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

Condensate drainage and retention in louver fin automotive evaporators

The wavy fin-and-tube heat exchanger is widely used in the air-conditioning industry. Hence, the ability of numerical codes to predict the thermo-hydraulic performance of this heat exchanger geometry is of considerable interest. Here, a numerical study has been conducted to predict the air-side heat transfer and pressure drop characteristics of a 2-row finned tube heat exchanger having a herringbone wavy fin geometry. The calculations were performed using the FLUENT CFD code. The calculations were performed in three dimensions and account for conduction within the fins. The computational domain was chosen to cover the entire fin length in the air flow direction. The calculations are implemented for the frontal air velocities between 1.0 and 3.0 m/s yielding hydraulic diameter Reynolds number from 380 to 1,150. The uniqueness of this work is inclusion of the tubes in the wavy channel geometry, and use of a three-dimensional (3D) calculation model. The flow and thermal fields in this finned tube heat exchanger as well as the temperature distribution of the fin are presented and described. The fin efficiency is numerically determined and compared with that given by the Schmidt equation (1966) and found to agree within {+-}2.3%. Predictions were performed for a herringbone channelmore » without and with tubes. The tubes considerably increase the pressure drop, but the effect on the average heat transfer coefficient is much smaller. The calculation results are compared with test data taken by Kang and Webb (1997) for a test sample having the same geometry. The FLUENT over predicts the air-side heat transfer coefficient by 13% and pressure drop by 31%.« less

Numerical predictions of wavy fin coil performance

(1979). A review of “ Handbook of Essential Formulae and Data on Heat Transfer for Engineers ”by H. Y. Wong Longman Group, Ltd., London, 1977, $ 11.50. Heat Transfer Engineering: Vol. 1, No. 1, pp. 55-55.

A review of “ Handbook of Essential Formulae and Data on Heat Transfer for Engineers ”by H. Y. Wong Longman Group, Ltd., London, 1977, $ 11.50

Th is article discusses the eﬀ ects of tube geometry on the performance of a multi-row ﬁ nned tube heat exchanger having herringbone wavy ﬁ ns. Th e air-side heat transfer and pressure drop characteristics of the heat exchanger were predicted numerically and the tube-side heat transfer coeﬃ cient and pressure drop were calculated using commonly adopted equations for turbulent ﬂ ow in a smooth tube. Th e numerical calculations were performed in three dimensions for three frontal air velocities of 1.0, 2.0, and 3.0 m/s, yielding hydraulic diameter Reynolds numbers from 297 to 999. Investigated were ﬁ ve tube geometries, including a round tube, three elliptical oval tubes, and a ﬂ at oval tube. Th e round tube has a 15.875 mm (⅝ ") outside diameter and serves as the baseline tube. Th e four oval tubes were made by reforming the baseline round tube and have the same perimeter as that of the round tube. Th e aspect ratios of the three elliptical tubes are 2.00, 3.00, and 4.29, respectively, and the aspect ratio of the ﬂ at oval tube is 3.00. As the tube aspect ratio is increased, the air-side heat transfer coeﬃ cient and pressure drop decrease, but the water-side heat transfer coeﬃ cient and pressure drop increase. At 2.0 m/s frontal velocity, the 3.00 aspect ratio elliptical tube yields a 6.9% lower air-side heat transfer coeﬃ cient and a 45.9% lower air pressure drop than the round tube. As compared to the 3.00 aspect ratio elliptical tube, the same aspect ratio ﬂ at tube has a 0.6% higher air-side heat transfer coeﬃ cient and a 2.5% higher air pressure drop.

Ralph L. Webb

Papers

Condensate drainage and retention in louver fin automotive evaporators

Numerical predictions of wavy fin coil performance

A review of “ Handbook of Essential Formulae and Data on Heat Transfer for Engineers ”by H. Y. Wong Longman Group, Ltd., London, 1977, $ 11.50

Numerical Analyses of Effects of Tube Shape on Performance of a Finned Tube Heat Exchanger

Rationally Based Heat Transfer and Friction Correlations for the Louver Fin Geometry