• Journal of ILASS-Korea
• /
• v.20 no.1
• /
• pp.7-13
• /
• 2015

In this study, the behavior of water or nanofluid droplets impacting upon a hot surface was investigated by visualization of impacting phenomena with time-delayed photographic technique. Changing the mass ratio of nanofluid and the temperature of the heated surface, the characteristics of the spreading behavior and the diameter of spreading liquid film was compared between water and nanofluid droplets. The impacting droplet spreaded as a liquid film after impact and nanofluid droplets spreaded more widely than water droplets. After reaching the maximum diameter, water droplets shrinked more than nanofluid droplets. Based on this, the heat transfer area from a hot surface to impacting nanofluid droplets would be wider than that of impacting water droplets. Considering individual impacting droplet only, spray cooling using nanofluid would be better than using water.

• Journal of Welding and Joining
• /
• v.25 no.3
• /
• pp.37-44
• /
• 2007

Mechanical and thermomechanical properties of the bulk metallic glass (BMG) are so unique that the deformation behavior is largely dependent on the temperature and the strain rate. Impacting behavior of NiTiZrSiSn bulk metallic glass powder during kinetic spraying was investigated in this study. Considering the impact behavior of the BMG, the kinetic spraying system was modified and attached the powder preheating system to make the transition from the inhomogeneous deformation to the homogeneous deformation of impacting BMG particle easy BMG splat formation is considered from the viewpoint of the adiabatic shear instability. It is suggested that the impact behavior of bulk metallic glass particle is determined by the competition between fracture and deformation. The bonding of the impacting NiTiZrSiSn bulk amorphous particle was primarily caused by the temperature-dependent deformation and fracture (local liquid formation) behavior.

• Journal of computational fluids engineering
• /
• v.2 no.1
• /
• pp.54-65
• /
• 1997

Wall wetting in diesel engines has been considered as a bad phenomenon because of fuel deposition which makes fuel/air mixing and evaporation worse. In order to avoid the problem, many research works have been carried out. One of the studies is on new combustion chamber systems which are using spray impacting on a wall. In this study a new type of chamber system is analysed using wall impaction model introduced and assessed in the coupled paper. The gas phase is modelled in terms of the Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction, The liquid phase is modelled following the discrete droplet model approach in Lagrangian form. With various conditions the spray distribution, vapor contour and gas flows are analyzed, and then design factors of those combustion systems are recommended.

• Journal of ILASS-Korea
• /
• v.17 no.1
• /
• pp.27-34
• /
• 2012

In this paper an experimental study is presented to investigate the effect of a step edge and a stationary droplet on the dynamic behavior of impacting droplet on a wall. The main parameters are the distance from the edge and the center-to-center distance between two droplets. Photographic images are presented to show coalescence dynamics, shape evolution and contact line movement. The emphasis is on presenting the spreading length of droplet for the step edge and two coalescing droplets along their original centers. It is clarified that the droplet exhibits much different dynamic behavior depending on the location of the step edge. The momentum of impacting droplet was better transferred to the stationary droplet as the center- to-center distance between two droplets was reduced, which results in more spreading of coalescing droplet.

• 한국연소학회:학술대회논문집
• /
• 2002.06a
• /
• pp.11-15
• /
• 2002

Experimental studies on effects of the interaction of duplex swirl injector and the liquid temperature on the spray characteristics were conducted. Water and fuel were used as a test fluid for the experiments. The drop size distributions of the liquid spray were measured with Malvern particle sizer. The liquid temperature and distance of injectors were adopted as the operating parameter. The results show that SMD decrease as the increases of fuel temperature and pressure. The spray angle increase as fluid temperature increases. For fuel spray, SMD of impacting surface increase as the distance of injectors is lengthened.

• Journal of ILASS-Korea
• /
• v.14 no.4
• /
• pp.178-183
• /
• 2009

Spray cooling heat transfer was experimentally investigated for water sprays impacting on mico-fins structured surfaces in the single phase and nucleate boiling regions. The heat transfer surfaces consist of cubic fins and triangular grooved fins. The spray produced using full cone spray nozzles, and experiments were made under the test condition of $Q=4.92{\times}10^{-6}{\sim}15.83{\times}10^{-6}\;m^3/s$, $T_f=35{\sim}55^{\circ}C$. From the experimental results, it was found that cubic fins surface had the largest heat flux enhancement relative to the smooth surface.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.6
• /
• pp.63-71
• /
• 1998

In a diesel engine the phenomenon of spray impaction on a combustion chamber wall has been taken as an undesirable matter because of the deposition of fuel on the surfaces, and the subsequent slow evaporation and mixing with air resulting in unburned hydrocarbons. Therefore many researches have concentrated on avoiding fuel impaction on surfaces. On the contrary done a number of studies using spray wall impactions in a positive way, which makes the droplets smaller, changes the direction into free spaces far from the wall and also improves mixing with air. In this paper the angle variations of the impaction land sufrace prepared for the injection spray is analysed as a simulative manner. The spray dispersions, vapor distributions and flow fields are compared with impacting angle variation. The results show more angle give more vapor distribution until $15^{\circ}$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.22 no.1
• /
• pp.33-39
• /
• 2010

The film boiling heat transfer was experimentally investigated for the water sprays impacting on an inclined hot surface. Full cone spray nozzles were employed for the spray cooling experiment, and experiments were made for different inclination angles of $\theta=0^{\circ}$, $15^{\circ}$, $30^{\circ}$ and $45^{\circ}$. The experimental results show that, in the downstream region of the inclined hot surface, increasing the inclination angle increases the local heat flux slowly because of increasing the number of rebound droplets. However, the inclination angle of heat transfer surface had no remarkable effect on the local heat flux of spray cooling under the present test conditions.

• Journal of ILASS-Korea
• /
• v.12 no.4
• /
• pp.179-184
• /
• 2007

The boiling heat transfer was experimentally investigated for the FC-77 sprays impacting a square heated test surface in a downward direction. Full cone spray nozzles were employed for the spray cooling experiment, and experiments were made under the test conditions of $Q=3.32{\times}10^{-6}{\sim}2.30{\times}10^{-5}\;m^3/s$, ${\Delta}T_{sub}=20{\sim}70^{\circ}C$. Also, heat transfer measurements were made using the copper block of $10{\times}10\;mm^2$ test area heated by nine cartridge heater. From the experimental results, correlation between the Nusselt number and Reynolds number based on droplet-flow-rate was developed. The correlation shows good predictions with ${\pm}30%$ error for FC-77.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.5
• /
• pp.55-65
• /
• 1999

Many researches have been investigating small direct-injection diesel engines using the spray impacting on walls. Those systems have one or more raised pips to break-up the fuel and spread it widely toward a desired direction in a combustion chamber. In this study, the sizes and heights of the pips are determined by using a computational fluid dynamics code employing non-orthogonal grid systems. In order to find out the suitable pip-shape to a small chamber, the spray behaviors, occupied spary volumes and averaged droplets sizes are calculated with the variation of shape of the pip, such as, size and heights and inclined degree. The desired shape of the impinging land is proposed for the design of combustion system in small diesel engines.