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Slack phonon conductivity model mainly considering acoustic phonon scattering (three-phonon interaction) is given as [27] [28] =, = /, / (>,, where M is the mean atomic weight of the atoms in the primitive cell, V a =1/n is the average volume per atom, T D,∞ is the high-temperature Debye temperature, T is the temperature, N o is the number of ...
When stated in terms of temperature differences, Newton's law (with several further simplifying assumptions, such as a low Biot number and a temperature-independent heat capacity) results in a simple differential equation expressing temperature-difference as a function of time. The solution to that equation describes an exponential decrease of ...
Such motion, in the presence of a temperature gradient, contributes to heat transfer. Because the molecules in aggregate retain their random motion, the total heat transfer is then due to the superposition of energy transport by random motion of the molecules and by the bulk motion of the fluid. It is customary to use the term convection when ...
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles.
Brownian motion is the random motion of particles suspended in a medium (a liquid or a gas). [2] This motion pattern typically consists of random fluctuations in a particle's position inside a fluid sub-domain, followed by a relocation to another sub-domain. Each relocation is followed by more fluctuations within the new closed volume.
Thus, the dynamics of particle motion can be treated classically, and the equations of motion are time-reversible. As a simplifying assumption, the particles are usually assumed to have the same mass as one another; however, the theory can be generalized to a mass distribution, with each mass type contributing to the gas properties ...
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The shiver response may be greatly diminished or even absent in the elderly, resulting in a significant drop in mean deep body temperature upon exposure to cold. Standard tests of thermoregulatory function show a markedly different rate of decline of thermoregulatory processes in different individuals with ageing.