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.

/pdf/turning-a-surface-superrepellent-even-to-completely-wetting-2dlo3glabg.pdf

Turning a surface superrepellent even to completely wetting liquids

This letter provides discussion of the previously published paper, Yi-Ye Yan and Tsing-Fa Lin, Evaporation heat transfer and pressure drop of refrigerant 134A in a small pipe Authors' reply

This paper presents a description of three computer algorithms developed to perform rating calculations of commercially available cooling towers, evaporative fluid coolers, and evaporative condensers. The paper illustrates the various simulations that are possible, including varying wet-bulb, inlet and exit temperatures, different fluid flow rates, altitude, or combinations of the above. The heat and mass transfer “characteristic equations, ”as a function of the fluid flow rates for a given evaporative heat exchanger, are derived from the manufacturer's rating data on one operating point, e.g., at the rating point. Or, one may use independently developed “characteristic equations” for any packing or tube bundle geometry of interest. The algorithms provide capability to predict the heat exchange capacity at any weather or process condition. They also allow the plant engineer to assess the effect of varying the air flow rate on the fan power for specified operating conditions. Example cases are ana...

Performance Simulation of Evaporative Heat Exchangers [Cooling Towers, Fluid Coolers, and Condensers]

Numerical Study of Turbulent Flow and Heat Transfer in Micro-Fin Tubes – Part 2, Parametric Study

Convective vaporization data were obtained for two different enhanced tube geometries in a staggered tube bank made of 18.9 mm (0.75 inch) outside diameter tubes having an equilateral pitch-to-diameter ratio of 1.25. Data are presented for pure refrigerants R-11, R-123, and R-134a at saturation temperatures of 4.4°C (40°F) and 26.7°C (80°F). The data span vapor qualities of 0.0 to 0.9, mass velocities (based on minimum flow cross section area) of 10 to 30 kg/(m2· s) (7,400 to 22,000 lb/h·ft2), and heat fluxes of 15 to 45 kW/m2 (4,760 to 14,300 Btu/h·ft2). The apparatus allowed independent control of vapor quality, mass velocity, and heat flux. The data were correlated in the form of an asymptotic model with a root mean squared error of less than 15%. A modified superposition model with a suppression factor of unity correlated all the Tu-B (R-11 and R-123) data and approximately 90% of the W-SE (R-134a) data within ±20%. The experimental results for the two enhanced tube geometries tested show that the tub...

Convective Vaporization Data for Pure Refrigerants in Tube Banks Part II: Enhanced Tubes

Analysis was performed to determine the performance and economic benefits of using enhanced condenser tubes in an existing nuclear plant. This work consisted of using measured heat transfer and friction performance of two enhanced tube geometries to calculate the resulting reduction of condenser saturation temperature. Using the known plant heat rate and heat rate correction factor, we calculated the increased plant generation capacity, relative to the plain tube condenser design. Detailed analysis was done for the Wieland NW-16 and the Wolverine Korodense-LPD tubes, which are estimated to cost about 23% more than plain tubes. Simple payback analysis of the Wieland NW-16 “new tube bundle” tube shows that the annual average heat rate is reduced 3.83% and the increased tube cost can be recovered in 0.036 years based on the increased generation capacity valued at $2000/kW. Tube-for-tube replacement provides a payback of 0.054 years. For the month of July, the heat rate (with new bundle) is reduced 3.83% and ...

Ralph L. Webb

Papers

This letter provides discussion of the previously published paper, Yi-Ye Yan and Tsing-Fa Lin, Evaporation heat transfer and pressure drop of refrigerant 134A in a small pipe Authors' reply

Performance Simulation of Evaporative Heat Exchangers [Cooling Towers, Fluid Coolers, and Condensers]

Numerical Study of Turbulent Flow and Heat Transfer in Micro-Fin Tubes – Part 2, Parametric Study

Convective Vaporization Data for Pure Refrigerants in Tube Banks Part II: Enhanced Tubes

Enhanced Condenser Tubes in a Nuclear Power Plant for Heat Rate Improvement