Single phase laminar convective heat transfer of nanofluids in a micro-tube

Abstract: Nanofluids are homogeneous mixture of dispersed solid particles in base fluids. These solid particles are usually smaller than 100nm. Suspended nanoparticles modify the properties of based fluids. It is claimed, in some literature, for nanofluids to have greater than expected heat transfer performance. Due to this, nanofluids have gained great attention from both research and development and industries active in cooling systems. This thesis reports several measurements of convective heat transfer coefficient in a horizontal open micro-tube test section under laminar flow regime. The test section has an inner diameter of 0.5mm made of stainless steel and it has a length of 30cm. Two different test sections have been built. The first one has 13 thermocouples attached on the wall and the second one has 10. These thermocouples are used to measure the wall temperature distribution along the tube. In addition, two more thermocouples are used inside the micro-tube, at the inlet and outlet, to measure the bulk temperature of the nanofluids. A syringe pump is used for injecting the nanofluids through the micro-tube. A DC power supply provides constant heat flux along the test section and a differential pressure transducer measures the pressure drop of the test section. Aqueous based Al2O3 (9 wt %), ZrO2 (9 wt %), TiO2(9 wt %), CeO2 (9wt %), CNT (0.15 wt %), and diamond (1 wt %) have been tested in this thesis. Local Shah’s correlation predicts very well the behaviour of these nanofluids. The results are compared with water in six different ways: heat transfer forconstant Reynolds numbers, volume and mass flow rates, pressure drops andpumping powers. Enhancement in heat transfer is recognisable only in thegraphs of Nu numbers for constant Reynolds numbers. This can be attributed to the higher viscosity for nanofluids. Moreover, friction factor for constant Reynolds numbers has been compared. All the nanofluids with the exception of Al2O3 and diamond suit quite well with Darcy-Weisbach correlation.