![Table 1. Validation of the numerical model against the experimental results of Gokalp et al. [31]](/figures/table-1-validation-of-the-numerical-model-against-the-1fpbsdlu.webp)
Q2. What are the main characteristics of droplet evaporation in high pressure and high temperature environments?
Transient characteristics of liquid- and gas-phases, the non-ideal behavior of the gas-phase, the real gas effects on the heat of vaporization and on the vapor–liquid equilibrium conditions at the droplet interface, and the solubility of the ambient inert species into the liquid droplet, become important at high pressure and high temperature environments.
Q3. What is the evaporation constant for a moving droplet?
As the ambient pressure increases, the evaporation constant increases with time monotonically and steeply, throughout the droplet lifetime.
Q4. What are the effects of thermal expansion on the liquid phase?
Changes in the liquid phase density due to both thermal expansion and change in species composition contribute to the rate at which the droplet surface recedes and are incorporated in the model.
Q5. What are the main assumptions used in the numerical model?
The following assumptions are employed in the numerical model: (1) the droplet shape remains spherical, (2) radiation effects are negligible, (3) second-order effects, such as the Soret and Dufour effects are negligible, (4) viscous dissipation is neglected and (5) the flow is laminar and axisymmetric.
Q6. What is the distance traveled with time for a solid sphere?
If a solid sphere with the same density and initial diameter as that of an n-heptane droplet is considered to be moving with the same initial velocity of 1.5 m/s, due to higher drag experienced by the solid sphere, its penetration distance (until its velocity reaches zero) is less than that of the n-heptane droplet (curves 5 and 6).
Q7. What methods are used to solve the unsteady equations of mass, species, momentum and?
The unsteady equations of mass, species, momentum and energy conservation in axisymmetric spherical coordinates are solved using the finite-volume and SIMPLEC methods.
Q8. What is the effect of the ambient pressure on the mass fraction of the droplet?
At a much higher ambient pressure (9 MPa), the mass fraction of N2 increases at the droplet surface for both moving and stagnant droplets, but more rapidly for the moving droplet, due to the additional convective transport of the species.
Q9. What is the average evaporation constant for a solid sphere?
The non-dimensional average evaporation constant increases almost linearly with the reduced ambient pressure p∞/pc, where pc is the critical pressure of n-heptane, till the ambient reduced pressure is approximately 2.
Q10. Why do the surface temperatures at the front and rear stagnation points tend towards the same value?
During the later part of the lifetime, the surface temperatures at the front and rear stagnation points tend towards a same value, because of the considerable decrease in the relative velocity between the droplet and the surrounding gas and also due to the internal mixing.
Q11. What is the evaporation constant at ambient pressure?
It can also be observed that at low ambient pressures, the evaporation constant reaches an almost constant value during the end of the droplet lifetime.
Q12. What is the mass fraction of the ambient gas at the droplet center?
At anambient pressure of 3 MPa, only a small and nearly constant amount of N2 is observed on the droplet surface, for both moving and stagnant droplets.
Q13. What is the average evaporation constant at ambient pressure?
For higher values, depending on the initial freestream velocity, the average evaporation constant either becomes a constant (at low initial freestream velocities) or it non-linearly increases (at high initial freestream velocities) with the ambient pressure.
Q14. What is the plot of the penetration distance with time?
It is clear from the plot that as the ambient pressure increases, the penetration distance decreases because of the increased rate of vaporization (shorter lifetime) at higher ambient pressures.
Q15. Why does the surface temperature of a moving droplet increase with time?
It is clear from Figure 3a that, because of increased energy transfer due to convection, the surface temperature increases rapidly with time for a moving droplet.
Q16. What is the average evaporation constant for ambient pressure?
The average evaporation constant increases with ambient pressure and the variation is almost linear for reduced ambient pressure smaller than approximately 2.