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1.
Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.  相似文献   

2.
The two-phase How patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the How pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R-I42b was achieved.  相似文献   

3.
Turbulent heat transfer characteristics in swirling flows downstream of an abrupt pipe expansion with a diameter ratio of 0.5 are predicted by full Reynolds stress model. The uniform heat flux condition is imposed on the downstream wall. The flows with weak and strong swirls as well as without swirl are computed. The governing differential equations are discretized by finite volume method. Results show that the Reynolds stress model predicts accurately the maximum local Nusselt number for the case with strong swirl, but that the effects of swirl are not fully accounted for the case with weak swirl.  相似文献   

4.
This article reviews the theoretical background of the measurement of pulsating flow using orifices as flow to pressure transducers, providing a synopsis of work done in this field. Special attention is paid to the temporal inertia and the applicability of expressions thereof given in the literature. Other factors influencing the measurement, such as changing flow profiles and the effect of connection tubes between the pressure sensor and the orifice are discussed. An experiment was performed to investigate the applicability of an equation taking reverse flow and temporal inertia into account for the measurement of pulsating flow with relative pulsation amplitudes around 1 and frequencies up to 50 Hz. It was found that the suggested equation may give tolerable results if the ratio of the pulsating part of the velocity to the angular frequency times orifice diameter is not too high. For high ratios, however, the results could not be explained by the suggested equation.  相似文献   

5.
A small-scale loop heat pipe (LHP) with polypropylene wick was fabricated and tested for investigation of its thermal performance. The container and tubing of the system were made of stainless steel and several working fluids were tested including methanol, ethanol, and acetone. The heating area was 35 mm×35 mm and nine axial grooves were provided in the evaporator to provide vapor passages. The pore size of the polypropylene wick inside the evaporator was varied from 0.5 μm to 25 μm. The inner diameter of liquid and vapor transport lines were 2.0 mm and 4.0 mm, respectively and the length of which were 0.5 m. The size of condenser was 40 mm (W) ×50 mm (L) in which ten coolant paths were provided. Start-up characteristics as well as steady-state performance was analyzed and discussed. The minimum thermal load of 10W (0.8W/cm2) and maximum thermal load of 80 W (6.5W/cm2) were achieved using methanol as working fluid with the condenser temperature of 20°C with horizontal position.  相似文献   

6.
In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40 vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90°. the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.  相似文献   

7.
Journal of Mechanical Science and Technology - Operational limits are critical in the continuous functioning of a pulsating heat pipe (PHP). A computational fluid dynamics study was conducted to...  相似文献   

8.
在已设计的翅片热板散热器基础上进行了传热性能实验,对于充装不同工质、工质充装量、翅片热板散热器的工作方式等因素都进行了较深入的传热测试,分析这些因素对翅片热板散热器传热性能的影响.同时对翅片热板散热器的瞬态和稳态传热性能也进行了实验测试,分析了瞬态、稳态表面温度变化曲线,并进行了传热性能比较分析,讨论了工质充装量、倾斜角度等对翅片热板散热器传热性能的影响.  相似文献   

9.
Unsteady separated flow around a square cylinder is simulated by using vortex tracing method to investigate the wake flow control by a splitter plate attached to the base of a bluff body. The numerical method is evaluated with selected numerical parameters for the case without the splitter plate. Then the method is applied to computations for different splitter plate lengths. Instantaneous flow patterns are scrutinized to see how the splitter plate affects the vortex formation behind the body and the downstream shedding. It is confirmed that the drag and the frequency are significantly reduced by the splitter plate, suppressing vortex shedding in the wake.  相似文献   

10.
Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.  相似文献   

11.
The isothermal characteristics of a rectangular parallelepiped sodium heat pipe were investigated for high-temperature applications. The heat pipes was made of stainless steel of which the dimension was 140 m(L) ×95m(W) ×46m(H) and the thickness of the container was 5 mm. Both inner surfaces of evaporator and condenser were covered with screen meshes to help spread the liquid state working fluid. To provide additional path for the working fluid, a lattice structure covered with screen mesh wick was inserted in the heat pipe. The bottom surface of the heat pipe was heated by an electric heater and the top surface was cooled by circulating coolant. The concern in this study was to enhance the temperature uniformity at the bottom surface of the heat pipe while an uneven heat source up to 900 W was in contact. The temperature distribution over the bottom surface was monitored at more than twenty six locations. It was found that the operating performance of the sodium heat pipe was critically affected by the inner wall temperature of the condenser region where the working fluid may be changed to a solid phase unless the temperature was higher than its melting point. The maximum temperature difference across the bottom surface was observed to be 114°C for 850 W thermal load and 100°C coolant inlet temperature. The effects of fill charge ratio, coolant inlet temperature and operating temperature on thermal performance of heat pipe were analyzed and discussed.  相似文献   

12.
Concentric annular heat pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4 mm in outer diameter and 200 mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was 2.3°C while that of the copper block of the same outer dimension was 5.9°C. The minimum thermal resistance of the CAHP was measured to be 0.04°C/W. In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag.  相似文献   

13.
以计算流体动力学(CFD)的多相流数值计算理论及方法为基础,对处于复杂工况的T型管连接装置腔内流场进行了数值模拟分析,采用标准湍流模型和标准壁面函数对T型管接头内部流场进行了数值模拟;同时以混合模型求得的解作为用欧拉多相流模型的初始条件,采用欧拉多相湍流模型进行了对T型管接头内部流场数值计算.最后对两种模型计算得到的T型管接头内部流场的压力场、速度场及气相的体积分数(VOF)分布进行了对比分析.计算结果将指导的结构优化设计及失效分析.  相似文献   

14.
The unsteady Couette flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.  相似文献   

15.
Effects of axial temperature gradient on heat transfer, momentum transfer and energy conversion mechanisms within a closed cylinder-piston apparatus are analyzed. Assuming that the gas density change is small, the first-order and steady second-order solutions of continuity, momentum and energy equations are obtained. The solutions show that there exists a steady circulating flow and the magnitude of the steady axial velocity increases as the axial temperature gradient increases. There exists not only an oscillating component of heat flux between the gas and the wall, but also a steady component whose direction depends on axial temperature gradient. It is shown that heat is pumped from the wall near the piston to the wall near closed-end for negative axial temperature gradient. Heat transfer relation for both oscillating pressure and oscillating flow conditions is proposed.  相似文献   

16.
采用有限元法,应用ANSYS软件的热分析功能对翅片热板散热器的传热性能进行了数值模拟,并计算出该散热器表面的瞬态温度变化曲线,与实验测试结果吻合得较好.最后的研究结果表明:所研制的新型功率电子元器件翅片热板散热器散热性能良好,具有良好的启动性能和等温性能.  相似文献   

17.
An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical wall, the average heat transfer coefficient in the cave-shaped cavity presented 10-15% lower values due to the fact that the average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about Ψcrit= 3-7%, Ψcrit=0.5-1.3%, respectively, in the range of heat fluxq” = 5-90kW/2  相似文献   

18.
在系统测试性分析领域,信息流模型是系统建模方面的主要方法之一,本文通过一个示例,给出了建立诊断信息流模型的整体框架。文章首先介绍了信息流模型的提出背景和国内外应用研究现状,然后在叙述模型的基本要素和诊断推理的相关概念的基础上.对一示例推理图进行了建模以及模型处理,最后提出了在国内研究该模型的必要性。  相似文献   

19.
The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important effects on the velocity distribution as well as the heat transfer. On leave from: Department of Engineering Math. and physics, Fac. of Engineering, El-Fayoum University, El-Fayoum, Egypt.  相似文献   

20.
Numerical modeling of the heat transfer and molecular mixing in an electrical furnace designed for the spectroscopic study of hydrogen/alkali-metal-vapor mixtures is described. The gases enter the furnace through three concentric tubes, the inner two of which contain the test gases while the outer contains a guard gas to protect the windows. The inner tubes terminate prior to the measurement section to allow the gases to mix. Heating is accomplished through contact with the wall of the outer tube. An implicit time-marching procedure including a preconditioning method is used to compute the coupled gas flows. The results show that optimum flow speeds occur at a Reynolds number of order ten. Higher speeds do not allow adequate heating or mixing and can become unsteady, while lower speeds allow considerable back diffusion in the concentric tubes.  相似文献   

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