Fine particles in the liquid feed to packed-bed reactors can be trapped in the catalyst bed, which eventually leads to excessive pressure drop. The fine particles can include coke, corrosion products, clays, and other minerals. The catalyst bed functions as a granular filter to remove particles much smaller than the size of the pores between the catalyst pellets. The efficiency for trapping the particles in the packed bed depends on the flow fields and the attractive forces between the packing and the fine particles. In order to understand the capture of fine particles from nonaqueous media, we studied a model system of carbon black in kerosene. Columns packed with glass beads and a catalyst were operated over a range of flow velocities to Reynolds numbers from 0.1 to 2.3, on the basis of the diameter of the packing in the bed. Flow was in the upward and in the downward direction. The filter coefficient and efficiency were sensitive to liquid velocity. Trapping was slightly more efficient with downward flow at low velocity. The pressure drop increased along the entire length of the packed bed, but the extent of increase at a given amount of deposit depended on the liquid velocity. Microscopy showed that the particles tended to deposit onto other particles, rather than smoothly coating the bed packing. At low velocities, more particles were deposited in the pores between the packing, giving a larger increase in pressure drop than that at high velocity. A model is presented for calculating pressure drop due to this type of deposition.

Background: Mesalamine loaded polymeric nanoparticles were prepared using three different polymers namely, Eudragit RS100, PLGA (50:50), or Eudragit RLPO, with an aim of targeted delivery to the inflamed colon. Materials and Methods: Nanoparticles were prepared by modified emulsification solvent evaporation and characterized for various physicochemical characteristics viz., size, size distribution, mesalamine entrapment, and in-vitro release. Results: Amongst the various formulations prepared, formulation F5 mesalamine nanoparticles made with Eudragit RS100 showed drug entrapment of 72.09% with comparative discrete nearing spherical particle size of 200 nm. In-vivo targeting potential of nanoparticles to the inflamed tissue was evaluated in acetic acid-induced colitis rat model and efficacy was compared with pristine mesalamine powder. Biochemical estimations were carried in colonic tissue homogenate to check the oxidative damage. The myeloperoxidase activity and lipid peroxides were significantly decreased and glutathione content increased after the oral administration of mesalamine nanoparticles compared to pure drug mesalamine. Conclusion: This delivery system enabled the drug to accumulate in the inflamed tissue with higher efficiency than the pure drug thus nanoparticulate system was efficient in mitigating the experimental colitis.

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An analysis is presented of a 1-2 divided flow exchanger where the temperature of shell and tube streams depend on tube arrangement. Effect of having unbalanced tube passes is assessed for two possible cases. Graphs are plotted that show the variation of thermal effectiveness and logarithmic mean temperature difference correction factor with ratio of heat capacity rates and number of transfer units. Combination of such exchangers is also studied.On a analysC un tchangeur Ccoulement divisC 1-2 pour lequel la temptiratwe des courants dans les tubes de la calandre est fonction de la disposition des tubes. L'effet de passe-tubes non tquilibrCs a CtC CvaluC pour deux cas possibles. On prCsente des diagrammes illustrant la variation de I'efficacitC thermique et du facteur de correction des differences des tempkratures moyennes logarithmiques avec le rapport des capacitks calorifiques et le nombre d'unitCs de transfert. La combinaison de tels Cchangeurs est Cgalement CtudiCe Keywords: divided flow, exchanger design, thermal effectiveness. divided flow exchanger performs equivalent to a A TEMA E exchanger and still leads to a pressure drop of about 118 times that of the latter on shell side. Hence when shellside pressure drop limitations arise, the divided flow exchanger is preferred.Several studies on divided flow or TEMA J exchangers and comparisons with PCF (parallel and counter flow) or TEMA E exchangers are reported in the literature (Shah and Mueller, 1985). Pioneering work was done by Kern and Carpenter (1951). From heat balance, a differential equation was set up for the fixed head end. The floating head end was taken to be a TEMA E exchanger. Heat loads and mean temperature difference for the two ends were first determined. Equating overall heat load divided by mean temperature difference with the sum of ratios gave the mean temperature difference of the exchanger. This was followed by the study of Iqbal and Stachiewicz (1962). Jaw (1964) determined expressions for thermal effectiveness for number of tube passes equal to 1, 2, 4 and infinity. In the analysis by Jaw, mean temperature difference for the exchanger is obtained only once and not by combining values of the two ends. This approach is followed in the present study because it does not involve trial and error.More recently, Murthy (1983) determined the performance of 1-1 and 1-2 TEMA J exchangers and showed that for 1-2 case it is beneficial to transfer slightly less heat in the tubesheet as compared to floating head end of the exchanger of Figure 1. This happens because increase in heat load to left half makes second pass of left half of the exchanger less effective. Zhuang (1987) analysed combinations of divided flow exchangers and presented the results in a graphical form. Xuan et al. (1991) pointed out that studies were restricted to the middle entrance of shellside flow and even distribution of mass flow rate in each half of the exchanger. The optimum entrance location of the shellside fluid depends on factors such as the number of tube passes, the...

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