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Alberto Mucci,Foster Kwame Kholi,Hariharan Kallath,Thierry Sibilli,June Kee Min(민준기) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.1
Experimental studies on gas turbines face severe difficulties in obtaining an accurate and representative model of the internal environment. High temperature and pressure in the core flow require specific test rigs to guarantee the safety and representativeness of the experiment. Moreover, complexities arise when testing novel designs. Due to increasing concerns about flying gas turbines environmental footprint, the Advisory Council for Aeronautics Research in Europe (ACARE) proposed a reduction in aircraft emissions. From a concept proposed by the NEW Aero Engine Core (NEWAC) grant, we developed a methodology to test a novel Cooled Cooling Air Heat Exchanger (CCAHX) system at real steady-state operative conditions. The method involves the creation of one- and three-dimensional Computational Fluid Dynamics (CFD) models to support the experiment and verify the safety of the testing environment. The study presents the steps required to achieve this test, which involves the correct definition of an ε-NTU method for the one-dimensional model and a correct design of the three-dimensional exchange model. Additionally, the CFD model provides insight into the CCAHX operations, showing the temperature gradient inside the bulk structure and inducing further studies on the unit. The experiment reached the required temperature reduction and induced testing in case of a cooling failure to verify the structural safety of the CCAHX device.
Foster Kwame Kholi,Albert Mucci,Mimbo Shim(심민보),J. K. Min(민준기),M. Y Ha(하만영) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
Heat pipes, HP, are phase change devices with high conductivities compared to existing technologies of the same dimensions. However, for HP with multi-layer wicks, the layers and location of the dense wicks significantly affect the thermo-fluidics of the device. The influence of these factors on the overall performance of HP is presented for a standard mesh-screen wick HP with different layers - uniform and non-uniform wick layers. An in-house code assisted in predicting the limit of HP, which show increased heat transfer limit as the number of layers increase, especially for a mixture of layers of uniform and non-uniform wicks. The heat transfer improves in different inclinations when the dense wicks located in the core of the HP, in contact with the vapour flow. This arrangement restricts the entrainment of liquid from the wick surface. The results have shown that the performance of HP can easily be improved through proper wick arrangement.
Foster Kwame Kholi,Alberto Mucci,Hariharan Kallath,하만영,Jason Chetwynd-Chatwin,민준기 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6
Previous correlations that have been used to predict the heat transfer performance of pulsating heat pipes (PHPs) offer limited thermal predictions within a narrow range of fluid-filling ratios and PHP inclinations. In this paper, a novel semi-empirical correlation with improved scope is proposed, with an increased range of fluid-filling ratios and PHP inclinations. The proposed correlation employs the dimensionless numbers governing the thermohydrodynamic operation of PHPs, and achieved ±30 % accuracy when predicting selected experimental data, showing reasonably good agreement. Unlike previous correlations, the new correlation can be used for different working fluids, geometrical aspect ratios, and heat loads. A comprehensive assessment of the relative significance of the correlation parameters on the total heat transfer performance is discussed. The new correlation with its flexible application range is expected to assist in faster and more enhanced thermal predictions as interest in PHPs grows.
Experimental study of effects of wicks and boundary conditions on thermal performance of heat pipes
Foster Kwame Kholi,Hariharan Kallath,Alberto Mucci,Man Yeong Ha,Jason Chetwynd-Chatwin,민준기 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1
The inherent two-phase heat transport of heat pipes (HPs) is progressively being examined for potential uses. These thermal devices are affected by many operating factors, prompting this study to investigate the effects of different types of wicks and working conditions on the time-dependent thermal behavior. Primarily, the effects of different wick performances were investigated under various operating conditions. The resulting surface temperatures depicted in the time to steady performance and the dry-out behavior revealed the conditions to improve the HPs design. The thermal resistance decreased from 0.6 K/W (at 25 W) to 0.05 K/W (at 200 W) by increasing the HP diameter from 6 to 10 mm; these values are relative to those of copper rods, which decrease from 2.70 K/W (at 25 W) to 0.40 K/W (at 200 W). Nonlinear and linear temperature responses were recorded when the HPs diameter and length were varied. Compared to conventional mesh and groove wicks, the composite groovesintered, mesh-sintered, and groove-mesh wicks recorded lower thermal resistance with distinctively faster startup times, lower startup temperatures, better temperature uniformity and less dynamic instability. Tilting the HPs relative to the horizontal position lessens failure tendencies. Usually, dynamic responses are typically first-order under the conditions studied. Hence, proper sizing of HPs and correct wick selection can improve their performance.
An Integrated Air Monitoring Approach for Assessment of Formaldehyde in the Workplace
Stefano Dugheri,Alessandro Bonari,Ilenia Pompilio,Marco Colpo,Nicola Mucci,Giulio Arcangeli 한국산업안전보건공단 산업안전보건연구원 2018 Safety and health at work Vol.9 No.4
The aim of this study is to validate an integrated air monitoring approach for assessing airborne formaldehyde (FA) in the workplace. An active sampling by silica gel impregnated with 2,4-dinitrophenylhydrazine, a passive solid phase microextraction technique using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine as on-fiber derivatization reagent, an electrochemical direct-reading monitor, and an enzyme-based badge were evaluated and tested over a range of 0.020–5.12 ppm, using dynamically generated FA air concentrations. Simple linear regression analysis showed the four methods were suitable for evaluating airborne FA. Personal and area samplings in 12 anatomy pathology departments showed that the international occupational exposure limits in the GESTIS database were frequently exceeded. This monitoring approach would allow a fast, easy-to-use, and economical evaluation of both current work practices and eventual changes made to reduce FA vapor concentrations.
An Integrated Air Monitoring Approach for Assessment of Formaldehyde in the Workplace
Dugheri, Stefano,Bonari, Alessandro,Pompilio, Ilenia,Colpo, Marco,Mucci, Nicola,Arcangeli, Giulio Occupational Safety and Health Research Institute 2018 Safety and health at work Vol.9 No.4
The aim of this study is to validate an integrated air monitoring approach for assessing airborne formaldehyde (FA) in the workplace. An active sampling by silica gel impregnated with 2,4-dinitrophenylhydrazine, a passive solid phase microextraction technique using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine as on-fiber derivatization reagent, an electrochemical direct-reading monitor, and an enzyme-based badge were evaluated and tested over a range of 0.020-5.12 ppm, using dynamically generated FA air concentrations. Simple linear regression analysis showed the four methods were suitable for evaluating airborne FA. Personal and area samplings in 12 anatomy pathology departments showed that the international occupational exposure limits in the GESTIS database were frequently exceeded. This monitoring approach would allow a fast, easy-to-use, and economical evaluation of both current work practices and eventual changes made to reduce FA vapor concentrations.
Kim, S.T.,Kang, J.O.,Yun, S.T.,O'Neil, J.R.,Mucci, A. Pergamon Press ; Elsevier Science Ltd 2009 Geochimica et cosmochimica acta Vol.73 No.15
Rhodochrosite crystals were precipitated from Na-Mn-Cl-HCO<SUB>3</SUB> parent solutions following passive, forced and combined passive-to-forced CO<SUB>2</SUB> degassing methods. Forced and combined passive-to-forced CO<SUB>2</SUB> degassing produced rhodochrosite crystals with a small non-equilibrium oxygen isotope effect whereas passive CO<SUB>2</SUB> degassing protocols yielded rhodochrosite in apparent isotopic equilibrium with water. On the basis of the apparent equilibrium isotopic data, a new temperature-dependent relation is proposed for the oxygen isotope fractionation between rhodochrosite and water between 10 and 40<SUP>o</SUP>C: 1000lnα<SUB>rhodochrosite-water</SUB>=17.84+/-0.18(10<SUP>3</SUP>/T)-30.24+/-0.62 or 1000lnα<SUB>rhodochrosite-water</SUB>=2.65+/-0.03(10<SUP>6</SUP>/T<SUP>2</SUP>)-0.26+/-0.35 where α<SUB>rhodochrosite-water</SUB> is the fractionation factor between rhodochrosite and water, and T is in kelvins. Over the temperature range investigated, rhodochrosite concentrates <SUP>18</SUP>O relative to both calcite and aragonite, a result that is consistent with the relative ionic radii of Ca<SUP>2+</SUP> and Mn<SUP>2+</SUP> and recent theoretical calculations.