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双行程红外辐射振动流化种子干燥的传热传质研究 总被引:2,自引:0,他引:2
在深入研究单行程红外辐射振动流化种子干燥的基础上,本文开拓出双行程振动流化干燥,其特点是在干燥过程中种子与供热热风均经两次行程,干燥装置总高度不变,其干燥行程增加20%.通过非稳态干燥动力学实验研究表明,增加内行程种子总脱水率增加87%,总干燥周期为单行程的1/1.8,料温为其0.82(47℃/57℃)倍.由于增加内筒使恒速段延长并提高了梅这段的干燥速率,整个干燥过程适应种子的生理生化特性,因而可保持种子的活力。文中根据干燥速率方程分别实验研究了辐射、对流与导热在强化种子传热传质过程中的各自贡献.这些研究为我国的‘种子工程’尤其是品种繁多、特性各异干燥难度较高的蔬菜种子干燥提供了理论依据与技术基础。 相似文献
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《工程热物理学报》2021,42(5):1282-1287
本文通过实验测试与数值预测结合研究了平纹、斜纹树脂基碳纤维复合材料的各向异性传热性能。实验方面,采用基于电加热膜加热的稳态"三明治"结构进行测试,得到了材料厚度与面内方向导热系数随温度的变化规律。模拟方面,观测复合材料内部微观结构,重构建立了代表性单胞模型,在三维方向分别模拟其一维稳态导热过程来预测材料不同方向的导热系数。研究结果表明,实验获得的树脂基碳纤维复合材料厚度与面内方向导热系数均随材料热面温度升高而近似线性增大,面内方向导热系数约为厚度方向的2.8倍,因密度相近,平纹、斜纹机织结构材料各主轴方向导热系数偏差小于10%。数值预测结果与实验结果基本符合,并对引起实验与数值结果偏差的来源进行分析。 相似文献
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具有微尺度传热特征的超常传热过程中,热流矢与温度梯度之间存在延迟效应,且热流的运动受到空间效应的影响.基于热质概念的普适导热定律,结合Clausius不等式和Helmholtz自由能公式,构建了计及热流矢和温度对时间和空间惯性效应的广义热弹性动力学模型,推导了各向同性材料超常传热行为的热弹性控制方程组.通过与已有广义热弹性动力学模型进行对比分析可得,当热流密度不大的条件下,热流矢与温度对空间的惯性效应可忽略时,基于热质概念的广义热弹性模型可分别退化为L-S,G-L和G-N的模型;对于尺度微观、稳态导热条件时,热流矢与温度对空间的惯性效应不可忽略,此时导热系数将受到热质运动惯性效应的影响,利用所建模型可揭示稳态导热时呈现的非傅里叶现象,并可避免基于已有广义模型得到的导热系数随结构特征尺寸变化的非物理现象. 相似文献
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利用稳态电热拉曼技术测量了碳纳米管纤维对流换热环境下的导热系数. 该方法基于材料拉曼信号与温度之间的关系, 实时探测一维材料在不同电加热(内热源)下的中心点温度, 利用对流环境下的稳态导热模型推导出材料的导热系数, 实现了一维微纳材料热物性的无损化和非接触式测量. 实验发现: 碳纳米管纤维的导热系数远低于单根碳纳米管的导热系数, 但高于碳纳米管堆积床的导热系数. 这表明碳纳米管体材料的热物性主要取决于内部管束的列阵和管束间的接触热阻. 相似文献
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In countless applications, there is a thoughtful necessity for augmenting the poor thermal conductivity of conventional liquids to improve effectual heat transfer liquids. Nanofluids are fluids interruptions of nanoparticles and broad scrutiny have been presented on nanoliquid solicitations in heat transfer progressions. The intention of this exertion is to scrutinize the dual nature solutions of unsteady magnetite Carreau nanofluid influenced by porous stretching/shrinking surface. The phenomena of heat and mass transfer have been established in the manifestation of combined convective conditions with heat sink/source and variable thermal conductivity. By utilizing compatible conversions to rehabilitate the structure of nonlinear partial differential equations (PDEs) into nonlinear ordinary differential equations (ODEs) which were then elucidated numerically via bvp4c. Under the impact of diverse somatic parameters the graphical depiction of all the probable dual solutions of velocity, temperature, concentration, skin-friction coefficient, local Nusselt and Sherwood numbers are scrutinized. These outcomes specify that the liquid velocity display similar tendency for both upper and lower solutions and decline for unsteadiness parameter, while it enhance for Weissenberg number. 相似文献
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Effects of variable properties on MHD heat and mass transfer flow near a stagnation point towards a stretching sheet in a porous medium with thermal radiation 下载免费PDF全文
The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic(MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented,taking into account thermal radiation and internal heat genberation/absorbtion.The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point.The Rosseland approximation is used to describe the radiative heat flux in the energy equation.The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung-Kutta method with the shooting technique.A comparison with previously published work has been carried out and the results are found to be in good agreement.The results are analyzed for the effect of different physical parameters,such as the variable viscosity and thermal conductivity,the ratio of free stream velocity to stretching velocity,the magnetic field,the porosity,the radiation and suction/injection on the flow,and the heat and mass transfer characteristics.The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1.In addition,the imposition of fluid suction increases both the rate of heat and mass transfer,whereas fluid injection shows the opposite effect. 相似文献
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应用非平衡分子动力学方法进一步研究了平均温度为300K、厚度为2.715nm-43.44nm的单晶硅薄膜的法向热导率,模拟结果表明,薄膜热导率低于同温度下单晶硅的实验值,存在显著的尺寸效应,当膜厚度在20nm以下时,法向热导率随尺度减小而线性减小,当膜厚度大于20nm时法向热导率随尺度呈现二阶多项式变化。法向热导率的变化规律与面向热导率的变化规律类似,表明薄膜厚度和表面晶格结构对声子传热影响的复杂性。 相似文献
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A loop thermosiphon thermal collector was developed for the waste heat recovery power generation with electric capacity of 500 W. The heat collector with heat transfer area of 0.159 m2 (500 mm width and 300 mm depth) was connected to the condenser with a shrunken heat transfer area by a loop. The thermal performance of the apparatus was declined when increasing the water filling rate to 90% as the working fluid occupied the internal volume. In the range of water filling rate between 30% and 60%, the effective thermal conductivity was around100 times of the conductivity of copper. 相似文献
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针对高超声速飞行器工作时头锥恶劣的热环境,为了保证飞行器头锥的尖锐外形, 提出疏导式热防护结构,利用内置高导热碳材料结构为飞行器头锥提供热防护. 采用流固耦合方法对头锥疏导式防热结构进行了分析,验证了头锥内置高导热碳材料具有较好防热效果, 其中来流马赫数(Ma)为9时头锥前缘壁面最高温度下降了21.9%,尾部最低温度升高了15.2%, 实现了热流由高温区向低温区的转移,削弱了头锥的热载荷,强化了头锥的热防护能力. 本文对外蒙皮结构参数、材料参数以及内部高导热碳材料导热率对头锥热防护性能的影响进行了分析, 其中头锥最高温度随着蒙皮材料导热系数的增加而降低到一个稳定值; 随着蒙皮材料表面黑度的增加而降低;随着蒙皮厚度的增加而升高;随着高导热碳材料导热系数的 增加而呈抛物线下降. 相似文献
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建立了考虑变截面、变热导率及界面接触热阻效应的组合热整流结构的温度场及热整流系数的理论模型和有限元解.数值算例证明了本文模型及算法的可靠性,进而通过参数影响研究确定了若干几何及材料参数对结构热整流系数的影响规律,揭示界面接触热阻对热整流效果的影响机理.研究结果表明长度比、截面半径变化率、热导率、边界条件温差和界面接触热阻等因素必须通过优化设计才能得到最大的热整流系数,同时界面接触热阻的引入也为调控热整流系数提供了一条新的途径. 相似文献
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Rabin Y 《Cryo letters》2000,21(3):163-170
The thermal conductivity value of pure water ice is inversely proportional to the temperature and decreases about 5-fold as the temperature increases from the liquid nitrogen boiling temperature (77 K to the freezing point of pure water. The temperature dependency of the thermal conductivity is typically overlooked in bioheat transfer simulations. A closed-form solution of the one-dimensional temperature distribution in frozen water and blood is presented in this study, based on a new thermal conductivity model. Results indicate that temperatures are overestimated up to 38K, and heat fluxes through the frozen region boundaries are underestimated by a factor of 2, when the temperature dependency of the thermal conductivity is neglected. 相似文献
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利用CFD软件数值研究了颗粒三维有序堆积多孔介质的对流换热问题. 采用颗粒直径分别为14 mm,9.4 mm和7 mm的球形颗粒有序排列构成多孔介质骨架,在多孔骨架的上方有一恒热流密度的铜板. 采用流固耦合的方法研究了槽通道内温度分布和局部对流换热系数的分布以及对流换热的影响因素. 研究结果表明:热渗透的厚度和温度边界层的厚度在流动方向上逐渐增大,并且随流量的增加而减小;当骨架的导热系数比较高时,对流换热随颗粒直径的减小而略有增大;对流换热系数随聚丙烯酰胺溶液浓度的增大而减小,黏性耗散减弱了对流换热.
关键词:
多孔介质
温度场
局部对流换热系数
数值模拟 相似文献
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Nanofluids are a new class of heat transfer fluids developed by suspending nanosized solid particles in liquids. Larger thermal
conductivity of solid particles compared to the base fluid such as water, ethylene glycol, engine oil etc. significantly enhances
their thermal properties. Several phenomenological models have been proposed to explain the anomalous heat transfer enhancement
in nanofluids. This paper presents a systematic literature survey to exploit the characteristics of nanofluids, viz., thermal
conductivity, specific heat and other thermal properties. An empirical correlation for the thermal conductivity of Al2O3 + water and Cu + water nanofluids, considering the effects of temperature, volume fraction and size of the nanoparticle is
developed and presented. A correlation for the evaluation of Nusselt number is also developed and presented and compared in
graphical form. This enhanced thermophysical and heat transfer characteristics make fluids embedded with nanomaterials as
excellent candidates for future applications.
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