Analytical and numerical studies on a single-droplet evaporation and combustion under forced convection

2015 ◽  
Vol 31 (4) ◽  
pp. 523-530 ◽  
Author(s):  
L. X. Zhou ◽  
K. Li
Energies ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4618
Author(s):  
Zhi-Fu Zhou ◽  
Dong-Qing Zhu ◽  
Guan-Yu Lu ◽  
Bin Chen ◽  
Wei-Tao Wu ◽  
...  

Drag force plays an important role in determining the momentum, heat and mass transfer of droplets in a flashing spray. This paper conducts a comparative study to examine the performance of drag force models in predicting the evolution of droplet evaporation for R134a single droplet and spray characteristics for its flashing spray. The study starts from single moving R134a droplet vaporizing in atomispheric environment, to a fully turbulent, flashing spray caused by an accidental release of high-pressure R134a liquid in the form of a straight-tube nozzle, using in-house developed code and a modified sprayFoam solver in OpenFOAM, respectively. The effect of the nozzle diameter on the spray characteristics of R134a two-phase flashing spray is also examined. The results indicate that most of the drag force models have little effect on droplet evporation in both single isolated droplet modelling and fully two-phase flashing spray simulation. However, the Khan–Richardson model contributes to different results. In particular, it predicts a much different profile of the droplet diameter distribution and a much lower droplet temperature in the radial distance. The nozzle diameter has a significant impact on the flashing spray. A smaller diameter nozzle leads to more internse explosive atomization, shorter penetration distance, lower droplet diameter and velocity, and a faster temperature decrease.


Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1011 ◽  
Author(s):  
Sara Rostami ◽  
Saeed Aghakhani ◽  
Ahmad Hajatzadeh Pordanjani ◽  
Masoud Afrand ◽  
Goshtasp Cheraghian ◽  
...  

Natural convection in cavities is an interesting subject for many researchers. Especially, in recent years, the number of articles written in this regard has grown enormously. This work provides a review of recent natural convection studies. At first, experimental studies were reviewed and, then, numerical studies were examined. Then, the articles were classified based on effective parameters. In each section, numerical studies were examined the parameters added to the cavity such as magnetic forces, fin, porous media and cavity angles. Moreover, studies on non-rectangular cavities were investigated. Free convection in enclosures depends more on the fluid velocity relative to the forced convection, leading to the opposite effect of some parameters that should essentially enhance rate of heat transfer. Nanoparticle addition, magnetic fields, fins, and porous media may increase forced convection. However, they can reduce free convection due to the reduction in fluid velocity. Thus, these parameters need more precision and sometimes need the optimization of effective parameters.


Author(s):  
Wei Xu ◽  
Lei Shi ◽  
Yanhua Zheng ◽  
Peng Liu ◽  
Liang He

Water ingress accident is one of the most severe accidents which must be analyzed in high temperature gas-cooled reactor pebble-bed modular (HTR-PM). The droplet could enter the primary circuit under the design basis accident of a double-ended guillotine break of a heat transfer tube. This paper simulates the behavior of single droplet evaporation and movement in the steam generator by numerical methods. Based on the structure characteristics of steam generator, the life time of droplet and the distance that the single droplet could move have been analyzed. The important parameters such as the droplet diameter, helium temperature, helium pressure and helium velocity which have an influence on the behavior of droplet evaporation and movement have also been discussed in detail. The preliminary numerical simulation results indicate that the droplet diameter, helium velocity and helium temperature play an important role in the life time of droplet in the accident situation in the primary circuit. Helium pressure has a little effect on droplet evaporation in practical situation. The numerical simulation results demonstrate that only certain droplets with a diameter in certain range could arrive to the bottom of the steam generator pressure vessel (SGPV) and enter into the steam generator annular channel after collision with the bottom of the SGPV. The distance that the single droplet could move in the primary circuit is decided by a various complex factors such as the structure of the primary circuit, the droplet diameter and helium velocity. The preliminary analyses indicate that there is little probability for the single droplet to enter into the reactor core of the HTR-PM.


2011 ◽  
Vol 383-390 ◽  
pp. 3068-3076
Author(s):  
Yu Po Ma ◽  
Xiang Rong Li ◽  
Xiang Yuan Wang ◽  
Fu Shui Liu

With the continuous improvement of power density,in the process of diesel fuel evaporation in cylinder, the interaction between droplets continues to grow. In order to study the mutual influence in the process of droplets evaporation, the evaporation phenomenas of single droplet, double-droplet and multi-droplet were studied experimentally in this paper. Firstly the influence of background temperature on single droplet evaporation rate was contrasted to verify the reasonableness of the experimental system. And then the influence of number of droplets and distance between droplets was compared and elicited the value of evaporation rate for each experimental condition. It can be found that when the number of droplets increases, the evaporation rate of droplets decreases; when the distance between droplets decreases, the evaporation rate of droplets also reduced.


Author(s):  
Birce Dikici ◽  
M. L. Pantoya ◽  
B. D. Shaw

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.


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