热探针法测量陶瓷粉末导热系数的实验研究

以Al2O3粉末为例,在分析探针法测量原理的基础上,用热探针法对Al2O3粉末的导热系数进行测量,研究在不同含水率和温度下Al2O3粉末导热系数的变化情况。试验结果发现,Al2O3粉末的导热系数随着秸秆密度,温度和含水率的增加而增加,并基本呈线性关系。     

烧结矿等效导热系数实验测量及分析

测量了某种烧结矿料的真密度、孔隙率及等效导热系数,研究了烧结矿等效导热系数随温度的变化规律.结果表明,烧结矿等效导热系数在323~750 K随温度升高而上升,在约750 K达到最大值,温度再升高,烧结矿发生部分相变,导致导热系数下降.实际烧结冷却过程中烧结矿温度低于723 K,模拟得出323~723 K下烧结矿固体导热系数呈线性增长,验证了测量结果优于经验值.     

甲基丙烯酸甲酯本体聚合体系导热系数的研究

根据热电阻法测量原理,测量了甲基丙烯酸甲酯(MMA)本体聚合模拟体系的导热系数。研究了导热系数随转化率和温度的变化规律,并建立了相应的关联式。测量结果表明,相同转化率时,MMA本体聚合体系导热系数随温度的升高而减小;不同温度下其导热系数均随转化率的增大而逐渐增加。该关联式计算值与测量值的最大偏差为1.6%,可较好地预测MMA本体聚合体系导热系数。     

轮胎胶料的导热系数测定及误差分析

采用稳态法测量轿车轮胎和航空轮胎各部位胶料在不同温度下的导热系数。测量结果表明,轿车轮胎在20~80℃、航空轮胎在20~110℃范围内,轮胎各部位胶料的导热系数与温度呈线性关系;轿车轮胎胎侧胶导热系数较大,胎面基部胶导热系数较小,航空轮胎胎侧胶导热系数较大,胎面胶导热系数较小。试验时采取使设备和试样充分干燥、以石棉做绝热材料、保持冰端温度等措施,可使试验误差小于4%。     

高炉炭砖的导热系数及其影响因素

对微孔、半石墨质和普通等级炭砖试样的导热系数与温度的关系做了回归分析,得到了导热系数和温度的关系表达式,由此,可以从室温导热系数预测高温导热系数。另外,还计算了导热系数与体积密度、显气孔率、透气度和原料等级之间的相关系数。结果表明,导热系数与透气度和原料等级有一定的相关关系,而与体积密度和显气孔率无关。     

矿物棉导热系数的影响因素试验

导热系数是评价绝热材料隔热效果的最重要因素之一,本文就密度、温度和纤维直径等参数对表观导热系数的影响进行了一系列试验,现分述如下:一.密度与表观导热系数的关系矿物棉原棉或毡状材料,有较大的蓬松度,密度随不同的压缩强度而变化.矿棉板的密实度高,密度随压力变     

传热传质强化介质石墨的膨胀工艺及导热性能研究

对膨胀石墨在不同膨胀温度及不同膨胀时间下进行了膨胀工艺与导热系数测试的研究.研究中,分别用平面热源法和称重法测出不同膨胀条件下石墨的导热系数和密度.然后根据导热系数最优化的原则,结合未膨胀晶体的观测状态以及密度的变化,找出膨胀石墨的最佳膨胀工艺.结果发现膨胀石墨在各个膨胀温度下都存在着自己的最佳膨胀工艺.经过不同膨胀温...     

用并联模型法测定泡沫塑料的导热系数

稳态热流计法操作简单,广泛用于测量保温材料的导热系数。但由于仪器设备和方法的限制,难以测试异型材料的导热系数。分别采用并联模型法和直接测量法分析了挤塑聚苯乙烯泡沫、硬质聚氨酯泡沫、橡塑泡沫在平均温度10、15、25℃下的导热系数。结果表明:在不同平均温度和不同材料中,采用并联模型法所计算的导热系数与测试结果误差较小,说明并联模型法可用于不规则泡沫塑料导热系数的测试。     

黄海海域海水热物理性质实验研究

海水热物理性质研究对确定合理的海洋油气田开发工艺参数具有重要意义。以黄海海域唐岛湾海水为研究对象,测试了在273.15~293.15K下,海水的密度、粘度、导热系数和比热容随温度的变化规律,回归了相应的热物性公式和检验了误差,并将实验结果与纯水及文献中海水的热物性参数进行了比较。结果表明,实验结果与文献数据随温度的变化趋势一致,海水的密度和粘度随温度的升高而减小,导热系数和比热容随温度的升高而增大;由于唐岛湾海水的盐度略低于文献中海水的盐度,海水密度、粘度和导热系数均小于文献中的值,比热容大于文献中的值。研究结果可为低温海水物理性质的确定及油气田开发提供理论指导。     

黄海海域海水热物理性质实验研究

海水热物理性质研究对确定合理的海洋油气田开发工艺参数具有重要意义。以黄海海域唐岛湾海水为研究对象,测试了在273.15~293.15K下,海水的密度、粘度、导热系数和比热容随温度的变化规律,回归了相应的热物性公式和检验了误差,并将实验结果与纯水及文献中海水的热物性参数进行了比较。结果表明,实验结果与文献数据随温度的变化趋势一致,海水的密度和粘度随温度的升高而减小,导热系数和比热容随温度的升高而增大;由于唐岛湾海水的盐度略低于文献中海水的盐度,海水密度、粘度和导热系数均小于文献中的值,比热容大于文献中的值。研究结果可为低温海水物理性质的确定及油气田开发提供理论指导。     

建陶坯体干燥过程中传热性能的实验研究

为研究建陶坯体干燥过程中的传热性能,使用导热系数测试仪对不同排水率下的建陶坯体的导热系数进行了实验研究;为降低接触热阻的影响,在坯体与铜板间涂以导热胶,最后对实验误差进行了分析。实验结果表明,坯体导热系数随温度线性增加,随着排水率的增加而减小。     

Calculation of thermal conductivity of gypsum plasterboards at ambient and elevated temperature

Plasterboard often protects steel structures of buildings because it conducts heat slowly and absorbs the heat of the fire by its volumetric enthalpy. The most important property governing the heat transfer is the thermal diffusion. This property depends on the density, specific heat and thermal conductivity. The first two can be calculated based on the mass composition of the board. The thermal conductivity is more difficult to derive since it is a directional property. This paper will focus on the calculation of the thermal conductivity at ambient and elevated temperatures. It is shown that the thermal conductivity of gypsum plasterboard (i.e. a porous medium) can be assumed to be a three‐phase system. Plasterboard consists of a solid phase and a water/air mix in the voids. The differences between different theoretical equations for both dry and moistured plasterboards are presented. The equation proposed by Zehner and Schlunder (Chem. Ing.‐Tech. 1972; 44 (23):1303–1308) with shape‐factor C of 5 gave good agreement with experimental data of the different boards. Furthermore, the influence of the composition of the boards on the thermal conductivity is investigated. This has an influence, especially since the composition is also related to its moisture content. Regression analysis points out that the moisture content depends only on the gypsum content. A value of 2.8% absorbed water on the mass of gypsum is found, and this water plays an important role in the thermal conductivity of plasterboard at ambient temperature. Finally, the thermal conductivity of board at elevated temperature is computed. A close fit between computed and experimental values derived from literature is found. Copyright © 2009 John Wiley & Sons, Ltd.     

充气式微型保鲜冷库纤维保温材料的筛选与评价

纤维材料将是充气式微型保鲜冷库的最佳保温材料之一,其导热系数、回弹力、密度、纤维细度、弯曲度、吸湿率等指标的评价,是库体保温层厚度定量与排列组合的理论基础。研究结果表明:导热系数、回潮率、密度、表面光滑度是影响纤维保温性能的关键因素;涤纶(120 g/m2)的导热系数为0.031 5 W/m·K,回潮率为0.18%,拉伸强度为0.35 MPa,断裂伸长率为127.48%,自熄性好,是一种很好的充气式微型保鲜冷库保温材料。     

Thermophysical Properties of Stone Fruit

The thermophysical properties of the stone fruits plum, peach, and nectarine were modeled from experimental data as functions of moisture content. Samples were dried to preset moistures in a laboratory cabinet dryer, and the thermal conductivity, specific heat, apparent density, bulk density, and porosity of the fruit were determined. The thermal conductivity and specific heat were found to be linear functions of moisture content, whereas apparent bulk density and porosity followed second-order polynomials. Temperature dependence was not found to be significant.     

Modeling of thermal conductivity and density of alumina/silica in water hybrid nanocolloid by the application of Artificial Neural Networks

In this research work, the thermal conductivity and density of alumina/silica(Al_2O_3/SiO_2) in water hybrid nanofluids at different temperatures and volume concentrations have been modeled using the artificial neural networks(ANN). The nanocolloid involved in the study was synthesized by the two-step method and characterized by XRD, TEM, SEM–EDX and zeta potential analysis. The properties of the synthesized nanofluid were measured at various volume concentrations(0.05%, 0.1% and 0.2%) and temperatures(20 to 60 °C). Established on the observational data and ANN, the optimum neural structure was suggested for predicting the thermal conductivity and density of the hybrid nanofluid as a function of temperature and solid volume concentrations. The results indicate that a neural network with 2 hidden layers and 10 neurons have the lowest error and a highest fitting coefficient o thermal conductivity, whereas in the case of density, the structure with 1 hidden layer consisting of 4 neurons proved to be the optimal structure.     

多壁碳纳米管冷冻机油密度和热导率的实验研究

采用超声振荡的方法制备稳定性良好的多壁碳纳米管冷冻机油。在不同温度(20~80℃)下,利用密度计和热导率测试系统对不同浓度的多壁碳纳米管冷冻机油(MWCNTs的质量分数为0.5%、1.0%、1.5%、2.0%)进行测试和分析。实验结果表明:冷冻机油的密度随MWCNTs质量分数的增加而增大,随温度的升高而减小;冷冻机油的热导率随MWCNTs质量分数的增大而增大,随温度的升高而增大,其中,热导率增大的效果随质量分数增加较随温度升高更为明显。当多壁碳纳米管质量分数为2%、温度为80℃时,纳米冷冻机油的热导率可达到0.1637W/(m·K),较同温度下纯RL68H冷冻机油热导率增大9.13%。     

Synthesis of meso-macro alumina using yeast cells as a bio-template and optimization using a genetic algorithm

Meso-Macro porous alumina was fabricated using yeast cells as a pore-forming agent. Alumina powder synthesis was achieved by a low cost process (recrystallisation of alum).The effect of the pore forming agent on the true porosity, bulk density and thermal conductivity of porous alumina was characterized. The results show that the true porosity increased with the increasi ng addition of yeast cells. The bulk density and thermal conductivity at room temperature decreased with the increasing yeast addition. A genetic algorithm method was used to minimize the thermal conductivity of the macro-porous alumina based on the amount of yeast cells used, the sintering temperature, and the hold time. The genetic algorithm found that the best thermal conductivity achievable was equal to 0.152 Watt/m. °C at 20wt% concentration of yeast, a sintering temperature of 1230°C and 1.5 hours of soaking time. The experimental value was 0.14 Watt/m. °C and the slight variance between these values were postulated to be due to experimental error in the measurements.     

Numerical simulation of the effect of moisture on the thermal conductivity of porous ceramic materials

A simulation model to analyze the influence of moisture content on the thermal conductivity of porous ceramic materials is developed based on the numerical integration of the energy equation. The experimental technique employed for thermal conductivity measurements is the hot wire parallel technique. The numerical model proposed is checked by evaluating the thermal conductivity of a hypothetical porous ceramic material containing different concentrations of water in its structure. The behaviour of the thermal conductivity as a function of temperature, as predicted by the model proposed in this work was experimentally verified by the authors for an unfired refractory concrete. ©     

MEASUREMENT OF COEFFICIENTS FOB SIMULTANEOUS HEAT AND MASS TRANSFER IN FOOD PRODUCTS

Two experimental devices were designed and built to determine four coefficients K_T K_M D_M D (or δ_T = D_T / D_M occurring in simultaneous heat and mass transfer equations, where,K _T and D_M are thermal conductivity and moisture diffcusivity respectively, D_T ( or δ _T is temperature gradient Induced moisture migration coefficient and K_M is moisture gradient Induced heat transfer coefficient. Three food materials, i.e. potato, bread dough and bread, were tested. From this study, it was found that the value of 5 was higher for low density food materials, such as bread, than for high density materials, such as potato. The coefficient & measures moisture migration contribution due to temperature gradient within the material. The average values of δ _T for potato, bread dough and bread were 0.0014, 0.0059 and 0.0127 per °C, respectively. The contribution of temperature gradient to the overall moisture migration is negligible In high density materials. However, this contribution may be important in the moisture migratlon analysls for low density materials. The moisture gradient induced heat transfer coefficient % as found to be negligible for the materials tested in this study