1. III The Heat Transfer Process
2. where cpis the heat capacity, L is the latent heat of vaporization, and B is the transfer number (as will be discussed in Sec. IV). The heat gain (Eq. 5) is proportional to the difference in the gas and droplet temperatures, unlike heat loss (Eq. 7). Therefore, the heat transfer rate decreases with increasing droplet temperature. The droplet temperature reaches a steady-state value (the wet-bulb temperature) lower than the boiling temperature of water (Tb). Equations 5 - 7 are applicabletoadropletpossessingadiametersignificantlylarger thanthemeanfreepathofthegas,typicallyforKnudsen numbers smaller than 0.1. However, for droplets with a diameterclosetothemeanfreepathλaofthegas,acorrection factor for the accurate determination of heating rate becomes necessary. Several researchers have proposed such corrections.14, 15ThemethodofFuks14most accurately predicts the change in heating rate as the Knudsen number increases.16This method takes into account a collisionless boundary (known as the limiting sphere) of thickness δ surrounding the droplet, based on the mean free path within the boundary layer as expressed by the following equation: δ +d
3. IV The Desolvation Process Desolvation of the droplet is calculated concurrently with droplet heating. Again, a continuum solution is used, with modifications to account for high temperature or low pressure environments. The mass flux of the droplet is described by:11, 12