Cavitation in nozzles of liquid injectors is known to affect the atomization of a discharged liquid jet. To understand how cavitating flow in a nozzle enhances the liquid jet atomization, liquid velocity distribution of cavitating flow in a two-dimensional transparent nozzle was measured using a Laser Doppler Velocimetry (LDV) system. As a result, the following conclusions were obtained: (1) The inception of cavitation occurs near the outer edge of separated boundary layer (SBL), where the time-averaged local velocity takes the highest value and the time-averaged pressure is almost equal to the vapor saturation pressure. (2) When the cavitation number σ is greater than 0.78 (in no cavitation and developing cavitation regimes), the reattachment of SBL occurs in the middle of the nozzle. A large velocity fluctuation, which appears just downstream of SBL, decreases near the nozzle exit. Hence the wavy jet is formed in these regimes. (3) For σ ≤ 0.65 (in super cavitation regime), the lateral flow directing from the core region toward the side walls just upstream of the nozzle exit is a major cause of the increase in the spray angle and drastic enhancement of liquid jet atomization. The strong turbulence just upstream of the exit must play an important role in the formation of ligaments on liquid jet interface.
The present study develops a theoretical investigation on the optimal design of a refrigeration plant with considerations on both the external and internal irreversibilities. With the total heat transfer area constraint or the total thermal conductance constraint, the analytical solutions of optimal area-ratio and the corresponding maximum COPare obtained under a fixed cooling rate. The results show that the internal irreversibility can penalize the plant’s COP, and the internal irreversibility has more significant effects on a freezing system than on an air-conditioning system. When there is no internal irreversibility, a special case of the analytical solution is exactly the same as that obtained from the previous study.
The total space and weight of the feedwater heaters in a nuclear power plant (NPP) can be reduced by replacing low-pressure feedwater heaters with high-efficiency steam injectors (SIs). The SI works as a direct heat exchanger between feedwater from condensers and steam extracted from turbines. It can attain pressures higher than the supplied steam pressure. The maintenance cost is lower than that of the current feedwater heater because of its simplified system without movable parts. In this paper, we explain the observed mechanisms of the SI experimentally and the analysis of the computational fluid dynamics (CFD). We then describe mainly the analysis of the heat balance and plant efficiency of the innovative-simplified NPP, which adapted to the boiling water reactor (BWR) with the high-efficiency SI. The plant efficiencies of this innovative-simplified BWR with SI are compared with those of a 1100MWe-class BWR. The SI model is adopted in the heat balance simulator as a simplified model. The results show that the plant efficiencies of the innovate-simplified BWR with SI are almost equal to those of the original BWR. They show that the plant efficiency would be slightly higher if the low-pressure steam, which is extracted from the low-pressure turbine, is used because the first-stage of the SI uses very low pressure.
The power output of gas turbines decreases as a result of increased ambient temperature. One way to recover the output loss is to cool the inlet air. In Taiwan, most gas turbines operate with combined cycle for base load. Only a small portion operates with simple cycle for peak load. Therefore, the power augmentation strategies for combined cycle power plants need to be studied in advance in order to recover the power loss due to increased ambient temperature in hot summer days. The objective of this research is to study the effects caused by adding an inlet fogging system to an existing gas turbine-based combined cycle plant. Moreover, this paper also includes a parametric study of plant performance with different effectiveness of the inlet fogging system based on the average ambient conditions. Results from this study can be used as a guideline for combined cycle power augmentation using inlet fogging.
Effects of H2O, CO2, CH4 and C2H4 contained in automotive exhaust gas on NO removal by using a DC corona discharge were investigated experimentally. In this experiment, N2/O2/NO mixture was used as a base gas of the simulated exhaust gas. To clarify the effect of the individual coexisting gas on NO removal, each coexisting gas was added to the base gas. The results showed that the existence of H2O or C2H4 was effective for NO removal with low energy density. Also, when negative corona discharge was applied to the simulated exhaust gas (N2/O2/NO/H2O/CO2/C2H4 mixture), the efficiency of DeNOx was more than 90%. However, the by-products such as CO, O3, HNO3 and N2O increased with increasing the energy density. It was found that the optimum energy density of corona discharge was about 250J/L for DeNOx of simulated exhaust gas.
A performance prediction model is developed for axial-type turbines that operate at partial admission. Losses generated within the turbine are classified into windage loss, expansion loss and mixing loss. This developed loss model is compared with an experimental result when a turbine operates with a rectangular-type nozzle at a partial admission rate from 22% to 37%. The present predicted results show better agreement with the experimental results than with those predicted by other models, as the expansion loss in this model is developed more closely to the real flow situation. If a turbine operates at a very low partial admission rate, a circular-type nozzle is more efficient than a rectangular-type nozzle. In this case, a performance prediction model is developed and an experiment is conducted with the circular-type nozzle. The predicted result is compared with the measured performance, and the developed model is found to be in good agreement with the experimental results. Thus, the developed model could be applied to predict the performance of axial-type turbines that operate at various partial admission rates or with different nozzle shapes.
Reduction in NOx and soot in light and medium duty diesel engines and meeting the U.S. emission standards is an important challenge. This paper shows how injection rate shaping should be performed to reduce NOx while engine performance and soot formation remain almost constant. Effects of intercooler with and without rate shaping on NOx reduction will be investigated. Results indicated that the rate shaping and pilot/split injection was an effective technique to reduce NOx at some operating condition. Combined effects of intercooler and rate shaping have shown a reduction of NOx by 50% for some operating conditions. At idle condition, a split injection was found to be a good solution for NOx reduction. A combustion simulation computer program was used in this analysis for six different operating conditions.
The response of a cylindrical premixed flame to periodic concentration fluctuation was investigated. The flame was formed in a porous cylinder by percolating a lean methane-air mixture uniformly through the cylinder wall. The burner used here was devised so as to cause fluctuations of the mixture concentration (equivalence ratio) only in the radial direction of the flow (vertically to the cylindrical flame surface) without varying the flow field. Using this burner, the time variations of burning velocity, burnt gas temperature and flame luminosity were measured for the mixture in a range of fluctuation frequencies from 3 to 50Hz, and the results were examined from the viewpoint of flame curvature effects. The results show that the variation width of the burning velocity of the dynamic flame is larger than that of the static flame in the concentration range corresponding to the fluctuation. Burnt gas temperature and flame luminosity also exhibit similar tendencies. The magnification ratio of the variation width depends on the flame curvature, and a large flame curvature results in a sustainable flame, even for a mixture leaner than the flammability limit of the static flame.
The purpose of this study is to elucidate of the primary air combustion zone in pulverized-coal combustion by means of advanced laser-based diagnostics with high temporal and spatial resolutions. An open-type burner is fabricated to apply various optical measurement techniques. Detailed and overall evaluation is performed by applying various optical measurement techniques to the flame, such as the velocity and shape of nonspherical pulverized-coal particles, temperature, and light emissions from a local point in the flame. It is observed that the particle mean diameter increases as the distance from the burner increases, and this is found to be caused by the decrease in the diameters of small particles and the increase in the diameters of large particles, which result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized-coal particles in the central region of the jet exhibit the same magnitude, whereas those in the outer region are different depending on the particle size. The behavior is well explained in terms of the particle inertia.
The purpose of this study is to elucidate of the primary air combustion zone in pulverized-coal combustion by means of advanced laser-based diagnostics with high temporal and spatial resolutions. An open-type burner is fabricated to apply various optical measurement techniques. In this paper, simultaneous measurement of OH-planar laser-induced fluorescence (PLIF) and Mie scattering images of pulverized-coal particles is performed, and the spatial relationship between the combustion reaction zone and the pulverized-coal particle zone is examined. It is found that, in the upstream region, combustion reaction occurs only in the periphery of the clusters of pulverized-coal particles where the high-temperature burnt gas of a methane pilot flame is entrained and oxygen supply is sufficient, and that, in the downstream region, however, combustion reaction can be seen also within the clusters of pulverized-coal particles. This is because, in the downstream region, the devolatilization process of the coal particles proceeds with the temperature rise of the particles, and the mixing process between the volatile matters and ambient air is prompted. From these results, it can be said that the present diagnostic techniques are effective for evaluating the pulverized-coal flames.
We have examined the laser extinguishment of a CH4-N2/Air counterflow diffusion flame. Laser extinguishment is to blow off flames by a laser-induced breakdown. A Q-switched Nd: YAG laser (energy; 200mJ/pulse) and a 100-mm focal-length lens were used. The laser-extinguishment probabilities were examined by varying the fuel concentration and the distance from the breakdown point to the flame. As a result, the two concentration limits were clarified. One was the laser extinguishable limit, below which the flame could be extinguished perfectly by laser. The other was the laser inextinguishable limit, over which any flame could not be extinguished. Moreover, it was considered that determination of the laser extinguishable limit was mainly influenced by the laser-induced blast wave. On the other hand, it could be considered that not only the blast wave but also hot gas and turbulence due to the optical breakdown influenced the determination of the laser inextinguishable limit.
An experimental study has been carried out to reveal the statistical characteristics for the onset of micro-explosion of an emulsion droplet evaporating on a hot surface. The measurements are made of the waiting time for the onset of micro-explosion at various ambient pressures, base fuels, water contents and surface temperatures. The Weibull analysis is applied to obtain the distribution function of the waiting time for the onset of micro-explosion and to derive the empirical formula for the rate of micro-explosion as a function of the water volume and emulsion temperature. The results show that the waiting time is correlated well with the Weibull distribution of the wear-out type. The waiting time decreases with an increase in the ambient pressure, the saturation temperature of base fuel, the water content and the surface temperature. An empirical formula is proposed for the rate of micro-explosion as a function of the water volume and emulsion temperature.
A simple correlation between particle size and the time-resolved laser induced incandescence signal is introduced and applied to a diesel engine for the measurement of primary particle size in the raw exhaust gas. The measurements from time-resolved LII signal are calibrated for all experimental conditions using Transmission Electron Microscope photographs to investigate the differences between particle size from TEM photographs and that estimated by LII. An evaluation of uncertainty in the LII measurements is also presented. From the comparison between the two measurements and uncertainty analysis, it can be concluded that the time-resolved LII theory employed in this study can be used as a useful tool for measuring primary particle size in engine exhaust since the measurements from LII are reliable and in a good agreement with those from TEM imaging. From a practical point of view, the strategy for particle size measurements presented here are simple and straightforward in its application.