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

Heat Transfer and Friction Characteristics of Turbulator Radiator Tubes

An experimental study has been carried out to investigate the long-term wetting characteristics of dehumidifying finned tube heat-exchangers (coils). The coils were subjected to up to 1000 cycles in which they were alternately dipped into distilled water for 15 minutes and then dried with a fan for 45 minutes. Wetting durability was determined for three uncoated coil, two were coated with proprietary coatings, and a coil with a zinc coating sprayed on the downstream face, and with different fin press oils. Wind tunnel tests on fully wet coils under dehumidification were conducted. The advancing and receding contact angles werer measured by periodically removing small fin samples from the coils. One coating maintained the receding contact angle below 15° throughout the cycle tests. The advancing contact angles were much higher than the receding contact angle. The best coating maintained the wet/dry pressure drop ratio below 1.34 throughout the 1000 cycles. The wet/dry pressure drop ratio was correlated as ...

Long-Term Hydraulic Performance of Dehumidifying Heat-Exchangers With and Without Hydrophilic Coatings

Plasma hydrophilic surface treatment for dehumidifying heat exchangers

Condensate formation and drainage on typical fin materials

Experimental studies were conducted to investigate the long-term wetting and corrosion characteristics of hot water treated aluminum and copper fin stocks. This was done by subjecting them to wet/dry cycling consisting of alternately dipping the fin samples into distilled water for 5 min followed by air drying with a fan for 25 min. To simulate the fins of a heat exchanger, fin stocks were formed in a wavy shape using hand operated fin dies and a typical lubricant oil. The fin samples, including the formed and the unformed aluminum and copper stocks, were treated using hot water by immersing them in either 82 or 100 °C water for 20 min. The wettability and corrosion evaluations consisted of periodic measurements of the advancing/receding contact angles and weights of the fin samples. SEM photos were taken to show the appearance of the sample surfaces. Further, X-ray photoelectron spectroscope examinations were performed to analyze the atomic composition at the sample surfaces. The test results suggest that the hot water soak is an effective means to improve the surface wettability of both aluminum and copper surfaces. The soaking procedure was capable of producing wettable fin that was durable to wet/dry cycling. The soaking operation and follow-on wet/dry cycling treatment did not cause significant material loss by general corrosion.

Ralph L. Webb

Papers

Heat Transfer and Friction Characteristics of Turbulator Radiator Tubes

Long-Term Hydraulic Performance of Dehumidifying Heat-Exchangers With and Without Hydrophilic Coatings

Plasma hydrophilic surface treatment for dehumidifying heat exchangers

Condensate formation and drainage on typical fin materials

Long-term wetting and corrosion characteristics of hot water treated aluminum and copper fin stocks