Amyn S. Teja

A NEW CUBIC EQUATION OF STATE FOR FLUIDS AND FLUID MIXTURES

Abstract A new cubic equation of state for pure fluids is presented in this work. The new equation requires the critical temperature and pressure, as well as two additional parameters to characterize each particular fluid. These parameters have been evaluated by minimizing deviations in saturated liquid densities while simultaneously satisfying the equality of fugacities along the saturation curve. Thus, good predictions of volumetric properties in the liquid region are obtained, while accuracy in vapour—liquid equilibrium calculations is maintained. Parameters for polar as well as nonpolar fluids are presented in this paper. In the case of nonpolar fluids, the two parameters required can be correlated with the acentric factor. No such relationship with independently measured quantities could be found for polar fluids. It is shown that the new equation reproduces many of the good features of the Soave and Peng—Robinson equations of state for nonpolar fluids, whilst overcoming some of the limitations of these equations for polar fluids. Applications of the equation of state to the correlation of phase equilibria are demonstrated.

Effect of particle size on the thermal conductivity of nanofluids containing metallic nanoparticles

A one-parameter model is presented for the thermal conductivity of nanofluids containing dispersed metallic nanoparticles. The model takes into account the decrease in thermal conductivity of metal nanoparticles with decreasing size. Although literature data could be correlated well using the model, the effect of the size of the particles on the effective thermal conductivity of the nanofluid could not be elucidated from these data. Therefore, new thermal conductivity measurements are reported for six nanofluids containing silver nanoparticles of different sizes and volume fractions. The results provide strong evidence that the decrease in the thermal conductivity of the solid with particle size must be considered when developing models for the thermal conductivity of nanofluids.

The critical temperatures and densities of the n-alkanes from pentane to octadecane

Abstract The critical temperatures and densities of n-alkanes from pentane to octadecane have been measured using a rapid heating sealed ampoule technique. The measurements were compared with critical properties reported in the literature and with the results of several estimation methods. In general, our measurements of the critical temperature compared well with values reported in the literature, but those for the critical density only agreed with literature values for the lower members of the alkane series. An interesting trend observed with the critical densities was that the experimental values decreased with carbon number after attaining a maximum. This is contrary to the trend predicted by all estimation methods, and suggests a need for new methods for this property.

Continuous hydrothermal crystallization of α-Fe2O3 and Co3O4 nanoparticles

Iron oxide (α-Fe 2 O 3 ) and cobalt oxide (Co 3 O 4 ) were produced via precipitation reactions carried out in a continuous hydrothermal apparatus. The resulting particles were nanometer-sized because of the high supersaturations generated when metal nitrate solutions are combined with sodium hydroxide or with hot, compressed water. The average particle size increased with the metal nitrate feed concentration and with residence time. A logarithmic relationship was obtained between the particle size and feed concentration and between particle size and residence time in the apparatus. The production of nanoparticles with narrow size distribution was shown to require low metal nitrate feed concentrations and short residence times. In the range of temperatures studied in this work, temperature apparently had no effect on the size except when cobalt nitrate was contacted with supercritical water in the absence of sodium hydroxide. In this case, large cobalt oxide particles were obtained when the temperature was above the critical temperature of water.

Continuous hydrothermal synthesis and crystallization of magnetic oxide nanoparticles

The continuous hydrothermal synthesis of nanoparticles of two metal oxides (α-Fe 2 O 3 and Co 3 O 4 ) is described. Two variations of the technique were investigated, involving the precipitation reaction between a metal saltsolution and a hydroxide solution at ambient conditions and at elevated temperatures. Elevated temperatures resulted in more uniform particles of α-Fe 2 O 3 and Co 3 O 4 , although the actual sizes of the particles were apparently unaffected by the temperature. This behavior was attributed to the species present in solution and the solubilities of the cation(s), both of which were calculated via a thermodynamic model for the systems under study.

Correlation of the critical properties of alkanes and alkanols

Abstract Recent measurements of the critical properties of n-alkanes (up to C 18 ) and isomeric alkanols (up to C 12 ) have been compiled and tested for consistency. In general, these measurements exhibit the expected trends in homologous series behavior. For example, the properties of the alkanols converge to those of the corresponding n-alkanes as the chain length increases. Existing estimation methods were compared for their ability to predict data for the higher members of the homologous series and were generally found to be unsatisfactory. Two new correlations based on the hole theory of long chain molecules were therefore developed in this work. Both correlations were able to fit the data within experimental error.

A generalized corresponding-states method for the prediction of surface tension of pure liquids and liquid mixtures

Abstract We recently developed an extension of the three-parameter corresponding-state principle based on the properties of two nonspherical reference fluids for the viscosity and thermal conductivities of liquids and liquid mixtures. We extend the method here to surface tension. We have tested the method on six binary mixtures using the pure components as reference fluids. Good agreement between experimental and predicted values of surface tension was obtained using only the data for the pure components. The agreement is even better if a single binary interaction constant, independent of temperature and composition, is used in the mixture calculations. It is also shown how the unknown surface tension of any given fluid can be obtained from the known properties of two (similar) reference fluids.

Solubility and diffusion of carbon dioxide in polymers

We have measured the solubility and diffusion coefficients of carbon dioxide in four polymer substrates at 313 K and 10.5 MPa. The polymer substrates included poly(chlorotrifluoroethylene), cross-linked poly(dimethylsiloxane), poly(methylmethacrylate), and cross-linked polystyrene. Solubilities were determined from maximum mass gain measurements when a film of each polymer was contacted with carbon dioxide, and diffusion coefficients were determined from timed absorption experiments. The highest solubility and the highest diffusivity were obtained with poly(methylmethacrylate).

The limiting behavior of the thermal conductivity of nanoparticles and nanofluids

We present experimental evidence of negative thermal conductivity enhancement in nanofluids consisting of 2 nm titania nanoparticles dispersed in 50% (w/w) water+ethylene glycol. This behavior is unlike that of other nanofluids, which have been shown to exhibit positive thermal conductivity enhancements. Our results for titania nanofluids suggest that the thermal conductivity of 2 nm titania nanoparticles is smaller than the thermal conductivity of the base fluid at the same temperature, indicating a dramatic decrease in the thermal conductivity of titania particles as the particle size becomes of the same order as the phonon mean free path. Although such a decrease has been predicted for semiconductor nanoparticles by theory and simulation, experimental evidence has hitherto been lacking. Our results provide indirect experimental evidence for this decrease in metal oxide particles, and validate our previous work on alumina nanofluids that showed an exponential decrease in the thermal conductivity of alum...

Supercritical extraction of taxol from the bark of Taxus brevifolia

Abstract Taxol has been found to be an effective drug for the treatment of ovarian cancer. However, the only current source of this compound is from trees of the Taxus genus and methods need to be developed for its separation from the natural plant source. The extraction of taxol from the ground bark of Taxus brevifolia using supercritical carbon dioxide and carbon dioxide + ethanol mixtures was studied in this work. The extractions were preformed at 318 K and at pressures ranging from 18.07 to 25.79 MPa. It was demonstrated that supercritical carbon dioxide is able to extract taxol from the ground bark, especially at the higher pressures and with the addition of ethanol. The supercritical extractions of taxol were also found to be more selective than a conventional liquid ethanol extraction. Furthermore, a significant portion of the taxol present in the bark could be removed in the supercritical process.