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1.
波纹通道板间距对通道内流动与换热影响的数值研究   总被引:4,自引:0,他引:4  
应用数值模拟方法,分析了流体在不同板间距的正弦型波纹通道内,周期性充分发展的稳态层流流动与换热的特性;探讨了板间距对流动与换热的影响,并对其综合性能进行评估。结果表明:在Re相同的条件下,通道内所形成旋涡的尺寸随相对间距A/H(波长/间距)的减小而增大。  相似文献   

2.
采用非稳态数学模型对突扩通道内横掠圆管流动与换热进行了数值模拟。分别对不同雷诺数Re以及圆柱的不同水平位置情况进行数值模拟。结果表明,随着Re的变化,数值解有稳态和周期振荡。同时随着雷诺数的增加,圆管附近的换热不断增强。对于圆管不同的位置,当10≤Re100和Re=300时,圆管的换热随着Xc的增加而变弱;当100≤Re≤200时,圆管换热并不单调减弱。  相似文献   

3.
张后雷  宣益民 《动力工程》2002,22(3):1824-1826,1797
采用红外热像技术在稳态条件下分别测量了波纹和波纹打孔板翅表面的对流换热系数,得到了换热无量纲准则式。对两种板翅表面的传热与阻力特性进行了比较分析,结果表明在Re=1000-3000的大部分范围内,波纹打孔型表面比波纹型表面的换热系数高5%-25%,在Re<2000的范围内,波纹打孔流道的阻力略小于波纹流道或基本相当。图6参3  相似文献   

4.
波纹管内流动与传热规律的数值计算   总被引:2,自引:1,他引:1  
采用三维层流及低雷诺数湍流模型对波纹管内流动与传热性能进行了数值模拟,模拟结果与试验结果吻合良好.通过数值计算拓宽了波纹管流动与传热关联式的参数范围,发现在较大雷诺数(RP)范围内波纹管阻力系数随Re的变化趋势表现为指数规律.考察了不同波纹高度、波纹间距对流动与传热的影响,并对模型参数进行了综合性能评价,结果表明:波纹高度对波纹管内流动与传热的影响较波纹间距更显著;波纹管结构的强化传热性能只有在高Re条件下才得以体现,Re越大,波纹管综合性能因子也越高.通过数值计算得到了波纹管流动与传热的最优结构参数及最佳传热雷诺数范围.  相似文献   

5.
在三维空间上对CC(Crosscorrugated)型原表面换热器通道内流体的流动与换热特性进行了数值模拟。通道表面为正弦型曲面,上、下波纹板交错角固定为60°,节距与高度的比P/H取值范围为1.5~4.0。结果表明:当雷诺数Re约大于100后,各通道在中平面处产生的旋涡所形成的螺旋型自由剪切层开始变得不稳定,加强了流体间的混合;Re在约100~500的范围内,随P/H的增大,阻力系数f和平均努谢尔特数Nu增加,当Re继续增加(约大于2000)时,以P/H=2.2为界,P/H对f及Nu的影响呈相反的趋势变化;在适中的Re范围内,不同表面均可获得较好的表面性能,且随P/H的增大,获得最佳表面性能的Re减小。图12参8  相似文献   

6.
采用三维数值模拟方法研究了网状肋用于圆形通道的流动换热特征,分析了雷诺数Re、肋的形状、肋的网格间距、肋的直径以及流体与固体的导热系数比kf/ks对通道平均阻力系数和换热性能的影响,并引入换热性能评价指标PEC对2种网状肋进行了比较.结果表明:管内插入网状肋对流动阻力系数和换热性能有很大影响;方形肋的换热效果比圆形肋好,但其阻力较大;随着Re的减小,2种肋的降温效果均增强;肋的网格间距越小,则换热效果越好但阻力越大;随着肋直径的增大和流体与固体导热系数比kf/ks的减小,换热效果增强.  相似文献   

7.
通过数值计算对紧凑换热器一种波纹翅片通道内除湿条件下周期性充分发展的对流传热传质情况进行数值研究。计算采用曲线坐标系下压力与速度耦合的SIMPLER算法,湿空气流动Re数的范围为100~1100,Pr数为0.71,Sc数为0.61。讨论了不同波纹高度、波纹间距对阻力与换热的影响,给出了不同Re数下的浓度场,并对动量、传热及传质进行了定量比较分析。计算结果表明,整体Nu数及fRe数随着波纹高度的增加或波纹间距的减小而增加;浓度随着Re数的增加沿着流动方向迅速降低;计算能较好的满足Chilton-Colburn相似,表明传热特性均可类推到传质特性中去。  相似文献   

8.
对内环壁面加热、外环壁面绝热的圆环型通道,数值研究了空气湍流正在发展流与壁面辐射的稳态耦合换热。采用低雷诺数k-ε模型与SIMPLEC算法求解气流的湍流流动与对流换热,采用蒙特卡罗法求解壁面间的辐射换热,对流换热与表面间辐射换热通过绝热壁面边界条件进行耦合。通过模拟计算,分析了相关参数及物性变化的影响。研究结果表明,入口Re数与壁面发射率均对通道内的换热有重要影响;考虑空气物性变化与否所预测到的对流热流分布形态相差非常大,常物性下的模拟结果会导致对通道内热输运特性的不正确认识。  相似文献   

9.
带扰流片的矩形直通道内的流动与换热   总被引:1,自引:0,他引:1       下载免费PDF全文
建立了矩形直通道内三维可压缩流动与换热模型 ,对来流雷诺数Re在 1× 10 5~ 3× 10 5范围内 ,带顺排和错排扰流片的通道内部对流换热过程进行了模拟计算。计算结果表明 ,矩形扰流片具有明显的强化冷却效果 ,扰流片表面的对流换热系数明显高于光滑表面的值 ,有扰流片区域的壁面温度明显降低 ;错排扰流片与顺排扰流片相比 ,对流换热系数增大 4 %左右。计算结果归纳了传热和流动压降关系式。  相似文献   

10.
非圆形微通道热沉的流动换热特性数值模拟   总被引:1,自引:0,他引:1  
建立了非圆形硅微通道内单相流动和换热过程的三维模型,并分别对三角形、矩形和梯形微通道中流动换热进行了数值模拟.研究发现,截面平均努塞尔数在通道入口处数值最大,然后沿流体流动方向急剧减小,直至流动充分发展时趋于恒定.固体和流体温度沿流动方向近似线性升高.换热面壁温仅沿流动方向升高,在垂直于流动方向,温度则基本保持均衡;雷诺数对微通道的流动与换热特性存在着较大的影响,雷诺数越大,其对应的努塞尔数也越大.对3种微通道的热经济性分析比较发现,三角形通道的热有效性最高.  相似文献   

11.
采用数值模拟的方法对高实度(45%)菱形扰流柱在恒定通道和收敛通道内的传热及流动特性进行三维数值模拟研究,分析了不同雷诺数下两种通道内的传热及压力损失。研究结果表明:随着雷诺数的增加,恒定通道和收敛通道传热效果均增强,两种通道内的流动阻力损失也减小,但减小的趋势逐渐降低;在相同雷诺数下,收敛通道内扰流柱的表面尤其是背风面能够被有效冷却;恒定通道的压力损失变化平缓且呈线性分布,而收敛通道内的压力损失存在急剧增大区域。  相似文献   

12.
The present study investigates numerically the simultaneously developing unsteady laminar fluid flow and heat transfer inside a two dimensional wavy microchannel caused by a sinusoidal varying velocity component at an inlet. The flow was both thermally and hydro dynamically developing while the channel walls were kept at a uniform temperature. The simulation was performed in the laminar regime for Prandtl number 7(water) and Reynolds number ranging from 0.1 to 100. A Wavy microchannel having non-dimensional hydraulic diameter 1 with varying pulsating amplitude and frequency represented by the Strouhal number was designed for the given Reynolds number range. Based on the comparison with steady flow in a wavy channel it was found that imposed sinusoidal velocity at the inlet can provide improved heat transfer performance at different amplitudes (0.2, 0.5, 0.8) and frequencies (1, 5, 10) while keeping the pressure drop within acceptable limits.  相似文献   

13.
The performance of direct air-cooled condensers in power plant is affected significantly by air-side flow and heat transfer characteristics of the wavy finned flat tube. Experimental investigations were conducted for air-side flow and heat transfer with and without delta winglet pairs punched on the surface of the wavy fin. The different temperature fields of the heated wavy fin surface with and without delta winglet pairs were obtained by the infrared thermography technology. Both experiments and numerical simulations showed that a substantial increase in the heat transfer with six delta winglet pair generators on the wavy fin was obtained with the Reynolds number varying from 1500 to 4500, which was the range of the air flow in practical direct air-cooled condensers. The average Nusselt number increased by 21–60% with the Reynolds number varying from 1500 to 4500 and the average friction factor increased by 13–83% with the Reynolds number varying from 500 to 4500 in experiments. The average performance evaluation criteria, PEC, can be up to 1.31 with six delta winglet pairs punched on the wavy fin surface, indicating the high potential of heat transfer enhancement to direct air-cooled condensers by longitudinal vortex generators.  相似文献   

14.
In this paper, laminar copper–water nanofluid flow and heat transfer in a two-dimensional wavy channel is numerically investigated. The Reynolds number and nanoparticle volume fraction considered are in the ranges of 100–800 and 0–5% respectively. Numerical solutions are obtained by solving the governing equation of stream function, vorticity transport and energy in curvilinear coordinates using the finite difference method. The effects of nanoparticle volume fraction, the wavy channel amplitude and wavelength and the Reynolds number on the local skin-friction coefficient, local and average Nusselt number and the heat transfer enhancement are presented and discussed. Results show that the friction coefficient and Nusselt number increase as the amplitude of wavy channel increases. As the nanoparticle volume fraction increases, the Nusselt number is found to be significantly increased, accompanied by only a slight increase in the friction coefficient. In addition, it was found that the enhancement in heat transfer mainly depends on the nanoparticle volume fraction, amplitude of the wavy wall and Reynolds number rather than the wavelength.  相似文献   

15.
The simultaneously developing unsteady laminar fluid flow and heat transfer inside a two dimensional wavy microchannel, due to sinusoidally varying velocity component at inlet has been numerically investigated. The flow was both thermally and hydrodynamically developing while the channel walls were kept at a uniform temperature. The transient solution of two-dimensional Navier-Stokes equation was obtained using the SIMPLE algorithm with the momentum interpolation technique of Rhie and Chow. The simulation was performed in the laminar regime for Prandtl number 7 and Reynolds number ranging from 0.1 to 100. Based on the comparison with steady flow in wavy channel it was found that imposed sinusoidal velocity at inlet can provide improved heat transfer performance at different amplitude (0.2, 0.5, 0.8) and frequency (1, 5, 10).  相似文献   

16.
EHD enhanced heat transfer in wavy channel   总被引:1,自引:0,他引:1  
Heat transfer enhancement with electrohydrodynamic (EHD) technique in laminar forced convection inside a wavy channel with different wire electrode arrangements is numerically investigated. The electric field is generated by the wire electrodes charged with DC high voltage. The mathematical modeling includes the interactions among electric field, flow field, and temperature field. The simulation is firstly conducted with the experimental data in case of rectangular flat channel and the results agree very well. Then the modeling is carried out in the case of wavy channel. It is found that the heat transfer coefficient with the presence of electric field increases with the supplied voltage but decreases when the Reynolds number and the distance between the wire electrodes and the wall surface are augmented. The heat transfer enhancement is also dependent on the number of the wire electrodes, the number of wave per length, and the wave aspect ratio.  相似文献   

17.
The rates of heat transfer for flow through a sinusoidally curved converging-diverging channel has been analyzed using a simple coordinate transformation method and the spline alternating-direction implicit method. The effects of the wavy geometry, Reynolds number and Prandtl number on the skin-friction and Nusselt number have been studied. Results show that the amplitudes of the Nusselt number and the skin-friction coefficient increase with an increase in the Reynolds number and the amplitude-wavelength ratio. The heat transfer enhancement is not significant at smaller amplitude wavelength ratio, however, at a sufficiently larger value of amplitude wavelength ratio the corrugated channel will be seen to be an effective heat transfer device, especially at higher Reynolds numbers.  相似文献   

18.
The current numerical study is conducted to analyze mixed convection heat transfer in lid-driven cavity with a sinusoidal wavy bottom surface. The cavity vertical walls are insulated while the wavy bottom surface is maintained at a uniform temperature higher than the top lid. In addition, the transport equations are solved using the finite element formulation based on the Galerkin method of weighted residuals. The validity of the numerical code used is ascertained by comparing our results with previously published results. The implications of Richardson number, number of wavy surface undulation and amplitude of the wavy surface on the flow structure and heat transfer characteristics are investigated in detail while the Prandtl number is considered equal to unity. The trend of the local heat transfer is found to follow a wavy pattern. The results of this investigation illustrate that the average Nusselt number increases with an increase in both the amplitude of the wavy surface and Reynolds number. Furthermore, optimum heat transfer is achieved when the wavy surface is designated with two undulations while subjected to low Richardson numbers.  相似文献   

19.
建立微型燃气轮机CW(交叉波浪型,Cross Wavy)原表面回热器三维周期性充分发展数值计算模型,对芯体内传热和阻力特性进行了分析,确定了质量流量和温度水平对换热量及压降的影响,给出了CW原表面芯体板内阻力、传热因子以及努塞尔数与雷诺数之间的经验关联式。传热及阻力性能分析结果表明:随着雷诺数的增大,回热器芯体单元传热系数增大,传热量逐渐增加,并且随着低压高温烟气侧的进口温度升高,传热量增加幅度增大;回热器芯体单元回热度随雷诺数的增大而减小,随燃气进口温度升高而减小。  相似文献   

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