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Motor Cooling
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
From the microscopic point of view, solid surfaces made by regular manufacturing processes are never perfectly smooth. Rather, the surfaces are constituted of asperities of different sizes and shapes. Therefore, when two solid surfaces are brought together, only a small portion of the matching surfaces make physical contact and most of the matching surfaces are separated by a layer of air. The voids/gaps formed between the contacted surfaces thus result in high thermal resistance as heat is transferred across the interface. Therefore, a variety of thermal interface materials have been developed for filling voids/gaps, thus improving surface contact and heat conduction across the interface. Because thermal interface materials generally have much higher thermal conductivities than that of air, the interfacial thermal resistance can be significantly reduced.
Nanoscale Effects in Multiphase Flows and Heat Transfer
Published in Anupama B. Kaul, Microelectronics to Nanoelectronics, 2017
Navdeep Singh, Donghyun Shin, Debjyoti Banerjee
Interfacial thermal resistance represents a barrier to heat flow at the boundary between two phases or two dissimilar materials. Thermal resistance at the interface was first reported by Kapitza, with his measurement of the temperature drop at the interface between helium and a solid (Kapitza, 1941). Hence, the interface thermal resistance is also known as Kapitza resistance.
Enhancing the Thermal Properties of Water and Ethylene Glycol with Nanoadditives and Surface Functionalization
Published in Alina Adriana Minea, Advances in New Heat Transfer Fluids, 2017
For many of the nanofluids in Table 8.3, their unexpectedly low thermal conductivities can be explained in part by the thermal resistance across nanoparticle contacts (although the magnitude of the thermal resistance seems low relative to that experience across other types of interfaces [Hopkins et al. 2012], the number of nanoparticle–nanoparticle contacts and/or the high surface-area-to-volume ratio of the nanoparticles results in a significant impediment to heat flow within suspensions of nanoparticles). That said, results for CNT- and graphene-based nanofluids suggest that the overall thermal conductivity of these nanofluids provide a clear path for their use in common industrial and commercial heat transfer devices as they approach the DOD-defined Technology Readiness Level (TRL) 4. In order for less resistance to adoption as a TRL 4 technology, it is expected that carbon nanoparticle–based nanofluids will have to exhibit the unique thermal transport characteristics that are predicted with effective medium approximations. In order to do this, the interfacial thermal resistance at nanoparticle–fluid and nanoparticle–nanoparticle interfaces will have to be reduced. In the final part of this chapter, a brief summary of techniques used to modify the surfaces of carbon-based nanoparticles (and thus augment the nature of heat flow at the interface) is discussed. Improvements in the thermal conductivity of the nanofluids are explained within the context of the surface additives at the nanoparticles’ interface(s).
A sub-interface thermal crack problem for bonded dissimilar plates with interfacial thermal resistance
Published in Journal of Thermal Stresses, 2019
It is known that thermal resistance exists at interfaces in bonded and composite materials [1]. The interfacial thermal resistance is due to the gaps associated with imperfect bonding at the interface between the constituent materials generated by external loads as well as during manufacturing of the materials owing to thermal expansion mismatch between the constituents [2]. Hasselman and Johnson [3] and Nan et al. [4] have showed that the effective thermal conductivity of composites is reduced by the thermal resistance at the interfaces between the constituents, which implies that interfacial thermal resistance has significant influences on heat conduction, and hence thermal stresses/thermal fracture in bonded and composite materials.
Molecular dynamics simulations of the effect of surface wettability on nanoscale liquid film phase-change
Published in Numerical Heat Transfer, Part A: Applications, 2019
The thermal resistance of heat conduction for a liquid film is much larger than the interfacial thermal resistance at the macroscopic scale, so the effect of the interfacial thermal resistance is negligible. When the thickness of a liquid film decreases to the nanoscale, the influence of the interfacial thermal resistance cannot be ignored. The interfacial thermal resistance is defined as follows: where ΔTk is the temperature difference at the solid-liquid interface, and qk is the heat flux through the solid-liquid interface. For simulation cell (2), the heat flows through the heat source and heat sink of the hydrophilic and hydrophobic surfaces are shown in Figure 8. It can be seen from Figure 8 that the absolute values of the heat flows through the heat source and heat sink are almost the same at every moment, which indicates that the energy of the whole simulation system is conserved. To obtain the temperature difference at the solid-liquid interface, the simulation system was divided into 31 slices every 3 Å along the z axis. The temperature profile was averaged over a 2 ns period and output every 10 ps when the system reached the steady state. Therefore, the temperature distribution of the copper and argon atoms along the z direction can be obtained. The temperature discontinuity at the solid-liquid interface was obtained by linear extrapolation [22] from both the solid copper plate and liquid argon film. From the heat flux and temperature difference at the solid-liquid interface, the interfacial thermal resistance can be calculated. The temperature distribution of copper and argon atoms along the z direction is shown in Figure 9, and the corresponding interfacial thermal resistance is given in Table 3, which is the same order of magnitude as the calculated results of previous studies [23]. We can find that solid-liquid interfacial thermal resistance is almost the same with thermal resistance between solid and liquid for hydrophilic surface, and the difference is 0.12 × 10−8 m2 K/W. However, the difference is 7.70 × 10−8 m2 K/W for hydrophobic surface, this is caused by the liquid-vapor-liked region near the surface. From the comparison, it is believed that solid-liquid interfacial thermal resistance is an important parameter in liquid film phase-change process at nanoscale.