Theoretical and experimental study of condensation rates on radiant cooling surfaces in humid air

The condensation rate on a radiant cooling surface in humid air is a basic index used to evaluate the risk of condensation and is beneficial to the engineering design of radiant cooling systems. In this paper, condensation rates were studied theoretically using simplified Navier-Stokes equations with Boussinesq approximation, and the heat and mass transfer analogy was also derived. In the experiments, the condensation rates on radiant cooling panels of different lengths at various positions (the floor, the wall, and the ceiling) were measured. The experimental results of the mass transfer coefficients are represented in a correlation of average Sh number vs. Ra number. With a sub-cooled degree of 5 °C, the mass transfer coefficients of the radiant floor, wall and ceiling were 1.22 mm/s, 3.35 mm/s, and 4.15 mm/s, respectively. As a result, the condensation rate on the radiant ceiling was 3.5 times greater than that on the radiant floor and 25% greater than that on the radiant wall.