In this study, subcritical water extraction (SWE) was applied to extract the essential oil (especially curcumin) from Curcuma longa L. (turmeric) rhizome. Response surface methodology was used to evaluate the extraction conditions. Experiments were carried out using a three-factor Box–Behnken design under following conditions: temperature (90, 120 and 150C), water flow rate (1, 2.5 and 4 mL/min) and mean particle size (0.5, 1 and 1.5 mm). This is the first time that effects of mentioned variables were considered on SWE of curcumin. The optimum conditions were temperature of 150C, water flow rate of 1 mL/min and mean particle size of 0.5 mm. The maximum curcumin extraction yield was 90.1947 ± 0.26%, which was in a good agreement with the predicted value of 92.0097%. The extracts were analyzed by gas chromatography and gas chromatography-mass spectrometry. Also, results of SWE were compared with conventional methods. Curcumin is an important pharmacological agent that can be extracted from turmeric rhizome. In recent years, subcritical water has been used as a solvent for extraction of flavors, fragrances and antioxidant components from plant materials. Subcritical water is a good solvent for curcumin as well as other organic compounds but is safer than the organic solvents. Subcritical water extraction of curcumin from turmeric rhizome is an alternative method for increasing the quality of the extract.

A three dimensional (3D) computational fluid dynamics (CFD) simulation and a neural network model are presented to estimate the behaviors of the Colburn factor (j) and the Fanning friction factor (f) for wavy fin - and - flat tube (WFFT) heat exchangers. Effects of the five geometrical factors of fin pitch, fin height, fin length, fin thickness, and wavy amplitude are investigated over a wide range of Reynolds number (600