干盘管用平行流换热器翅片参数对空气侧换热系数及压降的影响

为了使平行流换热器在干盘管中得到推广应用,本文根据传热及压降关联式,采用数值模拟计算的方法,研究了干盘管用平行流换热器翅片参数对其空气侧换热性能及压降的影响,为干盘管用平行流换热器的设计提供参考依据。     

基于蒙特卡罗法的平行流冷凝器的翅片参数优化

运用蒙特卡洛法,在家用空调运行工况下,对平行流冷凝器空气侧的传热和流动性能进行了优化计算,分析了翅片的各种几何参数组合对换热系数和压力损失的影响.得出了影响换热系数的主要因素是翅片高度和百叶窗长度,同时增大两者既可以快速增大换热系数又可以降低压力损失;影响压力损失的主要因素是翅片宽度,因为翅片宽度的微减能带来压力损失的大大将低,但换热系数不受翅片宽度的影响;并同时得出影响换热系数和压力损失的次要影响因素是翅片间距和百叶窗角度.翅片间距减少、百叶窗角度增大均会引起换热系数与压力损失的增大.用这种优化方法得出的结论进行翅片参数组合的平行流冷凝器,可以在满足压力损失需要的情况下大大提高其换热性能.     

空气侧结构对多元微通道平行流冷凝器传热流动性能的影响

建立了多元微通道平行流冷凝器的稳态分布参数模型,与实验对比验证了模型的正确性。利用所建立的模型,研究了翅片高度、翅片间距、百叶窗开窗间距、百叶窗开窗角度变化对多元微通道平行流冷凝器传热和流动性能的影响。结果表明,随着翅片高度的增大,换热量逐渐增大,空气侧压降逐渐减小;随着翅片间距或者百叶窗开窗间距的增大,换热量和空气侧压降都是逐渐减小;随着百叶窗开窗角度的增大,换热量和空气侧压降都是逐渐增大。     

多元平行流冷凝器传热流动性能研究

平行流冷凝器空气侧采用间断型扩展表面的波纹型百叶窗翅片,制冷剂侧采用小水力直径的非圆截面微通道多孔铝制扁管,选用适合于该微尺度强化换热结构的传热和压降关联式,对某规格的平行流冷凝器建立数学模型并在一定工况下进行数值模拟.结果分析表明,制冷剂在非圆截面微通道内的冷凝过程中,表面张力对表面传热系数的强化效果明显;通过改变流程数和各流程管数来改变冷凝过程中的流通截面而达到调整流速的作用,从而可以保持较高的冷凝换热系数和较低的流动压降,与常规换热器相比具有显著的优越性.     

平行流冷凝器百叶窗翅片结构优化

建立平行流冷凝器百叶窗翅片的三维流动和换热模型,并对不同迎面风速下百叶窗翅片的流动和换热性能进行数值模拟,计算结果与试验结果具有较好的一致性,验证计算模型和方法的正确性。在此基础上,建立8种结构形式的百叶窗翅片模型,并对其空气侧的换热和流动过程进行仿真,分析结构形式和排列方式对百叶窗翅片换热量和空气阻力的影响,结果表明:增加开窗区域数能够有效提高翅片的换热性能,增加百叶窗的转向区数目能够有效降低进出口的压降。     

R404A和R410A应用于平行流冷凝器的模拟分析比较

采用分布参数法对平行流冷凝器建立数学模型，对目前广泛使用的制冷剂R134a和低温制冷剂R404A和R410A在平行流冷凝器中的换热和流动性能进行模拟计算和分析比较。分别在相同和不同工况下。比较3种制冷剂的换热系数及压降等换热和流动性能参数。结果表明，在采用平行流冷凝器的汽车空调工况范围内，R410AR404A的流动和传热性能均优于R134a，更适宜用于汽车空调用平行流冷凝器。     

多元平行流冷凝器数值模拟

介绍了多元平行流冷凝器的结构特点和前人的研究成果,对平行流冷凝器的流动和传热特点进行了深入分析,在此基础上运用分布参数法建立了稳态数学模型,对某种规格的平行流冷凝器在一定工况下数值模拟,计算得到不同迎面风速下平行流冷凝器流动换热情况。结果表明,多元平行流冷凝器在冷凝换热时较常规换热器具有显著优越性,迎面风速对冷凝换热的影响存在一个临界范围。     

机房空调用平行流冷凝器的设计及性能测试

针对数据中心全天候空气调节需求,采用平行流冷凝器设计空调样机,在标准焓差法试验室进行性能试验。结果表明:组合式平行流冷凝器采用两进一出流程的布置方式,并以3:1比例分配扁管,冷凝效率高;制冷冷凝器和热管冷凝器间隔3~5 mm进行叠加组合,节省机组空间,优化空气侧换热效率;不同工作模式下,冷凝器均具有较好制冷能力;平行流换热器的换热系数升高与压降增大是相辅相成的,适当增加系统制冷剂循环流量能够增强换热效果。     

家用热泵空调器室外机换热器的流路优化

针对家用热泵空调器用的9.52 mm和7 mm双排室外换热器,在额定制冷制热工况下,利用仿真分析的方法研究流路数对换热器性能的影响,对9.52 mm换热器的流路的进一步优化,得到制冷制热综合性能更优的流路布置方式,并在整机上进行试验验证。结果表明,制冷剂侧压降对冷凝器和蒸发器的换热都有较大影响,特别是对较小管径的换热器;由于蒸发器中制冷剂侧压降较大,热泵空调器室外机用的换热器作冷凝器时对应的最佳流路数少于作蒸发器时的;适当增加过冷管数会进一步提高热泵空调器室外机换热器的综合换热能力;试验结果与仿真结果趋势大致相同。     

基于表面及迎风面改性的锯齿翅片强化传热研究

为了在提高锯齿型翅片散热器换热性能的同时尽量控制压降损失的增大，本文采用数值模拟的方法对锯齿型翅片性能进行研究，分析了不同翅片表面、迎风面结构及尺寸参数对传热Nu、流动压降损失Δp以及综合性能η的影响规律。结果表明：无论翅片表面设置何种形状凹槽和凸起对传热的影响差异较小，但圆形凹槽和凸起对压降损失的增加最少，综合性能最优。在翅片表面设置圆形凹槽和凸起的基础上继续将翅片两端迎风面改为圆形，可使传热提高的同时减小压降损失，综合性能最多提高12.2%。圆形凹槽和凸起尺寸R=0.15 mm时，传热和压降损失的平衡达到最佳，与传统锯齿型翅片相比，平均压降损失基本不变，传热和综合性能平均提高均为8.7%。     

Decorrelation-based blood flow velocity estimation: effect of spread of flow velocity,linear flow velocity gradients,and parabolic flow

In recent years, a new method to measure transverse blood flow, based on the decorrelation of the radio frequency (RF) signals has been developed. In this paper, we investigated the influence of nonuniform flow on the velocity estimation. The decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter are studied by means of computer modeling. Blood was simulated as a collection of randomly located point scatterers; moving this scattering medium transversally across the acoustical beam represented flow. First-order statistics were evaluated, and the signal-to-noise ratio from the signals were measured. The correlation coefficient method was used to present the results. Three velocity profiles were simulated: random spread of blood-flow velocity, linear blood-flow velocity gradient, and parabolic blood-flow. Radio frequency and envelope signals were used to calculate the decorrelation pattern. The results were compared to the mean decorrelation pattern for plug blood-flow. The RF signals decorrelation patterns were in good agreement with those obtained for plug blood flow. Envelope decorrelation patterns show a close agreement with the one for plug blood flow. For axial blood flow, there is a discrepancy between decorrelation patterns. The results presented here suggest that the decorrelation properties of an IVUS array catheter for measuring quantitative transverse blood flow probably will not be affected by different transverse blood-flow conditions     

流量测量临界流文丘里喷嘴的进展

简介颁布国际标准ISO9300《临界流文丘里喷嘴测量气体流量》(1990年)，十余年来国际上对该流量计的研究情况。主要在以下几方面有显著的进展：雷诺数使用范围的拓宽；流量方程中系数的研究；小型音速喷嘴的开发应用；小型音速喷嘴组合方法的研究；绝对测量法的探索等。国际标准化组织正在为修订ISO9300进行准备工作。     

流式细胞仪样品流速及聚焦流测量方法研究

为提高流式细胞仪的探测分辨率和数据检测的稳定性,需要精确控制样品流速,并分析样品流速和鞘液流速对样品聚焦流的影响,可通过样品聚焦流直径和样品聚焦流在流动室流道中的相对位置来评价样品的聚焦状况。利用蠕动泵运动特点,设计了一种平均流量称重法测量样品流速的方法,并与微流量传感器测量结果作比较;采用最小二乘法线性拟合蠕动泵的控制电压和样品流速之间的函数关系,并采用显微成像法直接测量和分析样品流速和鞘液流速对样品聚焦流直径、偏离流动室流道中心线的距离的影响。实验结果显示,采用平均流量称重法与微流量传感器测得的样品流速的线性相关系数高达0.982 8;蠕动泵的样品流速与其控制电压的线性相关系数高于0.99,说明利用该线性关系可以实现样品流速的精确控制;采用的显微成像法能快速方便地测得样品聚焦流的直径及位置,为流式细胞仪样品流速、鞘液流速的调控以及液流器件组装精度的测试提供了指导方法。     

Secondary flow in non-isothermal viscoelastic parallel-plate flow

The non-isothermal, parallel-plate flow of a viscoelastic fluid is investigated. Using the singular perturbation method the problem for the stream function is reduced to a non-homogeneous boundary-value problem for the biharmonic operator in an infinite strip. An exact solution is then obtained using Fourier integral transforms. Our analysis shows the existence of thermally induced recirculating eddies, even when inertia is neglected.     

流量控制电磁阀的小流量特性分析

介绍可调无级输出流量控制电磁阀在小流量输出区域的输出原理与特性。通过改变小流量区域的流道几何结构,改变电磁阀小流量区域的流量性能。     

Stability of Couette flow and Dean flow in micropolar fluids

In this article, we have investigated the onset of instability in the flow of the micropolar fluid between two rotating concentric cylinders and the flow in a curved channel, under small gap approximation. The solution of the eigenvalue problems, governing the onset of instability, are obtained by using the Shooting Method. It is seen that the flows are stable when the micropolar elements are present in the fluid.     

Nonsteady flow of a vapor-drop flow in a heated channel

Flow of a vapor-drop mixture in a heated channel is studied under steady and non-steady conditions using a model which considers direct thermal interaction of drops with the heating surface.Translated from Inzhen-erno-Fizicheskii Zhurnal, Vol. 61, No. 6, pp. 939–946, December, 1991.     

Measurement of flow in supercritical flow regime using cutthroat flumes

Cutthroat flume is commonly used for measurement of subcritical flow in open channel because of its simplicity and ease of construction. No experimental data is available in literature for measurement of flow in supercritical regime using cutthroat flume. The present paper finds the feasibility of cutthroat flume as a measurement device for flow in supercritical regime. Experimental data are generated to develop the relation between discharge and observed head at a specified location on upstream of throat section. Regression analysis for discharge and head indicated a good correlation. Based on all the experimental data generated, a relationship between discharge and head is proposed.     

Optimal tracking control of flow velocity in a one-dimensional magnetohydrodynamic flow

This article considers a dynamic optimization problem arising in a one-dimensional magnetohydrodynamic flow, which can be modelled by coupled partial differential equations, where the external control input (external induction of magnetic field) takes a multiplicative effect on the system states (momentum and magnetic components). The aim is to drive the flow velocity to within close proximity of a desired target of flow velocity at the pre-indicated terminal time. First, the Galerkin method is utilized to reduce the original dynamic optimization problem to a lower finite-dimensional dynamic optimization problem governed by a set of ordinary differential equations. Then the control parameterization method is employed to parameterize the finite-dimensional optimization problem and thus obtain an approximate optimal parameter selection problem, which can be solved using gradient-based optimization techniques, such as sequential quadratic programming. The exact gradients of the cost functional with respect to the decision parameters, which are the key advantages of this approach, are computed using the analytical equations. Finally, numerical examples are illustrated to verify the effectiveness of the proposed method. The novel scheme of this article is to develop an effective computational optimal control method for realizing the optimal tracking control of flow velocity in a one-dimensional magnetohydrodynamic flow.