Theoretical Evaporation Model of a Single Droplet in Laser Treatment of PWS in Conjunction With Cryogen Spray Cooling

2008 ◽  
Author(s):  
Zhifu Zhou ◽  
Hui Xin ◽  
Bin Chen ◽  
Guo-Xiang Wang
Keyword(s):  
Gas Phase ◽  
Laser Treatment ◽  
Deep Understanding ◽  
Theoretical Models ◽  
Spray Cooling ◽  
Droplet Evaporation ◽  
Evaporation Process ◽  
Single Droplet ◽  
Equilibrium Evaporation ◽  
Cryogen Spray Cooling

Cryogen spray is an effective cooling technique used for laser treatment of Port Wine Stain. The cooling process involves complex droplet evaporation and strong convective heat and mass transfer, therefore a deep understanding of spray characteristics is essential in order to optimize the nozzle design and improve the cooling efficiency of the spray. This paper improves a theoretical model to describe the equilibrium evaporation process of a single cryogen droplet in cryogen spray. The results of comparative analysis of gas phase models for single droplet heating and evaporation are presented. Six different semi-theoretical models based on various assumptions are compared and their effects on a single droplet heating and evaporation characteristics in the process of cryogen R-134a spray cooling are compared. It is pointed out that the gas phase model, in which the effect of superheat is taken into account, predicts the evaporation process closest to the experimental data. Finally, a parametric study of the influences of initial diameter and velocity on the droplet evaporation is then carried out. The results can be used to guide the Cryogen Spray Cooling of laser therapy.

Evaporation Characteristics of a Single Droplet in Laser Treatment of Port Wine Stain in Conjunction with Cryogen Spray Cooling

2008 ◽  
Vol 35 (6) ◽  
pp. 952-956 ◽  
Author(s):  
周致富 Zhou Zhifu ◽  
辛慧 Xin Hui ◽  
陈斌 Chen Bin ◽  
王国祥 Wang Guoxiang
Keyword(s):  
Laser Treatment ◽  
Spray Cooling ◽  
Port Wine Stain ◽  
Port Wine ◽  
Single Droplet ◽  
Cryogen Spray Cooling

Numerical Study of Bicomponent Droplet Vaporization in a High Pressure Environment

1996 ◽  
Author(s):  
J. Stengele ◽  
H.-J. Bauer ◽  
S. Wittig
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Gas Phase ◽  
Numerical Study ◽  
Droplet Evaporation ◽  
Single Component ◽  
Vapor Concentration ◽  
Diffusion Limit ◽  
Evaporation Process ◽  
Droplet Vaporization

The understanding of multicomponent droplet evaporation in a high pressure and high temperature gas is of great importance for the design of modern gas turbine combustors, since the different volatilities of the droplet components affect strongly the vapor concentration and, therefore, the ignition and combustion process in the gas phase. Plenty of experimental and numerical research is already done to understand the droplet evaporation process. Until now, most numerical studies were carried out for single component droplets, but there is still lack of knowledge concerning evaporation of multicomponent droplets under supercritical pressures. In the study presented, the Diffusion Limit Model is applied to predict bicomponent droplet vaporization. The calculations are carried out for a stagnant droplet consisting of heptane and dodecane evaporating in a stagnant high pressure and high temperature nitrogen environment. Different temperature and pressure levels are analyzed in order to characterize their influence on the vaporization behavior. The model employed is fully transient in the liquid and the gas phase. It accounts for real gas effects, ambient gas solubility in the liquid phase, high pressure phase equilibrium and variable properties in the droplet and surrounding gas. It is found that for high gas temperatures (T = 2000 K) the evaporation time of the bicomponent droplet decreases with higher pressures, whereas for moderate gas temperatures (T = 800 K) the lifetime of the droplet first increases and then decreases when elevating the pressure. This is comparable to numerical results conducted with single component droplets. Generally, the droplet temperature increases with higher pressures reaching finally the critical mixture temperature of the fuel components. The numerical study shows also that the same tendencies of vapor concentration at the droplet surface and vapor mass flow are observed for different pressures. Additionally, there is almost no influence of the ambient pressure on fuel composition inside the droplet during the evaporation process.

Evaporation Characteristics of Single R404a Droplet in Laser Treatment of PWS in Conjunction with Cryogen Spray Cooling

2009 ◽  
Vol 36 (10) ◽  
pp. 2691-2695
Author(s):  
辛慧 Xin Hui ◽  
周致富 Zhou Zhifu ◽  
王国祥 Wang Guoxiang ◽  
陈斌 Chen Bin ◽  
王跃社 Wang Yueshe
Keyword(s):  
Laser Treatment ◽  
Spray Cooling ◽  
Cryogen Spray Cooling

Deflagration Analysis of Aluminum Droplet Combustion

2012 ◽  
Author(s):  
Birce Dikici ◽  
M. L. Pantoya ◽  
B. D. Shaw
Keyword(s):  
Gas Phase ◽  
Flame Propagation ◽  
Diffusion Flame ◽  
Dominant Role ◽  
Experimental Studies ◽  
Droplet Evaporation ◽  
Combustion Model ◽  
Single Droplet ◽  
Aluminum Particles ◽  
Combustion Dynamics

The evaporation and combustion of nanometric aluminum particles with an oxidizer MoO3 is analyzed. The analysis was performed to correlate individual Al particle gasification rates to macroscopic flame propagation rates observed in flame tube experiments. Examination of various characteristic times relevant to propagation of a deflagration reveals that particles below about 1.7 nm in diameter evaporate before appreciable chemical reactions occur. Experimental studies use Al particles greater than 1.7 nm in diameter such that a diffusion flame model was developed to better understand the combustion dynamics of multiphase Al particles. The results showed that it is unlikely that droplets will fully evaporate before reacting in the gas phase. A droplet evaporation and combustion model was further applied to quantify single droplet reaction velocities in comparison to the bulk flame propagation measurements observed in the literature. The diffusion flame model predicted orders of magnitude slower propagation rates than experimentally observed. These results imply that another reaction mechanism is responsible for promoting reaction propagation or modes other than diffusion play a more dominant role in flame propagation.

scholarly journals Intermittent cryogen spray cooling for optimal heat extraction during dermatologic laser treatment

2002 ◽  
Vol 47 (18) ◽  
pp. 3275-3288 ◽  
Author(s):  
Boris Majaron ◽  
Lars O Svaasand ◽  
Guillermo Aguilar ◽  
J Stuart Nelson
Keyword(s):  
Laser Treatment ◽  
Spray Cooling ◽  
Heat Extraction ◽  
Optimal Heat ◽  
Cryogen Spray Cooling

scholarly journals Cryogen Spray Cooling and Pulsed Dye Laser Treatment of Cutaneous Hemangiomas

2001 ◽  
Vol 46 (6) ◽  
pp. 577-583 ◽  
Author(s):  
Cheng-Jen Chang ◽  
Kristen M. Kelly ◽  
J. Stuart Nelson
Keyword(s):  
Laser Treatment ◽  
Spray Cooling ◽  
Dye Laser ◽  
Pulsed Dye Laser ◽  
Cryogen Spray Cooling

Bioheat transfer analysis of cryogen spray cooling during laser treatment of port wine stains

2000 ◽  
Vol 26 (2) ◽  
pp. 145-157 ◽  
Author(s):  
T. Joshua Pfefer ◽  
Derek J. Smithies ◽  
Thomas E. Milner ◽  
Martin J.C. van Gemert ◽  
J. Stuart Nelson ◽  
...  
Keyword(s):  
Laser Treatment ◽  
Spray Cooling ◽  
Bioheat Transfer ◽  
Port Wine ◽  
Port Wine Stains ◽  
Cryogen Spray Cooling
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