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Original scientific paper https://doi.org/10.2298/TSCI170703303O This paper deals with the improvement of thermal performance of the heat recovery system in air-to-air unit by using a nanofluid of TiO particles and distilled water. The 2 experimental set-up equipped with 15 copper pipes of a 1000 mm length, 10.5 mm inner diameter, and 12 mm outer diameter was used. The evaporator section consists of 450 mm of heat pipes, the condenser section is 400 mm, and the adiabatic section is 150 mm. In experimental studies, 33% of the evaporator volumes of heat pipes were filled with working fluids. Experiments were carried out at temperatures between 25 ºC and 90 ºC by using five different cooling air-flows (40, 42, 45, 61, and 84 g/s), and two different heating powers (3 kW and 6 kW) for the evaporation section, to determine heat removed from the condensation section. Trials were performed for distilled water and nanofluid respectively, and the results were compared with each other. Results revealed that a 50% recovery in the thermal performance of the heat pipe heat recovery system was achieved in the design using TiO nanofluid as the working liquid, at a heating power of 3 kW, air 2 velocity of 2.03 m/s and air-flow of 84 g/s.

This study reports on the mechanical and flame-retardancy properties of polyamide 12 (PA 12) based composites reinforced with antimony trioxide, sepiolite, or boron powders. These composites were fabricated by the twin-screw extruder and hot-press techniques. The microstructural characteristics and flame-retardancy of the PA 12-based composite samples were obtained by using a scanning electron microscope, a vertical UL-94 burning, and limiting oxygen index tests. The Shore-D hardness, Charpy impact, and tensile tests were conducted to reveal the mechanical performance of composites. The PA 12/antimony trioxide/sepiolite sample presented the best mechanical performance. The additions of antimony trioxide/boron into the PA 12 matrix gave the best contribution to the flame-retardancy.

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