A lifted laminar axisymmetric diffusion flame is stabilized in the downstream region of a diluted methane jet that is surrounded by a lean methane-air co-flow and an outer co-flow of air. The flame shows a distinct triple flame structure in the stabilization region. It is investigated experimentally by PIV for the velocity field, OH-LIPF imaging, C2H(x)-LIF imaging, and a 1D-Raman technique for major species concentrations, combined with a Rayleigh technique for temperature. This is complemented by numerical simulations solving the two-dimensional axisymmetric Navier-Stokes equations in the zero Mach number limit on an adapted mesh, coupled with balance equations for temperature and species. A simplified model for molecular transport properties was used with constant, but non-unity, Lewis numbers for all species. Chemistry is represented by a ten-step reduced mechanism for methane oxidation, which was derived starting from a 61-step elementary mechanism that includes the C1 and C2 chains. The agreement between the measured and the predicted flow field is very satisfactory. Owing to gas expansion, the velocity decreases immediately ahead of the flame and increases strongly at the flame front. Further downstream acceleration due to buoyancy is dominant and is predicted accurately. There is a good agreement between measurements and computations for flame shape and flame length. The measured OH-LIPF image and the computed OH concentrations indicate that OH is concentrated in the vicinity of stoichiometric mixture. The results from a newly developed C2H(x)-LIF method are also supported by calculations. While these measurements were only qualitative, the temperature and mole fractions of the major species could be measured quantitatively with the combined Raman-/Rayleigh technique along a line and were found to agree well with the numerical predictions. It is found that the structure is a triple flame and is influenced essentially by two external parameters: heat exchange between the branches and heat loss at the curved flame front near the triple point.

A lifted laminar axisymmetric diffusion flame is stabilized in the downstream region of a diluted methane jet that is surrounded by a lean methane-air co-flow and an outer co-flow of air. The flame shows a distinct triple flame structure in the stabilization region. It is investigated experimentally by PIV for the velocity field, OH-LIPF imaging, C2H(x)-LIF imaging, and a 1D-Raman technique for major species concentrations, combined with a Rayleigh technique for temperature. This is complemented by numerical simulations solving the two-dimensional axisymmetric Navier-Stokes equations in the zero Mach number limit on an adapted mesh, coupled with balance equations for temperature and species. A simplified model for molecular transport properties was used with constant, but non-unity, Lewis numbers for all species. Chemistry is represented by a ten-step reduced mechanism for methane oxidation, which was derived starting from a 61-step elementary mechanism that includes the C1 and C2 chains. The agreement between the measured and the predicted flow field is very satisfactory. Owing to gas expansion, the velocity decreases immediately ahead of the flame and increases strongly at the flame front. Further downstream acceleration due to buoyancy is dominant and is predicted accurately. There is a good agreement between measurements and computations for flame shape and flame length. The measured OH-LIPF image and the computed OH concentrations indicate that OH is concentrated in the vicinity of stoichiometric mixture. The results from a newly developed C2H(x)-LIF method are also supported by calculations. While these measurements were only qualitative, the temperature and mole fractions of the major species could be measured quantitatively with the combined Raman-/Rayleigh technique along a line and were found to agree well with the numerical predictions. It is found that the structure is a triple flame and is influenced essentially by two external parameters: heat exchange between the branches and heat loss at the curved flame front near the triple point.

The real and imaginary parts of the relative permittivity (ε′t and ε″t) as well as the a.c. resistivity of the mixed ferrite CoxZn1-xFe2O4 (x = 0.1 → 1.0) were measured as a function of temperature and frequency. The calculated values of the activation energy indicate that the conductivity of the system increased with increasing Zn concentration. The Curie temperature of the system as determined from a.c. conductivity measurements agree well with that of the relative permittivity. The calculation of the relaxation time (τ) from Cole-Cole plots indicates that its maximum value occurs at the critical concentration (x = 0.6). The grain size was calculated at different Co concentration with values ranged from 0.995 × 10-7 to 0.617 × 10-7 mm.

The real part of the relative permittivity ε′t as well as the dielectric loss as represented by ε″t for the compounds (CH2)x(NH3)2MCl4-xBr x (where x = 0, 2, n = 2, 3 and M = Cu, Co) have been measured. The measurements were carried out as a function of temperature and frequency. Both ε′t and ε″t show the same relaxation phenomena which involves large reorientable dipoles in the total polarization. The phase transition observed at ∼312K for ε′t and ε″t is expected from the variation in the spacing between the adjacent metallic layers arising from the increase in the number of carbon atoms and/or introducing Br- ions in the out of plane position.

4-Hexadecyloxyphenyl-4′-substituted benzoates, Ia-d, and 4-substituted phenyl-4′-hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.

The dielectric characteristics for some cellulose derivatives, namely chlorodeoxycellulose (Cell-Cl; degree of substitution of chlorine, DSCl = 0·87), bromodeoxycellulose (Cell-Br; DSBr = 0·92)and thiocyanatodeoxycellulose (Cell-SCN; DSSCN = 0·88), all substituted only at C-6, together with those of regenerated cellulose, have been investigated in the temperature range -60 to 120°C, and in the frequency range 0·2-100 kHz. Only one relaxation process, designated as β, was identified within the frequency and temperature ranges studied. The activation energy of this relaxation increases in the order Cell-Cl < Cell-Br < Cell-SCN, suggesting that the bulkiness of the substituent was the determining factor of the activation energy. The characteristic dielectric parameters, namely polarization magnitude (Δε) and shape parameter (α or β̄), were obtained by the analysis of absorption bands and are discussed in relation to the substituent effect.