of the proposed method.Finally,we simulate the unsteady fractional MHD flow and heat transfer of the generalized second-grade fluid through a porous medium.The effects of the relevant parameters on the velocity and temperature are presented and analyzed in detail.

Temperature field analysis of main steam pipe under local post weld heat treatment

In local post weld heat treatment, the temperature difference is the criterion of the process. The temperature field in the main stream pipe under local post weld heat treatment is simulated by finite element method. A close-loop control program is designed to simulate the temperature field of two different pipes. Both the skin effect of induction heating and electro-thermal coupled effect are considered in the heating model. The local heat treatment temperature difference at the inner and outer side of the pipe is analyzed and the different convection conditions are also considered. The simulation results show that in appropriate induction heating process, the temperature difference in the pipe can be controlled within 30 ℃.

储粮生态系统通风干燥机理及数值模拟应用研究进展

粮食是人类生存和社会发展的重要资源,确保粮食的安全储存对保障粮食供应、维持市场稳定具有重要意义。分析了储粮生态系统通风干燥过程中粮食热湿传递机理,探讨了影响通风干燥效率的主要因素。综述了国内外在数值模拟技术方面的研究进展和应用现状,评估了这些技术在储粮生态系统中的应用效果。最后,展望了数值模拟技术在储粮生态系统通风干燥应用的发展趋势。

微波注热与传导注热对煤层瓦斯运移的激励效应对比分析

为探究微波注热和传导注热对煤层瓦斯运移的影响,建立了热-流-固耦合模型,通过COMSOL Multiphysics数值软件分别模拟传统传导注热和2450 MHz微波注热对煤层瓦斯运移的激励效应,以相同注热功率为基础,对比分析了2种注热方式下煤层温度、渗透率比例、瓦斯含量、瓦斯抽采率、热损失的演化规律。结果表明:2种不同注热方式对瓦斯运移的激励效应相似,随着抽采时间的延长,煤层温度逐渐升高,渗透率比例先减小后增大,煤层总瓦斯含量逐渐减小,瓦斯抽采率先增大后减小;相对于传导注热,微波注热效果更佳,煤层渗透率整体较大,吸附瓦斯含量较低,残余瓦斯含量整体较高,瓦斯抽采量较高,瓦斯抽采率较大、热损失较小。微波注热比传导注热对煤层具有更好的激励效应,能更好地加速煤层瓦斯吸附解吸,更有利于煤层瓦斯的抽采,且传热效率高,热损失小,更节能。

热管堆固态堆芯燃料辐照-热-力耦合性能分析

热管冷却反应堆(简称:热管堆)具有高可靠性和固有安全性、体积小、模块化和全固态堆芯等特点。固态堆芯燃料服役过程在高温、强辐照、固态约束多因素作用下堆芯的传热和力学性能受到严重影响,基体接触导致应力与间隙换热都随燃耗加深而发生较大非线性改变,且两者相互影响,因此基体在服役过程中的多物理场耦合的辐照-热-力行为复杂。本文基于有限元多物理场分析软件针对固态堆芯燃料开展辐照-热-力耦合分析,考虑UO2芯块与316不锈钢基体的辐照变形效应以及蠕变效应,并在固态堆芯间隙中引入间隙传热模型,探究固态堆芯寿期内间隙变化特点以及传热和力学耦合作用特性。结果显示:基体与燃料包壳的完全接触会导致芯块温度上升以及基体与包壳蠕变现象加强,燃料棒周围平均热管数量较少会导致附近区域较高的温度和应力分布,且寿期中该区域包壳因燃料棒内压和基体-包壳接触压力具有蠕变失效风险。分析结果表明间隙接触会对热管堆固态堆芯的传热和力学性能造成影响,甚至提高包壳的失效风险。

基于粮堆尺度的稻谷干燥过程中流体流动及热湿耦合传递的研究

谷物的质量受干燥条件的影响很大,应尽量减少干燥过程中的干物质损失。本研究采用离散元法和计算流体力学方法,构建了由稻谷颗粒组成的粮堆。基于流固耦合的传热传质原理,建立了热湿传递模型,并通过对稻谷的干燥温度和初始含水率的控制,探讨了干燥过程中谷堆内温度和含水率的变化规律。数值模拟工作提供了对干燥过程中粮堆内部流体流动和热湿耦合传递的深入理解,并讨论了温度和湿度对干燥的影响。研究结果表明,粮堆的非均匀孔隙结构以及稻谷表面的间隙导致了复杂的气流模式,导致“通风死角”的形成。在整个干燥过程中,观察到不同粮层之间的温度和湿度差异。由于水分扩散系数的作用,稻谷内部和表面的含水量存在差异。粮堆中的热量和水分通过加热空气的流动和稻谷的热湿扩散从底层传递到上层。同时,研究发现干燥曲线的曲率随着干燥条件的变化而变化,尤其是在温度达到60℃时变化最为显著。该研究可为粮食的安全储存提供参考和理论依据。

超临界CO_(2)池式传热流固耦合传热特性数值模拟

超临界类沸腾传热已有初步研究,对类气-类液界面的定义仍不统一.采用层流模型对超临界CO_(2)池式传热特性进行流固耦合数值模拟研究,d=70μm的铂丝为加热件,热流密度q_w范围为0-2000 kW/m^(2),压力P范围为8-10 MPa,加热丝附近采用多尺度网格进行建模,模拟值与实验数据吻合较好.通过与亚临界传热类比通过计算导热占比Q_(con)/Q_(t)沿r方向变化规律,将超临界划分为3个区,当TT_(M)为类气区(vapor-like,VL),与用超临界类沸腾干度x分区规律相同;根据通过计算导热占比确定的类气膜内平均导热λ_(ave)和导热热阻R_(G)随热流密度q_(w)变化曲线可很好地解释类蒸发区换热系数h随q_(w)的变化规律.本文提出了确定超临界池式传热类气-类液界面的新方法,较好地解释了类蒸发区传热机理,为后续超临界类沸腾池式传热的发展提供了理论基础.

不同截面肋柱-软尾结构单相流动传热比较

基于任意拉格朗日-欧拉(ALE)方法,利用动网格技术和重叠网格技术数值模拟研究了不同Reynolds数、截面形状以及长径比下的肋柱-软尾结构在通道中的双向流固耦合换热问题。模拟工况为:Reynolds数Re=200,275,351;肋柱截面形状:圆形和方形;长径比k=2,3,4。研究表明:Re=275时圆形截面肋柱-软尾结构的流动换热综合能力优于方形截面结构,k=3时圆形截面肋柱-软尾结构的流动换热综合能力最佳,肋柱周围的局部换热能力方形截面结构好于圆形截面结构;k=3时,随着Reynolds数的增大,不同截面形状的肋柱-软尾结构的流动换热综合能力逐渐升高,并且高Reynolds数、高长径比的圆形截面综合流动换热能力最佳;与不加软尾肋柱结构的流动换热能力进行对比发现,对于圆形截面形状的肋柱结构,增加软尾后综合换热能力增大了19.46%。

双轴搅拌反应器内Ca(OH)_(2)/CaO热化学储热体系的放热研究

针对Ca(OH)_(2)/CaO热化学储热体系的放热过程,提出了双轴搅拌反应器并对其“三传一反”过程进行了数值研究,揭示了体系反应的多物理场耦合机理,分析了双轴搅拌反应器用于热化学储热的可行性,讨论了体系在双轴搅拌反应器内进行放热反应的特性。结果表明,双轴搅拌反应器改善了体系放热反应的传热传质性能;体系1200 s放热过程的转化率为0.49,峰值放热功率和稳定放热功率分别可以达到5.4 kW和3 kW;通过调节水蒸气分压可以控制体系的反应温区,而较低的初始进口温度不仅可以加快反应进程,还能减少体系的额外预热量;反应器的换热能力会明显影响放热过程进行,特别是在高转速和高填充高度的反应条件下,实际应用中应考虑需求来匹配合适的换热装置。

套管换热器的三维数值模拟与分析

采用FLUENT软件对平直和弯曲套管的整体换热性能进行了数值模拟,并与经验公式进行了对比。数值计算结果表明:FLUENT耦合算法得到的套管总传热系数与经验公式计算结果吻合良好。与平直套管相比,弯曲套管内热空气所受到的离心力使其换热效率提高,在相同等效长度和流动条件下弯曲套管换热器可使总传热系数提高10%。