A comparative study with respect to the scaling of heat transfer of Newtonian titania nanofluid with concentrations of 5.0 vol.% and 10.0 vol.% is undertaken. For that purpose, experiments in circular flow pipe with inserted twisted tape having a pitch to diameter ratio of nearly 6 under constant heat flux are carried out in a Reynolds number range from 300 to 1300. The experimental data are ordered according to three different scaling approaches based on Reynolds number, on Reynolds and Prandtl numbers, and based on Reynolds and Prandtl numbers and nanoparticle concentration. It is found that, despite its relevance with respect to the flow dynamics, the first scaling is not sufficient to capture the heat transfer features properly. While the second approach is already based on the necessary and sufficient similarity numbers, the third approach does not provide deeper insight into the flow physics. It is concluded that description of laminar nanofluid pipe flow with inserted twisted tape based on a combination of Reynolds and Prandtl numbers is sufficient because two-phase flow effects like Brownian and thermophoretic diffusion are of minor importance. This finding is in agreement with most recent experimental results for the entrance region of laminar flow in empty pipes.

The need for new heat transfer agent for many applications, namely in the consumer electronics industry, requires materials, liquids at room temperature, with high thermal conductivity. From the different possibilities, Galinstan, a eutectic alloy of Gallium, Indium, and Tin with a melting point (T_m = 283.4 K) has been proposed for many applications, namely for replacing the toxic mercury element, used for many years. It is the purpose of this paper to report thermal conductivity measurements of Galinstan, product name Gallium/Indium/Tin Eutectic (NL-011), Ga_68.4In_21.5Sn₁₀. The method used was the transient hot strip (THS), using a platinum metal-film sensor, produced by PVD in ceramic substrates, and electrically insulated with a heat-shrinkable coating. The details of the data acquisition system and measuring procedure are reported. Measurements were performed between 28 °C and 103 °C (301 K to 376 K), at atmospheric pressure, with an estimated uncertainty of 6%, and compared with available literature. Data were correlated for linear interpolation. This type of sensor is applied to molten metals for the first time, proofing to concept to future applications in molten metals and molten salts at higher temperatures. Graphical

Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120–1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from these findings is that magnetic forces are rather a tool to control heat transfer locally than to enhance the overall heat transfer of heat exchangers or the like. Magnetically caused disturbances decay due to viscous dissipation and the flow approaches the basic state again.