Action of Attached Water Drop Drying on the Surface of Satsuma Orange(Cirus unshiu Marc)

Abstract

It was found that the drying processes of the water drop attached to the surface of Satsuma Orange(Citrus unshiu Marc.)were divided into two steps: (1) drying with the constant area of the attached base of the drop, and (2) drying with the shrinking area, The shrinking of the area began when the contact angle became sma11er than the critical value(backward contact angle), and the shrinking proceeded at a uniform rate that meant a constant radius of the curvature of the drop. From these observations the following formulae for the estimation of the drying period were derived:
t=2√w₀w_cr/0.8/R, w₀/0.8<w_cr
t=(w₀/0.8+w_cr)/R, w₀/0.8>w_cr
where R: average drying rate per unit wetted area [mg/mmm²·sec]
w₀: initial average mass of water per unit area of the orange surface [mg/mmm²]
w_r: critical mass of water drop per unit attached area to the surface determined by the critical contact angle (φ_cr=10°27')[mg/mmm²]
The calculated values by the formulae agreed with the observed values.