Water-based suspensions of Al2O3 nanoparticles and MEPCM particles on convection effectiveness in a circular tube

This work compares experimentally the effectiveness of substituting the water-based suspensions of Al2O3 nanoparticles (nanofluid) and of micro-encapsulated phase change material particles (PCM suspension) for the pure water for laminar forced convective cooling through an iso-flux heated circular horizontal tube. Convection heat transfer experiments have been undertaken for the tube using the pure water, the PCM suspensions (ωPCM = 2, 5, and 10 wt.%) and the nanofluids (ωnp = 2, 6, and 10 wt.%) as the working fluids under the following operating conditions: the volume flow rate Q = 25-240 cm3/min (the Reynolds number Ref = 195-1801), the heating power applied at the outer wall of the tube qo = 20, 30, 40 W, and the inlet fluid temperature Tin = 32.8-33.2 °C. In addition, a scale analysis together with integral energy balance is presented concerning thermally developing heat transfer characteristics of the water-based suspension flow in the tube. The convective cooling performance of the water-based suspensions was gauged in terms of local and surface-averaged temperature control effectiveness along the tube wall compared with that obtained for the pure water. Furthermore, the water-based suspensions were compared based on the figures of merit for their heat transfer performances against the corresponding pressure drop penalty.