Three-dimensional heat transfer coefficient distributions in horizontal tube falling film evaporation

Three-dimensional heat transfer during falling film evaporation was numerically investigated with spray densities varying from 0.0183 kg/(m⋅s) to 0.17 kg/(m⋅s). The flow characteristics and the heat transfer coefficient distribution were investigated for droplet flow, column flow and sheet flow over the tube. The simulations agree well with previous experimental data. The heat transfer coefficient with droplet flow is improved by each droplet impact and the resulting saddle-shaped waves. At lower spray densities, dryout patches appear that reduce the heat transfer until parts of the dryout patches are rewet. The local heat transfer coefficients for column flows have non-uniform three-dimensional distributions with the smallest heat transfer coefficients at φ = 165 ∼ 180° for l*=0 or 1. For sheet flows, the local heat transfer coefficient first decreases and then increases with increasing circumferential angle, while it varies only a small amount in the axial direction.