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Water Flow in Graphene Nanochannels
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
As macroscale simplifications, such as continuum, no interfacial velocity slip, and no fluid density oscillation, should be adjusted in nanoscale hydrodynamic modeling, the approximation of interfacial fluid temperature to the channel surface temperature cannot be justified in nanoscale thermal transport. Due to the mismatch in thermal vibration and finite strength of interfacial interaction, thermal boundary resistance, also called the Kapitza resistance (Rt,s/f, m2-K/W), exists between water and surface, which causes the interfacial temperature jump; i.e., ΔT s/f = T s – T f,z=0≠= 0. The temperature jump is proportional to heat flux as well as the thermal boundary resistance (ΔT s/f = qs/f Rt,s/f). Similar to the velocity slip length, the thermal slip (or Kapitza) length (Lk) can also be defined using temperature distribution as Lk=-Ts-Tf,z=0(∂Tf∕∂z)z=0.
Oxidation induced emissivity evolution of silicon carbide based thermal protection materials in hypersonic environments
Published in Journal of Asian Ceramic Societies, 2021
Liping Liu, Lingwei Yang, Haojun Ma, Jie Luo, Xueren Xiao, Changhao Zhao, Jun Zhang, Guolin Wang, Yiguang Wang
In order to acquire ε at a wide temperature range, in this work stepped wind tunnel experiments were carried out on the Cf/C, SiCf/SiC, Cf/SiC and ZrB2-SiC hemispheres, at each step the surface temperature was stabilized for a few seconds and the radiation characteristics were acquired instantaneously at the measured temperatures. Figure 2 (a) plots typical thermal responses of the Cf/C and SiCf/SiC during the stepped wind tunnel experiments. E.g. for the Cf/C, the surface temperature was stepped increased from ≈1000 to ≈2115°C by increasing qcw from ≈0.85 to ≈3.37 MW/m2. Unlike the Cf/C, the SiCf/SiC, Cf/SiC and ZrB2-SiC are all SiC-based composites and a “thermal instability” may emerge at higher qcw due to abrupt changes in the surface oxidized microstructures [26]. The mechanism may interrupt the thermal balance, thus triggering an abrupt “temperature jump”. As shown in Figure 2 (a), the “temperature jump” of the SiCf/SiC emerged when raising qcw from ≈2.52 to ≈2.68 MW/m2. During the process, the surface temperature was rapidly increased from ≈1406 to ≈2297°C in a few seconds. Similar “temperature jump” phenomena emerged at ≈1750°C in the Cf/SiC [4], and in our wind tunnel it was triggered when increasing qcw from ≈3.68 to ≈4.74 MW/m2, as shown in Figure 2 (b). For the ZrB2-SiC, the oxidation temperature was continuously increased, and thermal balance was hardly achieved when increasing qcw from ≈2.98 to ≈3.45 MW/m2. As will be shown later, the oxide scale at the temperature range is continuously evolved, which leads to an evident temperature-sensitive emissivity in the plasma environment. This may be a mechanism interrupting the thermal balance and leading to the temperature increase.