共查询到19条相似文献,搜索用时 187 毫秒
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实验研究了三角形硅微通道中的流动冷凝.通道中的冷凝流型沿程主要有珠状流、环状流、喷射流和弹状-泡状流等.在同一通道中,喷射流位置随着工质流量的增大而延后;在相同蒸气入口雷诺数下,喷射流位置则随着通道尺度的增大而延后.喷射流频率随着蒸气入口雷诺数和冷凝液韦伯数的增大而增大.较小水力直径的三角形通道中的流动冷凝不稳定性较高.冷凝通道的壁面温度呈沿程下降趋势.在同一通道中,流动冷凝的平均冷凝传热系数和平均努塞尔数,皆随着蒸气入口雷诺数的增大而增大,通道尺度的减小显著强化冷凝传热. 相似文献
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为研究不连续冷源边界对内置发热体多孔介质方腔内传热及流动的影响,采用格子Boltzmann方法对REV尺度下多孔介质方腔内的自然对流进行计算,并研究瑞利数(Ra)、达西数(Da)、孔隙度对多孔介质方腔内传热流动的影响.发现Da对方腔内的流体流型影响很大,Da为10-4时,多孔介质方腔内只有一个涡流,而Da为10-2时,方腔内有两个涡流.增大Ra、Da、孔隙度可以提高冷源壁面的平均努赛尔数(Nu),增强散热效果,孔隙率对平均Nu影响程度和Da的大小有关.当冷源布置在壁面上方,壁面的平均Nu随Ra的增加剧烈变化,方腔处于高Ra条件下时,将冷源布置在边界的上方可以提高散热效果.6种布置方案中Case 6的散热效果最好. 相似文献
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This article presents the experimental heat transfer results of an impinging jet onto a flat surface with discrete ribs in a reciprocating confinement. The test flows were systemically varied from static to reciprocating conditions with oscillating frequencies of 0.83, 1.25, and 1.67 Hz. Parametric ranges of tests in terms of Reynolds, pulsating, and buoyancy numbers were 10,000-25,000, 0-0.15, and 0-4.12 x 10-7, respectively. It was found that the nonreciprocating heat transfer close to and away from the stagnation point was respectively reduced and improved from the smooth-walled values, which led to the more spatially uniform heat transfer distribution. An empirical correlation was developed to permit the evaluation of nonreciprocating local Nusselt numbers. Under reciprocating environment with relatively weak pulsating force effects, a tendency of heat transfer deterioration from static reference developed, which trend could lead to about 20% of heat transfer reduction. Further increase of pulsating force ratio caused the subsequent heat transfer recovery, and the local reciprocating Nusselt number could be enhanced to a level about 240% of the equivalent static value at a pulsating number of 0.014. Considerable influence of reciprocating buoyancy interaction on heat transfer was detected to impede local heat transfer. As the present flow system in a reciprocating confinement could result in higher and more spatially uniform heat transfer rates in general, it could be an applicable cooling method for pistons. 相似文献
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采用Boltzmann方法模拟部分热活跃边界下的多孔腔体内自然对流,探讨不同热边界布置方案、孔隙度、Da数及Ra数对其流动传热的影响.数值计算表明:Da=10-4时,腔体内中央出现一个循环流模式,只在Ra数很大时孔隙度才对传热有影响; Da=10-2时,腔体内出现两个循环流,在Ra数很小时孔隙度对传热产生强烈的的影响.热活跃边界位置影响腔体内流体对流传热的强度,加热边界布置在底部、而冷却边界布置在顶部(Bottom-Top布置方式),对多孔腔体内对流传热最有利,优于全热边界布置方式的传热效果. 相似文献
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The paper presents results on heat transfer from a cylinder in pulsating flow. The results are local heat transfer distributions that match four different flow modes identified previously by the authors. A new kind of dimensionless number was introduced for pulsating flows: this is a ratio of flow acceleration during unsteady movement to the centrifugal acceleration due to streamlines bending over the cylinder. The experimental data were generalized as a dependency of the average heat transfer on the new dimensionless criterion. The generalization offered a correction factor to a traditional relation for heat transfer between a cylinder and air flow past the cylinder; this correction takes into account the effect of parameters of forced flow pulsations on the average heat transfer. 相似文献
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非牛顿幂次流体沿竖直平板层流自然对流为非线性两点边值问题,其速度场与温度场需耦合求解。采用几种数值方法对该问题进行了计算,研究了各种普朗特数(Pr)及不同幂次流体对沿壁面平均努赛尔数(Nu)的影响变化,并与有关文献的结果进行了对比分析。 相似文献
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圆管层流脉冲流动对流换热数值分析 总被引:3,自引:0,他引:3
对等热流和等壁温边界条件下圆管内层流脉冲流动对流换热问题进行了数值模拟。在等热流边界条件下的数值计算结果与理论解吻合很好。计算结果表明:在等热流和等壁温边界下脉冲流动可引起速度、温度以及努塞尔数随时间波动,振幅越大,脉冲频率越小,波动越大。但它们的时均值均等于在相同雷诺数下稳态流动的值,脉冲流动不能强化换热。 相似文献
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This paper presents the numerical modeling of complex flows and heat transfer. The Finite Analytic method is used to discretize the transport equations. The diagonal Cartesian method is proposed to model fluid flows and heat transfer over complex geometries. A three-dimensional channel flow with conjugate heat transfer is simulated. By the diagonal Cartesian method and 5-point Finite Analytic scheme, a grooved channel flow and flow in a casting bank at different Reynolds numbers are modeled. Simulations by both the diagonal Cartesian method and the traditional saw-tooth Cartesian method indicates the diagonal Cartesian method improves the modeling of flows, due to the more accurate approximation of complex boundaries. Heat transfer in two-dimensional finned compact heat exchanger is also studied. An improved heat exchanger is proposed based on the numerical prediction of heat transfer. 相似文献
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This paper presents a numerical analysis of turbulent periodic flow and heat transfer in a rectangular channel with detached V-baffles. The computations are based on the finite volume method with the SIMPLE algorithm for handling the pressure–velocity coupling and using the QUICK scheme for the convection terms. Air is used as the test fluid with the air flow rate in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of different detached-clearance ratios (c/H, CR) of 0.0, 0.05, 0.1, 0.15, and 0.2, baffles-pitch to square channel-diameter ratio (pitch ratio (p/H), PR) is 1.0, baffles-height to square channel-diameter ratio (blockage ratio (b/H), BR) is 0.10, and attack angle (α) is 45? on heat transfer, friction factor and thermal enhancement factor are investigated numerically. It is found that a pair of counter-rotating vortices (P-vortex) caused by the baffles can induce impingement/attachment flows repeatedly on the rectangular channel walls leading to a greater increase in the heat transfer over the test channel. The maximum thermal performance and heat transfer are found to be about 1.5 and 3.3, respectively for CR = 0.05 and Re = 3000, while the highest pressure loss is about 21.5 in the case of CR = 0.2 and Re = 20,000. 相似文献
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采用格子Boltzmann方法对可变形腔体内自然对流问题进行数值研究,给出平均努赛尔数的经验关系式.腔体左壁加热长度分为左壁面的整个区域(H)和左壁面的中间区域(0.5H)两种情况,右壁向外界环境开放,上下边界绝热且可以上下移动,以此调节右出口尺寸.主要研究瑞利数(104 ≤ Ra ≤ 106),右出口尺寸(1.0H ≤ L ≤ 2.0H),左壁加热尺寸(Lh=0.5H或Lh=H)对腔体内等温线、流线、局部努塞尔数和平均努赛尔数的影响.结果表明:腔体内换热随着瑞利数的增大越来越强烈,表现为椭圆形准静止区域更加靠近上绝热壁,且热分层厚度逐渐变小,平均努赛尔数增加.而右出口尺寸的增加,对于两种加热尺寸下腔内的换热效果有不同程度影响,其中与加热尺寸为左壁面的全部区域Lh=H相比,加热尺寸为左壁面的中间情况Lh=0.5H时,右侧开口尺寸的增加对换热效果的影响不显著.此外,左壁加热尺寸为0.5H时显示出比加热尺寸为H时更高的平均传热效率.最后,针对不同的加热尺寸,提出加热面平均努赛尔数与Ra数及右壁面开口尺寸L*之间函数关系的经验预测,拟合效果满足工程实践与设计需要. 相似文献