Research efforts have been made to increase the heat transfer rate, energy, and efficiency. Some of these efforts include the application of fins, compact heat exchangers, microchannel, and many others. Recently, nanofluids have been introduced to enhance the thermal conductivity of heat transfer fluids by adding a certain concentration of nanoparticles into the heat transfer media. Hence, most of the work that has been published in the literature focuses on measuring the thermal conductivity of the nanofluid for the overall heat transfer coefficient. In this work, we developed a local heat transfer probe that can measure the heat transfer coefficient to study the effect of the nanofluid with various concentrations and size of nanoparticles on the local heat transfer coefficient in a developed separate effect experimental setup. The experiential setup in general consists of a flow loop made of copper material, a heating unit, a measuring, and control unit. The heat transfer probe, manufactured at Missouri University of Science and Technology and consist of a heat flux sensor (0.15 in x0.08 in) with a fast response time of about 0.02 sec and a thermal resistance of 0.003 °F/BTU/ft2hr. The sensor was placed in a slit inside the test section wall without disturbing the nanofluid inside and used to measure the heat flux and the surface temperature. In addition, two thermocouples (type T) were mounted inside the test section to measure the bulk temperature at the entrance and exit of the test section. The sensor was placed on the middle distance between the two thermocouples. Water with iron (III) oxide (Fe2O3) nanoparticles were used as the nanofluids flowing through the test section. The nanoparticle sizes of the Fe2O3 were varying between 20 and 40nm. The concentrations for the different nanoparticle sizes were ranged between 0 and 0.09 % in volume fractions. The results show that use of aqueous Fe2O3 nanoparticles can significantly enhance heat transfer coefficient in turbulent flow regime, and the enhancement increases with Reynolds and Nusselt number, as well as particle concentration under the conditions of this work, there is an increase of 73.7% at 0.09% volume concentration. The enhancement of the heat transfer coefficient could not be only credited to the improvement of the effective thermal conductivity. The reason for the improvement, Particle passage which leads to reducing the thermal boundary layer thickness and a non-uniform distribution of thermal conductivity.
Journal: TechConnect Briefs
Volume: 2, Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2017
Published: May 14, 2017
Pages: 247 - 250
Industry sector: Energy & Sustainability
Topic: Water Technologies