Continuous droplet generators and methods are provided. In one embodiment, a continuous droplet generator includes an outer housing that defines a working liquid reservoir configured to maintain a working liquid. The continuous droplet generator also includes one or more heaters configured to change the phase of the working liquid and an evaporation-condensation tube positioned at least partially within the outer housing. The evaporation-condensation tube includes a gas inlet configured to receive a particle-containing gas flow, a gas outlet configured to export generated condensed droplets, a wall, an outer wall surface configured to be in contact with the working liquid, and an inner wall surface in contact with the particle-containing gas flow. The vapor is transported to the particle-containing gas flow through the evaporation-condensation tube by diffusion and vapor pressure difference to increase a relative humidity and grow particles within the particle-containing gas flow by nuclei heterogeneous condensation.