Abstract:Motivated by the study of spray combustion, this work addresses the combustion of non-spherical droplets. The combustion of spray is usually understood through the theory of droplet combustion, and improving this latter theory is the narrow aim of this work. The current work uses perturbation theory to derive a novel model for the vaporization of non-spherical droplets. Compared to previous efforts in this area, the work uses a physics-based approach by incorporating ideas from the asymptotic analysis of Taylo… Show more
“…previous theory of lower curvature, lower local evaporation flux given in [22], [23], [24]. This emphasizes the importance of boundary layer development in evaporation for higher Reynolds number flow.…”
Section: Acknowledgementsupporting
confidence: 54%
“…In this region, the droplet has lower curvature in comparison to the front of it. This seems to contradict the theoretical analysis by Tonini and Cossali [22], [23] and Palmore [24] where the local evaporation rate was directly proportional to the local interface curvature. As these studies were performed at Re ≈ 0, the evaporation was isometric and spherical in nature.…”
Section: B Effect Of Droplet Shape On Evaporationmentioning
confidence: 63%
“…They also quantified that the local evaporation flux depends on the fourth root of local Gaussian curvature of the droplet. This was expanded upon by Palmore in his recent work [24]. The use of more realistic droplet shapes than the ellipsoid is one of the novelties in this work.…”
This work covers the effect of droplet deformation on its evaporation rate under convective flow conditions. A single component jet fuel surrogate n-decane is used as a liquid fuel. The large droplets in sprays tend to deform due to an imbalance of aerodynamic force and surface tension, hence deviate from a spherical shape. This influence of the deformation and planar flow on evaporation is investigated by varying the relevant non-dimensional groups such as Weber number (W e) ranging from 1 − 12 and Reynolds number (Re) ranging from 25 to 120. These numerical studies utilize a numerical framework for interface capturing Direct Numerical Simulation (DNS) for multiphase flows. The framework is built upon an in-house code NGA. A grid-independent study is performed in order to find an accurate and computationally feasible grid for this work.Furthermore, the numerical results are compared against the analytical correlations by Abramzon and Sirignano (Int. Journal of heat and mass transfer, 1989) to validate the accuracy of the solver.The results for grid size N d = 24 are found to be in good agreement with the analytical solution with 5% of difference.Finally, the effect of droplet shape on the evaporation rate at various Re is quantified in terms of total evaporation rate and its contributors: local evaporation rate and the total surface area.Results suggest that the evaporation of the droplet has a weak dependency with Weber number at low Re. However, as the deformation is significant for W e = 4, 8, 12 at Re = 120, it plays a key role in altering the total evaporation rate ( ṁ) by altering the flow around it.
“…previous theory of lower curvature, lower local evaporation flux given in [22], [23], [24]. This emphasizes the importance of boundary layer development in evaporation for higher Reynolds number flow.…”
Section: Acknowledgementsupporting
confidence: 54%
“…In this region, the droplet has lower curvature in comparison to the front of it. This seems to contradict the theoretical analysis by Tonini and Cossali [22], [23] and Palmore [24] where the local evaporation rate was directly proportional to the local interface curvature. As these studies were performed at Re ≈ 0, the evaporation was isometric and spherical in nature.…”
Section: B Effect Of Droplet Shape On Evaporationmentioning
confidence: 63%
“…They also quantified that the local evaporation flux depends on the fourth root of local Gaussian curvature of the droplet. This was expanded upon by Palmore in his recent work [24]. The use of more realistic droplet shapes than the ellipsoid is one of the novelties in this work.…”
This work covers the effect of droplet deformation on its evaporation rate under convective flow conditions. A single component jet fuel surrogate n-decane is used as a liquid fuel. The large droplets in sprays tend to deform due to an imbalance of aerodynamic force and surface tension, hence deviate from a spherical shape. This influence of the deformation and planar flow on evaporation is investigated by varying the relevant non-dimensional groups such as Weber number (W e) ranging from 1 − 12 and Reynolds number (Re) ranging from 25 to 120. These numerical studies utilize a numerical framework for interface capturing Direct Numerical Simulation (DNS) for multiphase flows. The framework is built upon an in-house code NGA. A grid-independent study is performed in order to find an accurate and computationally feasible grid for this work.Furthermore, the numerical results are compared against the analytical correlations by Abramzon and Sirignano (Int. Journal of heat and mass transfer, 1989) to validate the accuracy of the solver.The results for grid size N d = 24 are found to be in good agreement with the analytical solution with 5% of difference.Finally, the effect of droplet shape on the evaporation rate at various Re is quantified in terms of total evaporation rate and its contributors: local evaporation rate and the total surface area.Results suggest that the evaporation of the droplet has a weak dependency with Weber number at low Re. However, as the deformation is significant for W e = 4, 8, 12 at Re = 120, it plays a key role in altering the total evaporation rate ( ṁ) by altering the flow around it.
“…This is accurate for the smallest spray droplets, however, in spray, droplets come in a range of sizes. The largest ones are large enough to see significant deformation which can fundamentally affect their behavior including drag [16] and evaporation rate [20]. Therefore, we will need to improve the physical understanding of droplets to better predict the dynamics of droplets represented by Lagrangian particles.…”
The current study uses numerical approaches to investigate the effect of droplet deformation and internal circulation on droplet dynamics. Although droplet drag is a classical area of study, there are still theoretical gaps in understanding the motion of large droplets. In applications like spray combustion, droplets of various sizes are generated and move with the flow. Large droplets tend to deform in the flow, and have complex interactions with the flow because of this deformation. To better model spray, the physical understanding of droplets need to be improved.Under spray conditions, droplets are subjected to a high temperature and pressure environment, and the coupling between liquid and gas is enhanced. Therefore, the deformation and internal circulation will affect droplet drag coefficient more significantly than in atmospheric conditions.To study the mechanism on how droplet shape and internal circulation influence droplet dynamics, we will use direct numerical simulation (DNS) to simulate a droplet falling at its terminal velocity in high pressure air. An in-house code developed for interface-capturing DNS of multiphase flows will be employed for the simulation. The drag coefficient is calculated, and the results are consistent with existing literature for slightly deformed droplets. The results show that the drag coefficient is directly related to the droplet deformation and droplet internal circulation. The paper also develops a theory to account the effect of Weber number and liquid/gas properties in droplet deformation.
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