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This article reports viscosity data on a series of colloidal dispersions collected as part of the International Nanofluid Property Benchmark Exercise (INPBE). Data are reported for seven different fluids that include dispersions of metal-oxide nanoparticles in water, and in synthetic oil. These fluids, which are also referred to as ‘nanofluids,’ are currently being researched for their potential to function as heat transfer fluids. In a recently published paper from the INPBE study, thermal conductivity data from more than 30 laboratories around the world were reported and analyzed. Here, we examine the influence of particle shape and concentration on the viscosity of these same nanofluids and compare data to predictions from classical theories on suspension rheology.

1. IntroductionSince the signing of the Executive Order establishing the Office of Homeland Security, Federal agencies have been working on ways to improve the security of the general public. In [...]

This paper provides a detailed account of the development of a fluorescence based measurement technique for measuring the mass of contaminant on solid surfaces in the presence of water flow. A test apparatus was designed and developed for the purpose of studying adsorption and desorption of diesel to and from a copper test surface in the presence of contaminated and fresh water flow, respectively. A calibration technique was developed to correlate the measured fluorescence intensity to the mass of diesel adsorbed per unit surface area (the excess surface density) and the bulk concentration of the diesel in the flow. Both bulk composition and the excess surface density measurements were achieved via a traverse of the fluorescent measurement probe perpendicular to the test surface. The measured diesel excess surface density varied between zero and 0.02 kg/m2for the variation in the bulk mass fraction and Reynolds number of the flow. [ABSTRACT FROM AUTHOR]

This article presents local convective boiling measurements in a micro-fin tube for three low global warming potential refrigerants: R448A, R449A, and R452B1R452B is the pending ASHRAE designation for the mixture R32/R125/R1234yf (67/7/26), which has the developmental designation DR-55.. An existing correlation was modified to predict multi-component mixtures, which predicted 98% of the measurements to within ±20%. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting comparison showed that refrigerant R452B exhibited the highest heat transfer, in large part due to its approximately 28% larger liquid thermal conductivity and smaller temperature glide as compared to the tested low-global warming potential refrigerants. For the example case, the heat transfer coefficient for R449A was approximately 8% larger than that for R448A, while the heat transfer coefficient for R452B was more than 59% larger than either R448A or R449A. The heat transfer coefficients for R448A and R449A were roughly between 26 and 48% less than that of R404A for the example case. In contrast, the model predicts that the R452B heat transfer coefficient was approximately 13% larger than that of R404A for the same conditions. [ABSTRACT FROM AUTHOR]

This article is an evaluation of the cycle performance of 39 refrigerants identified in the AHRI Low Global Warming Potential Alternative Refrigerants Evaluation Program in a typical air conditioner. This program was initiated in response to environmental concerns raised by the use of high global warming potential refrigerants with the intent to identify and evaluate promising alternative refrigerants. The cycle performance of each refrigerant is calculated assuming the same evaporator heat duty and sink temperatures for the condenser. The evaluation included the effects of heat transfer and pressure drop in the evaporator and the condenser. Four performance variables were investigated: (1) the coefficient of performance, (2) the required volumetric displacement of the compressor, (3) the mean temperature difference of the evaporator, and (4) the compressor discharge superheat. Ratios of the above four parameters relative to the refrigerants that are intended to be replaced are provided for each replacement refrigerant. In addition, a methodology was developed using weighting factors to rank the alternative refrigerants either emphasizing the importance of a large coefficient of performance or the importance of reduced system size. The two ranking methodologies produced different rankings of the alternative refrigerants, although the top three ranked refrigerants had at least two refrigerants in common with each other. Both ranking methodologies identified R1234yf, R32, and R1270 as having ranking factors within those of the best three alternative refrigerants. [ABSTRACT FROM PUBLISHER]

Numerical simulation of bubble growth during pool boiling under the influence of low frequency vibration was performed to understand the influence of common vibrations such as those induced by wind, highway transportation, and nearby mechanical devices on the performance of thermal systems that rely on boiling. The simulations were done for saturated R123 boiling at 277.6 K with a 15 K wall superheat. The numerical volume-of-fluid method (fixed grid) was used to define the liquid-vapor interface. The basic bubble growth characteristics including the bubble departure diameter and the bubble departure time were determined as a function of the bubble contact angle (20°-80°), the vibration displacement (10 µm-50 µm), the vibration frequency (5 Hz-25 Hz), and the initial vibration direction (positive or negative). The bubble parameters were shown to be strongly dependent on the bubble contact angle at the surface. For example, both the bubble departure diameter and the bubble departure time increased with the contact angle. At the same vibration frequency and the initial vibration direction, the bubble departure diameter and the bubble departure time both decreased with increasing vibration displacement. In addition, the vibration frequency had a greater effect on the bubble growth characteristics than did the vibration displacement. The vibration frequency effect was strongly influenced by the initial vibration direction. The pressure contour, the volume fraction of vapor phase, the temperature profile, and the velocity vector were investigated to understand these dynamic bubble behaviors. The limitation of the computational fluid dynamics approach was also described.