Yuan-Yuan Duan

Experimental vapor pressure data and a vapor pressure equation for trifluoroiodomethane (CF3I)

Abstract Sixty four vapor pressure data points for trifluoroiodomethane (CF3I) have been measured for the temperature range from 243.15 to 393.15 K. The maximum total pressure uncertainty of these data is estimated to be within ± 1.0 kPa. The purity of the sample used in this work is 99.95% with 3.4 ppm of water. Based on this data set, a vapor pressure equation for CF3I has been developed. This equation contains four coefficients and correlates the measured vapor pressures within ± 0.03%.

Improved determination of the Boltzmann constant using a single, fixed-length cylindrical cavity

We report improvements to our previous (Zhang et al 2011 Int. J. Thermophys. 32 1297) determination of the Boltzmann constant kB using a single 80 mm long cylindrical cavity. In this work, the shape of the gas-filled resonant cavity is closer to that of a perfect cylinder and the thermometry has been improved. We used two different grades of argon, each with measured relative isotopic abundances, and we used two different methods of supporting the resonator. The measurements with each gas and with each configuration were repeated several times for a total of 14 runs. We improved the analysis of the acoustic data by accounting for certain second-order perturbations to the frequencies from the thermo-viscous boundary layer. The weighted average of the data yielded kB = 1.380 6476 × 10−23 J K−1 with a relative standard uncertainty ur(kB) = 3.7 × 10−6. This result differs, fractionally, by (−0.9 ± 3.7) × 10−6 from the value recommended by CODATA in 2010. In this work, the largest component of the relative uncertainty resulted from inconsistent values of kB determined with the various acoustic modes; it is 2.9 × 10−6. In our previous work, this component was 7.6 × 10−6.

Experimental and analytical analyses of the thermal conductivities and high-temperature characteristics of silica aerogels based on microstructures

An analytical heat transfer model based on scanning electron microscopy, Brunauer–Emmett–Teller and pycnometry measurements and a 3D random diffusion-limited cluster–cluster aggregation structure is proposed to calculate the temperature-dependent microstructural parameters and thermal conductivities of silica aerogels. This model is a pure prediction model, which does not need experimentally fitted empirical parameters and only needs four measured structural parameters as input parameters. This model can provide high-temperature microstructural and thermophysical properties as well as theoretical guidelines for material designs with optimum parameters. The results show that three stages occur during the thermal evolution processes of the aerogel structure with increasing temperature from 300 to 1500 K. The current analytical model is fully validated by experimental data. The constant structure assumptions used in previous heat transfer models are found to cause significant errors at higher temperatures as the temperature-dependent structure deformation significantly increases the aerogel thermal conductivity. The conductive and total thermal conductivities of silica aerogels after high-temperature heat treatments are much larger than those with no heat treatment.

A Critical Review of Dynamic Wetting by Complex Fluids: From Newtonian Fluids to Non-Newtonian Fluids and Nanofluids

Dynamic wetting is an important interfacial phenomenon in many industrial applications. There have been many excellent reviews of dynamic wetting, especially on super-hydrophobic surfaces with physical or chemical coatings, porous layers, hybrid micro/nano structures and biomimetic structures. This review summarizes recent research on dynamic wetting from the viewpoint of the fluids rather than the solid surfaces. The reviewed fluids range from simple Newtonian fluids to non-Newtonian fluids and complex nanofluids. The fundamental physical concepts and principles involved in dynamic wetting phenomena are also reviewed. This review focus on recent investigations of dynamic wetting by non-Newtonian fluids, including the latest experimental studies with a thorough review of the best dynamic wetting models for non-Newtonian fluids, to illustrate their successes and limitations. This paper also reports on new results on the still fledgling field of nanofluid wetting kinetics. The challenges of research on nanofluid dynamic wetting is not only due to the lack of nanoscale experimental techniques to probe the complex nanoparticle random motion, but also the lack of multiscale experimental techniques or theories to describe the effects of nanoparticle motion at the nanometer scale (10(-9) m) on the dynamic wetting taking place at the macroscopic scale (10(-3) m). This paper describes the various types of nanofluid dynamic wetting behaviors. Two nanoparticle dissipation modes, the bulk dissipation mode and the local dissipation mode, are proposed to resolve the uncertainties related to the various types of dynamic wetting mechanisms reported in the literature.

Vapor pressure of 1,1,1,2,3,3,3-heptafluoropropane

Abstract A total of 84 vapor pressure data points for 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) have been measured in the temperature range from 243 to 375 K. The maximum total pressure uncertainty of these data is estimated to be within ±1 kPa. The purity of the sample used in this work is 99.9 mol%. Based on this data set, a vapor pressure equation for HFC-227ea has been developed. The root-mean-square (RMS) deviation of the experimental data from the vapor pressure equation is 0.057%. The normal boiling point of HFC-227ea was also determined.

Visualization of Two-Phase Flows in Nanofluid Oscillating Heat Pipes

Two-phase flows in an oscillating heat pipe (OHP) charged with deionized (DI) water and a nanofluid (0.268% v/v) were experimentally investigated. The OHP was made of quartz glass tube (with an inner diameter of 3.53 mm and an outer diameter of 5.38 mm) and coated with a transparent heating film in its evaporating section. The internal two-phase flows at different heat loads were recorded by a charge-coupled device (CCD) camera. Only column flow was observed in the DI water OHP while in the nanofluid OHP the flow first was column, then slug and annular flows as the heat load was steadily increased. Heat transfer in the OHP was strongly related to the two-phase regime. The flow regime transitions effectively increased the operating allowable heat loads in the nanofluid OHP two- to threefold relative to the DI water OHP. The nanofluid OHP had a much lower thermal resistance than the DI water OHP with the most effective heat transfer in the nanofluid OHP occurring in the slug flow regime.

Surface Tension of 1,1,1-Trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), and Their Binary Mixture HFC-143a/227ea

The surface tension of 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-hepta-fluoropropane (HFC-227ea), and their binary mixture HFC-143a/227ea at 3 nominal mass fractions of 27.91%/72.09%, 49.44%/50.56%, and 74.11%/25.89% were measured in the temperature range from 253 to 333K using the differential capillary rise method (DCRM) under vapor-liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN⋅m−1, respectively. The present data were used to develop a van der Waals-type surface tension correlation for pure HFC-143a and HFC-227ea. Correlations for pure HFC-143a and HFC-227ea were used to develop a surface tension correlation for the experimental data of the HFC-143a/227ea mixtures as a function of the mass fraction.

Does macroscopic flow geometry influence wetting dynamic

The macroscopic flow geometry has long been assumed to have little impact on dynamic wetting behavior of liquids on solid surfaces. This study experimentally studied both spontaneous spreading and forced wetting of several kinds of Newtonian and non-Newtonian fluids to study the effect of the macroscopic flow geometry on dynamic wetting. The relationship between the dynamic contact angle, θ(D), and the velocity of the moving contact line, U, indicates that the macroscopic flow geometry does not influence the advancing dynamic wetting behavior of Newtonian fluids, but does influence the advancing dynamic wetting behavior of non-Newtonian fluids, which had not been discovered before.

Dynamic wetting of non-newtonian fluids: multicomponent molecular-kinetic approach.

Hydrodynamic models are generally applied to describe the dynamic wetting of newtonian or non-newtonian fluids on a solid surface. Conversely, the molecular-kinetic paradigm is only utilized for spreading newtonian fluids while considering the movement of a contact line as a molecular hopping process. This study extended the molecular-kinetic paradigm to the wetting behavior of non-newtonian fluids, while assuming there are n fluid components at the contact line regime interacting simultaneously with a solid surface during front movement. The limiting cases of the derived model at slow and fast moving speeds were discussed. Moreover, the derived model was validated based on dynamic contact angle data of three carboxymethylcellulose (CMC) aqueous solutions measured using the force-balance method. Best-fit parameters were used to interpret the wetting dynamics of CMC solutions.

Dynamics of Spreading of Liquid on Solid Surface

Based on assuming that there is the precursor film in the front of the apparent contact line (ACL), a model was proposed to understand the dynamic wetting process and associated dynamic contact angle. The present model indicated that a new dimensionless characteristic parameter, λ, affects the dynamic wetting process and asso- ciated dynamic contact angle as well. However, the previous model suggested that the dynamic contact angle is de- pendent on the capillary number and static contact angle only. An experimental investigation was conducted to measure the dynamic wetting behavior of silicon oil moving over glass, aluminum and stainless steel surfaces. It concluded that when the value of λ was selected as 0.07, 0.16 and 0.35 for glass, aluminum and stainless steel, re- spectively, the experimental results were in good accordance with the prediction of the model. Furthermore, the comparison of the model with Stroms experimental data showed that λ is independent on the species of liquids. Apparently, λ should be interpreted as the effect of the solid surface properties on the dynamic wetting process. Meanwhile, it is found in the present experiment that the Hoffman-Voinov-Tanner law, which is valid at very low capillary number (Ca� 1 or θD<10°) recommend by Cazabat, still holds for higher contact angles, even up to 70°—80°. This is explained by the present model very well. Keywords dynamic wetting, dynamic contact angle, stress singularity, precursor film, slip