Experimental Investigation of Electrospraying Properties Based on Ring Electrode Modification.

Electrospraying uses a high-voltage potential difference to create fine droplets. This study conducts a comparative analysis of the spray pattern and droplet properties using ring electrode parameters. The spray pattern and droplet characteristics are analyzed based on the experimental parameters of the ring electrode. The results show that the cone-jet mode forms quickly for the ring electrode. In addition, as the ring diameter decreases, the ring voltage increases and an increase in the distance between the ring and the nozzle in the bottom direction decreases the Sauter mean diameter and its standard deviation. The optimal conditions for the formation of fine and uniform droplets include a ring diameter of 15 mm, a ring voltage of 7 kV, and a nozzle-to-ring distance of (+) 20 mm.

Asymmetric Spray Characteristics According to Y-Jet Nozzle Orifice Shape and Spray Conditions.

The Y-jet nozzle is a twin-fluid nozzle that has a larger operating range and simpler structure than other twin-fluid nozzles. Furthermore, it offers outstanding atomization quality even at low flow rates, mak ing it simple to atomize viscous liquids. However, because of the structure of the Y-jet nozzle, having an asymmetrical spray pattern is limited. Most existing experimental studies focused on the orifice diameter and mixing tube length. In this study, two types of elliptical nozzles and one type of circular nozzle were tested. We found that the elliptical nozzle's asymmetric spray characteristics are different from those of the circular type. Furthermore, it was demonstrated that the spray characteristics were different even in ellipsoids, with only the major and minor axes differing.

Spray Mode and Monodisperse Droplet Properties of an Electrospray.

As a method of fluid atomization via application of a high voltage, electrospraying forms more uniform droplets than other spraying modes. This approach involves various spraying modes depending on the applied voltage. Most previous studies on electrospraying focused on the cone jet mode, which has limited applications since the applied voltage has a narrow range. To overcome this limitation, it is necessary to consider alternative spray modes, which require an in-depth understanding of their characteristics. To compare different spray modes, an investigation was conducted based on experimental parameters and fluid properties. In this study, a total of nine modes were identified, and the droplet characteristics in four modes were compared. The maximum deviation of the Sauter mean diameter (SMD) between the spray modes was approximately 1.7 times, and the SMD standard deviation was up to 2.8 times. In addition, the conditions required to realize Coulomb fission and monodisperse distribution depending on the Rayleigh critical charge (RSD < 6.76) were compared and examined.

A Study on the N2O Reduction Rate According to Temperature and Residence Time in the Exhaust Gas Atmosphere Emitted on Combustion of Air and Oxygen.

N2O is a hazardous greenhouse gas. It should be reduced to solve global warming problems. In this study, experiments of N2O thermal decomposition were conducted by simulating the exhaust gas atmosphere emitted during the combustion of air and pure oxygen in an actual circulating fluidized bed system and incinerator system. As a result of comparing the N2O reduction rate in N2 and CO2 atmospheres, the N2O reduction rate in the CO2 atmosphere was 20% higher than that in the N2 atmosphere. It is judged that the N2O reduction rate is high in a CO2 atmosphere (exhaust gas from pure oxygen combustion) due to complex factors such as the reverse reaction, the diffusion coefficient, and static pressure-specific heat. Therefore, pure oxygen combustion increases the reduction rate of nitrous oxide. In addition, when operated with an appropriate residence time and temperature, a reduction effect of more than 95% can be expected, and the fuel consumption rate is also expected to improve.

Viscosity Effect on the Electrospray Characteristics of Droplet Size and Distribution.

Electrostatic spraying is a method of atomizing a fluid using a high voltage as an atomization auxiliary device, and various spraying modes exist according to experimental parameters and viscosity. A maximum of 11 spray modes were identified according to the changes in the applied voltage and flow rate. To produce fine droplets and a uniform size, which are the advantages of electrostatic spraying, in this experiment, the Sauter mean diameter (SMD) and SMD distribution were evaluated in each spray mode of electrostatic spraying. By comparing the other spray modes with the cone jet mode, it was confirmed that the maximum difference of the SMD was less than 1.5 times and the standard deviation of the rotated and pulsed jets was 2.5 times or more. In the cone shape range, the SMD and SMD distribution according to the applied voltage confirmed that the droplet size was the smallest in the middle of the cone jet mode, and the droplet distribution was also narrow. In the cone jet mode, the droplet size increased linearly with the viscosity and flow rate. In addition, the droplet distribution range was distinctive depending on the type of fluid. In the case of the relationship between the droplet size and current, it was proven that the higher the viscosity, the higher the current value for the same SMD; furthermore, the difference in the current-SMD increase rate was insignificant. Through experiments, this work presents experimental data of SMD, SMD distribution, and current-SMD in electrostatic spray experiments under various conditions.

Effect of the Oxygen Concentration and Temperature on Thermal Decomposition of N2O in an Inert Gas.

Nitrous oxide (N2O) is one of the greenhouse gases that contribute to global warming. But, there are few methods for controlling N2O directly. It is essential to reduce N2O to solve environmental problems. In this study, we investigate the O2 concentration dependence of N2O decomposition under an argon-based gas mixture in a high-temperature thermal reactor. The gas concentrations are calculated using CHEMKIN. The results confirm that more N2O is converted to N2 or NO at lower O2 concentrations. Therefore, the conversion process is hindered by increasing the O2 concentration. We propose a modified parameter of N2O decomposition, and it is employed in the CHEMKIN calculations. With the modified parameter, the experimental results are in a similar tendency to the calculated results.

Effects of Y-Jet Nozzle Mixing Chamber Length and the GLR on Spatial Asymmetric Spray.

The Y-jet nozzle is simpler to design than other twin-fluid nozzles and has various advantages such as having a wide turn-down ratio. For this reason, it is mainly used for industrial boilers and combustion. The Y-jet nozzle comprises liquid and assist gas supply ports, a mixing chamber, where two fluids (liquid and the assist gas) are mixed, and an exit orifice. The time it takes to mix the two fluids in the mixing chamber depends on the length of the chamber, which determines the spray and particulate properties. Therefore, the mixing chamber is one of the most important factors when designing the Y-jet nozzle. The gas to liquid mass flow rate ratio (GLR) is an important variable that affects the spray characteristics of the Y-jet nozzle. In this work, a laboratory-scale Y-jet nozzle spray experimental setup was developed to perform spray experiments. In particular, we observe the spray properties in the front and right directions to observe spatial spray properties. Significant results were obtained depending on the length of the mixing chamber, the spray pattern, and the Sauter mean diameter according to the GLR. We found that a mixing chamber with longer length reduces the effect of asymmetric spray and confirm that the central axis of spray is more stable.

Combustion Using Oxygen-Lancing in a Reheating Furnace.

Fuel economy has been a primary issue in the steel industry because it uses large amounts of energy, such as the gaseous fuel of byproduct gas. Furthermore, reheating throughput capacity has been a key issue because it can improve furnace efficiency, leading to fuel economy. Many attempts have tried improving fuel economy using oxygen in a reheating furnace. Oxygen-lancing technology was developed to increase fuel economy and maintain the same level of NO x concentration simultaneously. Mechanisms that inject oxygen into flames locally causing flame quenching and at the same time suppressing the increase in NO x concentration due to recirculation of reheating furnace-burned gases are key to this study. Various oxygen concentrations for its lancing were used to investigate its effects on furnace temperature and NO x concentration in a test furnace. It was determined that 30% of oxygen was optimal regarding fuel economy and NO x concentrations. Oxygen was injected into the flame using two lancing pipes at 11° in a design capacity of 125 MW. The results showed a 3-5% increase in fuel economy and the same level of NO x concentration in the furnace.