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Physics of cavitation near particles

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Journal of Hydrodynamics 2024年第1期36卷 102-118页

作者： Jia-xin Yu Xiao-yu Wang Jun-wei Shen Jin-sen Hu Xiang-qing Zhang Da-qing He Yu-ning Zhang Key Laboratory of power Station energy Transfer Conversion and System(Ministry of Education) School of Energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing102206China

The combined effect of cavitation and silt abrasion presents a great challenge and threat to secure the operation and the efficiency of hydraulic machineries working in sediment-laden fluid.The present paper critically reviews the current research progress on the interaction mechanisms of the bubbles and the particles.Firstly,the analytical models including boundary treatment methods for predicting the jet dynamics of the bubble collapse near particles are demonstrated.Secondly,the bubble collapsing dynamics,jet dynamics and shock wave characteristics near particles are revealed both experimentally and numerically.Finally,the bubble-particle-wall system is investigated with a focus on microjets.

关键词： Cavitation bubble particle jet shock wave

Investigations of Water Flow Behaviors Induced by Local Temperature Variations through a Single Rough Fracture for the Enhanced Geothermal Systems

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Journal of Thermal Science 2024年第3期33卷 1055-1064页

作者： LI Jiawei YE Lin Department of energy and power engineering Tsinghua UniversityBeijing100084China school of power and energy Northwestern Polytechnical UniversityXi’an710072China

In recent years,Enhanced Geothermal System(EGS)technologies have been applied to the geothermal resources production in the Hot Dry Rock(HDR).The core of EGS technologies is to adopt hydraulic fracturing in the reservoir to create a connected network of discrete fractures with the consideration of water as a working fluid for hydraulic fracturing and heat production.This paper investigates the characteristics of water flow behaviors through a single rough fracture under different temperature and pressure conditions.A single fracture model with rough fracture surfaces is constructed and then characterized,and influences of the anisotropic factor on the average tortuosity and frictional resistance coefficient of water flow through a single fracture with rough surfaces have been compared and analyzed.With consideration of other impacting factors(temperature,pressure,fracture roughness),the impact of mass flow rate has also been presented.Numerical simulation results present that changes of average tortuosity for water flow through a single rough facture are mainly affected by temperature.It can be observed that higher temperature leads to larger average tortuosity but the frictional resistance coefficient shows an opposite trend.As for pressure conditions,it is found that effects of pressure on average tortuosity and frictional resistance coefficient is very small,which can be neglected under high pressure conditions.Furthermore,the average tortuosity shows a progressively linear relationship with the mass flow rate.On the contrary,the frictional resistance coefficient has a negative relationship with the mass flow rate.It is revealed that when the mass flow rate reaches a critical point,the influences of temperature on the frictional resistance coefficient will be negligible.Comparisons of single rough fractures with different anisotropic factors show that values of average tortuosity and frictional resistance coefficient have positive relationships with the increase of anisotropic factors.

关键词： single rough fracture tortuosity frictional resistance enhanced geothermal system

Ionic thermal up-diffusion in nanofluidic salinity-gradient energy harvesting

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National Science Review 2019年第6期6卷 1266-1273页

作者： Rui Long Zhengfei Kuang Zhichun Liu Wei Liu School of Energy and Power Engineering Huazhong University of Science and Technology

Advances in nanofabrication and materials science give a boost to the research in nanofluidic energy harvesting. Contrary to previous efforts on isothermal conditions, here a study on asymmetric temperature dependence in nanofluidic power generation is conducted. Results are somewhat counterintuitive. A negative temperature difference can significantly improve the membrane potential due to the impact of ionic thermal up-diffusion that promotes the selectivity and suppresses the ion-concentration polarization,especially at the low-concentration side, which results in dramatically enhanced electric power. A positive temperature difference lowers the membrane potential due to the impact of ionic thermal down-diffusion,although it promotes the diffusion current induced by decreased electrical resistance. Originating from the compromise of the temperature-impacted membrane potential and diffusion current, a positive temperature difference enhances the power at low transmembrane-concentration intensities and hinders the power for high transmembrane-concentration intensities. Based on the system’s temperature response, we have proposed a simple and efficient way to fabricate tunable ionic voltage sources and enhance salinity-gradient energy conversion based on small nanoscale biochannels and mimetic nanochannels. These findings reveal the importance of a long-overlooked element—temperature—in nanofluidic energy harvesting and provide insights for the optimization and fabrication of high-performance nanofluidic power devices.

关键词： energy harvesting ionic thermal up-diffusion ionic voltage source nanofluidics

Numerical study on non-uniform heat transfer deterioration of supercritical RP-3 aviation kerosene in a horizontal tube

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Chinese Journal of Chemical engineering 2020年第6期28卷 1542-1557页

作者： Yanhong Wang Yingnan Lu Sufen Li Ming Dong School of Energy and Power Engineering Northeast Electric Power UniversityJilin 132012China School of Energy and Power Engineering Dalian University of TechnologyDalian 116024China

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-εturbulence 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(Grq/Grth)max≤0.8 is satisfied,the effect of buoyancy could be ignored.The new correlations work well for non-uniform heat transfer predictions.

关键词： Supercritical pressure Aviation kerosene Non-uniform heat transfer Heat transfer deterioration Buoyancy Prediction correlation

考虑旋涡效应的非定常空化流数值模型修正研究

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Acta Mechanica Sinica 2023年第4期39卷 157-165页

作者：洪伯杰胡常莉邢浩杰 School of Energy and Power Engineering Nanjing University of Science and TechnologyNanjing210094China

本研究的目的是考虑旋涡运动对非定常空化流动的影响,提出了一种空化模型和湍流模型的修正方法.在Zwart空化模型和SSTγ-Re_(θt)湍流模型中分别引入了由应变率张量和旋转率张量之比构建的函数.将该修正方法用于模拟绕Clark-Y水翼的非... 详细信息

本研究的目的是考虑旋涡运动对非定常空化流动的影响,提出了一种空化模型和湍流模型的修正方法.在Zwart空化模型和SSTγ-Re_(θt)湍流模型中分别引入了由应变率张量和旋转率张量之比构建的函数.将该修正方法用于模拟绕Clark-Y水翼的非定常云空化流动,并通过与实验数据对比进行评估.研究结果表明,修正模型能够更好地捕捉到云空化的非定常过程,特别是充分发展的附着空穴和大尺度的云空泡脱落行为.这都得益于修正方法中单位能量的湍流耗散率和蒸发率的提高.此外,修正模型所预测的升力系数随时间的波动和时均流向速度分布与实验结果有较好的一致性.

关键词：蒸发率修正模型非定常空化湍流耗散率空化模型升力系数旋涡运动数据对比

kεNet湍流模型研究及其在低雷诺数槽道流中的应用

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Acta Mechanica Sinica 2023年第5期39卷 65-75页

作者：侯龙锋朱兵王莹 School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai200093China

我们提出了一种基于物理信息的深度学习网络(kεNet),可用于RANS方程中发现封闭的湍流模型.kεNet由一个传统的典型神经网络结构和若干个基于物理信息的方程组成,如雷诺应力方程、k方程和ε方程.以低雷诺数下的槽道流动的湍流模型的修... 详细信息

我们提出了一种基于物理信息的深度学习网络(kεNet),可用于RANS方程中发现封闭的湍流模型.kεNet由一个传统的典型神经网络结构和若干个基于物理信息的方程组成,如雷诺应力方程、k方程和ε方程.以低雷诺数下的槽道流动的湍流模型的修正为例,通过训练基于物理信息的神经网络,模型参数得到了修正.修正后的湍流模型参数应用于OpenFOAM软件进行计算,能够非常好地预测Re_(τ)=5200和2000下的槽道流动.

关键词： Physical informed neural network(PINN) RANS Turbulent model Channel flow

A novel hydrodynamic suspension micropump using centrifugal pressurization and the wedge effect

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Science China(Technological Sciences) 2023年第7期66卷 2047-2058页

作者： XING GuanYing XUE Song HONG Tao ZUO HuaiYu LUO XiaoBing School of Energy and Power Engineering Huazhong University of Science and TechnologyWuhan 430074China

The micropump is the heart of microfluidics systems.However,for mechanical micropumps,bearing wear failure has been a major obstacle to performance and reliability.Hydrodynamic suspension,which can make the rotating components levitate in liquid without any mechanical friction,is applied to break this bottleneck.In this paper,a novel kind of hydrodynamic suspension micropump(HSMP) without a grooved thrust bearing is proposed.Based on the centrifugal effect,the HSMP uses a rotating rotor to accelerate and pressurize adjacent fluid,and thus reacting forces are generated on the rotor surfaces to levitate it.The mechanisms of suspension forces formation,the centrifugal effect and the wedge effect in the liquid films near the rotor are identified using theoretical analysis and simulation.The variation in suspension forces with rotor position is investigated,revealing that the suspension bearings of the HSMP,similar to a spring damper,can self-adjust suspension forces along with a change in rotor position.Moreover,the suspension stiffness is positively correlated with the rotating speed.The HSMP prototype designed herein,whose overall size is only 34 mm × 34 mm × 31 mm,can provide a maximum output performance of3230 mL/min and 96.3 kPa at 20000 r/min,which is manyfold greater than other micropumps.The proposed HSMP is demonstrated to be more powerful with a simple structure,high power density,and high reliability.

关键词： hydrodynamic levitation suspension micropump

Desiccant Performance Evaluation of Desiccant-Coated Heat Exchanger-Based Heat Pump by Equilibrium Model

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Journal of Thermal Science 2023年第6期32卷 2361-2373页

作者： LIU Yuexin LIU Zhilu XIA Xiaoxiao LI Wei TU Zhengkai CAI Shanshan LI Song School of Energy and Power Engineering Huazhong University of Science and TechnologyWuhan430074China

By combining the advantages of desiccant dehumidification and vapor compression refrigeration,the desiccant-coated heat exchanger-based heat pump(DCHE HP)is regarded as a promising alternative to the traditional vapor-compression air conditioning system(VCAC).Selecting proper desiccants from a large number of candidates is of great importance to improve the performance of DCHE HP.However,this task is challenging using current experimental or modelling strategies.In this work,we developed an equilibrium model to evaluate the power consumption of 39 DCHE HPs coated with different desiccants under various operating conditions.Eventually,five desiccants with low power consumption were selected.It was also demonstrated that under given operating conditions,the DCHE HP based on the five selected desiccants can save 21.3%–32.9%power compared with the VCAC.The power consumption of the DCHE HP is largely dependent on the heat of adsorption,the cyclical water uptakes and the remained moisture contents of the coating desiccants.It was further revealed that the moderate heat of adsorption,the larger cyclical water uptake and the lower remained moisture content are preferable for reducing the system energy demand.This work reported a quick evaluation of 39 desiccants for DCHE HP by an equilibrium model,which may also offer insights into the choosing and designing of desiccants for DCHE HP.

关键词： adsorption metal-organic frameworks dehumidification power consumption relative humidity

Nonlinear stochastic dynamics research on a Lorenz system with white Gaussian noise based on a quasi‐potential approach

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International Journal of Mechanical System Dynamics 2023年第1期3卷 85-94页

作者： Yong Huang School of Energy and Power Engineering Nanjing University of Science and TechnologyNanjingChina

Environmental noise can lead to complex stochastic dynamical behaviors in nonlinear systems.In this paper,a Lorenz system with the parameter region with two stable fixed points and a chaotic saddle subject to white Gaussian noise is investigated as an example.Noise‐induced phenomena,such as noise‐induced quasi‐cycle,three‐state intermittency,and chaos,are observed.In the intermittency process,the optimal path used to describe the transition mechanism is calculated and confirmed to pass through an unstable periodic orbit,a chaotic saddle,a saddle point,and a heteroclinic trajectory in an orderly sequence using generalized cell mapping with a digraph method constructively.The corresponding optimal fluctuation forces are delineated to uncover the effects of noise during the transition process.Then the process will switch frequently between the attractors and the chaotic saddle as noise intensity increased further,that is,noise induced chaos emerging.A threshold noise intensity is defined by stochastic sensitivity analysis when a confidence ellipsoid is tangent to the stable manifold of the periodic orbit,which agrees with the simulation results.It is finally reported that these results and methods can be generalized to analyze the stochastic dynamics of other nonlinear mechanical systems with similar structures.

关键词： stochastic dynamics Lorenz system quasi‐potential chaos transition phenomenon