09. Heat and Mass Transfer

Characteristics of heat transfer enhancement of a magnetic nanofluid by applying two active methods which are ultrasound wave and magnetic field were investigated experimentally. Product water-based magnetic fluid were used as a magnetic nanofluid in this study. The experiments were conducted in a closed-circuit loop with a rectangular duct as a test section. The dimensions of the rectangular duct were 18 mm × 18 mm × 950 mm. Reynolds number based on hydraulic diameter and bulk mean velocity was varied from 470 to 5000. The ultrasonic transducers were attached on the upper wall of the test section and operated at 200 kHz. In contrast, magnetic field is applied to magnetic nanofluid flow at the center of the test section by an electromagnet in horizontal direction. The diameter of cylinder iron core of the electromagnet is 120 mm, and a uniform magnetic field of 500 mT was applied to magnetic nanofluid flow. The following three active methods for heat transfer enhancement were tested: application of 200 kHz acoustic wave (Method 1), application of 500 mT magnetic field (Method 2) and application of their combination (Method 3). Heat transfer is enhanced by all methods under all Reynolds number cases. Heat transfer enhancement ratio by Method 3 is larger than that by each method, but is smaller than the sum of heat transfer ratio by applying Method 1 and Method 2 in small Reynolds number. However, in the high Reynolds number, Method 3 provides additional improvement, and heat transfer ratio by Method 3 is larger than the sum of that by application of Method 1 and Method 2.

Weerachai CHAIWORAPUEK

Prof.