Nanofluids are engineered colloids made of a base fluid and nanoparticles (1-100 nm) Nanofluids have higher thermal conductivity' and single-phase heat transfer coefficients than their base fluids In particular the heat transfer coefficient increases appear to go beyond the mere thermal-conductivity effect, and cannot be predicted by traditional pure-fluid correlations such as Dittus-Boelter's In the nanofluid literature this behavior is generally attributed to thermal dispersion and intensified turbulence, brought about by nanoparticle motion To test the validity of this assumption, we have considered seven slip mechanisms that can produce a relative velocity between the nanoparticles and the base fluid These are inertia, Brownian diffusion, thermophoresis, diffusioplwresis, Magnus effect, fluid drainage, and gravity We concluded that, of these seven, only Brownian diffusion and thermophoresis are important slip mechanisms in nanofluids Based on this finding, we developed a two-component four-equation nonhomogeneous equilibrium model for mass, momentum, and heat transport in nanofluids A nondimensional analysis of the equations suggests that energy transfer by nanoparticle dispersion is negligible, and thus cannot explain the abnormal heat transfer coefficient increases Furthermore, a comparison of the nanoparticle and turbulent eddy time and length scales clearly indicates that the nanoparticles move homogeneously with the fluid in the presence of turbulent eddies so an effect on turbulence intensity is also doubtful Thus, we propose an alternative explanation for the abnormal heat transfer coefficient increases: the nanofluid properties may vary significantly within the boundary layer because of the effect of the temperature gradient and thermophoresis For a heated fluid, these effects can result in a significant decrease of viscosity within the boundary layer, thus leading to heat transfer enhancement A correlation structure that captures these effects is proposed

Convective Transport in Nanofluids

Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

Author(s): Vogel, Alfred; Venugopalan, Vasan | Abstract: The mechanisms of pulsed laser ablation of biological tissues were studied. The transiently empty space created between the fiber tip and the tissue surface improved the optical transmission to the target and thus increased the ablation efficiency. It was found that the structure and morphology also affect the energy transport among tissue constituents.

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Mechanisms of pulsed laser ablation of biological tissues.

This paper reviews the development of latent heat thermal energy storage systems studied detailing various phase change materials (PCMs) investigated over the last three decades, the heat transfer and enhancement techniques employed in PCMs to effectively charge and discharge latent heat energy and the formulation of the phase change problem. It also examines the geometry and configurations of PCM containers and a series of numerical and experimental tests undertaken to assess the effects of parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid (HTF). It is concluded that most of the phase change problems have been carried out at temperature ranges between 0 °C and 60 °C suitable for domestic heating applications. In terms of problem formulation, the common approach has been the use of enthalpy formulation. Heat transfer in the phase change problem was previously formulated using pure conduction approach but the problem has moved to a different level of complexity with added convection in the melt being accounted for. There is no standard method (such as British Standards or EU standards) developed to test for PCMs, making it difficult for comparison to be made to assess the suitability of PCMs to particular applications. A unified platform such as British Standards, EU standards needs to be developed to ensure same or similar procedure and analysis (performance curves) to allow comparison and knowledge gained from one test to be applied to another.

A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS)

A general correlation for flow boiling in tubes and annuli

Heat Exchangers—Theory and Practice

A major portion of the safety analysis effort for the liquid-metal fast breeder reactor is involved in assessing the consequences of a hypothetical core disruptive accident. A postulated loss-of-fl...

The Effects of Sodium Entrainment and Heat Transfer with Two-Phase UO2 During a Hypothetical Core Disruptive Accident

A survey of the state of data for condensation of metal vapors is presented and includes a discussion of the influence of measurement precision and traces of non-condensable gas on the observed res...

Film condensation of liquid metals

A thermal contact conductance equation was developed which considers both the effect of surface roughness and waviness. It was shown that the overall thermal contact conductance is determined by the roughness at large contact pressures or rough surfaces. It is also shown that surface roughness increases the contour radius over that predicted by the theory of Hertz. The surface roughness influences the magnitude of the waviness resistances by spreading the load at the contact over a larger region. The theory was seen to be in very good agreement with experimental data.

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Warren M. Rohsenow

Papers

Heat Exchangers—Theory and Practice

The Effects of Sodium Entrainment and Heat Transfer with Two-Phase UO2 During a Hypothetical Core Disruptive Accident

Film condensation of liquid metals

The effect of surface roughness and waviness upon the overall thermal contact resistance

Discussion: “On the Rohsenow Pool-Boiling Correlation” (Frost, C. W., and Li, K. W., 1971, ASME J. Heat Transfer, 93, pp. 232–234)