Numerical Study on the Interaction of Transverse and Longitudinal Roughness on Elastohydrodynamic Lubrication Contact Surfaces With Different Thermal Conductivities and Elastic Moduli

2020 ◽  
Vol 143 (9) ◽  
Author(s):  
Motohiro Kaneta ◽  
Kenji Matsuda ◽  
Jing Wang ◽  
Jinlei Cui ◽  
Peiran Yang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Finite Length ◽  
Elastic Moduli ◽  
Elastohydrodynamic Lubrication ◽  
High Thermal Conductivity ◽  
Low Thermal Conductivity ◽  
Longitudinal Roughness ◽  
Transverse Roughness ◽  
Contact Surfaces ◽  
Thermal Conductivities

Abstract The interaction and surface features between point contact surfaces composed of longitudinal roughness with infinite or finite length and transverse roughness were discussed based on a transient non-Newtonian thermal elastohydrodynamic lubrication (EHL) model. Each surface shape is greatly affected by the difference in elastic moduli, thermal conductivities, and velocities of both contact surfaces. There is a large difference in pressure behavior when the transverse roughness is in contact with the longitudinal roughness with finite length and when it is in contact with the longitudinal roughness with infinite length. In the contact between surfaces with infinitely long longitudinal and transverse roughness, the friction coefficient is lower when the surface with longitudinal roughness has a low thermal conductivity than when it has a high thermal conductivity. Furthermore, the pressure fluctuation is larger when the transverse roughness surface has a high thermal conductivity than when it has a low thermal conductivity.

An Exact Solution to Steady Heat Conduction in a Two-Dimensional Annulus on a One-Dimensional Fin: Application to Frosted Heat Exchangers With Round Tubes

2005 ◽  
Vol 128 (4) ◽  
pp. 397-404 ◽  
Author(s):  
A. D. Sommers ◽  
A. M. Jacobi
Keyword(s):  
Thermal Conductivity ◽  
Analytical Solution ◽  
High Thermal Conductivity ◽  
Two Dimensional ◽  
One Dimensional ◽  
Low Thermal Conductivity ◽  
Fin Efficiency ◽  
Coated Metal ◽  
The One ◽  
Term Approximation

The fin efficiency of a high-thermal-conductivity substrate coated with a low-thermal-conductivity layer is considered, and an analytical solution is presented and compared to alternative approaches for calculating fin efficiency. This model is appropriate for frost formation on a round-tube-and-fin metallic heat exchanger, and the problem can be cast as conduction in a composite two-dimensional circular cylinder on a one-dimensional radial fin. The analytical solution gives rise to an eigenvalue problem with an unusual orthogonality condition. A one-term approximation to this new analytical solution provides fin efficiency calculations of engineering accuracy for a range of conditions, including most frosted-coated metal fins. The series solution and the one-term approximation are of sufficient generality to be useful for other cases of a low-thermal-conductivity coating on a high-thermal-conductivity substrate.

Preparation and Properties of Rigid Carbon Felt Thermal Insulation

2015 ◽  
Vol 833 ◽  
pp. 48-51 ◽  
Author(s):  
Wei Shi ◽  
Jia Yan Li ◽  
Qi Fan You ◽  
Tong Lu ◽  
Yi Tan
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Compressive Strength ◽  
Thermal Insulation ◽  
Bending Strength ◽  
High Thermal Conductivity ◽  
Carbon Felt ◽  
Matrix Concentration ◽  
Thermal Conductivities

Matrix derived from resin after carbonization in rigid carbon felt thermal insulation has many advantages. The microstructures and properties of these materials were investigated in this paper. Results showed that matrix tend to accumulate at the intersections of fibers. This can improve mechanical properties and have a little influence on thermal conductivities of the composites. The excellent bending strength of 2.66MPa, compressive strength of 0.91MPa and a high thermal conductivity of 0.81W/(m·K) (at 1500°C) with a matrix concentration of 32.7% is achieved. However, high thermal conductivity is harmful for those materials which are used as thermal insulators.

Thermal-Wave Probing at Various Spatial Scales

MRS Bulletin ◽  
2001 ◽  
Vol 26 (6) ◽  
pp. 465-470 ◽  
Author(s):  
Danièle Fournier
Keyword(s):  
Thermal Conductivity ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Thermal Wave ◽  
Spatial Scales ◽  
High Thermal Conductivity ◽  
Heterogeneous Microstructures ◽  
Thermal Conductivities

In recent years, high thermal conductivity has been found in materials with heterogeneous microstructures, that is, ceramics and films with granular microstructures having different phases. Understanding the thermal conductivities and microstructures of these materials is more difficult, however, than in the case of single-crystal materials because they consist of grains and grain boundaries.

Effects of Elastic Moduli of Contact Surfaces in Elastohydrodynamic Lubrication

1992 ◽  
Vol 114 (1) ◽  
pp. 75-80 ◽  
Author(s):  
M. Kaneta ◽  
H. Nishikawa ◽  
K. Kameishi ◽  
T. Sakai ◽  
N. Ohno
Keyword(s):  
Elastic Moduli ◽  
Elastohydrodynamic Lubrication ◽  
Tangent Plane ◽  
Squeeze Film ◽  
Entrainment Velocity ◽  
Squeeze Film Effect ◽  
Contact Surfaces ◽  
The Difference ◽  
Surface Deflections ◽  
Film Profile

Using the optical interferometry technique the film profile in circular elastohydrodynamic contacts is examined with several kinds of fluid under wide ranges of loads and speeds. It is found that under a sliding condition a deep conical depression (dimple) occurs in the contact surface in place of the flat plateau predicted by the EHL theory. This dimple phenomena can be explained by the squeeze film effect acting parallel to the contact plane attributable to the difference in surface deflections of the contact bodies. That is, if the contacting bodies are different in their elastic moduli, EHL film shape is markedly influenced by the slide/roll ratio even if the rolling or entrainment velocity is kept constant. This result suggests that the establishment of a new EHL theory, which takes into consideration the effects of the difference in elastic moduli of the contacting surfaces and surface pressure components parallel to the contact tangent plane, is necessary for deeper understanding of the EHL regime.

Enhancement of thermal conductivity in ceramics obtained from a combustion synthesized AlN powder by microwave sintering and reheating

2008 ◽  
Vol 23 (3) ◽  
pp. 819-827 ◽  
Author(s):  
Shyan-Lung Chung ◽  
Cheng-Yu Hsieh ◽  
Chih-Wei Chang
Keyword(s):  
Thermal Conductivity ◽  
Oxygen Content ◽  
Microwave Sintering ◽  
Starting Material ◽  
High Thermal Conductivity ◽  
Secondary Phases ◽  
Soaking Time ◽  
Low Thermal Conductivity ◽  
Carbon Particles ◽  
Reducing Atmosphere

A combustion-synthesized AlN powder was investigated for use as a starting material in obtaining a high thermal conductivity AlN by microwave sintering followed by microwave reheating under a reducing atmosphere. Microwave sintering was found to proceed very quickly so that a density of 99.5% of theoretical with a thermal conductivity of 165 W/mK was achieved after sintering at 1900 °C for 5 min. The thermal conductivity could be improved by prolonging the soaking time, which is attributed to decreases in both oxygen content and secondary phases by evaporation and sublimation of the secondary phases. The reducing atmosphere was created by adding carbon particles to the AlN packing powder surrounding the specimen. The thermal conductivity could be significantly improved by microwave reheating of the sintered specimen under the reducing atmosphere. This is considered to be due to enhanced removal of the secondary phases by the reducing atmosphere. Sintering under the reducing atmosphere was found to retard densification because of the earlier removal of the secondary phases, thus resulting in a poor densification and a low thermal conductivity.

Experimental Investigation on the Thermal Insulation Properties of Eic-Cellulose

2014 ◽  
Vol 554 ◽  
pp. 322-326 ◽  
Author(s):  
Wuryanti Sri ◽  
Suhardjo Poertadji ◽  
Bambang Soegijono ◽  
Nasution Henry
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Thermal Insulation ◽  
Cellulose Fibers ◽  
Extraction Process ◽  
Thermal Capacity ◽  
Insulation Material ◽  
Low Thermal Conductivity ◽  
Thermal Conductivities

The material with low thermal conductivity means it has a high insulating capability for reducing heat transfer. One of materials for insulation is cellulose. This study presents a insulation material of cellulose made from reeds imperata cylindrical type with the extraction process. The extraction of cellulose fibers to form a sheet by adding 3.5% Na-CMC (Sodium Cellulose Carboksil Metyl). The process of forming the sheet uses blender for 30 minutes, 45 minutes, and 60 minutes. Furthermore, each mixture are put into the oven with temperature of 40°C for 36 hours. There are three parameters will be investigated, i.e. thermal conductivity, density and thermal capacity. The results showed that the lowest and the highest of thermal conductivities were 0.22 W/m K and a maximum 0.36 W/m K, respectively.

Conduction Characteristics of Frosting Circumferential Fin of Rectangular Profile

2011 ◽  
Vol 354-355 ◽  
pp. 779-783
Author(s):  
Kun Feng Sun ◽  
Xiao Lu Wang ◽  
Heng Liang Zhang
Keyword(s):  
Thermal Conductivity ◽  
Mathematical Model ◽  
Analytical Solution ◽  
High Thermal Conductivity ◽  
Engineering Practice ◽  
Low Thermal Conductivity ◽  
Rectangular Profile ◽  
Alternative Approaches ◽  
Frost Layer ◽  
Form Of Expression

Through the appropriate assumptions, a mathematical model was derived on circumferential fin of rectangular profile coated with frost layer, and a new analytical solution is presented and compared to alternative approaches for calculating the fin temperature and efficiency. The analytical solution enhances the accuracy ,and have a simpler form of expression. It can be easily used in engineering practice. The solution is useful for other cases of a low-thermal-conductivity coating on a high-thermal-conductivity substrate .

An electron microscopy study of high-thermal-conductivity ribbon-shape carbon fibers

1993 ◽  
Vol 51 ◽  
pp. 618-619
Author(s):  
Kerry E. Robinson
Keyword(s):  
Electron Microscopy ◽  
Thermal Conductivity ◽  
Liquid Crystalline ◽  
Structural Information ◽  
Low Cost ◽  
Microscopy Study ◽  
High Thermal Conductivity ◽  
Mesophase Pitch ◽  
Thermal Conductivities ◽  
Shaped Fibers

In an effort to develop a low-cost high thermal conductivity carbon fiber, ribbon-shaped fibers were meltspun from a liquid crystalline, mesophase pitch precursor. Initial tests indicated that the ribbon-shaped fibers could be processed more easily and exhibited improved thermal conductivities when compared to commercial round fibers. Evidently, it is the more linear, polycrystalline structure within these fibers that accounts for their improved thermal conductivities. Thus, studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to fully analyze the transverse and longitudinal structure of these high thermal conductivity fibers.Ribbon-shaped fibers, melt-spun from a synthetic mesophase pitch and then heat treated, were tested to determine their tensile strengths, tensile moduli and thermal conductivities. A Jeol JSM-I C848 SEM at an accelerating voltage of 20 kV was used to obtain general structural information, such as extent and texture of lamellar organization of the graphitic layers within the fibers, and the microstructure of the fibers was studied by TEM.

High Thermal Conductivity Graphite Copper Composites with Diamond Coatings for Thermal Management Packaging Applications

1995 ◽  
Vol 390 ◽  
Author(s):  
Chris H. Stoessel ◽  
C. Pan ◽  
J. C. Withers ◽  
D. Wallace ◽  
R. O. Loutfy
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Management ◽  
Heat Sinks ◽  
High Thermal Conductivity ◽  
Graphite Fiber ◽  
Fiber Reinforced ◽  
Cathode Sputtering ◽  
Large Expansion ◽  
Thermal Conductivities

ABSTRACTHigh thermal conductivity heat sinks for thermal management in electronic packaging is enabling to a variety of advanced electronic applications. Heat sinks in industrial semiconductor application have thermal conductivities generally less than 180 W/mK, and frequently have large expansion mismatch with chips such as silicon and gallium arsenide. A unique technology of producing graphite fiber reinforced copper (Cf/Cu) composite has been developed that produced thermal conductivities up to 454 W/mK utilizing a K=640 W/mK fiber reinforcement (with a potential for 800 W/mK when utilizing a K = 1100 W/mK P130 fiber) and thermal expansion that can be matched to chip materials. The process consists of utilizing a hollow cathode sputtering process to deposit a bonding layer followed by copper on spread graphite fibers, which are then consolidated into composites with architectures to achieve desired thermal conductivity and thermal expansion. The copper thickness determines graphite fiber loading up to 80 %. In heat sink applications, where the electrical conductivity of the graphite fiber reinforced copper composite is a problem, processing has been developed for applying electrically insulating diamond film, which has high thermal conductivity and acts as a heat spreader.

Tunable Thermal Conductivity of TiO2 Films of Close-Packed Nanoparticles

2011 ◽  
Author(s):  
Patrick E. Hopkins ◽  
Manish Mittal ◽  
Leslie M. Phinney ◽  
Anne M. Grillet ◽  
Eric M. Furst
Keyword(s):  
Thermal Conductivity ◽  
Time Domain ◽  
Orientational Order ◽  
Colloidal Nanoparticles ◽  
Tio2 Films ◽  
Low Thermal Conductivity ◽  
Coated Glass ◽  
Glass Substrates ◽  
Nanoparticle Films ◽  
Thermal Conductivities

We report on the ultra-low thermal conductivity of a series of convectively assembled, anisotropic titania (TiO2) nanoparticle films. The TiO2 films are fabricated on aluminum coated glass substrates by flow coating a suspension of ellipsoidal colloidal nanoparticles, resulting in structured films with tailored order. Time domain thermoreflectance is used to measure the thermal conductivity of the TiO2 films. The thermal conductivities of these nanoparticle films are dependent on nanoparticle orientational order and films with more randomly oriented particles exhibit thermal conductivities less than the amorphous limit.

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