Nanofluids are nano-size-powder suspensions in liquids that are mainly studied for their abnormal thermal transport properties, and hence as enhanced alternatives to ordinary cooling fluids. The tribological effects of nanofluids are, however, largely unknown, in particular their likely wear and/or erosion effects, because of their interaction with cooling-system (heat-exchanger) materials. The thesis presents research to establish methodologies for testing and evaluating surface-change by nanofluid impact. The work is presented on development of novel test rigs and testing methodologies, and on the use of typical surface analysis tools for assessment of wear and erosion that may be produced by nanofluids; prediction of such effects in cooling systems is discussed.
Two new tests rigs were designed and developed: a multiple nozzle test rig and a parallel flow test rig. A main purpose of this research work was to assess the use of these new test rigs to evaluate nanofluid wear, and the ad-hoc newly proposed testing methodologies are discussed. Experimental results are presented on typical nanofluids (as 2%-volume of alumina nanopowders in 50/50 water/ethylene glycol solution, and in distilled water) which are jet-impinged (on aluminum and copper specimens) with 3.5 m/s to 15.5 m/s jet-speeds and in a 1 m/s parallel-flow (along the test specimen surface) during long test periods. The obtained surface modifications were assessed by roughness measurements, by weighing of removed-material, and by optical-microscopy. The results are presented on the observed substantially different surface modifications when same tests are conducted in aluminum and copper, and by both the base fluids and its alumina-nanofluids. The likely mechanisms of early erosion and abrasion, and the possibility of extrapolating the test-rig results and methodologies to typical cooling systems are discussed
