Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.

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Investigation on Convective Heat Transfer and Flow Features of Nanofluids

An introduction to heat transfer

In this review we focus on recent developments in applications of bio-inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio-inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.

Applications of Bio‐Inspired Special Wettable Surfaces

This paper explores the recent research developments in high-heat-flux thermal management. Cooling schemes such as pool boiling, detachable heat sinks, channel flow boiling, microchannel and mini-channel heat sinks, jet-impingement, and sprays, are discussed and compared relative to heat dissipation potential, reliability, and packaging concerns. It is demonstrated that, while different cooling options can be tailored to the specific needs of individual applications, system considerations always play a paramount role in determining the most suitable cooling scheme. It is also shown that extensive fundamental electronic cooling knowledge has been amassed over the past two decades. Yet there is now a growing need for hardware innovations rather than perturbations to those fundamental studies. An example of these innovations is the cooling of military avionics, where research findings from the electronic cooling literature have made possible the development of a new generation of cooling hardware which promise order of magnitude increases in heat dissipation compared to today's cutting edge avionics cooling schemes.

Assessment of high-heat-flux thermal management schemes

Superhydrophobic and superoleophobic surfaces have so far been made by roughening a hydrophobic material. However, no surfaces were able to repel extremely-low-energy liquids such as fluorinated solvents, which completely wet even the most hydrophobic material. We show how roughness alone, if made of a specific doubly reentrant structure that enables very low liquid-solid contact fraction, can render the surface of any material superrepellent. Starting from a completely wettable material (silica), we micro- and nanostructure its surface to make it superomniphobic and bounce off all available liquids, including perfluorohexane. The same superomniphobicity is further confirmed with identical surfaces of a metal and a polymer. Free of any hydrophobic coating, the superomniphobic silica surface also withstands temperatures over 1000°C and resists biofouling.

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Turning a surface superrepellent even to completely wetting liquids

We trace the evolution of enhanced boiling surfaces. Early work was highly empirical and done in industrial research. The 1968 Milton patent described the first porous coated surface, and the 1972 Webb patent described a structured tube surface geometry. The first fundamental understanding of the pore-and-tunnel geometry was published by Nakayama. Webb and Chien's flow visualization allowed observation of the evaporation in the subsurface tunnels. They also performed an experimental parametric study that defines the effect of pore diameter and pitch on the boiling performance. The progression of work on analytical boiling models is also reviewed

Donald Q. Kern Lecture Award Paper: Odyssey of the Enhanced Boiling Surface

This paper addresses two-phase flow distribution phenomena in multiple header–tube junctions used in heat exchangers. Because of phase separation, it is very difficult to obtain uniform two-phase flow distribution to the branch tubes. The flow distribution is strongly influenced by the header orientation (horizontal or vertical) and the number of branch tubes. Other factors that influence the flow distribution are the flow direction in the header (upflow or downflow), the header shape and tube end projection into the header, and the location and orientation of the inlet and exit connections. The source of maldistribution is the flow in the dividing headers. Work performed by the authors and others (including patents) are discussed. The possibilities for eliminating two-phase flow maldistribution are identified and discussed. This investigation shows that solutions, which provide uniform flow distribution, are very design-specific. Change of the geometry or operating parameters will require modifi...

Two-Phase Flow Distribution to Tubes of Parallel Flow Air-Cooled Heat Exchangers

Three types of phenomenological models are used for calculating heat transfer coefficients in convective vaporization—the superposition, asymptotic, and enhancement models. These models were originally proposed for in-tube vaporization. The objective of the present study is to critically assess these models, and to establish a rational basis for a modified model. Saturated convective vaporization is of key interest in this review. Much more work has been done on in-tube flow than for tube banks. This article surveys the currently available models, and establishes the commonality and differences of the correlations. Separate emphasis is given for tube bank correlations. The correlations for tube banks are compared to those used for in-tube flow. We show that the current correlations may be grouped into three basic types—superposition, enhancement, and asymptotic models. Each type is discussed in order to address the concepts involved in them. Problems associated with certain published models are d...

A Critical Review of Correlations for Convective Vaporization in Tubes and Tube Banks

Construction d'un modele theorique pour la prevision des coefficients de condensation sur des tubes a ailettes pour des fluides a tension superficielle elevee et faible. Utilisation du modele au calcul du coefficient de condensation du freon 11 sur des tubes a ailettes horizontaux avec 748, 1024 et 1378 ailettes/metre. Comparaison avec des donnees experimentales

Ralph L. Webb

Papers

Donald Q. Kern Lecture Award Paper: Odyssey of the Enhanced Boiling Surface

Two-Phase Flow Distribution to Tubes of Parallel Flow Air-Cooled Heat Exchangers

A Critical Review of Correlations for Convective Vaporization in Tubes and Tube Banks

Prediction of the Condensation Coefficient on Horizontal Integral-Fin Tubes

Measurement of bubble dynamics on an enhanced boiling surface