The influence of key factors on the heat and mass transfer of a sessile droplet

Heat transfer, temperature and velocity fields of droplets of water and aqueous salt solutions have been studied. The initial concentration of salt solutions C₀₁ = 30% in accordance with advanced technological applications. It is shown that the heat flux q for a water droplet is several times higher than for salt solutions. During the droplet evaporation, this difference increases, since q for aqueous salt solutions is many times reduced. While maintaining the wall temperature under the drop quasi-constant (T_w = 83 °C), the heat transfer coefficient α (for the time t < 150 s) for a drop of water 1.5–2 times exceeds α for the salt solution, and is 7 times higher for water than for the salt solution at t = 280 s. Using PIV measurements the liquid velocity fields have been obtained; and for the first time it has been shown that only for very small times and at high ΔT, the important role is played by thermo-gravitational convection in the droplet (the Rayleigh number Ra). But already for t > 10 s, the thermal and solutal Marangoni flows have a greater influence on the flow in a drop of the salt solution.