共查询到18条相似文献,搜索用时 93 毫秒
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热泳力作用下柴油机微粒在冷却通道中沉降规律研究 总被引:1,自引:0,他引:1
对热泳力作用下柴油机微粒在冷却通道中的沉降规律进行了研究。推导建立了热泳沉降率数学模型,在此基础上分析了在热泳力作用下,微粒大小、排气流速、排气与壁面温差以及通道尺度等因素对柴油机微粒在冷却通道中热泳沉降率的影响规律。研究结果表明,热泳力对柴油机微粒具有一定的脱除作用,通过合理设计和控制冷却通道的结构和运行参数,可以有效地提高柴油机微粒在冷却通道中的沉降率。热泳沉降技术为柴油机微粒的净化以及柴油机微粒分布的改善提供一条有效的途经。 相似文献
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利用文丘里管和VNT提高柴油机EGR率的研究 总被引:3,自引:0,他引:3
利用文丘里管和可变喷嘴增压器(VNT)提高柴油机的EGR率,旨在降低柴油机NOx的排放.采用试验的方法研究,对文丘里管喉口直径进行了优化,分析不同的喉口直径对发动机外特性参数的影响;对于VNT系统,分析VNT叶片开度对EGR系统的影响,并在最佳的EGR率下,进行了VNT与旁通增压器的柴油机性能对比.通过文丘里管喉口直径的合理选取和VNT喷嘴环叶片位置的调节,增加涡前与文丘里管喉口的压差及EGR率.结果表明,基于VNT的EGR系统,扩展了EGR率的范围,小负荷的EGR率能达到30%,在保证柴油机动力性、经济性不变的前提下,大大地降低了NOx的排放. 相似文献
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《内燃机学报》2017,(6)
运用AVL-FIRE软件建立柴油机微粒捕集器(DPF)三维模型,模拟柴油机微粒捕集器内部压降和微粒沉积特性.针对DPF不同排气流量、进口温度、微粒沉积量及分布类型,对DPF压降特性进行模拟,并着重研究非对称孔结构(ACT)和灰分沉积量及分布形式对DPF压降和微粒沉积特性的影响.结果表明:随着DPF排气流量、进口温度、微粒沉积量和灰分沉积量的增加,DPF的压降增大,且DPF压降变化与进口温度呈非线性关系;沿DPF轴线方向,微粒沉积量呈先减小后增大趋势;"逐渐减少"型微粒分布形式压降损失较小,且再生速率较快.灰分在壁面上的层状分布对DPF压降和微粒沉积影响较大;非对称孔结构有利于降低DPF压降和提高微粒沉积能力,从而延长DPF寿命. 相似文献
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《International Journal of Thermal Sciences》2007,46(11):1084-1094
The steady-state convective heat transfer for laminar, two-dimensional, incompressible rarefied gas flow in the thermal entrance region of a tube under constant wall temperature, constant wall heat flux, and linear variation of wall temperature boundary conditions are investigated by the finite-volume finite difference scheme with slip flow and temperature jump conditions. Viscous heating is also included, and the solutions are compared with theoretical results where viscous heating has been neglected. For these three boundary conditions for a given Brinkman number, viscous effects are presented in the thermal entrance region along the channel. The effects of Knudsen and Brinkman numbers on Nusselt number are presented in graphical and tabular forms in the thermal entrance region and under fully developed conditions. 相似文献
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Yurong He Yubin Men Yunhua Zhao Huilin Lu Yulong Ding 《Applied Thermal Engineering》2009,29(10):1965-1972
A numerical study has been performed by using both single phase method and combined Euler and Lagrange method on the convective heat transfer of TiO2 nanofluids flowing through a straight tube under the laminar flow conditions. The effects of nanoparticles concentrations, Reynolds number, and various nanoparticle aggregates sizes are investigated on the flow and the convective heat transfer behaviour. The results show significant enhancement of heat transfer of nanofluids particularly in the entrance region. The numerical results are compared with the experimental data and reasonable good agreement is achieved. 相似文献
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《International Communications in Heat and Mass Transfer》1999,26(2):249-257
A simple approach for evaluating the effect of wall suction and thermophoresis on aerosol particle deposition from a laminar flow over a flat plate is proposed. The plate considered is a cold surface. The procedure is based on the concept of high-mass transfer with a blowing parameter. The thermophoresis is treated with two parts that include a suction-like convection term and a first-order reaction-like term. The results are easily calculated and have a very good agreement with the numerical solutions for self-similar boundary flow. 相似文献
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The laminar flow of a plasma in the entrance region of a circular tube has been analyzed using an implicit finite-difference scheme. The solution is based upon the boundary-layer equations with the plasma radiation term retained in the energy equation, and the transverse convection term retained in both the momentum and energy equations. Numerical results have been obtained for an argon plasma having a linear enthalpy and cubic velocity profile at the tube entrance. At the low temperature limit of the analysis, the friction factor is in agreement with previously published results; and in all but a very small region near the tube entrance the local Nusselt number agrees with the Nusselt number for constant property, fully-developed flow to within approximately 17 per cent. 相似文献
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《International Communications in Heat and Mass Transfer》2005,32(7):902-912
In this work the analysis of the heat transfer in the entrance region of a channel composed by a corrugated profile and a flat wall is presented. The laminar and incompressible flow of a Newtonian fluid is assumed inside the channel, and an uniform heat flux is imposed on the external surface of the corrugated wall. The governing equations are solved with the help of a finite-element method, and the results are compared with the heat transfer coefficient in the entrance region of a flat channel. In order to investigate the sensitivity of the convective heat transfer coefficient to the Reynolds number under laminar conditions, the analysis have been performed for different values of the flow rate. The effect on the flowfield of the of the corrugated profile amplitude is also discussed. 相似文献
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This article presents a numerical simulation procedure for studying soot particle deposition in diesel exhaust systems, with a particular focus on fouling layer thickness evolution. In the proposed algorithm, particle transport toward the wall, adhesion, and reentrainment of particles from the surface have been modeled, including Brownian motion and turbulent diffusion, thermophoresis, adhesion, and removal. This model has been implemented in ANSYS Fluent, which makes the inclusion of local effects possible. A cross-flow device, with a tube positioned transverse to the flow, has been simulated and tested. A comparison of the predicted fouling layer at several angular positions with the experimental observation shows acceptable agreement. This model makes it possible to predict the real depth of the fouling layer and its effects on the hydrodynamics of the flow. This model represents a valuable tool for the prediction of the main aspects of the performance of heat exchangers exposed to fouling. 相似文献
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This study investigates the performance of various types of exhaust gas recirculation (EGR) coolers, that is, smooth tube, corrugated tube, and plate–fin, when subjected to particulate fouling by soot particles. Experiments were carried out for different temperature gradients of 170 and 320°C (thermophoretic) and 0°C (isothermal). Soot particles with an average diameter of 130 nm were produced by a soot generator. Experimental results showed that generally soot deposition under isothermal conditions is negligible compared to thermophoresis for any given cooler geometry, but is not universal. It may become appreciable when complex coolers with extended surfaces, that is, plate–fin type, are used due to impaction and settlement of soot particles onto the extended surfaces, which act as barrier to the flow. Contrariwise, under thermophoretic conditions, the plate–fin cooler performed best, followed by the corrugated tube and smooth tube cooler. Coolers with larger heat transfer surface area are also found to be less sensitive to the loss in effectiveness, but show a higher pressure drop. 相似文献
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T.H. Hwang 《International Communications in Heat and Mass Transfer》1990,17(6):703-710
Forced convective heat transfer to laminar droplet flow in the combined hydrodynamically and thermally developing region of a circular tube is studied numerically for constant heat flux conditions. The saturated liquid droplets in the vapor flow are considered as equivalent heat sinks distributed in the superheated vapor stream. Numerical calculations are performed for the variations of droplet size, mean vapor velocity, and the local Nusselt number in the streamwise direction until the single-phase fully developed condition is reached. The important roles of the liquid droplets and the developing vapor velocity on the forced convective heat transfer to droplet flow in the combined entrance region of a circular tube are clearly demonstrated. 相似文献