Fabrication of novel core–shell PLGA and alginate fiber for dual‐drug delivery system

Biodegradable fibers for the controlled delivery of anti‐inflammatory agent dexamethasone were developed and studied. Mono and core–shell structure fiber are prepared by wet‐spinning solutions of hydrophobic poly (lactide‐co‐glycolide) and hydrophilic alginic acid shell. The two model drugs, dexamethasone and dexamethasone‐21‐phosphate, were entrapped in core and shell, respectively. These fibers were characterized in terms of morphology, diameters, mechanical properties, in vitro degradation, and drug release. The optical microscopy and scanning electron microscopy photos revealed directly that fibers possessed core–shell structure. The release of dexamethasone and dexamethasone‐21‐phosphate was investigated, and the results showed that alginate shell retarded dexamethasone release significantly in both early and late stages. The core–shell structure fiber release shows a two stage release of dexamethasone and dexamethasone‐21‐phosphate with distinctly different release rates, and minimal initial burst release is observed. The results indicated that the prepared fibers are efficient carrier for both types of dexamethasone. Copyright © 2016 John Wiley & Sons, Ltd.     

Heat transfer characteristics of a new helically coiled crimped spiral finned tube heat exchanger

In the present study, the heat transfer characteristics in dry surface conditions of a new type of heat exchanger, namely a helically coiled finned tube heat exchanger, is experimentally investigated. The test section, which is a helically coiled fined tube heat exchanger, consists of a shell and a helical coil unit. The helical coil unit consists of four concentric helically coiled tubes of different diameters. Each tube is constructed by bending straight copper tube into a helical coil. Aluminium crimped spiral fins with thickness of 0.5 mm and outer diameter of 28.25 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Ambient air is used as a working fluid in the shell side while hot water is used for the tube-side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. The effects of the inlet conditions of both working fluids flowing through the heat exchanger on the heat transfer coefficients are discussed. The air-side heat transfer coefficient presented in term of the Colburn J factor is proportional to inlet-water temperature and water mass flow rate. The heat exchanger effectiveness tends to increase with increasing water mass flow rate and also slightly increases with increasing inlet water temperature.