-The polymer hydrogel was synthesized by photo-polymerization process (UV light, 60 O C) in presence of Photo-initiator (Irgacure R ) and Cross-linker (NN'-methylene bisacrylamide; MBAM). In the present work, the drying of polymer hydrogel was carried out to study the effect of temperature, gel-sheet thickness, monomer ratio of acryl acid to acrylamide (AA/AM), concentration of MBAM and quantity of monomers. A correlation has been developed for modified sheet thickness as a function of contraction coefficient and degree of drying. Effective diffusivity was estimated from Fickian-diffusive model considering modified sheet thickness and was found to be in the range of 1.1 × 10 -10 -5.93 × 10 -10 m 2 /s. The activation energy obtained using Arrhenius type equation was found to be in the range of 2979-10737 kJ/kmol H 2 O. The drying behavior shows an initial shoot-up in drying rate followed by constant rate and two falling rate periods.
This article presents results of an experimental study on the flow characteristics of a pilot-size screw conveyor dryer (SCD). In particular, the effects of granular solids flow rate (15.2-206 kg/h) and screw speed (10.8-28 rpm) on the residence time distribution (RTD) were studied using sand as the model material. The RTD was measured using a dynamic step change in the solids flow rate. Parameters such as solids holdup, degree of fullness, mean residence time, and uniformity of the discharge flow were studied. The solids holdup and hence the degree of fullness was found to decrease with increase in the screw speed and decrease with the solids flow rate. The mean residence time was found to decrease with an increase in the screw speed, as expected. The screw speed and the solids flow rate strongly affected the discharge uniformity. An optimum value of the degree of fullness was observed with regard to the solids flow rate. Over the operating range examined, the solids flow pattern was close to plug flow, as indicated by high values of N and Pe number.
Maize starch (Zea mays) was gelatinized and dried using a jacketed single-screw extruder. The degree of gelatinization (DG), color, swelling properties, solubility, apparent and true densities, expansion ratio, and porosity of extruded maize starch were analyzed. The effects of temperature, feed moisture content, screw speed, and feed rate on the extrusion process and final product properties were also studied. The apparent density of the extruded product was found to increase with an increase in the feed moisture content and residence time, whereas it decreased with an increase in the extrusion temperature. It was observed that the porosity and expansion ratio of the extruded product decreased significantly with increased feed moisture content and residence time. In addition, an increase in temperature led to a product of higher porosity and expansion ratio. Also, the degree of gelatinization increased with an increase in the temperature and screw speed. A correlation was developed for the throughput and specific consumption of mechanical energy for the studied single-screw extruder.
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