Επιστημονικές Δημοσιεύσεις
Μόνιμο URI για αυτήν τη συλλογήhttps://repository2024.ihu.gr/handle/123456789/30488
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Πλοήγηση Επιστημονικές Δημοσιεύσεις ανά Συγγραφέα "Albanakis, C."
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Τεκμήριο Effect of turbulence intensity on the pressure drop and heat transfer in a staggered tube bundle heat exchanger(2015-01) Vlahostergios, Z.; Missirlis, D.; Flouros, M.; Albanakis, C.; Yakinthos, K.This paper investigates experimentally the correlation and the effect of the turbulence intensity on the pressure drop and the heat transfer mechanism of a heat exchanger with elliptic tubes in a staggered arrangement. The heat exchanger studied in this work is an air–water cross flow heat exchanger with air being the external fluid and water the internal one. The heat exchanger consists of 144 elliptic tubes placed in a staggered arrangement. The experiments were carried out for two setups. The first setup was referring to isothermal conditions for which only air was used, flowing around the tubes. The second setup was referring to non-isothermal conditions with air as the external fluid and water as the internal working fluid, flowing inside the tubes. The Reynolds number for the external air for the isothermal experiments ranged between 3100 and 5200 based on the maximum velocity between the elliptic tubes. The turbulence intensity values varied between 0.9% and 3%. For the non-isothermal measurements the Reynolds number took values from 3100 to 7700 and the turbulent intensity ranged from 0.9% to 3%. The measurements showed that the increase of turbulent intensity led to a decrease in the total pressure drop of the external flow of the heat exchanger together with an enhancement of the heat transfer mechanism.Τεκμήριο Flow, thermal and structural application of Ni-foam as volumetric solar receiver(2013-02) Michailidis, N.; Stergioudi, F.; Omara, H.; Missirlis, D.; Vlahostergios, Z.; Tsipas, S.; Albanakis, C.; Granier, B.Open-cell nickel foams with 92% porosity and uniform pore size and distribution were used in this study. The main objective of this work was to evaluate the behaviour of Ni-foam, when treated as volumetric receivers under concentrated solar radiation while improving their oxidation resistance, in order to make them attractive for such applications. The experimental investigation showed that their efficiency was depending on both materials parameters and flow conditions, the latter affecting the pressure drop and the heat transfer behaviour. The microstructural characterisation of oxide surface morphologies formed on the open-cell Ni foams exposed to concentrated solar radiation is investigated by the use of SEM and EDXS. SEM observations revealed a rapid homogeneous oxidation in the Ni-foam with three different surface oxide structures formed in relation with the process temperature. A novel slurry-based process for aluminising nickel foams while retaining their geometrical properties is applied in order to develop an aluminide–nickel intermetallic coating on a Ni foam thus enhancing the oxidation resistance. Scanning electron microscopy and X-ray diffraction were applied to assess the effectiveness of the aluminising process and determine the optimum parameters of the procedure (slurry composition, holding temperature and time).