Consistency index temperature effect

A wide range of temperatures are encountered during processing and storage of fluid foods, so that the effect of temperature on rheological properties needs to be documented. The effect of temperature on either apparent viscosity at a specified shear rate (Equation 2.42) or the consistency index, K, of the power law model (Equation 2.43) of a fluid can be described often by the Arrhenius relationship. The effect of temperature on apparent viscosity can be described by the Arrhenius relationship ... 

The flow behavior index (n) is assumed to be relatively constant with temperature and concentration, and the combined effects of temperature and concentration on the power law consistency index, K, are described by ... 

Effect of temperature model based on consistency index, K = K x ... 

Initially assume a constant value of the consistency index and subsequently account for its temperature-dependence using equation (6.36). Also, ascertain the importance of free convection effects in this case, using equations (6.37) and (6.38). The coeflflcient of thermal expansion, yS is 3 X lO ... 

Thus, the critical screw speed depends on the heat flux, channel depth, temperature coefficient, initial melt temperature, reference temperature, consistency index, screw diameter, and power law index. The critical screw speed increases with the heat flux and channel depth, and reduces with the power law index, consistency index, and screw diameter. The effect of the power law index is shown in Fig. 7.96. 

The average temperature rise is directly proportional to the consistency index m and the tangential flight width w/sincp. The temperature rise is strongly dependent on the radial clearance S, the power law index of the polymer melt n, and the screw speed N. Figure 11.24 shows the effect of flight clearance 6 and the power law index n for a 114-mm (4.5-in) extruder running at 100 rpm the specific heat is 2250 J/kg°C, the melt density is 900 kg/m, and the consistency index is 10 Pa - s . 

Whereas, the effect of temperature on n is not great, the same cannot be said for K, the consistency index. Here it is found that temperature has an exponential effect as in an Arrhenius relation ... 

Effect of Ammonia. a,a,a-TRiCHLOROTOLUENE (VIII). A dry stream of gaseous ammonia was passed for 4 hours into 19.6 grams of VIII (0.1 mole) at room temperature. Within 5 minutes, the originally colorless, transparent liquid became slightly turbid, but no heat evolution was noticeable. The introduction of ammonia was discontinued and the reaction contents were subjected to vacuum distillation. The entire reaction yielded only one component which was identified as unchanged VIII. Of the two boiling points, b.p.23 110.7° C. (18) and b.p.25 105° C. (19), cited in the literature, the one found in this distillation agrees with the latter. The experimental refractive index, was 1.5573 and is consistent with the literature value (5). 

Methods. The diffusion experiments were performed at room temperature (23 C) utilizing a glass diffusion cell consisting of two compartments each with a volume of 175 ml. Each chamber was stirred at a constant rate to reduce boundary layer effects. Solute concentrations were monitored by h or C tracers, refractive index, or U.V. spectroscopy. Partition coefficients, defined as the ratio of the concentrations in the membrane and in the bulk aqueous phase were determined by solution depletion technique. 

Hydrostatic pressure up to 300 MPa had no effect on the absorption and emission spectra (2 = 511 nm) of Pt2(POP)4 in ambient temperature aqueous solution. There was a modest decrease in the phosphorescence lifetime from t = 8.8 ps at 0.1 MPa to 7.6 ps at 300 MPa and a corresponding 13 % decrease in the phosphorescence quantum yield (C>°- = 0.55, 0, = 0.48). Since the intersystem crossing to the LEES was estimated to be unity in both cases, these data demonstrate that pressure has little effect on k, (Eq. 6.9) [22], consistent with the relative insensitivity of the refractive index of water to pressure [23]. 

---