The d-square law or formula_1-law is a relationship between diameter and time for an isolated, spherical droplet when it evaporates quasi-steadily, which was first observed by Boris Sreznevsky in 1882, and was explained by Irving Langmuir in 1918. If formula_2 and formula_3 are the droplet diameter and time, then formula_1-law pertains to the relation
formula_5
where formula_6 is the initial time, formula_7 is the initial droplet diameter and formula_8 is called the evaporation constant. 
Crespo–Liñán correction.
Crespo–Liñán correction refers to a small correction of the order formula_9 to the d-square law in terms of the small parameter formula_10, the ratio of gas to liquid density. Antonio Crespo and Amable Liñán showed that the quasi-steady approximation is correct in the inner zone having the size on the order of droplet diameter, but becomes invalid in an outer zone with a size larger than the droplet diameter by the factor of formula_9, where the unsteady terms cannot be neglected.