Seungro Lee

High-brightness gallium nitride nanowire UV–blue light emitting diodes

We report on high-brightness GaN nanowire UV–blue light emitting diodes (LEDs), which are fabricated by coupling of n-GaN nanowires and p-GaN substrates using two assembly methods, random dispersion (RD) and dielectrophoresis assisted assembly deposition (DAAD). These GaN nanowire LEDs have bright UV–blue emission (411–437 nm) from the n-GaN nanowire/p-GaN substrate junction and the light emission is strong enough to be observed with the naked eye even for a single GaN nanowire LED. The results reported here should have significant implications for the fabrication of highly efficient, low-cost UV–blue LEDs with low power consumption, as compared to conventional thin-film based GaN LEDs.

Assessment of Achilles enthesitis in the spondyloarthropathies by colour Doppler energy ultrasound in the context of the ‘enthesis organ’

Objectives: To identify the characteristic features of Achilles enthesitis of the spondyloarthropathies (SpA) detectable by colour Doppler energy ultrasound (CDEU) in the context of the ‘enthesis organ’. Methods: Seventy patients with SpA and 15 healthy subjects were clinically evaluated and underwent CDEU examination of the Achilles entheses. The CDEU images were evaluated according to five distinctive CDEU features of enthesitis in the context of the enthesis organ. Results: Fifty-six of the 70 SpA patients (80%) showed at least one abnormal finding of the enthesitis on CDEU examination, affecting 91 of 140 Achilles entheses examined (65%). Only 22 of 140 Achilles entheses (15.7%) showed abnormal vascularization in the peri-sesamoidal and periosteal areas or in the area of enthesis fibrocartilage. In addition, 67 (47.9%) and 18 (12.9%) of 140 Achilles entheses examined showed cortical bone irregularities and erosions, respectively, at areas of the periosteal and the enthesis fibrocartilage. Sixteen (88.9%) of 18 clinically detected Achilles enthesitis and six (75%) of eight Achilles entheses with swelling on clinical examination presented corresponding abnormalities on CDEU examination. The Doppler twinkling artefact (TA) was observed consistently in all normal entheses and completely disappeared upon stabilization of the probe application. The C-reactive protein (CRP) level was higher in the patients with cortical bone erosion than in those without erosion. Conclusions: This study demonstrates the characteristic features of enthesitis detectable by CDEU in the context of the enthesis organ and shows a good correlation with clinical as well as with laboratory findings.

Estimation Method of the Interchangeability Using Equivalent Gases in a Partial Premixed Gas Appliance

The estimation method of the interchangeability in a partial premixed appliance about various compositions of natural gases using equivalent gases, experimentally. The results of the experiment in which equivalent gases were used compared with those obtained in experiments in which natural gases were used; Images of flames, lift-off limits, CO emissions, and incomplete combustion indices in KS standard for the domestic gas range were considered. From the comparison, it was observed that the length and color of the flame of the equivalent gases were almost the same as those of imported natural gases. Further, in the case of gases with Wobbe indices greater than 51 MJ/m

Characteristics of Combustion and Thermal Efficiency for Premixed Flat Plate Burner Using a Porous Media

The purpose of this study is investigated on the combustion and the thermal characteristics of porous media burners which are many using for a condensing boiler recently. In addition, results of this study will be used the fundamental information to decide the burner type which will be applied to the future development of EGR(Exhaust gas recirculation) condensing boiler. Two flat type of burners made of a the metal fiber(MF) and the ceramic(CM) were selected and examined, experimentally. As experimental results, the emitted CO concentration of CM was higher than that of MF. However, the NO concentration of MF was higher than that of CM. The efficiencies of both burners were increased as increasing the burner capacity. While the efficiency of MF was higher than that of CM, regardless of the burner capacity. In the experimental range, MF is appropriated for the burner material and 0.8 of equivalence ratio is an optimal operation condition, regarding of the proportional control, the thermal efficiency and emitted NO and CO concentration based on the regulations of KS B standard and EN 677 standard.

Thermal Characteristics of Cross-flow Small Scale Heat Exchanger

This study was experimentally investigated NOx and CO emissions characteristics with various equivalence ratios using premixed type of burner installed small heat exchanger. The effectiveness of heat exchanger and the entropy generation number were also calculated. As results, the heat transfer rate increases with increasing equivalence ratio due to increase the flame temperature. According to the emission characteristics and the effectiveness, the optimal operating equivalence ratio is 0.75 in the range of this experiment. Consequently, the area of the heat exchanger should be increased to reduce the entropy generation number and to increase the effectiveness.

Heat Transfer and Pressure Drop of Cross-flow Heat Exchanger on Modules Variation

This study investigated the characteristics of heat transfer and pressure drop for cross-flow heat exchanger of premixed combustion system. The premixed burner was in front of a heat exchanger, and the number of heat exchanger modules was changed to investigate the characteristics of NOx and CO emissions with various equivalence ratios. In addition, the effectiveness, entropy generation and pressure drop were calculated by various number of heat exchanger modules and the performance of heat exchanger was analyzed by the exergy loss.

Examination of validation for equivalent gas to replace natural gas

In order to estimate the combustion characteristics and the gas interchangeability for natural gas with various compositions per each production area, equivalent gas are using to replace natural gas. It is known that an equivalent gas has the same the heating value, the compression factor, the relative density, CO emission and the burning velocity as the original natural gas. However, it is not reported that the flame shape and thermal efficiency and NOx emission by real gas appliance. In this study, equivalent gas was examined the validation to replace natural gas. The CO emission the burning velocity and the flame temperature were reconfirmed, and the flame shape, the NOx emission and the thermal efficiency were numerically and experimentally investigated. As results, there was not a large difference between natural gas and equivalent gas. This result demonstrated that there was no problem using equivalent gas to replace natural gas.

Thermal Flow Characteristics of Impinging Air Jet by Shape of Turbulence Promoter

In this study, it was experimentally investigated the effect of the clearances distance between the rod and the impinging plate on characteristics of the thermal flow. For the heat transfer enhancement of wall jet region, the right triangle and the square rods were arranged in front of the impinging plate with various clearance distances. As results, the heat transfer enhancement rate of potential core region at H/B

Heat Transfer Characteristics with Changing Distances between Burner and Heat Exchanger

In this study, the heat transfer characteristics and NOx and CO emissions of a heat exchanger were investigated using a premixed burner. The experiments involved changing the distance between the burner and heat exchanger to 30, 40, and 50 mm with various equivalence ratios. The results showed that the NOx and CO emissions increased as the equivalence ratio was increased because the flame temperature increased, regardless of the distance between the burner and heat exchanger. In particular, the CO emission increased significantly as the distance between the burner and heat exchanger was decreased. The optimal equivalence ratio for the A-type heat exchanger (distance between the burner and heat exchanger: 30 cm) was 0.7 in the experimental range. In this case, the CO and NOx emissions were 94.5 ppm and 11.2 ppm, respectively, and the efficiency was 84.1%.