Longitudinal mixing in the dispersed phase in pulsed perforated-plate columns

A method is presented to identify flow model parameters from radioactive signals with a high noise content. The method is based on the two detection points method with a highly accurate identification of the parameters by optimization in the frequency domain. The study of dispersed phase of a pulsed column with perforated plate using this method has shown evidence that there are operating conditions for which the piston-diffusion flow does not describe well the behavior of the dispersed phase.     

ESTIMATION OF EFFECTIVE SHEAR RATE FOR AERATED NON-NEWTONIAN LIQUIDS IN AIRLIFT BIOREACTOR”“

Effective shear rate is one of the indispensable parameters for the design of aerobic fermentors using a viscous non-Newtonian system. The estimation of effective shear rate in airlift loop bioreactors has been investigated with liquid circulation velocity. An empirical correlation of effective shear rate in airlift loop reactors is proposed.

γ_eπ= 3.26-3.51 ; 10²U_G + 1.48 10⁴U²_G

It is found that the effective shear rate is lower in airlift reactors than in bubble columns. This equation can be used for the cultivation of cells sensitive to shear stress.     

Comparison of bioactive phytochemical content and release of isothiocyanates in selected brassica sprouts

The consumption of brassica sprouts as raw vegetables provides a fair amount of glucosinolates (GLs) and active plant myrosinase, which enables the breakdown of GLs into health-promoting isothiocyanates (ITCs). This study reports the determination of the main constituents related to human health found in edible sprouts of two Brassica oleracea varieties, broccoli and Tuscan black kale, and two Raphanus sativus varieties, Daikon and Sango. Radish sprouts exhibited the highest ability to produce ITCs, with Daikon showing the greatest level of conversion of GLs into bioactive ITCs (96.5%), followed by Sango (90.0%). Tuscan black kale gave a value of 68.5%, whereas broccoli displayed the lowest with 18.7%. ITCs were not the exclusive GL breakdown products in the two B. oleracea varieties, since nitriles were also produced, thus accounting for the lower conversion observed. Measuring the release of plant ITCs is a valuable tool in predicting the potential level of exposure to these bioactive compounds after the consumption of raw brassica sprouts.     

Influence d'une agitation rotative sur le mélange en retour dans une colonne pulsée à plateaux perforés

The efficiency of a pulsed perforated plate extraction column can be improved, particularly at low values of A.f, by superimposing a rotary agitation. The hold up and the Peclet number have been measured in such a column in order to calculate the coefficient of backmixing of the continuous phase. A comparison of the results with those for a conventional pulsed column has indicated that the improved performance is due to an increase in hold up and not, as might have been supposed, to reduced backmixing.     

TOTAL NITROGEN CONTENT IN SINGLE KERNEL MALTING BARLEY SAMPLES

It was demonstrated that the Dumas method is suitable to analyse single kernel barley samples for their total nitrogen content directly without milling. The method was compared to the nitrogen analysis in milled samples over a range of 1.5-3.0%N. These samples consisted of kernel size grading fractions from barley cultivated at different N-dressings and using a shading regime. A good correlation was found between milled and whole barley kernels (r²=0.852). The method was used to determine the nitrogen content of individual kernels in the barley grading fractions. The nitrogen content in these fractions decreased with increasing kernel size depending on growth conditions. A large variation in nitrogen content between individual kernels was found for all grading fractions. In a study of barley main spikes the variation in kernel nitrogen content within spikes was smaller than the variation between spikes, especially when the barley was grown at a 60% light reduction regime during the kernel filling period. The average kernel total nitrogen content under the latter condition was about two times as high as in the control experiment. The kernel position along the spike did not clearly affect its nitrogen content. Acid and SDS polyacrylamide gel electrophoresis (PAGE) revealed similar banding patterns for proteins from kernels at different positions of both low and high N barley spikes. The single kernel method for nitrogen may be used by the breeder as a quality criterion for new barley varieties to test their spike development at different cultivation conditions. It can suit the maltster to screen rapidly the homogeneity in nitrogen (protein) content of barley batches.     

General method for the evaluation of complex heat pump cycles

Whenever the fractional temperature lift ΔT/T_c of a heat pump is 0.15, simple cycles with one-stage throttling exhibit unsatisfactory energy performance. The adoption of multi-stage throttling, both in non-regenerative and regenerative cycles, is the most direct way of improving the cycle coefficient of performance (COP). The performance of these complex cycles is found to be a function of the molecular complexity of the working fluid, the reduced evaporation temperature, the fractional temperature lift and the number of stages of throttling. Furthermore, complex cycles are shown to be equivalent to a combination of simple cycles and their performance may be directly inferred by this route. Such calculations show that for a given fractional temperature lift an optimum molecular complexity (between that of R12 and n-butane) exists. Fluids with simpler molecules exhibit excessive vapour superheating during compression, and those with more complex molecules have excessive throttling losses. Also, with complex cycles, regeneration should be applied only to the cycle at the lowest temperature in order to improve the cycle COP and to prevent condensation during compression. As a general trend, however, complex cycles suffer a significant loss in performance compared to optimized simple cycles due to the adverse area of the two-phase diagram in which they work.