滴群からの熱および物質移動に関する相互干渉についての基礎的実験

抄録

Although the effect of surrounding droplets on heat and mass transfer from a droplet is essentially important for the design of spray dryers, few experimental or theoretical studies have been made. To study this problem, heat and mass flux from a water droplet placed in the following three arrays were measured. They were then compared with those measured without surrounding glass beads. (1) A droplet was placed downstream at various distances from a glass bead along the flow (series type). (2) A droplet was placed at the center between two glass beads across the flow (parallel type). (3) A droplet was placed downstream of two glass beads (zig-zag type).
Mass flux was determined from the change of droplet diameter by using a photographic technique, and heat flux was considered to be equal to the amount of latent heat transfer.
Heat and mass transfer coefficient, namely Nu and Sh, obtained in the above three arrays were compared with Nu₀ and Sh₀ determined without the surrounding glass beads. As a result, the ratio of Nu/Nu₀ in series type was found to be a function of b/d_g and d_p/d_g, where b, d_g, and d_p are respectively the distance between surfaces of a droplet and glass bead, the diameter of a glass bead, and the diameter of water droplet. On the other hand, in parallel type, Nu and Sh were not affected by the presence of glass beads. In the zig-zag type, they were also not affected when the ratio of droplet diameter to distance between surfaces of two glass beads was smaller than 2. However, when this ratio exceeded 4, the value of Nu/ Nu₀ took a constant value of 0.57.