National Technical University of Athens

About: National Technical University of Athens is a education organization based out in Athens, Attiki, Greece. It is known for research contribution in the topics: Large Hadron Collider & Nonlinear system. The organization has 13445 authors who have published 31259 publications receiving 723504 citations. The organization is also known as: Athens Polytechnic & NTUA.

Removal of Heavy Metals from Calcareous Contaminated Soils by EDTA Leaching

Abstract: The performance of EDTA for the treatment of calcareous soils contaminated with heavy metals from mining and smelting activities was evaluated in this study. Soil samples containing variable levels of contamination, from 500 to 35 000 mg kg-1 Pb and 700 to 20 000 mg kg-1 Zn, were subjected to EDTA treatment and the extraction of heavy metals was found to vary, ranging between 50 and 98% for Pb and 50 to 100% for Zn. Total residual concentrations were above the limits set by regulatory authorities; leachable metals, however, were efficiently removed and treated soils were all acceptable in terms of toxicity. The effect of EDTA concentration and pulp density was studied on a soil sample containing 12 000 mg kg-1 Pb and 10 000 mg kg-1 Zn. Heavy metals removal was improved at low pulp densities and when EDTA concentration was increased from 0.025 to 0.25 M. The tetrasodium salt Na4-EDTA was found to be less effective for metals removal compared to the disodium salt Na2-EDTA, though applied at higher concentrations. This experimental work has also demonstrated the great importance of soil matrix for the overall evaluation of the EDTA leaching as a cost effective remedial option. The simultaneous dissolution of calcite was found to consume approximately 90% of the available EDTA. It was thus concluded that for the treatment of calcareous soils the design criteria and cost estimations should be based on the calcite content of the soil.

Enhancing the performance of automotive radiators using nanofluids

Abstract: Advanced heat removal technologies are critical for high-performance automotive engines. The conventional fluids being used today are based on a mixture of distilled water (DW) and ethylene glycol (EG), which widens the operational temperature range but at the same time limits the heat removal. Therefore, the use of nanofluids for improving heat transfer performance has soared over the past few years. The problem is that most of the reports highlight the short-term heat transfer results which may not be true over time. In this paper, a suggested best practice for analyzing the usage of nanofluids in heat transfer applications is presented, specifically for an actual car radiator. This work investigates the use of aluminum oxide (Al2O3) and titanium dioxide (TiO2) nanoparticles dispersed in DW and EG at 50:50 volumetric proportions. The choice of these oxide-based nanofluids is motivated by their anti-corrosive properties that are usually not analyzed or discussed in most of the articles. Furthermore, the emphasis is given on the presentation of a comprehensive characterization of the nanofluids including thermophysical properties (size, density, viscosity, thermal conductivity, corrosive behavior) and long-term stability (zeta potential) which are essential for an end-user to have. The results showed a maximum enhancement of the thermal performance by 24.21% using Al2O3 at a volume fraction of 0.3%. Friction factor and performance evaluation criterion (PEC) for the radiator experiments are calculated in order to determine the penalty in the pressure drop and to evaluate it properly. Finally, it is found that the values of PEC lie in the range of 1.03–1.31 which indicates significant flow enhancement.