scholarly journals Estimation of in-situ thermal conductivities from temperature gradient measurements

1980 ◽  
Author(s):  
V Hoang
Keyword(s):  
Temperature Gradient ◽  
Gradient Measurements ◽  
Thermal Conductivities

XXV.—The Determination of Temperature Gradients over the Greenland Ice Sheet by Optical Methods

1957 ◽  
Vol 64 (4) ◽  
pp. 381-397
Author(s):  
R. A. Hamilton
Keyword(s):  
Temperature Gradient ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temperature Gradients ◽  
Lower Atmosphere ◽  
Optical Methods ◽  
Snow Surface ◽  
Vertical Angle ◽  
Gradient Measurements

SynopsisThe temperature gradient in the lower atmosphere can be directly determined by measuring the optical refractive index of the air. This method is suitable for use on the Greenland ice sheet where errors introduced by water vapour are small, and where the strong solar radiation reflected by the snow surface makes it difficult to measure temperature differences over height differences of about I metre.The refraction was measured by observing the apparent vertical angle of each of a set of targets at distances up to 4 km. from a theodolite. The refraction was found to vary linearly with the distance of the target. The true vertical angle to the targets was determined when a second theodolite was available and reciprocal sights could be taken with it from the site of target to the fixed theodolite. The true vertical angle varied with time due to slow descent of the theodolite as the firn slumped; a correction for this was made. The standard error of the temperature gradient measurements was about 1.5 × 10−2 C.° per metre. It is considered that the method could be developed and improved so that over a range of only 100 metres temperature gradients could be measured to an accuracy of about 0·1° C. per metre.

Significantly enhanced and precisely modeled thermal conductivity in polyimide nanocomposites with chemically modified graphene via in situ polymerization and electrospinning-hot press technology

2018 ◽  
Vol 6 (12) ◽  
pp. 3004-3015 ◽  
Author(s):  
Yongqiang Guo ◽  
Genjiu Xu ◽  
Xutong Yang ◽  
Kunpeng Ruan ◽  
Tengbo Ma ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
In Situ Polymerization ◽  
Hot Press ◽  
Conductivity Model ◽  
Chemically Modified ◽  
Thermal Conductivity Model ◽  
Modified Graphene ◽  
Thermal Conductivities

Significantly improved thermal conductivities and a more accurate thermal conductivity model were achieved.

Enhanced thermal conductivities of epoxy nanocomposites via incorporating in-situ fabricated hetero-structured SiC-BNNS fillers

2020 ◽  
Vol 187 ◽  
pp. 107944 ◽  
Author(s):  
Yixin Han ◽  
Xuetao Shi ◽  
Xutong Yang ◽  
Yongqiang Guo ◽  
Junliang Zhang ◽  
...  
Keyword(s):  
Epoxy Nanocomposites ◽  
Thermal Conductivities

Investigation of Liquid Water Distribution under Temperature Gradient in PEFC Using in-situ X-ray Visualization

2020 ◽  
Vol 98 (9) ◽  
pp. 27-35
Author(s):  
Takahiro Komiyama ◽  
Takashi Sasabe ◽  
Hiroshi Naito ◽  
Katsuyuki Kawamura ◽  
Toshiyuki Suzuki ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Liquid Water ◽  
Water Distribution ◽  
X Ray

Axisymmetric thermal-creep flow of a slightly rarefied gas induced around two unequal spheres

1984 ◽  
Vol 144 ◽  
pp. 103-121 ◽  
Author(s):  
Yoshimoto Onishi
Keyword(s):  
Reynolds Number ◽  
Temperature Gradient ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Thermal Creep ◽  
Creep Flow ◽  
Low Reynolds ◽  
Thermal Creep Flow ◽  
Slightly Rarefied Gas ◽  
Thermal Conductivities

A thermal-creep flow of a slightly rarefied gas induced axisymmetrically around two unequal spheres is studied on the basis of kinetic theory. The spheres, whose thermal conductivities are assumed to be identical with that of the gas, for simplicity, are placed in an infinite expanse of the gas at rest with a uniform temperature gradient at a far distance. Owing to the poor thermal conductivities of the spheres, a tangential temperature gradient is established on the surfaces, and this causes a thermal-creep flow in its direction. Consequently, the spheres experience forces in the opposite direction.The flow considered here is a low-Reynolds-number flow in the ordinary fluid-dynamic sense (except for the Knudsen layer), and the solution is obtained in terms of bispherical coordinates, with respect to which the system of equations of Stokes type is well developed. The velocity field around the spheres and the forces acting on them are given explicitly. The results show the interesting feature that the smaller sphere experiences the minimum force at a value of the separation distance that depends on the radius ratio. This is in contrast with the case of the axisymmetric motion of two spheres treated by Stimson & Jeffery (1926) in ordinary fluid dynamics at low Reynolds number.The ultimate velocities that the spheres would have under the action of the present thermal force when they are freely suspended are also obtained by utilizing the results for the forces of axisymmetric translational problems of two spheres at low Reynolds number. For a given temperature gradient in the gas, both spheres acquire larger velocities than those they would have if they were alone, and the smaller sphere tends to move faster than the larger one in the direction opposite to the temperature gradient.Also presented, for completeness, are the results for the sphere–plane case and for the case of eccentric spheres, the solutions for which are derived as special cases of the preceding problem of two unequal spheres.

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