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Comparative wind tunnel experiments were performed on passive flow separation control on a at plate model equipped with a flap. The purpose of these tests was to investigate the flow control capabilities of off-surface mounted elements. A comparison was made of delta-shaped vortex generators of 1 to 1/3 boundary layer height and cylinders close to the wall. Surface pressure as well as PIV measurements were performed to investigate the influence of the layout of the VGs as well as the diameter of the cylinder and the position of the elements. The results showed that the off-surface devices performed better than the on-surface VGs for the fully separated case, and were equally good in improving the state of boundary layer that is on the verge of separation. It was also found that the off-surface devices could be positioned over a wider range with respect to the separation point. The experiments furthermore indicated that for the optimum cylinder configuration the vortex shedding frequency was consistent with the frequencies found in literature on periodic flow excitation.

Comparative wind tunnel experiments were performed on passive flow separation control on a at plate model equipped with a flap. The purpose of these tests was to investigate the flow control capabilities of off-surface mounted elements. A comparison was made of delta-shaped vortex generators of 1 to 1/3 boundary layer height and cylinders close to the wall. Surface pressure as well as PIV measurements were performed to investigate the influence of the layout of the VGs as well as the diameter of the cylinder and the position of the elements. The results showed that the off-surface devices performed better than the on-surface VGs for the fully separated case, and were equally good in improving the state of boundary layer that is on the verge of separation. It was also found that the off-surface devices could be positioned over a wider range with respect to the separation point. The experiments furthermore indicated that for the optimum cylinder configuration the vortex shedding frequency was consistent with the frequencies found in literature on periodic flow excitation.

Abstract Over a period of more than 10 years, fundamental research on frost formation and defrosting behaviour of lamel type air coolers has been pursued at the Delft University of Technology. Many experiments have been performed to support the Dutch Standard for testing air coolers, NEN 1876. This standard gives an objective description of the performance of air coolers under frosting conditions. For the system designer it is very important to judge the average cooling performance and coefficient of performance during the total cycle, consisting of cooling period and defrosting period. For this purpose two dimensionless numbers were derived, which also make it possible to determine, by using computer models, the optimum cooling period before defrosting starts. Finally the use of the developed theories for cost optimization of refrigerating plants and the latest experiences with the Dutch Standard for air coolers, NEN 1876, are discussed.

Abstract Over a period of more than 10 years, fundamental research on frost formation and defrosting behaviour of lamel type air coolers has been pursued at the Delft University of Technology. Many experiments have been performed to support the Dutch Standard for testing air coolers, NEN 1876. This standard gives an objective description of the performance of air coolers under frosting conditions. For the system designer it is very important to judge the average cooling performance and coefficient of performance during the total cycle, consisting of cooling period and defrosting period. For this purpose two dimensionless numbers were derived, which also make it possible to determine, by using computer models, the optimum cooling period before defrosting starts. Finally the use of the developed theories for cost optimization of refrigerating plants and the latest experiences with the Dutch Standard for air coolers, NEN 1876, are discussed.

Abstract Hybrid TiO2/SiO2 thin films deposited by material printing technique on flexible substrates were prepared, characterized and tested for solar photocatalytic disinfection. Effect of surface hydrophilicity/hydrophobicity of printed coatings on photocatalytic disinfection was studied by means of (i) drinking water contaminated with natural consortia of fecal bacteria (gram-negative: Escherichia coli and total coliforms; gram-positive: Enterococci), and (ii) seawater containing pathogenic gram-negative bacteria (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi). Inactivation of gram-negative bacteria in drinking water with fecal contamination by solar photocatalysis was slightly more efficient than solar disinfection, while for gram-positive bacteria similar efficiency was observed. These results, in combination with observed release of titanium from coatings (detected by means of inductively coupled plasma atomic emission spectrometer), indicate that TiO2/SiO2 needs further improvements for solar photocatalytic disinfection of drinking water. Efficiency of seawater disinfection towards gram-negative Vibrio spp. (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi) was significantly enhanced when TiO2/SiO2 coatings were used under natural solar light. Moreover, hydrophobic thin films led to faster Vibrio spp. inactivation as compared to hydrophilic ones, which was attributed to higher bacteria adhesion on hydrophobic coatings. However, decrease of photocatalytic activity of hydrophobic TiO2/SiO2 coatings was observed after ten experimental cycles mainly due to deposition of salts on the surface of photocatalyst. Generally, results of this study suggest that autochthonous bacteria such as Vibrio spp. in seawater are significantly more resistant to solar disinfection in comparison with not autochthonous bacteria such as Escherichia coli, total coliforms and Enterococci in contaminated drinking water.

Abstract Hybrid TiO2/SiO2 thin films deposited by material printing technique on flexible substrates were prepared, characterized and tested for solar photocatalytic disinfection. Effect of surface hydrophilicity/hydrophobicity of printed coatings on photocatalytic disinfection was studied by means of (i) drinking water contaminated with natural consortia of fecal bacteria (gram-negative: Escherichia coli and total coliforms; gram-positive: Enterococci), and (ii) seawater containing pathogenic gram-negative bacteria (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi). Inactivation of gram-negative bacteria in drinking water with fecal contamination by solar photocatalysis was slightly more efficient than solar disinfection, while for gram-positive bacteria similar efficiency was observed. These results, in combination with observed release of titanium from coatings (detected by means of inductively coupled plasma atomic emission spectrometer), indicate that TiO2/SiO2 needs further improvements for solar photocatalytic disinfection of drinking water. Efficiency of seawater disinfection towards gram-negative Vibrio spp. (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi) was significantly enhanced when TiO2/SiO2 coatings were used under natural solar light. Moreover, hydrophobic thin films led to faster Vibrio spp. inactivation as compared to hydrophilic ones, which was attributed to higher bacteria adhesion on hydrophobic coatings. However, decrease of photocatalytic activity of hydrophobic TiO2/SiO2 coatings was observed after ten experimental cycles mainly due to deposition of salts on the surface of photocatalyst. Generally, results of this study suggest that autochthonous bacteria such as Vibrio spp. in seawater are significantly more resistant to solar disinfection in comparison with not autochthonous bacteria such as Escherichia coli, total coliforms and Enterococci in contaminated drinking water.

Abstract The dynamics of isolated-photon plus two-jet production in pp collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to an integrated luminosity of 36.1 fb−1. Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state, γ + jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from Sherpa and Pythia as well as the next-to-leading-order QCD predictions from Sherpa are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data.