Study on Comparison of Thermal Conductivities of Thermal Insulations Using Different Measurement Methods in Wide Range of Temperature

2007 ◽  
Author(s):  
Takahiro Ohmura
Keyword(s):  
Thermal Conductivity ◽  
Measurement Methods ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Standard Material ◽  
Temperature Range ◽  
Hot Disk ◽  
Cyclic Heat ◽  
Thermal Insulations ◽  
Thermal Conductivities

Guarded hot plate method (GHP method) is the most popular way of measuring thermal conductivity of thermal insulation. However, there are large differences among the thermal conductivities measured by different apparatuses which are made in different institutions in the temperature range above 100 °C. It is considered the reason that we have no standard material for measurement of thermal conductivity. The standard material is only glass wool which are produced by NIST (National Institute of Standards and Technology) in a temperature range from about 7 to 67 °C. Then, I have researched how far the influence of the difference in measurement methods and apparatuses extends. Furthermore, I have investigated how to measure accurately thermal conductivity in the temperature range which there are few reference materials. In this study, I proposed to increase the accuracy of thermal conductivity of thermal insulation by comparing with values obtained using different methods. I investigated the practicality of the comparison of the results obtained by different methods, which are the GHP, cyclic heat, transient hot wire, and Hot Disk methods, for the accurate measurement at the temperature range from −170 to 1300 °C. First, I developed the three types of measurement apparatuses; one can measure thermal conductivity by using both the GHP and cyclic heat methods in the temperature range from 100 to 1300 °C, the second can measure using both the cyclic heat and transient hot wire methods in the temperature range from 100 to 1000 °C, and the third can measure using both the cyclic heat, transient hot wire, and Hot Disk methods in the temperature range from −170 to 25 °C. Next, I measured thermal conductivities of various thermal insulations using these apparatuses. In the temperature range above 100 °C, the results obtained by using the GHP and cyclic heat methods agree with each other within ± 10% deviations. In like manner, the results obtained by using the cyclic heat and transient hot wire methods agree with each other within ± 10% deviations. Furthermore, in the temperature range from −120 °C to 25°C, the results obtained by using the cyclic heat, transient hot wire, and Hot Disk methods agree with each other within ± 10% deviations. Therefore, it is thought that to compare the thermal conductivities obtained by the different measurement methods will be practical for improvement of the accuracy measurement at the temperature range in the absence of reference materials.

Measuring Thermal Conductivity of Fluids Containing Oxide Nanoparticles

1999 ◽  
Vol 121 (2) ◽  
pp. 280-289 ◽  
Author(s):  
S. Lee ◽  
S. U.-S. Choi ◽  
S. Li ◽  
J. A. Eastman
Keyword(s):  
Thermal Conductivity ◽  
Particle Shape ◽  
Experimental Results ◽  
Oxide Nanoparticles ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Transient Hot Wire Method ◽  
Wire Method ◽  
Al2o3 Particles ◽  
Thermal Conductivities

Oxide nanofluids were produced and their thermal conductivities were measured by a transient hot-wire method. The experimental results show that these nanofluids, containing a small amount of nanoparticles, have substantially higher thermal conductivities than the same liquids without nanoparticles. Comparisons between experiments and the Hamilton and Crosser model show that the model can predict the thermal conductivity of nanofluids containing large agglomerated Al2O3 particles. However, the model appears to be inadequate for nanofluids containing CuO particles. This suggests that not only particle shape but size is considered to be dominant in enhancing the thermal conductivity of nanofluids.

Effect of Volume Fraction and Temperature on Thermal Conductivity of SiO2 Nanofluids

2011 ◽  
Vol 306-307 ◽  
pp. 1178-1181 ◽  
Author(s):  
Bao Jie Zhu ◽  
Wei Lin Zhao ◽  
Dong Dong Li ◽  
Jin Kai Li
Keyword(s):  
Thermal Conductivity ◽  
Ethylene Glycol ◽  
Volume Fraction ◽  
Experimental Results ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Transient Hot Wire Method ◽  
Wire Method ◽  
Thermal Conductivities

Thermal conductivities of two kinds of nanofluids (SiO2-water and SiO2-ethylene glycol) were measured by transient hot-wire method at different volume fraction and temperature. Influences of volume fraction of particles and temperature on thermal conductivities of nanofluids were analyzed. The Experimental results show that thermal conductivities of nanofluids are higher than those of base fluids, and increase with the increase of volume fraction and temperature. When approximately 0.5% volume fraction of SiO2nanoparticles are added into water and ethylene glycol at the temperature 50°C, the thermal conductivities are enhanced 46.2% and 62.8% respectively.

scholarly journals Apparatus for routine measurements of the thermal conductivity of ice cores

1999 ◽  
Vol 29 ◽  
pp. 151-154 ◽  
Author(s):  
Crescenzo Festa ◽  
Aristide Rossi
Keyword(s):  
Thermal Conductivity ◽  
Ice Cores ◽  
Maximum Temperature ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Standard Samples ◽  
Experimental Conditions ◽  
Heating Source ◽  
Central Segment ◽  
Wire Method

AbstractAn apparatus is described for measuring the thermal conductivity of ice by the transient hot-wire method. Thermal conductivity A, is determined by tracking the thermal pulse induced in the sample by a heating source consisting of a platinum resistor. A central segment of the same platinum heating resistor acts also as a thermal sensor. A heat pulse transferred to the ice for a period of 40s gives a maximum temperature increment of about 7-14°C. In good experimental conditions, the expected reproducibility of the measurements is within ±3%. The accuracy of the method depends on whether the instrument has been calibrated by reliable standard samples, certified by absolute methods.

Effects of Nb doping on thermoelectric properties of Zn4Sb3 at high temperatures

2009 ◽  
Vol 24 (2) ◽  
pp. 430-435 ◽  
Author(s):  
D. Li ◽  
H.H. Hng ◽  
J. Ma ◽  
X.Y. Qin
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
High Temperatures ◽  
Thermoelectric Properties ◽  
Figure Of Merit ◽  
Thermoelectric Performance ◽  
Temperature Range ◽  
A Value ◽  
Nb Doping ◽  
Thermal Conductivities

The thermoelectric properties of Nb-doped Zn4Sb3 compounds, (Zn1–xNbx)4Sb3 (x = 0, 0.005, and 0.01), were investigated at temperatures ranging from 300 to 685 K. The results showed that by substituting Zn with Nb, the thermal conductivities of all the Nb-doped compounds were lower than that of the pristine β-Zn4Sb3. Among the compounds studied, the lightly substituted (Zn0.995Nb0.005)4Sb3 compound exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity. Its figure of merit, ZT, was greater than the undoped Zn4Sb3 compound for the temperature range investigated. In particular, the ZT of (Zn0.995Nb0.005)4Sb3 reached a value of 1.1 at 680 K, which was 69% greater than that of the undoped Zn4Sb3 obtained in this study.

Design of a Steady-State, Parallel-Plate Thermal Conductivity Apparatus for Nanofluids and Comparative Measurements With Transient HWTC Apparatus

2010 ◽  
Author(s):  
Milivoje M. Kostic ◽  
Casey J. Walleck
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Parallel Plate ◽  
Measurement Method ◽  
Mixture Theory ◽  
Hot Wire ◽  
Electro Magnetic ◽  
Magnetic Phenomena ◽  
Thermal Conductivities

A steady-state, parallel-plate thermal conductivity (PPTC) apparatus has been developed and used for comparative measurements of complex POLY-nanofluids, in order to compare results with the corresponding measurements using the transient, hotwire thermal conductivity (HWTC) apparatus. The related measurements in the literature, mostly with HWTC method, have been inconsistent and with measured thermal conductivities far beyond prediction using the well-known mixture theory. The objective was to check out if existing and well-established HWTC method might have some unknown issues while measuring TC of complex nano-mixture suspensions, like electro-magnetic phenomena, undetectable hot-wire vibrations, and others. These initial and limited measurements have shown considerable difference between the two methods, where the TC enhancements measured with PPTC apparatus were about three times smaller than with HWTC apparatus, the former data being much closer to the mixture theory prediction. However, the influence of measurement method is not conclusive since it has been observed that the complex nano-mixture suspensions were very unstable during the lengthy steady-state measurements as compared to rather quick transient HWTC method. The nanofluid suspension instability might be the main reason for very inconsistent results in the literature. It is necessary to expend investigation with more stable nano-mixture suspensions.

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