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建立了一套可应用于真空条件下的双试件防护热板法导热系数测量装置,装置中设计了真空调节装置和低放气率的多层隔热结构,可实现真空度为10^(-4)Pa量级~常压下的环境压力调节;通过液氮(或恒温浴)降温和电加热共同控温,可实现-160—280℃的温度控制和导热系数测试。而后通过国家标准样品检验了装置的测量准确性,表明本装置对国家标准样品的测试偏差小于1%;并测量了不同真空度和不同温度条件下的样品导热系数;最后给出了装置的不确定度分析,计算表明本装置在全量程的测量不确定度优于±5%。 相似文献
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导热仪的温度测量和控制水平不高是导致测量结果产生偏差的重要原因。防护热板导热仪具有较大的热惯性,需要被控制温度的单元多,彼此有热传递作用,形成非线性的相互干扰,如果控制参数的整定不合适,系统各个单元的温度就会随时间波动。在国产精密工业温度计、测温仪、直流电源,LabVIEW虚拟PID控制器构成的导热仪温控系统上,分段优化整定导热仪系统PID控制参数,并研究了导热仪各部件温度控制顺序对整体控温效果的影响。实验结果表明在常温至400℃的范围,导热仪各个单元的温度被长时间稳定控制在±0.01℃以内,此参数整定方法可满足高精度防护热板导热仪的技术要求。 相似文献
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《纳米技术与精密工程》2017,(3)
防护热板法(guarded hot plate,GHP)是测量隔热材料导热系数最精确的方法,此方法的传统系统稳态判断方法耗时长,采用的时间间隔固定,导致整体测量时间较长.为了缩短测量时间,本文提出一种基于动态周期识别的系统稳态判断方法,对热板加热功率进行卡尔曼平滑滤波和动态周期识别,变固定时间间隔为动态时间间隔,再对连续测量的4组导热系数进行判断,使其实时准确地反映系统的测量状态.利用此判断方法对绝热材料标准参比板的导热系数进行了测量,结果表明,测量时间缩短了大于25!,测量效率明显提高. 相似文献
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采用防护热板法测试了一种低密度莫来石在150~500℃的导热系数,分析了测试温度、压力、试样厚度、设定温差等测试参数对测试结果的影响,在此基础上拟合得到了3组该低密度莫来石导热系数的计算模型,并根据实际测试结果对3组计算模型分别进行了验证。结果表明:该低密度莫来石试样的导热系数随测试温度的升高而升高,温度-压力、温度-温差的计算模型在所选温度范围内的相对偏差小于5%,温度-厚度的计算模型在所选温度范围内的相对偏差小于10%。 相似文献
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低导热率材料测量装置研究 总被引:3,自引:0,他引:3
采用保护热板法在室温至80℃温度范围内对标准参考物质进行了多次导热率测量,同时也对实验材料实施加热保护的热平板法稳态测量导热系统装置进行了数值模拟分析. 相似文献
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V. Ya. Chekhovskoi R. A. Belyaev Yu. V. Vavilov 《Journal of Engineering Physics and Thermophysics》1972,22(6):728-731
An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation
thermal conductivity at the mean temperature of specimens, W/m· °C
- Q
power of the central heater, W
- F
cross section area of a specimen, m2
- t1,2
temperature drop across the specimens, °C
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1,
2
difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m
- t
temperature, °C
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time coordinate, min
- d1= (d1u+d1l
)/2
mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m
- d2= (d2u+d2l
)/2
mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m
- dt(d1,)/d
rate of temperature rise at section d1 of the specimen at time, °C/h
- t=t1+t2
sum of temperature drops in the specimens at time, °C
- m
heating rate, h–1
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a
thermal diffusivity of specimens, referred to their mean temperature, m2/h
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=m/a, m–1 b=¦(tu–tl)/tu¦
heating nonuniformity factor
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972. 相似文献
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V. V. Kurepin A. F. Begunkova 《Journal of Engineering Physics and Thermophysics》1975,29(4):1235-1241
A comparative method is developed for measuring the thermal conductivity of solid and dispersed materials with λ=0.1-80 W/(m · °K). The method is accurate, rapid, and simple to use. 相似文献
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E. A. Tombasov V. Ya. Cherepanov P. S. Glazyrin G. P. Polukeev V. E. Chelmodeev 《Journal of Engineering Physics and Thermophysics》1978,34(5):599-603
A method of measuring the thermal conductivity of poor heat conductors under monotonic conditions is described which enables one to make measurements on large specimens at different rates of heating and over a wide temperature range.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 34, No. 5, pp. 875–879, May, 1978. 相似文献
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U. Hammerschmidt 《International Journal of Thermophysics》1995,16(5):1203-1211
The thermal conductivity of the refrigerants R22, R123, R134a, R142b, R143a, and R152a has been determined as a function of temperature in the range from 300 to 460 K. Measurements were carried out at atmospheric pressure with an improved guarded hot-plate apparatus. The width of the instrument's gas layer and the temperature difference across the metering section were varied to detect any stray heat transfer. Radiation correction factors were derived from IR absorption spectra. The uncertainty of the measurements is estimated to be 2% at a standard deviation of less than 0.1%. All values are correlated with respect to temperature in the range covered. The equations are found to represent the results with average deviations of 1%. Our data sets are compared with corresponding hot wire results. In contrast to the generally preferred hot wire technique, with its possible electrical and chemical interactions between the wire and the polar refrigerant, there are no such difficulties using a guarded hot-plate apparatus. Our data sets may thus contribute to the discussions on discrepancies in thermal conductivity values from various authors using hot wire as one particular method.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, USA. 相似文献
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Means for accelerated measurement of the thermal conductivity of building materials are described. Most of the operations involved may be performed automatically. 相似文献
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K. Hisano 《International Journal of Thermophysics》1997,18(2):535-545
Thermal radiation calorimetry was applied to measure the thermal conductivity of insulating solid specimens. We consider the
system in which a disk-shaped specimen and a flat heater are mounted in a vacuum chamber with the specimen heated on one face
by irradiation. A temperature difference between two faces was observed at elevated temperatures under steady-state conditions.
An apparatus was developed using a thin graphite sheet as the heater element. Disk-shaped Pyrex glass and Pyroceram specimens,
whose surfaces were blackened with colloidal graphite, were used in the measurements. Noncontact temperature measurement was
performed using pyrometers and a thermocouple set in the gap between the heater and the specimen. Deviations of the estimated
thermal conductivities from the recommended values were about 5% in the temperature range 250 to 800°C.
Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan. 相似文献
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To measure thermal conductivity of materials of low conductivity (0.1 to 1 W·m–1·K–1), a method using a specimen of small size (2×25×25 mm) has been developed. This method applies a well-defined, steady, and uniform heat flux perpendicular to the surface of a small plate sample of polymers or ceramics jointly by means of radiative heat exchange as well as by an areal heater on the sample surface and allows a reasonably rapid (5-min) measurement of thermal conductivity. This method of measuring conductivity is an absolute and direct measurement method which does not need any standard reference materials or information about heat capacity. The principle of the method has been demonstrated by constructing a measurement apparatus and measuring thermal conductivity of a few materials. The thermal conductivities of silicone rubber and Pyrex (Corning 7740) glass measured by the present method between 30 and 90°C are compared with recommended values. 相似文献
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