流体在粗糙管管内及管隙间湍流流动阻力与传热的数据关联

本文分析了流体在规整型粗糙强化管束的管内和管隙间的流动和传热特性,讨论了湍流流体在规整型粗糙壁面上和在光滑壁面上动量与热量传递的差别,推导出光滑管和粗糙管管内及管隙间湍流流动的流体摩擦阻力系数和传热准数方程的关联式,并能较好地关联螺旋槽管、螺旋低翅片管和缩放管管内与管隙间的流体阻力和传热的实验数据.     

大粗糙度横肋管摩擦阻力与传热特性

在凝结换热实验台上 ,采用恒壁温法和恒热流法对油品在大粗糙度横肋管中的层流与湍流摩擦阻力与传热特性进行了实验研究 .实验过程中Re为 5 0～ 6 2 0 0 ,Pr为 75～ 2 6 0 ,管子粗糙高度为 5mm ,导程为 30mm .实验结果表明 ,由于实验管特殊几何结构 (大粗糙度 )和油品物性参数的相互作用 ,使其表现出与以水或空气为工质的常用强化管不同的流动传热规律 ,并且实验方法对实验结果的影响不大 .根据实验结果 ,提出了层流区和湍流区油品量纲 1摩擦系数及传热系数的关联式 ,并将实验数据与Ravigururajan和Bergles关联式的计算值进行了比较 .研究结果可用于大粗糙度横肋管换热器的设计及运行参数优化 .     

螺旋槽管管内流阻和传热特性的研究

本文以空气为工质,在雷诺数Re=10~4～10~5以及较大的管参数范围内对13条螺旋槽管进行了阻力和传热实验。实验结果证明就强化管内单相流体的湍流传热而言在粗糙雷诺数e~+=10～500范围内,螺旋角β≈90°的单头管比多头管具有更好的强化传热性能。用热线风速仪测定了螺旋槽管中的速度分布,定性地分析了管内沿轴向方向湍流强度的强弱,用壁相似定律、混合长理论以及热动量传递相似理论推导了螺旋糟管的阻力和传热模型。最后对螺旋槽管的管参数进行最优化计算,并讨论了Pr数对最佳管参数和最佳操作雷诺数的影响。     

冷却条件下渐扩/渐缩管内超临界压力二氧化碳的传热特性

采用SST k-ω湍流模型,数值计算了冷却条件下超临界压力二氧化碳(SCO₂)在三种水平管(等截面管、渐扩管和渐缩管)内的传热特性,研究了不同运行参数(压力、质量流量及热通量)对传热性能的影响。结果表明,与等截面管相比,渐扩管有效地强化了传热,采用渐扩管时,SCO₂的总传热系数最大提高了47.98%。然而,相比等截面管,渐缩管却削弱了传热。最后,从类冷凝和湍流场分布的角度阐明了传热强化的物理机理。为SCO₂冷却器的优化设计提供了新的思路和理论指导。     

用正交配置技术估计固定床内的传热参数

用正交配置技术与非线性最小二乘估计固定床内的传热参数.用多通道巡回检测装置同时测定沿床层径向分布的40个正交配置点上的温度.系统地考察了床高、Re_p、d_t/d_p、气体入口温度、壁温对K_(er)和h_w的影响,并提出了以下的关联式k_(er)=0.199+0.015d_t/d_p+0.0020/1+14.15(d_p/d_t)~2Re_ph_w=33.4+4.23d_t/d_p+0.331/1+8.45(d_p/d_t)~2Re_p(5.5相似文献   

三角翼纵向涡内扰管传热机理及数值模拟

基于Fluent软件对相同管径的光管、波纹管、横槽管和三角翼纵向涡内扰管的数值模型都分别采用k-e湍流模型,管内壁设定为等温边界条件,在Re=3×10~4~1.5×10~5范围内和不同流速下,对四种管内不同流速下的流体的温度场进行数值模拟,得出多组不同流速流体通过四种不同的管下的工况性能差异,通过对比多组工况的出口截面温度分布和管内流体迹线分布,结合传热机理分析比较得出三角翼内扰管和光管、波纹管、横槽管内流体的流动传热性能优劣和各自的适用场合。结果表明,纵向涡传热管和其他三种管道比较,传热性能明显提高,在Re=3×10~4~1.5×10~5的范围内,对流换热系数h较光管提高了90%以上,内置三角翼纵向涡的传热管出现大的纵向涡状的螺旋流,主流区和边界层充分混合,但压降较大。     

煤油在内螺纹管中流动沸腾强化传热特性

针对石油化工过程中沸腾传热设备技术改造的需要 ,在 3× 1 0 5Pa (绝对压力 )的条件下 ,对煤油在垂直内螺纹管中的上升流动沸腾传热进行了实验研究 ,将实验结果同煤油在光管中的实验结果进行了比较 .实验结果表明 ,内螺纹管中的沸腾换热系数是光管的 1 6～ 2倍 ,并且可在小温差条件下实现流动沸腾传热 .提出了煤油在内螺纹管中的流动沸腾换热系数的关联式 ,并对煤油在内螺纹管中的流动沸腾特性和强化传热机理进行了分析 .     

应用CFD对D-T型双轴卧式搅拌装置功率特性和传热特性的模拟

针对自主开发的适用于高黏度、高凝固点、强热敏性物料的一种新型带搅拌结构的卧式双轴再沸器的搅拌功率特性和传热及温度分布特性进行了流体力学模拟研究.应用动网格技术计算分析了该卧式双轴搅拌装置的功率特性和传热特性,得出结论:任意一轴的功率准数以及总的功率准数均近似满足N_p·Re=K_p;当1.1 < Re< 20且30 000< PR< 130 000时,总的传热关联式为Nu=2.55 Re~(0.61)Pr~(0.31)Vis~(0.14).     

螺旋扭曲管内部流动与传热特性试验研究

螺旋扭曲管是一种新型的强化传热元件，具有传热效率高、流动阻力小等优势，在石油化工、船舶、采矿、动力以及钢铁行业中具有广泛的应用前景。采用试验的方法，研究了螺旋扭曲管管内在湍流(Nu>20 000)范围内的流动与强化传热特性，并与同规格的光滑圆管进行了比较。试验结果表明，在相同的Re数下，螺旋扭曲管管内Nu数大于光滑圆管，增大了约30%～50%,表明螺旋扭曲管能有效地提高管内对流换热效果；在相同的Re数下，螺旋扭曲管阻力因子比光滑圆管小；在相同的流量下，螺旋扭曲管管内阻力损失与光滑圆阻力损失基本相当，表明采用螺旋扭曲管不会显著的增加摩擦阻力。     

横纹槽管结构优化的正交数值模拟试验研究

运用正交试验法设计了横纹槽管结构优化的试验,试验运用数值模拟方法进行,采用标准K-ε方程湍流模型和速度分布两层模型进行模拟计算,研究了横纹槽管结构参数e/d,p/d, a/e和流动Reynolds数对热阻力性能的影响.试验结果表明：在试验参数范围内,影响横纹槽管综合传热性能的主要结构参数为肋节距p/d和肋形a/e,而肋高e/d影响较小,并且传热综合因子随流动Reynolds数增大而迅速降低.通过分析正交试验结果,提出了较佳横纹槽管管型.     

Wall to fluid heat transfer in liquid fluidised beds: Part 2

Wall to fluid heat transfer coefficients and radial temperature profiles have been obtained for beds of hydrodynamically similar spheres fluidized with water in a 2.058 inch pipe at a constant heat flux. From packed bed to open pipe conditions, heat transport occurs mainly by turbulent mixing, although conduction through the particles and possibly particle convection have some effect at low porosities. This result contradicts a previously published prediction based on model calculations using erroneous temperature profiles⁽²⁴⁾. The model predicts a minor role for particle convection when appropriate temperature profiles are used. A series model based on the observed shift of thermal resistance from the wall region to the bulk of the bed with decreasing porosity is used to correlate heat transfer coefficients. The shift in resistance largely accounts for the maximum in heat transfer coefficient plots.     

On turbulent pipe flow with heat transfer and chemical reaction

A theoretical model has been developed to describe heat transfer to a fluid which is flowing turbulently in a pipe and within which a first-order endothermic irreversible chemical reaction is taking place. It is based on the penetration model for the fluid boundary layer close to the pipe wall and enables the calculation of the effect of chemical reaction on the heat transfer coefficient of turbulent pipe flow.The model has been checked against experimental results for flow distribution and heat transfer in turbulent pipe flow without chemical reaction. Good agreement between the calculated and experimental results was found. The measured heat transfer coefficients for turbulent pipe flow with a uniformly distributed heat source within the fluid were also well predicted. Unfortunately no accurate experimental data on the effect of a first-order chemical reaction on the heat transfer coefficient of turbulent pipe flow are available. However, calculations made with the model show that this effect can be considerable and thus may not always be neglected in practice.     

Convective heat transfer in a rotary kiln

An experimental study of convective heat transfer from hot air to the solid charge and walls in a non-fired rotary kiln is reported. Ottawa sand was heated by passing it counter-current to a flow of preheated air in a 2.5 m × 0.19 m I.D. rotary kiln. Axial temperature profiles of gas, wall and solids were measured. Local and average convective heat transfer coefficients from gas to solids and from gas to wall were determined assuming plug flow of gas and solids. Solid feed rates to 1750 kg/m² h and air rates to 3300 kg/m² h were investigated at rotational speeds to 6 r/min, holdup ratios to 17% and gas temperatures from 350–590 K. The gas/solids convective coefficient was found to depend on the gas through-put and to a lesser extent on solids holdup and rotational speed. Over the range tested, the angle of kiln inclination, solids throughput and particle size showed no significant effect on heat transfer. Gas/wall coefficients were about a factor of ten below gas/solid coefficients. Heat transfer results are compared to the limited data available in the literature, and to commonly used equations. Correlations of the experimental data on gas/solids, and gas/wall coefficients are presented; data from the literature on the wall/solids heat transfer coefficient are summarized.     

Non-isothermal laminar pipe flow — II. Experimental

In a previous article [1] theoretical predictions of velocity distributions, pressure drops and mean Nusselt-numbers are given for non-isothermal pipe flow of power-law fluids having a temperature dependent consistency-index. In the present investigation these solutions are checked for Newtonian fluids with extensive experimental data.A flow visualization technique was used for measuring the non-isothermal, laminar velocity profiles of glycerol in a round tube. Furthermore, accurate pressure drop measurements were carried out for non-isothermal tube flow of a viscous. Newtonian liquid. Finally logarithmic mean heat transfer coefficients were measured in laminar flow heat transfer.The experimental velocity profiles, pressure drops and heat transfer coefficients show a good agreement with those predicted theoretically.     

Ébullition par Convection Forcée des Mélanges Eau‐Ammoniac dans un Tube Vertical

An experimental study has been conducted on the forced convective boiling heat transfer of ammonia‐water mixtures flowing inside a 6 mm inner diameter vertical smooth tube. Using a water‐heated double pipe type generator, the local heat transfer coefficients are measured inside the inner tube for a range of heat flux density (29.93 — 99.79 kW/m²), mass flux density (35.36 — 99.04 kg/m²·s), mass flow rate (0.001 — 0.03 kg/s) and ammonia mass concentration (49%, 55% and 61%). The effect of the experimental parameters on the heat transfer coefficients is analysed. Three methods are used to predict the boiling heat transfer coefficients. Experimental data were compared with the available correlations. The obtained results confirm the good performance of the Mishra et al. (1981) and Bennett‐Chen's (1980) correlations in predicting the convective boiling heat transfer coefficient of NH₃‐H₂O mixtures. These methods are able to predict the boiling heat transfer data within an average accuracy of ± 20 %.     

Impingement heat transfer under a confined slot jet. Part I: Effect of surface throughflow

Local and average heat transfer coefficients were measured for a confined turbulent slot jet impinging on a permeable surface at which there may be throughflow. Local Nusselt number was obtained using a unique porous sensor designed for measurement of local heat transfer at a permeable surface which is subjected to rapidly and widely varying heat transfer. Measurements were performed for a wide range of jet Reynolds number and throughflow rates. Convective heat transfer coefficients was found to be enhanced by throughflow, and the enhancement factor in terms of Stanton number to be independent of jet Reynolds number and of extent of heat transfer area.     

Two-phase interactions through turbulent events as described by fluid–particle correlations

An experimental investigation of a vertical upward, two-phase pipe flow was undertaken to measure kinematic parameters of the fluid and solid phases. The kinematic parameters included Reynolds stress distributions based on quadrant analyses that provided insight in understanding the behavior of two-phase kinematic correlation profiles. The data collected was based on a two-color digital particle image velocimetry (DPIV) technique that simultaneously measured the velocity fields of the fluid and solid phases.From quadrant analysis results, differences in Reynolds stress quadrant profiles between the single- and two-phase conditions were observed near the wall in the range 0.8>r/R>0.55, corresponding to wall distances between 35 and 75 viscous lengths (y+). Correlation coefficients between the two phases were then calculated, using the fluctuating velocity components of each phase. The extent of the interaction between the two phases was tracked by the changing correlation values versus distance from the wall. The correlation of the fluid and solid phase velocities was highest in the core region of the pipe (y+∼120), where the effect of turbulent events is reduced; low correlation coefficient values were found at y+<75, where differences of magnitudes, inflection points, etc. of burst and sweep event quadrant analysis profiles were observed.The extent of the influence of wall dynamic turbulent events on the solid phase was observed both by the differences in the relative Reynolds stress quadrant profiles and, more readily, by the changing values of two-phase axial and radial correlation coefficients determined from the simultaneous fluid and solid fluctuating velocities measured by the two-color DPIV methodology. These changing values of the correlation coefficients across the tube reflect the different responses of low inertia (fluid tracers) and high inertia (solid phase glass spheres) particles to the turbulent events. Similar profiles of the axial and radial correlation coefficients were observed, indicating that for the geometry and flow conditions considered, one velocity component of each phase was sufficient to track the spatial extent of turbulent event effects and their interactions with the fluid and solid phases. It is found that the two-color DPIV methodology and two-phase correlation results can give critical insight into the performance of thermal-fluid processes, as burst and sweep events have a large impact on the kinematics and dynamics of particles in the two-phase flow.     

Heat transfer study in a pilot-plant scale bubble column

The effects of superficial gas velocity on heat transfer coefficient and its time-averaged radial profiles along the bed height have been investigated in a pilot-plant scale bubble column of 0.44 m diameter using air-water system. Notable differences were observed in heat transfer coefficients along the bed axial locations particularly between the sparger (Z/D = 0.28) and the fully developed flow (Z/D = 4.8) regions. In the fully developed flow region larger heat transfer coefficient values were obtained compared to those in the sparger region. About 14-22% increase in heat transfer coefficients measured in the fully developed flow region has been observed compared to those measured in the distributor region when the superficial gas velocity increases from 0.05 to 0.45 m/s. The heat transfer coefficients in the column center for all the conditions studied are about 9-13% larger than those near the wall region. It has been noted that in the fully developed flow region, the axial variation of the heat transfer coefficients was not significant.     

异形整体式热管散热器传热实验与分析

针对电子电气设备散热和均温的需求,提出了一种新型结构形式的异形整体热管散热器：平板热管形式的蒸发段与具有高肋化比翅片的冷凝铜管集成。对该热管进行了传热实验与分析,研究热管在不同工况下温度数值及分布,探究影响热管性能的因素和规律,验证其传热能力。结果表明：在各种工况下热管温差始终在1.75℃之内,均温性能良好。加热功率和对流散热状况对热管启动性能、总体热阻、当量热导率、传热系数都有影响。随着加热功率和对流速度增加,热管启动时间和热阻均降低,当量热导率和传热系数则逐渐上升。热阻最低为0.189℃·W^-1,最佳当量热导率为20964 W·m^-1·K^-1。相比于同等尺寸的传统热管,热阻降低了37%,传热效率提升15%。     

HEAT TRANSFER WITH PULSATING FLOW

This report concerns the frequency dependence of the heat transfer coefficient for water flowing in a tube. The investigation of this phenomenon was conducted in a double pipe heat exchanger in which the center stream was pulsed. The frequencies used ranged from 10 to 160 cycles per minute, and the average flow rates corresponded to a Reynolds number range of 3700 to 21,400.

The data obtained indicate that pulsing can increase the individual heat transfer coefficient by as much as a factor of 5 or more, with the greatest increase occurring when the average Reynolds number is in the range typically considered as corresponding to the transition from laminar to turbulent regimes in steady flow. The percentage increase in the heat transfer coefficient also appears to be a function only of a dimensionless group which represents the frequency divided by the flow reversal frequency