In this study, the process of carbonate rock acidification with three-phase immiscible fluid [water, oil, and supercritical carbon dioxide (scCO2)] reactive flow in nonisothermal condition at pore scale was simulated by the lattice Boltzmann method (LBM). The three immiscible fluids' flow, solute transport, and heat transfer were solved by the Shan-Chen multiphase multicomponent lattice Boltzmann model, mass transport lattice Boltzmann model, and multicomponent thermal lattice Boltzmann model, respectively. The solid phase was updated by the volume-of-pixel method. In addition, the effect of temperature on the multiphase multicomponent reactive flow was numerically investigated. The results show that the dissolution rate is determined by three-phase distribution. The increase of temperature can accelerate the dissolution rate and decrease the inhibition influence of the non-acid phase on dissolution. Furthermore, the influence of temperature decreases with the increase of inlet velocity and oil wettability.

针对空-油换热器的冷却换热问题,开展了竖直螺旋管中超临界RP-3航空煤油换热的数值研究.探究了不同运行参数和结构参数下的换热特性和换热机理,包括沿流动方向的平均换热情况和沿管道周向的局部换热情况.考察管截面温度和二次流的分布情况,通过流速和湍动能径向差别阐述了离心力对换热的作用机制,基于误差分析得到合理的换热关联式.结果表明:管下游表现为强化换热机制,低压力下还观察到局部传热恶化问题;离心力导致流体域温度横向异常分层,边界层厚度周向不均匀,管截面出现二次流;管外侧流速和湍动能高,换热显著优于管内侧;提高运行压力、降低热质比、增大绕径、增大螺距均抑制离心力作用,致使二次流强度减弱;Merkel换热公式可以较好实现螺旋管内航空煤油的换热预测.

基于航空发动机间冷器的冷却换热问题,进行竖直螺旋管内超临界压力CO2换热数值研究.探究运行参数对沿流向和周向换热的影响机制.通过管截面温度场和流场分布阐述了浮升力和离心力引起的周向非均匀换热机制,评估二次流速度和强度.根据管道结构特性提出新的浮升力参数和浮升力影响判别准则,建立新的换热关联式.结果表明:管上游非均匀换热源于浮升力与离心力综合作用,管下游非均匀换热由离心力主导.当满足浮升力因子Bu≥1.6×10?5时,浮升力在换热中起主导作用.新换热关联式可以较好地适用于螺旋管内换热预测.

The peculiar convective heat transfer characteristics of supercritical pressure hydrocarbon fuel in vertical tubes (inner diameter of 1 and 2 mm) were investigated experimentally. The purpose of this study is to analyze the heat transfer phenomena observed from experiments and correlate the Nusselt number based on the theoretical framework of supercritical pseudo-boiling. The operating parameters covered pressures of 3-5 MPa, Reynolds numbers of 3,000-141,500, and various wall heat fluxes. An enhanced heat transfer regime was found under large mass flux condition within the temperature range of 0.6 < Tb/Tpc < 1.05. Two types of deteriorated heat transfer phenomena were observed under small mass flux condition, which could be attributed to low values in cp for the entrance region and pseudo-film-boiling for the high enthalpy region, respectively. It was proposed to use Nu/Nuref,pb to identify the heat transfer regimes of supercritical pressure hydrocarbon fuels under various operating parameters, in which the reference Nusselt number was calculated based on an assumption of a ho-mogenous mixture of the liquid-like and gas-like fluid. In addition, a new correlation was developed by including a term characterizing the effect of pseudo-boiling on heat transfer, the K number. Promising findings on un-derstanding the complex heat transfer behaviors and improvement in the prediction of heat transfer charac-teristics have been obtained.

基于高超声速飞行器布雷顿循环中印刷电路板换热器(PCHE)的应用,对PCHE通道中的超临界换热进行了数值研究.阐述了热侧运行参数和冷侧运行参数对换热的影响机制.考察了热侧流体温度、流线和湍动能的分布情况.评价了热侧(火积)流、壁面(火积)流和通道综合换热系数,建立了热侧换热关联式.计算结果表明:热侧压力提高、热侧进口温度下降、冷侧进口温度减小,均导致热侧换热增强.局部高湍动能是强化换热的原因.提高热侧参数可使通道的(火积)耗散性更小.

针对空-油换热器的冷却换热问题,对竖直上升圆管内超临界压力RP-3航空煤油的不稳定流动换热开展了实验研究.探究了由稳定流动换热向不稳定流动换热的过渡过程,考察了测量参数的振荡特性和机理,阐述了质量流量、进口压力、进口温度对壁温振荡和不稳定边界的影响.提出了两个无量纲参数,建立了不稳定边界预测准则.结果表明:通道施加高热流密度时,边界层对热流的动态响应转化为不稳定振荡,出现不稳定流动换热问题.随着压力提高,边界层内密度梯度减小,高热流密度时边界层稳定性增强,不稳定流动换热的临界热流密度增大.提出的预测准则能合理反映不稳定流动换热的临界热流密度,满足空-油换热器设计的工程需求.

针对空-油换热器的结构优化问题,对竖直蛇形管内超临界压力RP-3航空煤油的换热特性开展了数值研究.探究了运行压力、进口温度、质量流速、热流密度对换热的影响,通过管截面流体温度、二次流、湍动能、局部质量流速分布情况阐述了周向非均匀换热机理,讨论了不同运行工况下离心力参数和迪恩数沿流动方向的变化情况,提出了竖直蛇形管换热关联式.结果表明:离心力致使管截面出现两对迪恩涡,强烈扰流作用是强化换热的原因.湍动能和局部质量流速异常分布导致周向不均匀的换热特征.离心力参数阶跃到峰值后周期性波动,迪恩涡沿流动方向先增强后减弱.提高质量流速和运行压力、降低热流密度和进口温度,均弱化离心力作用.修正后的关联式预测偏差处于±20％范围内.

为深入理解空-油换热器的主动冷却问题,开展了 S型圆管中超临界RP-3航空煤油的换热数值研究.通过管截面温度和流线的分布情况解释了内壁温度、内壁热流密度、换热系数沿流动方向的变化特征.探究了两个弯管段密度、流速和湍动能的分布情况,以揭示离心力对换热的作用机制.通过离心力参数、迪恩数、二次流动能对离心力影响进行了量化评估.结果表明:离心力导致两次壁温和热流周向非均匀分布以及强化换热问题.相比上游弯管段,下游弯管段的离心力作用更强,迪恩涡更显著,二次流动能更大.提高压力、降低热流密度、提高质量流速对离心力影响起到抑制作用.

为理解空-油换热器中的冷却换热特性,对竖直下降圆管内超临界压力RP-3航空煤油的换热进行了实验研究.探究了稳态换热特征和换热机理,探讨了质量流量、热流密度、运行压力和进口温度对换热的影响;基于拟沸腾数提出了传热恶化的临界准则以及壁温最大飞升值的预测准则;通过浮升力和热加速判别准则分析了两者对换热的影响;实现了换热关联式预测.结果表明:浮升力和热加速对换热的影响可以忽略.拟沸腾换热机制,即近壁流体膨胀力相比惯性力占主导时,类气态流体层覆盖壁面是传热恶化的原因.当拟沸腾数高于2.5×10-4时,拟沸腾换热机制起作用.最后,探究了泄压过程中的瞬态换热特征.泄压过程中拟沸腾数不断增大,传热恶化加剧,高泄压速率下甚至出现壁温波动.

In this study, the effect of single bubble behaviour on the carbonate crack seawater frozen crystallization was investigated using the LBM-PFM (lattice Boltzmann method-phase field method) coupled method at the pore scale. Firstly, a new LBM-PFM model is proposed and validated. Then, the coupled model is applied in the simulation of crystallization process in two-phase (seawater-bubble) flow. In addition, the effects of bubble spacing and bubble velocity are also discussed numerically. The results show that, the existence of bubble can inhibit the growth of ice crystals below them, but could promote the crystallization process above them. Besides, the change of the spacing and velocity of the bubble may not affect the icing area, but can change the appearance and distribution of dendrites.

为深入理解航空发动机再生冷却热防护中的换热机理,对竖直上升圆管内超临界压力RP-3航空煤油的传热恶化开展了实验研究.探究了两类传热恶化的换热特征和形成机理,考察了热流密度、质量流量和进口压力对传热恶化的影响机制.获得了两类传热恶化的起始条件判别准则.以Nu/Nu0=0.75作为依据,建立了浮升力影响评价准则.通过格拉晓夫数修正实现了换热关联式预测.结果表明:两类传热恶化出现在不同条件下,低温区传热恶化源于边界层转捩和浮升力的综合作用,当进口雷诺数大于5730时其不再出现;高温区传热恶化的临界热流密度可以表述为质量流量的函数关系.当浮升力参数Grb/Re2.7和Gr/Re2分别大于10-7和10-3时,浮升力作用不可忽略.改进的换热关联式具有合理的预测精度,满足热防护系统设计的工程运用.

基于开源计算软件OpenFOAM建立求解器,采用RANS方法,针对凹腔不同深度、长度、后壁面倾角对氢气在燃烧室中超声速燃烧进行数值模拟研究.分析比较了在燃料当量比为0.28时不同凹腔结构的速度场、温度场、燃烧效率和总压损失.结果 表明:凹腔是燃烧室中主要蓄热和燃烧部分且不同凹腔结构的燃烧室流场边界层形状相似;凹腔长度影响燃烧室的总压损失,但是凹腔深度和后壁面倾角对其影响不大;凹腔的面积和长深比均可以影响燃烧室的燃烧效率,凹腔面积越大,燃烧效率越高,长深比为4.5左右时凹腔附近燃烧效率增幅最快.

In this study, we propose and validate a new phase change source term based on the Gong and Cheng's lattice Boltzmann (LB) model (Gong and Cheng, 2012) [1]. A modified phase transition LB model, combined with a multicomponent LB method, was applied to simulate co-existing boiling and condensation phenomena interesting a multicomponent fluid (i.e., water and non-condensable gas (NCG)) in a confined space. Additionally, we investigated and discussed numerically the effects of the NCG concentration on the heat and mass transfer performances during the phase change of multiphase and multicomponent fluids in a confined space. In particular, these effects were studied considering variable solid wettability and confined scale conditions.

In this study, a geochemical lattice Boltzmann model is developed to model multi-component reaction flow in porous media at the representative elementary volume (REV) scale. Then, we use the modified model to simulate the acid seafloor hydrothermal transport process (13.2 MPa, 603-631 K) with dissolution in fractured rock at the REV scale. In addition, we investigate the effect of the hydrothermal inlet flow rate (v = 0.01, 0.025, 0.05), Rayleigh number (Ra=1x 10(6),5x 10(6),1x 10(7)) and permeability (10 14, 10 13, 10 12m(2)) on the fluid flow behaviour in a vertical fractured porous media with the porosity (epsilon = 0.2). Under the same acid flux (4x 10(-5)mol/s), increasing the inlet velocity (from 0.01 to 0.05) and increasing the Ra number (from 1 x 10(6) to 1 x 10(7)) elevate the fracture dissolution degree by 1.6% and 6.9%, respectively. Furthermore, we numerically explain the formation mechanism of several typical shapes (pyramidal, cylindrical and conical ducts, with a dome observed by experiments) of vent conduits at 1786-7090 m for the dissolution reaction, which can facilitate the understanding of hydrothermal energy transportation and mining.

基于航空发动机空-油换热器的冷却换热问题,开展了竖直U形圆管内超临界压力RP-3航空煤油换热的数值研究.探究了进口竖直段、弯管段、出口竖直段的换热特征和换热机理,阐述了运行压力和热质比对换热的影响机制.结果表明:进口竖直段呈现均匀换热的特征.弯管段离心力作用致使流体温度出现异常分层,周向密度不均匀,横向不平衡动能诱发强二次流问题,最大二次流速度达到0.45 m·s-1.固体热传导过程也受到影响,出现固体温度异常分层.两者综合作用下导致管壁温度和热通量的周向差别.出口竖直段的周向换热差别依然存在,二次流被削弱.提高运行压力或降低热质比,管截面热物性变化趋缓,周向换热差别减弱.

In this study, the effect of the gas-liquid phase separation caused by seawater boiling on the carbonate crack dissolution process was investigated using the lattice Boltzmann (LB) method at the pore scale. The gas-liquid two-phase flow with phase change, heat transfer, and solute transport is described by a single-component multiphase LB model, thermal LB model, and mass transport LB model, respectively. In addition, the dissolved solid mass is calculated via the Volume of Pixel method. The main conclusions are as follows: the phase separation negatively affects dissolution, especially in the upper boundary of the crack. Moreover, the negative effect is strengthened with the increase in inlet velocity and the decrease in crack width while the influence of wettability on dissolution is non-linear and its degree depends on the phase distribution of the two phases. In addition, slug flow greatly hinders solute transport but may accelerate the dissolution reaction near the inlet.

针对超燃冲压发动机再生冷却热防护问题,开展了顶部加热和底部加热水平圆管内超临界压力正癸烷换热的模拟研究.探究了两种加热模式下的换热特征和换热差别,阐述了通道外表面热通量、质量流速、运行压力及通道热导率对换热的影响机制.实现了周向平均换热的预测.结果表明:两种加热模式下的浮升力作用不同,通道内壁面周向呈现了不同的管壁温度和热通量分布情况.顶部加热时随周向角增大传热恶化逐渐减弱,底部加热时二次流更强,周向始终存在传热恶化问题.高温流体拟膜态热阻是传热恶化的原因.采用高热导率通道、增加运行压力、降低热质比可以缩小周向壁温和热通量差别.提出的关联式能合理预测周向平均换热情况,满足热防护设计的工程应用.

The normal restitution coefficient is an important parameter in particle deposition which is widely used in industrial fields. The normal restitution coefficient can be affected by many factors, and a typical factor is the surface roughness. Furthermore, a rough surface will influence the adhesion force and friction coefficient. The adhesion force and friction coefficient have effects on the normal restitution coefficient. However, the relationship between the normal restitution coefficient and the surface roughness has not been obtained. Therefore, an experimental study of microspheres impact on a rough surface is developed. The normal restitution coefficient decreases with the increasing surface roughness. The adhesion force is calculated by the Rabinovich model, and the results indicated that the adhesion force increases with the increasing surface roughness within the surface roughness range in this paper. Moreover, the adhesion energy and friction coefficient dissipation increase with the increasing surface roughness.

By utilizing airborne hydrocarbon fuels working as coolant, active regenerative cooling method is a significant method for maintaining the reliability of the scramjet engine components. At high temperatures, the pyrolysis of hydrocarbon fuels occurs and provides extra heat absorption capacity. Investigation on coupled heat transfer and pyrolysis of fuels is essential for the design of cooling channels. This paper aims to study the pyrolysis effects on convective heat transfer of supercritical aviation kerosene RP-3 in vertical upwards. Firstly, a simple molecular kinetic model was proposed for RP-3 pyrolysis. Then the performance of two Reynolds-averaged Navier-Stokes turbulence models with three constant turbulent Prandtl numbers in predicting the fluid-thermal behaviors of reacting flow were evaluated. At last, the mechanisms of pyrolysis effect on heat transfer in the heat transfer deterioration region and the cracked region were investigated. The results showed that the pyrolysis affected heat transfer from two aspects: providing heat absorb or release capacity through the endothermic (exothermic) pyrolysis reactions, changing the fuel properties by the variations in composition. In the heat transfer deterioration region, the effect of heat absorption dominants over the effect of additional decreased in density and specific heat capacity by pyrolysis on the heat transfer, thus a lower wall temperature and larger heat transfer coefficients were observed when considering pyrolysis. In the cracked region, under the present condition, the competitive outcome of the above two led to an improved heat transfer by pyrolysis, and the improved effect first increased and then decreased as the fuel conversion increasing. This work provides a fundamental understanding of the behaviors of hydrocarbon fuel inside the cooling channels, which is valuable for the cooling structure design.

The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3) aviation kerosene in a horizontal circular tube has been numerically studied, focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction. The governing equations of mass, momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method. The re-normalization group(RNG) k-ε turbulence model with an enhanced wall treatment was selected. Considering the heat conduction in the solid wall, the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed. The evolution of secondary flow was analyzed. Effects of the outer-wall heat flux,mass flux, pressure and tube thermal conductivity on heat transfer were investigated. Moreover, the buoyancy criterion and the heat transfer correlation were obtained. Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling, further leads to the heat transfer deterioration. The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube, and weakening the heat transfer at the top of tube, which results in the non-uniform inner-wall temperature and heat flux distributions. Decreasing the ratio of outer-wall heat flux and mass flux, increasing the pressure could weaken the heat transfer difference along the circumferential direction, while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated. When the buoyancy criterion of(Gr q /Gr th ) max ≤ 0.8 is satisfied, the effect of buoyancy could be ignored. The new correlations work well for non-uniform heat transfer predictions.