共查询到20条相似文献,搜索用时 807 毫秒
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通过以液氨为制冷工质的开式喷雾冷却系统,在相同实验条件下研究了二极管激光器(DL)热沉喷雾表面分别为光滑表面、均匀密排微孔、深孔和多孔表面结构时的冷却效果,实验结果表明:在热流密度达到300W/cm2时,冷却表面温度均保持在28℃以内,适用于高热流密度下的DL热管理问题;喷雾表面均布微结构能显著强化喷雾冷却性能,当采用均匀密排多孔表面时,散热功率达511.5 W/cm2,对流传热系数为346 701.1W/(m2·℃),传热系数较光滑表面时提高了83.9%。 相似文献
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靠近燃气透平叶片顶端或根部的叶片表面的热负荷强烈地受到那里的二次流的影响。叶片进口边缘首先与高温燃气相接触,因此,端壁对叶片进口边缘传热的影响值得进行研究。Schmidt和Wenner的文章提供了早期对圆柱体传热的研究结果。Kestin和Maeder的工作充分证明了自由流的湍流度对传热系数有很大的影响。Johnston在文献中对二次流给出了甚为清楚的说明。本文用一个在横向流动中的圆柱体,并在圆柱体上安置一块平板,来模化靠近端面的透平叶片进口边缘处的流动。 相似文献
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根据递推法测定滴状冷凝传热系数原理,搭建了滴状冷凝传热系数测定试验台,并对聚四氟乙烯材料表面的传热特性进行了试验测定,分析了影响滴状冷凝传热系数的因素。 相似文献
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针对两种不同时序位置热斑在大冷气量燃气涡轮通道内的迁移对涡轮气动性能、叶片表面热负荷和气动激振力的影响开展了数值模拟研究,对比分析了涡轮效率、叶片表面温度分布、出口总温分布、非定常激振力时域/频域特征等,对进口热斑时序位置的选取方式进行了讨论。结果表明对于气冷燃气涡轮,与热斑正对通道中心相比,热斑正对导叶前缘可以有效降低动叶热负荷、改善第二级导叶温度分布均匀性、抑制效率下降、降低非定常激振力水平,有利于改善燃气涡轮气动热力性能。研究结果为大冷气量双级燃气涡轮热斑时序位置选取提供了依据。 相似文献
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原表面回热器换热阻力特性试验研究 总被引:1,自引:0,他引:1
本文对研制加工的适用于 100 kW 微型燃气轮机的 CW(Cross Wavy) 原表面回热器进行了试验研究,通过对两侧流体进、出口温度、压力等的测量,重点分析了燃气流量、入口温度及空气进口压力变化对换热阻力的影响,得出了在变工况下回热器的流动与换热性能规律,结果表明:所研制的 CW 原表面回热器空、燃气两侧换热均匀,提高了换热效率,两侧压降都有不同程度降低,并得出了有工程应用价值的 Nu-Re 及 f-RE 准则关系式,可为原表面回热器的设计制造提供参考. 相似文献
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A model is presented to simulate the cooling processes during tumor cryosurgery with different kinds of flows through the cryoprobe. The heat flux between the cryoprobe wall and the tumor, the heat transfer coefficient under different inflow conditions are obtained numerically. The impact of the inlet mass flow rate, gas volume fraction on these parameters is investigated. It is found that the heat transfer coefficient decreased significantly when inflow changed from two-phase annular flow to droplet flow, and to gas flow. The inlet gas volume fraction and flow velocity only significantly affect the freezing ability of the probe when the inflow is gas or in droplet phase. Simulation of the tumor temperature profiles under different flow conditions show that the heat transfer coefficient is a crucial parameter in temperature prediction during cryosurgery. Results indicate that when the cryoprobe wall is assumed at a constant temperature conventionally, the cooling effect could be overestimated. It would be more reasonable to use the constant wall heat transfer coefficient to simulate the cooling progress under a specific flow. 相似文献
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S. P. Aktershev 《Journal of Engineering Thermophysics》2009,18(2):138-150
Heat transfer in a viscous liquid film moving under the action of gravity and a gas flow on a substrate with a locally heated
rectangular area is investigated. The heat exchange coefficient is given on the liquid-gas surface; the heat flux to the liquid
is given on the heated area; the substrate surface outside the heated area is heat-insulated. An analytical solution in a
form of a convergent series is obtained for the liquid temperature distribution in the film. The influence of the dimensionless
criteria on the obtained solution is analyzed. The effect of heat flux inhomogeneity on the temperature distribution is considered. 相似文献
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Experimental and analytical investigation was carried out to show the effect of surface tension on the heat transfer coefficient of gas flow inside micropipe heat exchangers during the condensation process. An empirical correlation was formulated for the coefficient of the convective heat transfer. A comprehensive comparison between the experimental results with published correlations in the literature and that obtained by the developed correlation was conducted. The results showed that the predicted heat transfer coefficient of the proposed correlation was closer to the experimental results than any other correlation, a finding related to the consideration of the surface tension. 相似文献
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1前言高温风洞的温度高达1700℃,流速达0.9马赫数。为了测量风洞中气流温度分布的均匀性,通常采用铂铑30-铂铑10热电偶温度传感器,但是它只能采用逐点移测法,因此它不可能在同一时刻将一条检测线上气流温度测量出来。同时在高温气流测量时,热电偶接点由... 相似文献
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Transient heat transfer coefficients for helium gas flowing over a horizontal plate (ribbon) were measured under wide experimental conditions. The platinum plate with a thickness of 0.1 mm was used as the test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0 exp(t/τ). The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 290 to 353 K, and the periods of heat generation rate, τ, ranged from 50 ms to 17 s. The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlation for transient heat transfer was also obtained based on the experimental data. 相似文献
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N. N. Simakov 《Technical Physics》2016,61(9):1312-1318
A numerical experiment on the simulation of heat transfer from a sphere to a gas flow in a cylindrical channel in the Stokes and transient flow regimes has been described. Radial and axial profiles of the gas temperature and the dependences of drag coefficient Cd of the body and Nusselt number Nu on Reynolds number Re have been calculated and analyzed. The problem of the influence of the early drag crisis for a sphere on its heat transfer to the gas flow has been considered. The estimation of this phenomenon has shown that the early drag crisis of the sphere in a strongly turbulent flow causes a reduction in heat transfer from the sphere to the gas by three to six times (in approximately the same proportion as for its drag coefficient). 相似文献
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A. A. Pikulev 《Technical Physics》2003,48(6):693-696
Heat exchange between a linear heat source and a gas flow is studied theoretically. The coefficient of source-to-gas heat
transfer is found as a function of the gas velocity in the limit of zero temperature drop. It is shown that the heat-transfer
coefficient depends linearly on the gas flow velocity for Peclet numbers 0.1–1.0. 相似文献
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Boiling heat transfer in a refrigerant R 21 flow in a microchannel heat sink is studied. A stainless steel heat sink with
a length of 120 mm contains ten microchannels with a size of 640×2050 μm at cross-section with a wall roughness of 10 μm.
The local heat-transfer coefficient distribution along the heat sink length is obtained. The ranges of parameters are: mass
flow from 68 to 172 kg/m2s, heat fluxes from 16 to 152 kW/m2, and vapor quality from 0 to 1. The maximum values of the heat transfer coefficient are observed at the inlet of microchannels.
The heat transfer coefficients decrease substantially along the length of channels under high heat flux conditions and, on
the contrary, change insignificantly under low heat flux condition. A comparison with the well-known models of flow boiling
heat transfer is performed and the range of applicability is defined. 相似文献