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    Possibility of metallic cobalt formation in the oxide scale during high-temperature oxidation of Co-27Cr-6Mo alloy in air
    (2023-01-01)
    Wongpromrat, Patthranit
    ;
    Tunthawiroon, Phacharaphon
    ;
    Bumrungthaichaichan, Eakarach
    ;
    Ponpo, Phisan
    ;
    Nilsonthi, Thanasak
    Co-based alloys are known to be high oxidation-resistant material and used in several high temperature applications. During high temperature oxidation, duplex oxides containing Co and Cr were formed. It was thermodynamically elucidated that when the growing scale was thick enough, the partial pressure of O<inf>2</inf> in the scale dropped. Then, the reduction of CoO occurred for promoting O<inf>2</inf> which was responsible for Cr<inf>2</inf>O<inf>3</inf> production. This work experimentally proved this point by in situ char-acterising Co-27Cr-6Mo at high temperatures in air by X-ray diffractometer in a grazing incident mode and metallic Co was confirmed to be formed by the reduction of CoO consistent with the image taken and analysed by field emission scanning electron microscope, energy-dispersive X-ray, and electron backscatter diffraction. Furthermore, the change in lattice parameter and the phase transition were observed when the temperature was altered.
      2
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    Evidence for chromium, cobalt and molybdenum volatilisations during high temperature oxidation of Co-27Cr-6Mo Alloy
    (2022-07-01)
    Wongpromrat, Patthranit
    ;
    Galerie, Alain
    ;
    Thublaor, Thammaporn
    ;
    Chandra-ambhorn, Walairat
    ;
    Ponpo, Phisan
    A Co-27Cr-6Mo alloy was oxidised in pure O<inf>2</inf> between 800 and 1000 °C for durations up to 96 h. The flow rate was varied between 2 and 5 cm.s<sup>–1</sup>. In these conditions, volatilisations of chromium, cobalt and molybdenum were observed. The chromium volatilisation values were in good agreement with calculations assuming (CrO<inf>3</inf>)g volatilisation limited by diffusion in the gas boundary layer. On the contrary, the measured flux of evaporated Co was higher than the calculated Co volatilisation flux from the metallic Co. The theoretical relation between the solid Co particle size and its vapour pressure was suggested to help explaining such difference.
      2
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    Modification of a solar thermal collector to promote heat transfer inside an evacuated tube solar thermal absorbe
    (2021-05-01)
    Supankanok, Rasa
    ;
    Sriwong, Sukanpirom
    ;
    Ponpo, Phisan
    ;
    Wu, Wei
    ;
    Chandra-Ambhorn, Walairat
    Evacuated-tube solar collector (ETSC) is developed to achieve high heating medium temperature. Heat transfer fluid contained inside a copper heat pipe directly affects the heating medium temperature. A 10 mol% of ethylene-glycol in water is the heat transfer fluid in this system. The purpose of this study is to modify inner structure of the evacuated tube for promoting heat transfer through aluminum fin to the copper heat pipe by inserting stainless-steel scrubbers in the evacuated tube to increase heat conduction surface area. The experiment is set up to measure the temperature of heat transfer fluid at a heat pipe tip which is a heat exchange area between heat transfer fluid and heating medium. The vapor/ liquid equilibrium (VLE) theory is applied to investigate phase change behavior of the heat transfer fluid. Mathematical model validated with 6 experimental results is set up to investigate the performance of ETSC system and evaluate the feasibility of applying the modified ETSC in small-scale industries. The results indicate that the average temperature of heat transfer fluid in a modified tube increased to 160.32 °C which is higher than a standard tube by approximately 22 °C leading to the increase in its efficiency by 34.96%.
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    Influence of jet discharge velocity profile on CFD simulation of pump-around jet mixing tank
    (2018-08-14)
    Jorakit, Thanwa
    ;
    Phaiboonsilpa, Natthanon
    ;
    Namkanisorn, Apinan
    ;
    Ponpo, Phisan
    ;
    Bumrungthaichaichan, Eakarach
    The present paper shows the effect of jet discharge velocity profile (or jet nozzle configuration) on CFD simulation of an open 45° inclined side entry pump-around jet mixing tank. The CFD model was carefully developed by using appropriate grid arrangement, boundary conditions, and numerical methods. The two different jet discharge velocity profiles, including top hat and fully developed profiles, were simulated by using the inlet mass flow rate of about 0.22 kg·s<sup>-1</sup>. The overall mixing times and normalized concentration profiles predicted by two different jet discharge velocity profiles were compared with the previous reliable experimental data. The results revealed that the different jet discharge velocity profiles resulted in different jet flow and mixing patterns inside the vessels.
      3