Enhancement of thermal exchanges in natural convection assisted by ultrasound

International audienceIn order to preserve fossil fuels, there is a path that consists of improving the energy efficiency of industrial systems, in particular in the thermal industry. Several approaches are explored in this sense such as the use of metallic foams, thermoacoustics, nanoparticles and phase change materials. These are heat transfer improvement approaches that do not require the use of moving parts, which is a definite advantage for the reliability of the proposed solutions. This work is part of this approach, which consist to study experimentally the effects of the application of a low frequency acoustic field (frequency 16-100KHZ) on the natural convection heat transfer between a heating element and water. Two liters of distilled water are heated by Joule effect through a resistance of variable power between 60W and 200W incorporated in a cylinder immersed in a rectangular water tank. Six K-type thermocouples was distributed in the water tank to measure the temporal evolution of the water temperatures in the heating and cooling phase. A piezoelectric transducer has been placed on one side of the tank and can vibrate at the fixed frequency of 35 kHz. Acoustic currents were generated in the tank which allowed to intensify the heat exchange by natural convection between the tank water and the heating element. The preliminary results obtained, as well as their discussion, are presented in this work

Double Diffusive Convection of Power Law Fluids Through Taylor–Couette Flow

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LBM-MRT simulation of vertical flow of a non-Newtonian fluid in a channel provided with obstacles

Forced convection heat transfer in channels with a block has been studied numerically. The vertical walls are differentially heated. The Lattice Boltzmann Method with multiple relaxation time (MRT) has been used to solve numerically the momentum and the heat transfer governing equations. This study details the effects of variations in the Reynolds number, Rayleigh number, and behavior index of fluid, to illustrate important fundamental and practical results. The results show that the recirculation caused by porous-covering block will significantly enhance the heat transfer rate on both top and right faces of second and subsequent blocks. In order to better understand the different elements of the study, we first analyzed the flow in a channel without obstacles in order to understand the behavior of non-Newtonian fluids. in such situations, we have observed that the speed profiles at establishment are essentially dependent on the behavior index, while the heat transfers are proportional to the Reynolds and Prandtl numbers but inversely to the behavior index