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对椭圆钎焊翅片管和双金属轧制翅片管换热器的传热及阻力性能进行试验对比研究,试验得到了一系列工况下的传热数据与管外空气流动阻力数据,给出了相应的传热系数、流动阻力曲线。从总传热系数中分离出管外空气侧的对流换热系数,得到了具有一定应用价值的管外换热的计算关联式;拟合得到了管外阻力计算关联式。结果表明:椭圆钎焊翅片管比双金属轧制翅片管的传热系数约高9%,管外换热系数约高17%,且管外空气流动阻力约低11%。 相似文献
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用Fluent数值模拟的方法对光管、横向和纵向掠过的圆形肋片管、纵向流开槽伞形翅片管的换热和阻力特性进行比较,同时研究5种不同α角的开槽伞形翅片管的流动、换热、阻力特性.结果表明:当管型排布方式及雷诺数相同时,纵向流开槽伞形翅片管的传热系数为普通光管的1.4~1.8倍,横向和纵向掠过的圆形肋片管为光管的1.1 ~1.5倍,不同α角的纵向流开槽伞形翅片管中,α=105°时的换热系数最高;开槽伞形翅片管的阻力是横向掠过的圆形肋片管阻力的0.25 ~0.75倍,但高于纵向掠过的圆形肋片管阻力,不同α角的纵向流开槽伞形翅片管中,α=105°时的阻力最小. 相似文献
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采用数值模拟方法,对径向错列翅片管内含不凝结气体水蒸气的凝结对流换热及阻力特性进行了综合分析。将编写的自定义函数(UDF)导入ANSYS FLUENT软件,对新型强化管传热性能和阻力性能进行了数值模拟,并根据管长方向壁面上蒸汽质量分数的变化情况,讨论分析了凝结过程中翅片管传热性能的变化规律。分析结果表明:与光管相比,内翅片管的强化传热效果随翅数增多、翅片换热接触面积增大而更加显著;另一方面,翅片管的流动阻力相应增大,对管路换热产生不良影响。在所研究翅型范围内16翅y=2x~2型翅片管综合强化换热效果更优;此外随着换热过程的持续,蒸汽凝结逐渐放缓;入口速度增大导致水蒸气凝结不充分,对换热效果的提升有一定制约。 相似文献
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本文通过对比实验,对双金属整体翅片管与绕簧管的换热性能和流动阻力进行了对比分析。实验结果表明,双金属整体翅片管具有高换热效率和低流动阻力的显著优点,且结构工艺简单。 相似文献
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燃气轮机透平叶片传热和冷却研究:内部冷却 总被引:2,自引:0,他引:2
随着燃气轮机透平进口温度的不断提高,其换热与冷却问题已然成为现代高性能燃气轮机研发中亟待解决的核心关键技术之一.透平叶片的冷却可以分为内部冷却和外部冷却,结合作者近年的研究工作,详细综述了燃气轮机透平叶片内部换热与冷却问题的研究现状与进展,着重介绍了叶片内部蛇形通道冷却、叶片内部冲击冷却和前缘的旋流冷却及尾缘柱肋冷却,指出了它们各自在相关方面需要进一步开展的工作.其中:在蛇形通道冷却方面,需要进一步研究旋转状态下蛇形通道内流动与换热特性、发展高性能的扰流装置及通道弯头结构、设计新颖高效的叶顶内部冷却结构、获得带气膜孔或冲击孔的蛇形通道内的换热与冷却特性;在叶片前缘内部冲击冷却方面,需要研究不同曲率面上的冲击冷却换热特性、旋转条件下的冲击冷却以及冲击气膜复合冷却特性;在旋流冷却方面,需要对其结构参数的影响开展进一步的广泛研究,并开展旋转状态下旋流冷却特性的研究;在尾缘柱肋冷却方面,需要进一步研究复杂流场下柱肋阵列通道中的流动换热与众敏感因子之间的关系. 相似文献
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水资源的匮乏使节水性能显著的直接空冷式发电厂在缺水富煤地区得到了迅速推广.翅片管换热器作为空冷凝汽器的基本组成单元,其流动特性是决定空冷凝汽器运行性能的关键因素.应用计算流体力学(CFD)方法,对不同迎面风速下单排及双排翅片管换热器的阻力特性进行了数值模拟.计算结果表明:对于2种不同形式的翅片管换热器,空气侧流动阻力皆随着迎面风速的增加而升高;双排管的流动阻力略大于单排管,且随着迎面风速的增加,双排管管束相对于单排管管束的压力损失增幅呈上升趋势.通过比较不同数量网格模型的数值模拟结果,验证了网格无关性,证明了模拟结果可靠.研究结果对提高空冷凝汽器乃至空冷电厂的运行经济性都具有重要的参考价值. 相似文献
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Numerical simulation of fluid flow and heat transfer in a microchannel heat sink with offset fan-shaped reentrant cavities in sidewall 总被引:1,自引:0,他引:1
Lei ChaiGuodong Xia Mingzheng ZhouJian Li 《International Communications in Heat and Mass Transfer》2011,38(5):577-584
The paper is focused on the investigation of fluid flow and heat transfer characteristics in a microchannel heat sink with offset fan-shaped reentrant cavities in sidewall. In contrast to the new microchannel heat sink, the corresponding conventional rectangular microchannel heat sink is chosen. The computational fluid dynamics is used to simulate the flow and heat transfer in the heat sinks. The steady, laminar flow and heat transfer equations are solved in a finite-volume method. The SIMPLEX method is used for the computations. The effects of flow rate and heat flux on pressure drop and heat transfer are presented. The results indicate that the microchannel heat sink with offset fan-shaped reentrant cavities in sidewall improved heat transfer performance with an acceptable pressure drop. The fluid flow and heat transfer mechanism of the new microchannel heat sink can attribute to the interaction of the increased heat transfer surface area, the redeveloping of the hydraulic and thermal boundary layers, the jet and throttling effects and the slipping over the reentrant cavities. The increased heat transfer surface area and the periodic thermal developing flow are responsible for the significant heat transfer enhancement. The jet and throttling effects enhance heat transfer, simultaneously increasing pressure drop. The slipping over the reentrant cavities reduces pressure drop, but drastically decreases heat transfer. 相似文献
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An experimental investigation has been carried out to study the heat transfer and pressure drop characteristics of nanofluid flow inside horizontal helical tube under constant heat flux. The nanofluid is prepared by dispersion of CuO nanoparticle in base oil and stabilized by means of an ultrasonic device. Nanofluids with different particle weight concentrations of 0.5%, 1% and 2% are used. The effect of different parameters such as flow Reynolds number, fluid temperature and nanofluid particle concentration on heat transfer coefficient and pressure drop of the flow are studied. Observations show that by using the helically coiled tube instead of the straight one, the heat transfer performance is improved. Also, the curvature of the tube will result in the pressure drop enhancement. In addition, the heat transfer coefficient as well as pressure drop is increased by using nanofluid instead of base fluid. Furthermore, the performance evaluation of the two enhanced heat transfer techniques studied in this investigation shows that applying helical tube instead of the straight tube is a more effective way to enhance the convective heat transfer coefficient compared to the second method which is using nanofluids instead of the pure liquid. 相似文献
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《International Communications in Heat and Mass Transfer》1998,25(1):43-58
In shell-and-tube heat exchangers, the shell-side fluid flow enters and leaves through nozzles which are mounted on the shell wall. The cross-flow in the nozzle region has an impact on the shell-side pressure drop and heat transfer. The influence on the heat transfer is investigated by means of experiments with four double-pipe heat exchangers.The results show that the influence is greater, the shorter the heat exchangers are, and the smaller the ratio of the free cross sectional areas of the nozzle to that of the shell-side. A correlation suitable for predicting the heat transfer coefficient is presented in this paper. The correlation consists of the Nusselt number for the flow in the nozzle region and that for the flow in the annulus. 相似文献
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In this paper we report the results of our modelling studies on two-phase forced convection in microchannels using water as the fluid medium. The study incorporates the effects of fluid flow rate, power input and channel geometry on the flow resistance and heat transfer from these microchannels. Two separate numerical models have been developed assuming homogeneous and annular flow boiling. Traditional assumptions like negligible single-phase pressure drop or fixed inlet pressure have been relaxed in the models making analysis more complex. The governing equations have been solved from the grass-root level to predict the boiling front, pressure drop and thermal resistance as functions of exit pressure and heat input. The results of both the models are compared to each other and with available experimental data. It is seen that the annular flow model typically predicts higher pressure drop compared to the homogeneous model. Finally, the model has also been extended to study the effects of non-uniform heat input along the flow direction. The results show that the non-uniform power map can have a very strong effect on the overall fluid dynamics and heat transfer. 相似文献
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Yan Li Xiumin Jiang Xiangyong Huang Jigang Jia Jianhui Tong 《International Journal of Heat and Mass Transfer》2010,53(21-22):4543-4551
This work investigates the flow field and the heat transfer characteristics of a shell-and-tube heat exchanger for the cooling of syngas. Finite volume method based on FLUENT software was used and the RNG k–ε turbulence model was adopted for modeling turbulent flow. The porosity rate, the distribution of the resistance and the distribution of the heat source are introduced to FLUENT by coupling the user defined function. The pressure drop, the temperature distribution and the variation of local heat transfer are studied under the effects of the syngas components and the operating pressure, and the effect of the arrangement of the baffles on the heat transfer is studied. The results show that higher operation pressure can improve the heat transfer, however brings bigger pressure drop. The components of the syngas significantly affect the pressure drop and the heat transfer. The arrangement of the baffles influences the fluid flow. 相似文献
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《Applied Thermal Engineering》2007,27(5-6):862-868
A double-pipe helical heat exchanger was numerically studied to determine the effects of thermally dependent viscosity and non-Newtonian flows on heat transfer and pressure drop for laminar flow. Thermally dependent viscosities were found to have very little effect on the Nusselt number correlations for Newtonian fluids; however significant effects on the pressure drop in the heat exchanger were predicted. Changing the flow rate in the annulus can significantly affect the pressure drop in the inner tube, since the average viscosity of the fluid in the inner tube would change due to the change in the average temperature.The effects of non-Newtonian power law fluids on the heat transfer and the pressure drop were determined for laminar flow in the inner tube and in the annulus. The Nusselt number was correlated with the Péclet number for heat transfer in the inner tube. For the annulus, the Nusselt number was found to correlate best with the Péclet number and the curvature ratio. Pressure drop data were compared by using ratios of the pressure drop of the non-Newtonian fluid to a Newtonian fluid at identical mass flow rates and consistency indices. 相似文献
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本文对CO_2在水平微细管内流动沸腾特性进行实验研究。实验结果表明:热流密度增加对强化核态沸腾换热和高干度区域流型转变具有显著影响,随着热流密度的增加换热系数增加,对摩擦压降影响很小;质量流率对于换热系数的影响较小,但随着质量流率的增加摩擦压降大幅增加,质量流率的大小直接决定了换热过程所经历流态;饱和温度升高换热系数相应升高,摩擦压降减小,且对流态转变特性有重要影响。在同样工况下摩擦压降最大值先于换热系数最大值出现,理论分析采用的流态形式与实际CO_2管内流动流动沸腾换热流态基本一致。 相似文献
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In this study, fluid flow and heat transfer in microchannel heat sinks are numerically investigated. The three-dimensional governing equations for both fluid flow and heat transfer are solved using the finite-volume scheme. The computational domain is taken as the entire heat sink including the inlet/outlet ports, inlet/outlet plenums, and microchannels. The particular focus of this study is the inlet/outlet arrangement effects on the fluid flow and heat transfer inside the heat sinks.The microchannel heat sinks with various inlet/outlet arrangements are investigated in this study. All of the geometric dimensions of these heat sinks are the same except the inlet/outlet locations. Because of the difference in inlet/outlet arrangements, the resultant flow fields and temperature distributions inside these heat sinks are also different under a given pressure drop across the heat sink. Using the averaged velocities and fluid temperatures in each channel to quantify the fluid flow and temperature maldistributions, it is found that better uniformities in velocity and temperature can be found in the heat sinks having coolant supply and collection vertically via inlet/outlet ports opened on the heat sink cover plate. Using the thermal resistance, overall heat transfer coefficient and pressure drop coefficient to quantify the heat sink performance, it is also found these heat sinks have better performance among the heat sinks studied. Based on the results from this study, it is suggested that better heat sink performance can be achieved when the coolant is supplied and collected vertically. 相似文献