共查询到20条相似文献,搜索用时 250 毫秒
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本文从节能观点简述了研制与推广应用多孔质换热表面的重要意义,就高温烧结法加工管内多孔质表面强化低温液体(液氮)沸腾传热进行了研究。实验结果表明,高温烧结管内多孔质表面的传热性能优于电镀多孔质表面与低肋(细螺纹)表面,其沸腾传热温差一般可降为光滑平表面的十分之一立右。根据实验数据,并用动力学型论模型分析讨论了不同的烧结金属材料及其粉末的平均颗粒直径,烧结层厚度等因素对传热性能的影响。运用因次分析法,由实验数据拟合出传热计算的关联式,可在一定范围内估计多孔质表面的传热性能。 相似文献
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多孔材料有效导热系数的实验和模型研究 总被引:1,自引:0,他引:1
《中国测试》2016,(5):124-130
为研究多孔材料的传热机理,采用实验测量验证理论模型的方式,利用瞬态热线法测量283~333 K范围内多孔保温材料挤塑式聚苯乙烯(XPS)的有效导热系数,并根据多孔材料各组成部分导热系数、密度以及结构特点,使用5种基本模型包括串联模型、并联模型、Kopelman isotropic模型、Maxwell-Eucken模型以及EMT模型,分别对其有效导热系数进行计算。结果证明:对于XPS,Kopelman iostropic和Maxwell-Eucken模型更具适用性,其计算结果与实验结果最大偏差均小于0.5%,为进一步开展多孔材料的有效导热系数模型和实验研究提供理论依据。 相似文献
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根据目前缺乏对多孔介质局部非热平衡的自然对流传热实验研究现象,设计了对竖直管外蓄冰过程中多孔介质局部自然对流传热的实验装置,并对实验装置进行了验证。结果也证实了本实验装置的可行性及实验数据的准确性。 相似文献
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相变储能材料(PCM)具有储热密度大、储/放热过程几乎恒温性等优点,是解决电子器件狭小空间下高热流密度问题的理想方案,但相变材料本身的导热系数较低、传热效率差等特性却限制了其应用范围。针对上述难题,以石蜡作为相变材料,通过3D打印制备多孔铝骨架,再采用水浴灌注法将石蜡灌注到多孔铝骨架中,制备出多孔铝骨架/复合相变材料(AS-PCM)。通过实验探究了95%、85%、75%3种孔隙率的温控性能。实验结果表明,添加多孔铝骨架可增强PCM的热传递,从而降低热源温度。在较大的功率下,AS-PCM对传热的改善更为明显。熔化完成前,低孔隙率AS-PCM热沉的底部温度和温度梯度更低,使用多孔铝骨架代替泡沫金属,为提高PCMs的导热性能提供了了新的多孔金属基体。 相似文献
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本文对我们研制的一种复合多孔表面——烧结多孔U型翅片螺纹管表面,垂直置于液氮孔中,在常压下对其沸腾传热的性能进行了实验研究。结果表明,该复合多孔强化表面的沸腾传热系数是U型翅片螺纹管表面的3~6倍;是光滑表面的6~10倍。本文还拟合出该复合多孔强化传热表面的无因次沸腾传热准则关系式,拟合误差在±15%之内,具有实用意义。 相似文献
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《低温学》1986,26(2):114-116
This Paper shows that porous plug material can serve as a control device during liquid transfer. The application of heat flux directly relates to the temperature and pressure gradient across the plug in the flow regime 1. For a given porous material an empirical relation exists that predicts the first critical state which is the upper limit for low pressure drop liquid transfer. Thus, the porous plug can serve a dual purpose for liquid helium transfer in space: the plug can serve as a phase separator during zero gravity storage: and the plug can serve as a low pressure drop control device during liquid transfer. 相似文献
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Menghao Qin Rafik Belarbi Abdelkarim Aït-Mokhtar Lars-Olof Nilsson 《Journal of Materials Science》2008,43(10):3655-3663
The paper presents a mathematical model for calculating the nonisothermal moisture transfer in porous building materials.
The simultaneous heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as principal driving
potentials. The coupled equations were solved by a numerical method. An experimental methodology for determining the temperature
gradient coefficient for building materials was also proposed. Both the moisture diffusion coefficient and the temperature
gradient coefficient for building material were experimentally evaluated. Using the measured moisture transport coefficients,
the temperature and vapor content distribution inside building materials were predicted by the new model. The results were
compared with experimental data. A good agreement was obtained. 相似文献
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Baili Zhang Yong Zhao 《International journal for numerical methods in engineering》2001,50(11):2443-2457
An upwind characteristic‐based finite volume method on unstructured grids is employed for numerical simulation of incompressible laminar flow and forced convection heat transfer in 2D channels containing simultaneously fluid layers and fluid‐saturated porous layers. Hydrodynamic and heat transfer results are reported for two configurations: the first one is a backward‐facing step channel with a porous block inserted behind the step, and the second one is a partially porous channel with discrete heat sources on the bottom wall. The effects of Darcy numbers on heat transfer augmentation and pressure loss were investigated for low Reynolds laminar flows. The results demonstrate the accuracy and robustness of the numerical scheme proposed, and suggest that partially porous insertion in a channel can significantly improve heat transfer performance with affordable pressure loss. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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泡沫金属是一种具有良好传热性能的多孔材料,将泡沫金属作为吸液芯应用于热管中有望提高热管的工作性能。研制了泡沫金属芯钠热管,并实验研究和对比分析了泡沫金属芯钠热管与无芯钠热管在不同加热温度下的启动性能和均温性能。结果表明,泡沫金属芯钠热管完全启动时所需的加热温度低于无芯钠热管,且在相同加热温度下泡沫金属芯的启动时间较短;随着加热温度的增加,钠热管的启动时间缩短,轴向温度分布均匀性越好;泡沫金属芯钠热管的启动性能和均温性能均优于无芯钠热管。实验研究初步证明了采用泡沫金属作为高温热管吸液芯的优越性。
相似文献15.
CFD simulation of coupled heat and mass transfer through porous foods during vacuum cooling process 总被引:8,自引:0,他引:8
A numerical simulation by using a computational fluid dynamics (CFD) code is carried out to predict heat and mass transfer during vacuum cooling of porous foods on the basis of mathematical models of unsteady heat and mass transfer. The simulations allow the simultaneous prediction of temperature distribution, weight loss and moisture content of the meats at low saturation pressure throughout the chilling process. The simulations are also capable of accounting for the effects of the dependent variables such as pressure, temperature, density and water content, thermal shrinkage, and anisotropy of the food. The model is verified by vacuum cooling of cooked meats with cylindrical shape within an experimental vacuum cooler. A data file for pressure history was created from the experimental pressure values, which were applied in the simulations as the boundary condition of the surface temperature. 相似文献
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采用多次真空灌注方法将石蜡吸附到多孔的泡沫石墨中,制备出了泡沫石墨/石蜡复合相变储热材料。利用Hot Disk热常数分析仪和差示扫描量热分析(DSC)对该复合材料的热性能进行了测试,结果表明,石蜡充分吸附到泡沫石墨的蜂窝状微孔中,泡沫石墨的填充极大地强化了相变材料的导热能力。研究了将该复合材料用作墙体围护结构时的隔热和调温性能,并与普通轻质墙体材料作围护结构进行了对比,结果表明,复合相变储热材料能够有效地利用昼夜温差进行储热放热,有效地阻止了热量进入室内,可明显降低室内温度波动和最大值,提高人体舒适度,具有较好的调温隔热效果。 相似文献
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《低温学》1987,27(10):590-591
Heat transfer characteristics of a fin having a novel structure are studied. The fins, manufactured by diffusion welding, have a multilayered porous structure. The experimental results show significant enhancement of heat flux over the entire temperature range. Maximum heat flux is increased up to 10 times compared with that for smooth surfaces. The new structure is effective for high heat flux cooling using boiling heat transfer. 相似文献
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A general numerical model developed to simulate the time‐dependent changes of moisture content, temperature and pore pressures is proposed for a porous material. The model is based on a coupled heat and mass transfer mathematical formulation. The model’s validation is conducted using experimental data for concrete. The gravimetric technique is used to obtain the experimental data on moisture content in cylinders made up of fully saturated concrete exposed to drying. Further to demonstrate the applicability of the model, it is also studied the moisture migration, temperature development and thermal stresses in a concrete element exposed to fire. The obtained results indicate that during fire, several degradation phenomena are taking place at the same time. Thermal stresses developed by the temperature differential, especially when temperature‐dependent material properties are taken into the account, along with the increase of pore pressures, may contribute to structural failure. 相似文献
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藕状多孔铜是一种具有长直圆孔的新型微通道结构,可用于对大功率电子器件进行散热。通过实验和Flow Simulation数值计算系统地研究了以水为工质,具有均匀微槽道结构的多孔铜热沉的散热性能。实验结果表明,该热沉具有很高的换热系数,在110 m L/s流量下,换热系数可达10.1 W/(cm~2·K)。模拟结果表明存在最佳的微槽道数和微槽道方向使得多孔铜热沉的散热性能最优。以水为工质时,最佳槽道数和微槽道方向分别为7~11和45°。随着微槽道宽度减小,热沉散热性能提高,对比了数值模拟结果与实验结果,并分析了其存在差异的原因。 相似文献