共查询到20条相似文献，搜索用时 163 毫秒
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为预测冻土路基安装热管后路基温度场的变化情况,对热管耦合冻土路基问题开展数值传热研究是一种比纯实验方法更经济可行的方法。根据是否考虑热管内部热阻及建立的热管耦合冻土路基相变传热模型,热管耦合冻土路基的数值传热算法可基本分为两类。针对这两类基本算法进行了对比分析。结果表明：通过忽略热管内部热阻,利用耦合边界处的等价第三类边界条件及根据实际地温气温条件建立的相变传热模型来研究热管耦合冻土路基问题在工程上更为可行。 相似文献
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以降低能耗为目标,以空调用热管式换热器为对象,对其几何参数、传热性能的分析,建立了应用于空调系统的热管换热器的设计数学模型.通过热管换热器的初步设计,并结合VB语言编程对热管进行的计算分析得出热管的结构、工况等对传热性能的影响,改善热管换热器的设计,从而提高传热性能. 相似文献
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通过利用热管和换热器,建立矿井回风余热回收系统。该系统以矿井通风技术和传热技术为理论基础,分别从经济性与技术性两个方面对其可行性做出论证;通过热管设计计算和换热器设计计算,最终求得分离式热管换热器所需热管数目及其自身级数,同时对矿井回风余热回收系统的布置进行了简单的介绍。 相似文献
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纳米流体脉动热管的性能实验研究 总被引：2，自引：0，他引：2
建立了脉动热管的可视化实验台,对以体积分数为1%的TiO2/H2O和CuO/H2O纳米流体及基流体为工质,55％充液率的脉动热管性能进行了实验研究。结果表明,工质静止时,纳米颗粒在脉动热管中会发生沉淀,但工质的运动能够使沉淀纳米颗粒再次悬浮,随着温度的升高,纳米颗粒悬浮性稳定减弱;与基流体工质相比,纳米流体脉动热管的最小启动功率低,启动时间较短,工作温度低,传热热阻小,温度波动振幅小、频率高;纳米流体能大幅提高脉动热管的传热性能,工作温度为110℃时,蒸馏水、TiO2/H2O及CuO/H2O脉动热管的传热热阻分别为0.23℃/W,0.11℃/W和0.13℃/W;两种纳米流体脉动热管的传热性能接近。 相似文献
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对低温重力热管的传热性能进行研究,采用的热管长800mm,外径15mm,管材为不锈钢,工质为水,充液率为0.5,冷凝段与蒸发段长度比为7：1。实验中主要研究了供水温度、供水流量、热管倾角的变化对热管性能的影响,为热管的近一步应用提供可靠的理论和实验依据。 相似文献
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微小型脉动热管的传热性能实验研究 总被引：2，自引：0，他引：2
本文针对毛细管结构变化会影响其性能这一问题，对毛细管截面为正方形和正三角形，水力直径为1mm左右的微小型脉动热管的传热性能进行了实验研究。结果表明，角管脉动热管底加热时的性能明显优于顶加热；正方形截面角管水平放置也能够运行；三角形截面脉动热管的热阻比正方形截面脉动热管的热阻更低。脉动热管在水力直径为1.5mm时比1mm时的性能要好。 相似文献
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关于外导流折流杆闭冷器首次在600 MW超临界燃煤发电机组行运情况的分析总结,该技术闭冷器具有换热效高、流动阻力小、结构紧凑、防振性强、不易结垢等优点,具重要应用价值。 相似文献
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The present study concentrates to make a complete thermal analysis on a rectangular fin with its primary surface by taking into consideration of radiation heat exchange with the surrounding along with the convective mode of heat transfer. The one side of the primary surface is heated by a fluid with high temperature which may be required to dissipate heat quickly by a fin array system. To analyze an actual case study, the thermal conductivity of the fin material and convective heat transfer coefficient over the surface are treated as a variable and they are as a function of the local fin surface temperature. With the aforementioned condition, the energy equations for both the fin and primary surface become nonlinear. The decomposition method is suggested to solve these highly nonlinear equations to obtain a closed form temperature distribution. The result of temperature distribution determined by the present analysis is compared with that of the numerical values. With the adaptation of the simplified case, the present method is also compared with the exactly closed form results. From both of these comparisons, an exact matching of results is found. The fin performances, namely, fin efficiency, surface efficiency and augmentation factor are evaluated for a wide range of thermogeometric parameters. 相似文献
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Andrew Sobczyk 《Journal of The Franklin Institute》1948,246(3):187-213
In a servomechanism using a two-phase alternating current control motor, a 90° difference is required in the phases of the carrier-frequency voltages applied to the fixed and control windings. This part describes and compares various methods of obtaining the phase difference.The question of the possibility of a phase-shifting proportional-derivative parallel “T” is answered in the negative, by the result that in any parallel “T” transfer characteristic, if the quadratic factor in the numerator is of the proportional-derivative form at the correct resonant frequency, the amount of phase shift which may be obtained from the remaining portion of the transfer characteristic is less than are tan , where n is twice the carrier frequency divided by notch width. Thus for values of n high enough to have an appreciable stabilizing effect, the maximum obtainable intrinsic phase shift is negligible.In order to obtain a large phase shift it is necessary to add either a series input or a load impedance to the parallel “T,” or to use a phase-shifting network preceding or following the parallel “T.” Formulae and design charts are given for determination of the values of the components of phase lag networks.The method of calculation of tolerance requirements on the components, in terms of allowable deviation from the correct phase, is illustrated by an example of a phase lag network used in conjunction with a bridge “T” proportional-derivative network. 相似文献
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Boundary control to stabilize a system of coupled linear plant and reaction-diffusion process is considered. Backstepping transformations with a kernel function and a vector-valued function are introduced to design control laws. For the situation without heat resource, the kernel function and the vector-valued function of the transformation are obtained, and an explicit control law is established, and simulation results are presented through figures. For the general situation with heat resource, the existence of the kernel and the vector-valued function of the transformations is shown, and an control law is derived. Stability of the closed loops is achieved for both the situations. 相似文献
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锅炉排烟温度过高会造成热损失,增设低压省煤器对于降低电厂排烟温度,提高电厂热经济性,保护空气预热器的安全运行具有重要意义。H型鳍片管是一种广泛应用于低压省煤器的换热元件。本文以一种H型鳍片管为例,通过数值模拟对其传热过程进行了分析,获得了H型鳍片管翅片侧表面传热系数和流动阻力随烟气流速和鳍片节距的变化规律。 相似文献
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微槽群相变式微冷系统的换热特性实验 总被引：2，自引：0，他引：2
本文对用于大功率电子器件冷却的微槽群相变微冷系统的冷却工质液位高度、蒸发元件表面微槽群尺寸及横向微槽的采用等因素对整个微冷系统散热性能的影响进行了实验研究。在其它条件保持不变的情况下，对液位高度变化、微槽群尺寸及横向微槽的采用对微冷系统散热影响进行了讨论，并确定了该微冷系统的最佳液位参数和最佳尺寸参数。 相似文献
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Stephen B. Margolis 《Journal of The Franklin Institute》1979,307(1):39-58
A multidimensional, time-dependent model of the thermocline degradation in a packed bed thermal storage tank is presented. The formulation includes the effects of finite tank length, multidimensional thermal conduction, heat transfer between the fluid and solid portions of the bed, and heat losses across all tank surfaces. The technique used to solve the coupled pair of parabolic partial differential equations describing the degradation of the thermocline is based on a vectorized separation of variables approach. Assuming cylindrical geometry, the analysis leads to separate eigenvalue problems for the radial, angular, and axial spatial dependencies of the fluid and solid temperatures in the bed. The eigenvalues are readily calculated and the corresponding eigenfunctions are shown to form a complete set of spatial basis functions for the solution space. The method and results are illustrated by several examples. 相似文献
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This paper investigates the steady laminar flow in a porous medium of an incompressible viscous fluid impinging on a permeable stretching surface with heat generation. The resulting system of coupled non-linear ordinary differential equations is solved analytically via homotopy analysis method (HAM). Analytical results are presented for the wall shear stress and the wall heat transfer coefficient as well as the velocity and temperature profiles for some values of governing parameters such as Prandtl number, stretching parameter, porosity parameter and the heat generation/absorption parameter. Appropriate auxiliary parameter, ?, is determined by minimizing Euclidean norm of residual. The convergence of the obtained series solutions is explicitly studied. 相似文献
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Here, we introduce a solution to low stability of a two-phase slug flow with a chemical reaction occurring at the phase interface in a microfluidic reactor where substantial merging of individual reacting slugs results in the loss of uniformity of the flow. We create a three-phase slug flow by introducing a third fluid phase into the originally two-phase liquid-liquid slug flow, which generates small two-phase liquid slugs separated by gas phase. Introduction of the third phase into our system efficiently prevents merging of slugs and provides beneficial reaction conditions, such as uniform flow pattern along the whole reaction capillary, interfacial area with good reproducibility, and intensive water-oil interface renewal. We tested the three-phase flow on an enzyme hydrolysis of soybean oil and compared the reaction conversion with those from unstable two-phase slug flows. We experimentally confirmed that the three-phase slug flow arrangement provides conversions and pressure drops comparable or even better with two-phase liquid-liquid arrangements. 相似文献