Mist Injection Research Articles

Agglomeration of Unipolar Charged Particles in an Alternating Current Field and Performance Comparison With Mist Injection

Agglomeration of Unipolar Charged Particles in an Alternating Current Field and Performance Comparison With Mist Injection

METHODOLOGY APPLIED TO STUDY WATER MIST AS AN INFRARED SIGNATURE SUPPRESSOR IN MARINE GAS TURBINES

This paper proposes a methodology for the reduction of marine gas turbine exhaust gas temperatures via water mist injection into exhaust gas ducts with the aim of reducing a ship’s infrared (IR) signature. Due to the difficulty of conducting live experimental tests on warships, Computational Fluid Dynamic (CFD) techniques can be employed to predict phase interaction behaviour (water mist and exhaust gases) within gas turbine exhausts. CFD techniques attempt to find numerical solutions to the equations that govern phase interaction phenomena through the setting and resolution of mathematical models.

외부 미스트 분사가 있는 사이클론 집진기의 성능 및 유동 특성에 대한 수치 연구

Cyclone separators play an important role in industry to separate solid particles from the fluid flow. This paper tries to estimate the internal flow behavior and performance of cyclone separators with various external mist injections by three-phase numerical simulations and find out comparatively the most appropriate mist injected locations for industrial applications. The external mist injection was described by Largrange’s approach, gas phase and particle phase were considered modelled by Euler-Lagrange approach following the previous researches. The internal flow behaviors and performance of cyclone separators have been numerically investigated and compared by using the Reynolds Stress Model(RSM) for modeling turbulent flow. The numerical models utilized in this study have been validated by the experimental work from previous studies. The results show that, the performance of cyclone separators is significantly affected with adjustment of the mist injection location. The inverse weighted sum performance of the best design is 9.273% and 3.369% higher than the worst design and overall averaged performance, respectively.

Effects of soot deposition and slot erosion on the mist film-cooling of a flat plate in the presence of upstream ramp

In the present work, the numerical analysis is conducted on the film cooling of a flat plate with the air and mist injection from a slot. The effect of soot deposition and erosion of the cooling slot has been investigated in the presence of an upstream ramp. Simulations are performed at blowing ratios, M = 1, 1.5 and 2 with the slot angles, θ = 30°, 45° and 60°. The effect of presence of upstream ramp is studied by varying ramp angles from α = 5° to 15°. The numerical study is carried out on Eulerian-Eulerian framework. Thermal phase change model based on the evaporation and condensation is used to account heat and mass transfer. It is found that the film cooling effectiveness is better for the mist injection as compared to the air injection. Soot deposition on the cooling slot has a significant influence on the film cooling effectiveness. The soot deposition is not always adversely affecting the film cooling effectiveness. Moreover, the film cooling effectiveness decreases for the eroded slot for all the investigated slot angles and ramp angles for mist injection. An increment in the film cooling effectiveness is observed for 0 < x/2w < 15 in the presence of the upstream ramp; thereafter film cooling decreases as compared to the case without the upstream ramp. The optimum slot angle to inject the mist is found to be θ = 45°.

Effect of Blowing Ratio on Mist-Assisted Air Film Cooling of a Flat Plate: An Experimental Study

Abstract A novel mist-assisted air film cooling scheme is proposed by Li and Wang (2006, “Simulation of Film Cooling Enhancement With Mist Injection,” ASME J. Heat Transfer, 128, pp. 509–519) to increase the film cooling effectiveness of a gas turbine cooled vane/blade. This scheme is further investigated experimentally in this article to determine the effect of the blowing ratio. The coolant is made to pass through the film holes on a flat plate mounted in a test facility. Tiny water droplets, characterized by Rosin-Rammler mean diameter of about 36.7 μm measured with a phase Doppler particle analyzer (PDPA) system is introduced into the cooling air. The effectiveness values are evaluated by measuring the plate surface temperature with the infrared (IR) camera. The maximum percentage of the mist-assisted film cooling effectiveness is 26% more than air film cooling effectiveness when 2.1% of mist is added to the air. In addition, the coolant coverage on the plate is found to be much better with mist cooling in both the streamwise and the spanwise directions. The net enhancement due to the mist-assisted air film cooling effectiveness (Δη) decreases with the increasing values of the blowing ratio in the range of 0.55–2.58 at a density ratio of 2.2.

Experimental Analysis of Mist Injection and Water Shower Indirect Evaporative Cooling in Harsh Climate

Experimental Analysis of Mist Injection and Water Shower Indirect Evaporative Cooling in Harsh Climate

Operational mode optimization of indirect evaporative cooling in hot climates

This study experimentally investigates the performance of an indirect evaporative cooling fresh air-handling unit at different modes of operation under harsh climatic conditions experienced in Qatar. Temperature and relative humidity are measured at various points within the fresh air handling unit for each mode of operation and, the measured data are stored and analyzed. Cooling performance indices are evaluated in terms of temperature difference across the heat exchanger, dry and wet bulb temperature effectiveness, thermal conductance, and cooling load. Different modes of operation are achieved by pre-treatment of the secondary air using either mist injection, water shower, or a combination of mist and water shower. It is found that indirect evaporation can achieve reductions of up to 43% of the unit's cooling capacity compared to dry operation. A sequence of operations to sustainably optimize energy consumption and reduce carbon emissions is determined.

Effect of water injection cooling on flow field characteristics in the cooling section of precooled turbine-based combined cycle engine

To explore the inlet air cooling effect in a precooled turbine-based combined cycle engine, a numerical investigation for air/droplet fully coupled cooling is performed in the cooling section with a spray system. The accuracy of numerical simulation program for mass injection cooling methodology is qualified with the experimental data. Results indicate that an even spray arrangement is beneficial to the uniform distribution of flow field, and it is also the major factor resulting in the flow loss. Although the flow loss of dry air is irreversible in the flow process, the additional new energy of water vapor can contribute total energy of wet air mixture. In contrast, under the lowest requirement qualified of mass injection cooling at two high-altitude simulation environments, the total-pressure drop coefficients are 3.22–4.22% before mist injection and 2.87–3.86% after mist injection; the total-temperature drop coefficient is 10.09% and 16.29%, respectively, for dry air and wet air conditions. After optimization for spray apparatus, the flow loss can decrease by about 55.84% before mist injection and about 64.53% after mist injection. Additionally, a little influence is for flow field temperature. Therefore, water injection cooling can effectively improve the flow field characteristics due to a larger total-temperature drop and a smaller total-pressure loss in the cooling section.

Sensitivity of air/mist non-equilibrium phase transition cooling to transient characteristics in a compressor of gas turbine

A comparative study of performance characteristics in a gas turbine compressor before and after water injection into the air is carried out to explore the relationships between the transient characteristic and mist injection. The Eulerian-Lagrangian particle tracking method is used for solving a process of phase transition cooling of water/air coupling, and the fast Fourier transform (FFT) is adopted to analyze the frequency attributions of fluctuating quantities with time-dependent including total pressure ratio, total temperature ratio, and efficiency. Results show, after mist injection into the compressor, droplet evaporation phase change leads to a higher characteristic fluctuation in the low-frequency region. The sensitivity of efficiency fluctuation is easily affected by the mist injection by comparing with the dry air condition. Within the mist conditions of 1–5 μm droplet sizes and 0.5–5% water/air ratios, the fluctuation of pressure in the compressor reaches a peak in small mist particle and low water/air ratio, resulting in a greater total pressure ratio. The temperature fluctuation gets the minimum in small droplet diameter and large water/air ratio, leading to a lower total temperature ratio. The fluctuation intensity of total pressure ratio, total temperature ratio and efficiency of compressor are increased to 3 times, reduced to 7/9 times and dropped to 3/5 times as water/air ratio increases from 0.5% to 5%, respectively; then, the fluctuation strength correspondingly increases 2 times, decreases 3/4 times and descends 6/7 times with the increase of droplet sizes from 1 μm to 9 μm. Thus, the fluctuation caused by low water/air ratio is higher than the small droplet diameter. Furthermore, efficiency fluctuation gets a minimum in small droplet size and appropriate water/air ratio.

Evaluation of mass injection cooling on flow and heat transfer characteristics for high-temperature inlet air in a MIPCC engine

Thermal management on high-temperature inlet air cooling is one crucial factor to improve the aero-engine performance. In this study, Mass Injection and Pre-compressor Cooling (MIPCC) technology is applied to a problem-solving way to reduce inlet air temperature. Numerical simulations are employed to investigate and predict the relationship between flow field characteristics and mass injection cooling at high altitude simulated pre-compressor section of MIPCC engine, which is based on the regression orthogonal analysis. The solution accuracy of numerical procedure is qualified with the experimental data. Results show that the flow loss and temperature reduction in the pre-compressor section are of non-linear and linear relationships with spray cooling conditions, respectively. Then, the dominant factors of influencing on the temperature reduction are droplet size and spray flow rate, and that of influencing on total-pressure reduction is droplet size. Especially, the effect of each spray factor on the flow field characteristics is of independence. According to the characteristic prediction in given spray conditions, the total-temperature drop and total-pressure drop coefficients after mist injection cooling are 1.57–29.13% and 0.461–1.683%, respectively. These observations signify that, by comparison with the dry air condition, a reduction of the temperature and flow loss in the pre-compressor section are correspondingly in the range of 7.3–135.5 K and 33.3–81.73% after mist injection. Thus, an appropriate mist injection condition can improve flow field characteristics at the most extent, and then heat management of inlet air can be controlled within a certain range.

Performance elucidation of a prototype vertical counter-flow heat exchanger with mist injection for waste heat management

Performance elucidation of a prototype vertical counter-flow heat exchanger with mist injection for waste heat management

Energy consumption in humidification process

The purpose of the air-conditioning system is to provide people in an air-conditioned room or facility with thermal-humidity comfort. For this purpose, the external air before entering into the room is processed for its treatment. These processes include, among others, humidification of the air. Too high a humidity level also does not benefit the building and its people. Humidification of the air can be realized as directly, then the steam or water mist injection takes place in the room, and indirectly, when the supply air to the room is humidified in the ventilation system. The energy consumption in the humidification process depends primarily on stream of humid air, methods of humidifying the air (water or steam), the type of energy carrier used to produce steam or secondary heating of humid air, range of relative humidity maintained, external humidity parameters. In the case where both the steam and the secondary heating use the same energy sources, the costs in both cases will be comparable. In this paper the calculation of energy demand in hourly and annual period as well as for water and steam humidifier unit have been calculated and presented in many tables and figures. The semidetached house were taken under consideration to analyzed the energy consumption for humidification process. The amount of energy needed to humid the air during the annual season varies from 127 to 545 kWh/ar, depending on the humidifier used and the pump power, while for steam humidification the amount of energy for humidification is less than 9421 kWh/a. As a result, water humidification should be considered more economical. The basic difference between water and steam humidification, as evidenced by the hx graphs is decrease in the air temperature during water humidification and need to reheat it. Taking into account the energy requirements in both cases is similar. The humidifying costs of the steam humidifiers are much higher than those of water humidification.

Fluctuating characteristics of air-mist mixture flow with conjugate wall-film motion in a compressor of gas turbine

A feasible method of injecting water mist into the air can improve the operation performance of gas turbine. This study aims to develop a deeper understanding of aerodynamic characteristics of fluctuating quantities and its influence caused by air-mist two phase flow with conjugate the liquid film. The effect of various mist injection conditions on transient characteristics of compressor was investigated by the frequency attribute analysis. The results show that the film attached to the blade surfaces will aggravate the aerodynamic fluctuation. Notably, the fluctuating quantities, such as pressure, temperature, mass flow, flow loss and compression work, center on the lower frequency region, indicating that the dominant component of disturbance source appears a weak fluctuation because of unevenly distributed flow field after mist injection. Within the range of 0.5–5% mist concentrations and 1–9 μm mist diameters, mist injection can weaken the fluctuation of pressure and tip leakage flow, meanwhile the fluctuations of temperature and entropy increase are a good improvement in large mist ratio or small mist size. However, the fluctuation reduction is marginal as mist concentration and particle size increase. Therefore, the fluctuation characteristics in the compressor can be controlled by manipulating mist injection conditions.

Effect of blockage configuration on film cooling with and without mist injection

Film cooling, as an effective protection technology, is widely applied in gas turbines to prevent components like vane blades from the hot mainstream. However, ash and other contaminants contained in the gas easily deposit on blade surfaces, which results in blockages inside the film holes and a reduction of the coverage area of the coolant air. Two blockage configurations (hemispherical and tetrahedral blockages) with a similar blockage ratio are analyzed in this study. In addition, mist injection with three droplet sizes (1 μm, 5 μm and 10 μm) is also considered. It is found that the position of the blockage configuration shows almost no influence on the cooling performance. In addition, the hemispherical blockage configuration results in a lower lateral film cooling effectiveness than the tetrahedral one. Finally, it is also concluded that the 5 μm droplet case shows more uniform distribution than other cases.

Effect of combined hole configuration on film cooling with and without mist injection

Turbine blades operate under a harsh environmental condition, and the inlet temperature of gas turbines is increasing with requirement of high engine efficiency. Some cooling schemes are adopted to prevent these blades from the thermal erosion of the hot mainstream. Film cooling technology is used widely and effectively in gas turbines. The coolant air is suppressed to the wall by the main-stream after jetting out of the film hole. A new hole configuration is first pro-posed to improve the film cooling characteristics in this paper. Comparison be-tween a conventional cylindrical hole and a new combined hole is conducted by CFD, and effects of various blowing ratios and droplet sizes are also investigated. Results show that the combined hole configuration provides a wider coverage than that in the cylindrical hole configuration case at high blowing ratios (M = 1.0 and M = 1.5). In addition, the film cooling with mist injection also provides a significant enhancement on cooling performance especially for the combined hole case with a small droplet size (10?5 m).

Effect of spherical blockage configurations on film cooling

With increasing inlet temperature of gas turbines, turbine blades need to be effectively protected by using cooling technologies. However, the deposition from the fuel impurities and dust particles in the air is often found inside film holes, which results in partial hole blockage. In this paper, the deposition geometry is simplified as a rectangular channel, and the effect of three blockage ratios is investigated by using the computational fluid dynamics. In addition, water droplets are also released from the coolant inlet to provide a comparison of the results with and without mist injection. It is found that the lateral film cooling effectiveness is reduced with increasing blockage ratio. For all the cases with the blowing ratio 0.6, 1% mist injection provides an improvement of the cooling performance by approximately 10%.

Performance elucidation of a prototype vertical counter-flow heat exchanger with mist injection

Performance elucidation of a prototype vertical counter-flow heat exchanger with mist injection

Optical emission spectroscopy of atmospheric-pressure non-equilibrium plasma with mist injection

This paper describes optical emission spectroscopic diagnostics of atmospheric-pressure non-equilibrium plasma with mist injection. Electron number densities and gas temperatures are estimated from Hβ (486 nm) and OH (309 nm) spectra to be on the order of 1015 cm-3 and 440–540 K, respectively, for the conditions tested in this study. Comparison of the rotational temperatures of N2 and OH indicates that two-temperature analysis of OH rotational spectra provides gas temperature even with mist injection.

Effect of an upstream bulge configuration on film cooling with and without mist injection

To meet the economic requirements of power output, the increased inlet temperature of modern gas turbines is above the melting point of the material. Therefore, high-efficient cooling technology is needed to protect the blades from the hot mainstream. In this study, film cooling was investigated in a simplified channel. A bulge located upstream of the film hole was numerically investigated by analysis of the film cooling effectiveness distribution downstream of the wall. The flow distribution in the plate channel is first presented. Comparing with a case without bulge, different cases with bulge heights of 0.1d, 0.3d and 0.5d were examined with blowing ratios of 0.5 and 1.0. Cases with 1% mist injection were also included in order to obtain better cooling performance. Results show that the bulge configuration located upstream the film hole makes the cooling film more uniform, and enhanceslateral cooling effectiveness. Unlike other cases, the configuration with a 0.3d-height bulge shows a good balance in improving the downstream and lateral cooling effectiveness. Compared with the case without mist at M = 0.5, the 0.3d-height bulge with 1% mist injection increases lateral average effectiveness by 559% at x/d = 55. In addition, a reduction of the thermal stress concentration can be obtained by increasing the height of the bulge configuration.

Two-phase flow simulation of mist film cooling with deposition for various boundary conditions

ABSTRACTAir film cooling is a conventional cooling technique that has been successfully used for gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes and blades. However, the increased benefit seems to approach a limit. This paper investigates the film cooling effectiveness considering mist injection. All the studies for various boundary conditions are conducted numerically, including the effects of droplet size, the flow rates of droplet injection, and the coolant air. Film cooling is also affected by the interaction between deposition and mist injection. A deposition configuration is located near the film hole with an inclination angle of 35°. Results show that the combined effect of injection and deposition is to weaken the film cooling effectiveness, especially upstream of x/d = 19. For the coolant air at a low speed, the mist injection cannot provide better cooling protection than without the mist injection.