Study and prediction of evaporation characteristics of n-heptane under turbulent conditions

This work focuses on turbulent evaporation characteristics under turbulent intensities of 0–0.437 m/s and ambient temperatures of 373–473 K. The diameter of n-heptane droplets is around 1.5 mm and ambient pressure is normal pressure. A single fuel droplet is placed at the junction of the thermocouple wires, which is also applied to measure droplet temperature. The experimental results show that the D2 law is satisfied under all conditions because the droplet temperature is stabilized at wet-bulb temperature. At the same ambient temperature, the wet-bulb temperature increases with increasing turbulent intensity for the turbulent intensity of 0–0.437 m/s and it is unchanged when the intensity is higher than 0.437 m/s. With the increase in turbulent intensity, the normalized evaporation rate increases and its growth rate gradually weakens. As the ambient temperature increases, the normalized evaporation rate decreases. The Stefan flow is very important for calculating the radial velocity of vapor transport on the droplet surface. From a view of vapor transport, a new evaporation Damkohler number is introduced to the expression of normalized evaporation rate and it is the ratio between the turbulent intensity and the radial velocity of vapor transport under static environment. A good correlation is established under all ambient temperatures.