Heat transfer enhancement in suspensions of agitated solids. Part III: Thermophoretic transport of nanoparticles in the diffusion limit

An Analysis of Heat Conduction Models for Nanofluids

“…Indeed, notice in Figure 5, a-d, that Blackwell's solution would not be considered appropriate for the measurement of the thermal conductivity for τ < 1.2 × 10 −4 (ln τ = -9) for test cases a and c, and for τ < 2.5 × 10 −3 (ln τ = -6) for test cases b and d. In other words, the increase generally detected with the line heat source probe for the thermal conductivity of nanofluids cannot be attributed to the non-Fourier heat transfer mechanisms examined earlier. In fact, recent theoretical predictions corroborate our findings and demonstrate that nanoparticles and the base fluid are in thermal equilibrium in nanofluids [23,34].…”

“…Experiments with nanofluids have indicated significant increases in thermal conductivity, as compared to base liquids without nanoparticles or with larger suspended particles [14,[16][17][18][19][20][21][22][23]. Generally, the observed increase in thermal conductivity of nanofluids was substantially larger than that predicted with the available theory.…”

“…In this context, such a fact resulted in a search for physical phenomena not accounted for in the theoretical predictions for suspensions of micrometer-sized or larger particles, which included Brownian motion, liquid layering, ballistic mechanisms, thermophoresis, aggregation of nanoparticles into clusters, etc. [16][17][18][19][20][21][22][23][24][25][26]. Due to previous experimental observations that non-Fourier effects are significant at small time and space scales [1][2][3][4][5][6][7][8][9][10][11], hyperbolic heat conduction models were naturally suggested to explain the heat transfer enhancement in nanofluids [12,13].…”

Thermophoresis of charged colloidal particles in aqueous media – Effect of particle size

“…Many questions still remain, one of which is the dependence of thermophoresis on particle size. Practically, the characteristic of size dependent thermophoresis has a potential application for the separation of particles of different sizes [9][10][11], the manipulation of DNAs [12][13][14], and the enhancement of heat transfer of nanofluids [15][16][17][18][19][20][21][22]. In the literature, although numerous theoretical and experimental studies have been reported on the size dependence of thermophoresis for dilute polystyrene (PS) beads dispersed in aqueous solutions, the results of these investigations are inconsistent and inconclusive.…”

Thermal wave effects on heat transfer enhancement in nanofluids suspensions

“…Possible explanations for the divergence between theory and experiments were suggested and explored very basically by Brownian motion of the particles [17,18], micro-convection due to Brownian motion [19], molecular-level layering of the liquid at the liquid/particle interface [17,18,20], the nature of heat transport within the nanoparticles and effects of nanoparticle clustering [17,18], thermo-phoresis [21,22], electro-phoresis [21], hyperbolic heat conduction [23], Dual-phase-lagging effect of heat conduction in the nanofluid suspension [21]. To this end, most of these proposed mechanisms have been eliminated due to the theoretical outcomes of more detailed investigations except the dual-phase lagging, and that of nanoparticle clustering.…”