Mechanisms of heat flow in suspensions of nano-sized particles (nanofluids)

▪ Abstract Nanofluids, consisting of nanometer-sized solid particles and fibers dispersed in liquids, have recently been demonstrated to have great potential for improving the heat transfer properties of liquids. Several characteristic behaviors of nanofluids have been identified, including the possibility of obtaining large increases in thermal conductivity compared with liquids without nanoparticles, strong temperature-dependent effects, and significant increases in critical heat flux. Observed behavior is in many cases anomalous with respect to the predictions of existing macroscopic theories, indicating the need for a new theory that properly accounts for the unique features of nanofluids. Theoretical studies of the possible heat transfer mechanisms have been initiated, but to date obtaining an atomic- and microscale-level understanding of how heat is transferred in nanofluids remains the greatest challenge that must be overcome in order to realize the full potential of this new class of heat transfer...

Thermal transport in nanofluids1

This work examines the lagging behavior for heat transport in small-scale and fast-transient processes. The experimental result by Qiu et al. for the femtosecond transient response in gold films and that by Bertman and Sandiford for the temperature pulse traveling through superfluid liquid helium are re-examined with emphasis on the lagging behavior. The model employing the phase-lag concept provides as competent or even better results when describing the special response observed in these experiments.

Experimental support for the lagging behavior in heat propagation

Heat transfer around nanometer-scale particles plays an important role in a number of contemporary technologies such as nanofabrication and diagnosis The prevailing method for modeling thermal phenomena involving nanoparticles is based on the Fourier heat conduction theory This work questions the applicability of the Fourier heat conduction theory to these cases and answers the question by solving the Boltzmann transport equation The solution approaches the prediction of the Fourier law when the particle radius is much larger than the heat-carrier mean free path of the host medium In the opposite limit, however, the heat transfer rate from the particle is significantly smaller, and thus the particle temperature rise is much larger than the prediction of the Fourier conduction theory The differences are attributed to the nonlocal and nonequilibrium nature of the heat transfer processes around nanoparticles This work also establishes a criterion to determine the applicability of the Fourier heat conduction theory and constructs a simple approximate expression for calculating the effective thermal conductivity of the host medium around a nanoparticle Possible experimental evidence is discussed

Nonlocal and Nonequilibrium Heat Conduction in the Vicinity of Nanoparticles

Review on thermal properties of nanofluids: Recent developments.

Ballistic and diffusive phonon transport under small time and spatial scales are important in fast‐switching electronic devices and pulsed‐laser processing of materials. The Fourier law represents only diffusive transport and yields an infinite speed for heat waves. Although the hyperbolic heat equation involves a finite heat wave speed, it cannot model ballistic phonon transport in short spatial scales, which under steady state follows the Casimir limit of phonon radiation. An equation of phonon radiative transfer (EPRT) is developed which shows the correct limiting behavior for both purely ballistic and diffusive transport. The solution of the EPRT for diamond thin films not only produces wall temperature jumps under ballistic transport but shows markedly different transient response from that of the Fourier law and the hyperbolic heat equation even for predominantly diffusive transport. For sudden temperature rise at one film boundary, the results show that the Fourier law and the hyperbolic heat equat...

A. Majumdar

Papers

Transient ballistic and diffusive phonon heat transport in thin films