Injection Of Mist Research Articles

Effect of mist/steam uniformity on heat transfer characteristics in unconfined jet impingement

This paper presents the numerical investigations of the injection of mist into an unconfined cooling steam jet to analyze the effects on the corresponding heat transfer characteristics. The infusion of mist into an confined cooling steam jet demonstrates a remarkable improvement in the heat transfer specifications as described in numerous previous studies. Therefore, the current research contributes to the knowledge by focusing on the uniformity configurations of the injected second phase to the unconfined regions and the influence of the surrounding environment on the mist injected. Several variables govern the physical model of the mist concentration and jet to plate distance, which is included in three-dimensional incompressible Navier-Stokes flow with the discrete phase model for the multiphase flow regime. The simulation was conducted over a range of common working Reynolds numbers. The results show that controlling the uniformity of the injected mist will redefine the cooling characteristics. The accumulated mist near the edge leads to the heat transfer enhancement at H/D = 2, 4, and 6. The surrounding environment had a significant influence on the droplet behavior at H/D = 8, thus causing a heat transfer reduction of 8%. The droplet Stock number can determine the droplet performance on the target wall and introducing mist generates a third heat transfer peak that results in an average increase of 38% for 1% mist.

Direct injection of water mist in an intake manifold spark ignition engine

The purpose of this study is to investigate the effects of water mist (WM) injected directly into an intake manifold spark ignition (SI) engine. WM flows through a nozzle at the throttle body of the four-cylinder four-stroke multi-point injection engine for testing the performance of exhaust emission system. The water is pumped in mist form into the intake manifold with an air-fuel mixture through the nozzle, which is located on the throttle body. Experimental work and simulation methods are combined by the presence and absence of WM addition, and the performance as well as emission produced by the engine is analyzed. The Gamma Technologies (GT) methods are used to simulate the model with and without WM addition. The experimental results indicate that the standard engine performance can be used to validate the simulation model. The engine measures include various parameters such as brake power, torque, volumetric efficiency, spark advance timing, and the concentration of CO and NOx with water and without water addition to the SI engine (i.e., the power, torque, volumetric efficiency of the engine is increased up to 10%). The emission of NOx is found to be significantly reduced and that of CO does not change.

Direct injection of water mist in an intake manifold spark ignition engine

Direct injection of water mist in an intake manifold spark ignition engine

Computational analysis of mist/air cooling in a two-pass rectangular rotating channel with 45-deg angled rib turbulators

Increasing the turbine inlet temperature can increase the gas turbine cycle efficiency. In order to increase the turbine inlet temperature significantly, an advanced cooling system has to be essentially developed. Injection of mist to the coolant fluid is considered a promising technique to protect the hot components such as combustor liners, combustor transition pieces, and turbine vanes and blades. A series of experiments conducted in the past proved the success of mist cooling technology in the laboratory environment. Favorable results from the numerical simulation further encourage continuous exploration of employing mist-cooling technology in the actual gas turbine working environment in various applications. The present study focuses on applying mist cooling to the rotating mist/air internal cooling passage with rib turbulators using numerical simulation.In the first part, the computational fluid dynamics (CFD) models of smooth and ribbed channels without mist and rotation are validated with the experimental results available in literature. The agreement between the predicted and experimental values in the lower Reynolds number (Re) range is within 3% deviation, and, at higher Re range, the deviation is about 10%. For the smooth channel, the agreement with experimental result is good for the entire range of Re values. In the second part, the rotational effect on the smooth and ribbed channels is predicted and analyzed. In the last part, the mist cooling enhancement on the ribbed channel with rotation is simulated. The secondary flows created due to channel bend and rotation are specifically analyzed. The results show that the mist cooling enhancement is about 30% at the trailing surface and about 20% at the leading surface of the first passage with 2% mist injection. In the second passage, 20% enhancement is predicted for both the surfaces.

Co-Gasification of Coal and Hardwood Pellets: A Case Study

This paper presents the effect of feedstock mixtures on the composition of syngas produced from a commercially available down-draft gasifier. Commercial hardwood pellets and bituminous coal (Pittsburgh seam) were used as fuel for the experiments. Five types of feedstock mixtures having composition(by weight) of 100% hardwood pellets, 20% coal-80% hardwood pellets, 50% coal-50% hardwood pellets, 80% coal-20% hardwood pellets and 100% coal were prepared. Air and an air plus water mist mixture were used as a gasifying agent. Syngas with 20.95% carbon monoxide and 16.05% hydrogen was produced from the gasification of wood pellets at 1200°C in the combustion zone and 450°C in the reduction zone of the reactor. The hydrogen and carbon monoxide content in the product gas decreased with an increase in the coal proportion in the mixtures. A significant increase in carbon efficiency was observed with an increase of coal proportion in the mixtures. Syngas carbon and syngas energy efficiency increased with injection of the water mist along with air in the system for the hardwood pellet gasification.

Full-scale experimental study on fire suppression performance of a designed water mist system for rescue station of long railway tunnel

Rescue stations have been newly designed in some super-long mountain railway tunnels of China such as over 30 km long, as a new type of strategic counteract design for fire accident in tunnels. Water mist fire suppression systems are needed to be installed in such rescue stations to control the train fire. However, there is no design engineering experience for it. In this article, a full-scale experimental facility was built to study the fire suppression performance of water mist system in such railway tunnel rescue station. A series of full-scale tests was preliminarily conducted considering the fire position was on top of, inside, and under the train carriage with gasoline pool fire and wood crib fire used as fire sources. A design of water mist suppression system for such a fire scenario was presented, and its performance was tested. Experimental data on temperature, CO concentration, and radiation flux were collected and analyzed. The results showed that the water mist system could control fires, cool the air temperature in the rescue station, and strongly reduce the radiant heat flux in the vicinity of the fire source under various ventilation conditions. However, the visibility of the rescue station was much deteriorated after the injection of water mist, so that emergency lights and evacuation lights are necessary for personnel evacuation. The changes of fire extinguishing time with longitudinal ventilation velocities showed that longitudinal ventilation could provide both favorable and unfavorable conditions for water mist fire extinguishment. So, to achieve efficient fire suppression performance of water mist system, attention might be paid to the controls of tunnel ventilation system in the event of a fire in a railway tunnel rescue station. The design of the water mist system and the full-scale experimental data on the fire suppression performance presented in this article may serve as a reference for such engineering applications.

Effect of mist injection position on particle separation performance of cyclone scrubber

Experimental and simulation studies have been conducted about the effect of mist injection position on particle separation performance of cyclone scrubber. The typical particle trajectories for the normal type cyclone are calculated. The optimum mist injection position is determined based on the simulation of particle trajectories. Two types of cyclone scrubbers that have different mist injection position were tested in this research. It was found that the particle separation efficiency is strongly depended on the mist injection position. With the injection of mist, the 50% cut size is smaller than the case with the injection of air only. It was also found that increasing liquid to gas flow ratio enhances the separation efficiency. The experimental data agreed with the numerical simulation based on the direct flow calculation method.

Experimental Study on the Effectiveness of the Extinction of a Pool Fire with Water Mist

In order to study the effectiveness of the extinction of a pool fire with one nozzle water mist, a series of experiments were conducted under different conditions in an open space. Fire sources are small-scale circular stainless steel pans of 130 and 200 mm in diameter with the fuel of alcohol and kerosene. Before and after the application of water mist, some K-type thermocouples along the pool centerline and a digital camera were used to measure the flame temperature and visualize the process of the fire extinction. A thermogage and a turbine flux sensor were used to measure the flame radiant heat flux and the application rate of water, respectively. A Particle Image Velocimetry and Sizing (PIVS) technique was developed to characterize the water mist. The experimental results show that both the flame of alcohol and kerosene cannot be extinguished in many cases when the pressure is lower than 0.4 MPa. In addition, the distance between the flame and the nozzle, and the application rate of water are two main factors which influence the effectiveness of the extinction of a pool fire when the working pressure is lower and the impulse injection of water mist can improve the effectiveness of fire extinction. However, it should be noted that the results are limited to the experimental conditions because it is still difficult to get the functional relationships of pool fire extinction mechanisms with water mist.