• 한국레이저가공학회지
• /
• 제6권1호
• /
• pp.1-8
• /
• 2003

A molten metal droplets are deposited onto solid substrate for solid freeform fabrication, Collision dynamic and substrate heat transfer associated with solidification determine the final shape of molten metal droplets. In this study, the experimental model, based on the variational condition with substrate temperature and falling height, was produced reliable optimal data of droplet pattern.

• 대한기계학회논문집B
• /
• 제27권11호
• /
• pp.1595-1603
• /
• 2003

Droplet combustion at high ambient pressures is studied numerically by formulating one dimensional combustion model in the mixture of n-heptane fuel and air. The ambient pressure is supercritical conditions. The modified Soave-Redlich-Kwong state equation is used in the evaluation of thermophysical properties to account for the real gas effect on fluid p-v-T properties in high pressure conditions. Non-ideal thermodynamic and transport property at near critical and supercritical conditions are also considered. Several parametric studies are performed by changing ambient pressure and initial droplet diameter. Droplet lifetime decreased with increasing pressure. Surface temperature increased with increasing pressure. Ignition time increased with increasing initial droplet diameter. Temporal or spatial distribution of mass fraction, mass diffusivity, Lewis number, thermal conductivity, and specific heat were presented.

• 대한기계학회논문집B
• /
• 제28권9호
• /
• pp.1093-1100
• /
• 2004

Numerical analysis of the heat transfer associated with droplet impact on a hot solid surface is performed by solving the equations governing conservation of mass, momentum and energy in the liquid and gas phases. The deformed droplet shape is tracked by a level set method which is modified to achieve volume conservation and to include the effect of contact angle at the wall. The numerical method is validated through the calculations for the cases reported in the literature. Based on the numerical results, the heat transfer rate is found to depend strongly on the droplet spread radius. Decreased advancing/receding contact angles enlarge the splat radius and in turn enhance the wall heat flux. The effect of impact velocity on the droplet spread is reduced as the droplet size decreases. Also, droplet atomization is observed to significantly enhance the heat transfer rate and the effect is pronounced for a smaller size of droplet. An existing model equation to predict the maximum spread radius is improved for application to a micro droplet.

• 한국전산유체공학회지
• /
• 제2권2호
• /
• pp.80-88
• /
• 1997

A new wall impaction model for diesel spray is described in this 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. The droplet parcel contains many thousands of drops assumed to have the same size, temperature and velocity components. The droplet parcel equations of trajectory, momentum, mass and energy are written in Lagrangian form. The new drop-wall interaction model is proposed, which is based on experimental investigations on individual drops, and it is applied for the general non-orthogonal grid. The model is then assessed through comparison with experiments over a wide range of test conditions of sprays. The results are in good agreement with experimental data.

• 한국분무공학회지
• /
• 제26권2호
• /
• pp.88-95
• /
• 2021

This study aims to investigate the influence of the droplet volume on the evaporation characteristics of the sessile droplet. In particular, the effect of the free convection in the vapor domain on the evaporation rate was analyzed through the numerical simulation. The commercial code of the ANSYS Fluent (V.2020 R2) was used to simulate the heat transfer in the liquid-vapor domain. Moreover, we used the diffusion model to estimate the evaporation rate for the different droplet volume under the room temperature. It was found that the evaporation rate significantly increases with the droplet volume because of the larger surface area for the mass transfer. Also, the effect of free convection on the evaporation rate becomes significant with an increment of droplet volume owing to the increase in the droplet radius corresponding to the characteristic length of the free convection.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1996년도 춘계 학술대회논문집
• /
• pp.137-142
• /
• 1996

A new wall impaction model for spray and its assessment are described in this 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. The droplet parcel contains many thousands of drops assumed to have the same size, temperature and velocity components. The droplet parcel equations of trajectory, momentum, mass and energy are written in Lagrangian form. The new drop-wall interaction model is proposed, which is based on experimental investigations on individual drops, and it is applied for the general non-orthogonal gird. The model is then assessed through comparison with experiments over a wide range of test conditions of sprays. The results are in good agreement with experimental data.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1891-1896
• /
• 2004

The present article proposes a new droplet collision model including the stretching separation regime and the formation of satellite droplets. The new model consists of a several equations to calculate the post-collision characteristics of colliding droplets and satellite droplets. These equations are derived from the energy balance of droplets between before and after collision. For binary collision of water droplets, the new model shows good agreement with experimental data for the number of satellite droplets. Nevertheless, it is thought that, in order to guarantee the generality of the new model, the improvements should be performed to consider the effects of the bouncing and the reflexive separation, which is essential process in the collision of hydrocarbon droplets.

• 한국전산유체공학회지
• /
• 제15권2호
• /
• pp.71-78
• /
• 2010

As a step toward accurate prediction of droplet impingement and ice accretion on aircraft, an Eulerian-based droplet impingement and ice accretion code for air flows around an airfoil containing water droplets is developed. A CFD solver based on the finite volume method was also developed to solve the clean airflow. The finite-volume-based approach for simulating droplet impingement on an airfoil was employed owing to its compatibility with the CFD solver and robustness. For ice accretion module, a simple model based on the control volume is combined with the droplet impingement module that provides the collection efficiency. To validate the present code, it is compared with NASA Glenn IRT (Icing Research Tunnel) experimental data and other well-known icing codes such as LEWICE and FENSAP-ICE. It is shown that the collection efficiency and shape of ice accretion are in good agreement with previous experimental and simulation results.

• International Journal of Automotive Technology
• /
• 제6권6호
• /
• pp.563-570
• /
• 2005

A numerical study of high pressure and temperature droplet vaporization and combustion is conducted by formulating one dimensional evaporation model and single-step chemical reaction in the mixture of hydrocarbon fuel and air. The ambient pressure ranged from atmospheric conditions to the supercritical conditions. In order to account for the real gas effect on fluid p-v-T properties in high pressure conditions, the modified Soave-Redlich-Kwong state equation is used in the evaluation of thermophysical properties. Some computational results are compared with Sato's experimental data for the validation of calculations in case of vaporization. The comparison between predictions and experiments showed quite a good agreement. Droplet surface temperature increased with increasing pressure. Ignition time increased with increasing initial droplet diameter. Temporal or spatial distribution of mass fraction, mass diffusivity, Lewis number, thermal conductivity, and specific heat were presented.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2022년도 가을 학술논문 발표대회
• /
• pp.247-248
• /
• 2022

The microfluidic controlled droplet production system is one of the most powerful methods for capsule manufacturing. However, stable production is not possible when the powder is included. We solved the above problem by developing an off-chip droplet production system. we checked the droplet creation mechanism and created a simple repair model. It was possible to produce a uniform and stable droplet regardless of the powder content.