José M. Navaza

Rheology of aqueous solutions of food additives: Effect of concentration, temperature and blending

Rheological properties of carboxymethyl cellulose and alginate sodium salts had been studied. The molecular weight of these polymers were calculated using Huggins and Kramer equations and intrinsic viscosity was determined for the polymers. The apparent viscosity and the influence of shear rate on different polymers concentration in aqueous solutions was measured. The effect of temperature on rheological behaviour was also studied. Blends of two aqueous solutions of these polymers were studied and a high deviation from the ideal behaviour was found.

Application of the Danckwerts method in a bubble column: Effects of surfactants on mass transfer coefficient and interfacial area

Abstract We determined interfacial areas, A, and individual mass transfer coefficients, kL, for the absorption of CO2 in a bubble column, with an anionic surfactant in the absorbent liquid. The results of experiments to determine the dependence of kL on surface tension of the liquid phase and the superficial velocity of the gas were fitted to within a 10% error by expressions of the form k L =K 4 σ 1.35 u G 0.5 where K4 depends exclusively on the kind of bubbling device. Likewise, the experimental values of specific area, a, were correlated with the column diameter dc and the physical properties by means the following equation: ad c =K· Re 0.98 · Sc 0.57 · Fr 0.09 · Bo −0.70 d p d c −0.19 that reproduces satisfactorily the experimental values.

Mass transfer and influence of physical properties of solutions in a bubble column

The absorption of CO2 by aqueous solutions of sucrose and surfactants was studied in a bubble column under batch conditions. The volumetric mass transfer coefficients, kLa, were determined for each of the solutions and of the gas rate flow, and the experimental values were correlated with the superficial gas velocity and the physical properties of the liquid phase. The proposed equation reproduces the experimental kLa with an error of less than 10%.

Influence of surfactants on absorption of CO2 in a stirred tank with and without bubbling

We determined volumetric mass transfer coefficients kLa for the absorption of bubbled and unbubbled CO2 in a stirred tank, with and without surfactants in the absorbent liquid. In the absence of surfactants, results obtained under continuous liquid flow regimes agreed closely with batch results; accordingly, for convenience, subsequent experiments with surfactant additives were performed only with continuous liquid flow. The results of experiments to determine the dependence of kLa on stirring rate and the kind of bubbling device were fitted to within a 4% error by expressions of the form kLa = K(PeN)0.4 where Pe is the effective power supplied to the tank, V is the volume of liquid in the tank and K depends on surfactant concentration and the bubbling device and increases linearly with the liquid flow rate. Surfactant reduced kLa by an amount that, to within a 3% error, was proportional to both the corresponding value of kLa in the absence of surfactant and the surface concentration of surfactant.

Absorption of CO2 by water and surfactant solutions in the presence of induced Marangoni effect

Abstract The absorption of CO 2 at a plane interface by water and aqueous solutions of surfactants was measured in the presence and in the absence of Marangoni effect induced by deposition of a variety of liquids of low surface tension on the gas-liquid interface. Measurement of the induced surface velocity distribution allowed mass transfer in the presence of induced convection to be related to interface hydrodynamics by correlation of Sherwood and Reynolds numbers, and also allowed the calculation of surface residence times for which the divergent interfacial flow in the experimental apparatus was taken into account. When used in Higbies equation the residence times afforded theoretical mass transfer coefficients which, for water as absorbent liquid, were within 4% of the experimental values. Surfactants were found to modify absorption not only through their hydrodynamic effects, but also by some other mechanisms, which was nevertheless estimated to contribute only about 15% of the total resistance to mass transfer in the presence of surfactant.

Effect of Temperature on the Viscosity of Honey

Influence of temperature on the viscosity of honeys was analysed in the present work. The viscosity value decreased with the increase of temperature. The effect caused by temperature in the range studied was more important in the low range of temperature, whereas at high temperature, the viscosity showed less variation. Water activity and glass transition temperature was determined to relate these characteristics. Four experimental viscosity models were checked using the experimental data to correlate the influence of temperature upon honey viscosity.

Intrinsic Viscosity and Flow Behaviour of Arabic Gum Aqueous Solutions

The intrinsic viscosity and flow behaviour of aqueous solutions of different concentrations of Arabic gum were studied. The molecular weight of this polymer was calculated using the value of the intrinsic viscosity, employing both Huggins and Kramer and Mark-Houwink equations. The value of the apparent viscosity and the influence of the shear rate on the rheological behaviour of different polymer concentrations in aqueous solution were determined. The effect of temperature over the flow behaviour was also studied. The Ostwald model has been employed to fit the experimental data and model parameters have been obtained.

Physicochemical characterization of Galician Honeys

The characterization of the north-west Spanish honeys was carried out on the basis of different parameters: density, viscosity, refractive index, glass transition temperature, pH, electrical conductivity, ash, sugars, and water activity. The influence of certain characteristics and honey composition (based on water content) on different physico-chemical properties was analysed.

Injection of steam into the mashing process as alternative method for the temperature control and low-cost of production

Steam may offer several advantages for commercial brewers as well. For those mashing in unheated tuns, direct steam injection might be a low-cost method of adding heating capability to the tuns for stepped mashes. This might be especially economical for those breweries that already use steam as a source of heat for the kettle. Furthermore, direct injection of steam offers certain advantages over steam jacketed tuns. The heat transfer rate will be higher, because of the absence of an intervening wall between the steam and the mash. Also, because the steam is injected directly into the bulk of the mash rather than at the periphery, the heat distribution will tend to be more even and require less stirring. This method was tested and the results are reported in this paper.

Density, speed of sound, refractive index and derivatives properties of the binary mixture n-hexane + n-heptane (or n-octane or n-nonane), T = 288.15 – 313.15 K

This article reports experimental values of refractive index nD , density ρ, speed of sound u, isentropic compressibility κs, excess molar volume of mixing V E, deviations of refractive index δnD and isentropic compressibility δκs of the binary mixture n-hexane + n-alkane from T = (288.15 to 323.15) K and atmospheric condition. The corresponding excess derived property was computed from the experimental data. Parameters of analytical expressions which represent the composition dependences of the derived property are reported. Values of physical properties were compared with the results obtained by different prediction methods.