Internal flow and heat transfer of a condensing water droplet in steam flow

The growth of a condensing water droplet of size millimeters in steam flow is experimentally measured using a CCD camera. The growth rate of the droplet is found to increase with the steam flowrate, which disagrees with previous theories. A CFD model is developed to simulate the internal flow and heat transfer of the droplet, and it predicts the droplet growth rate increases with the steam flowrate in good agreement (about 2% in deviation) with the experimental results. It is demonstrated that the steam shearing at the droplet surface causes an internal flow in the droplet. The internal flow, though small (less than 1% of the external steam flow in magnitude), convects the temperature profiles to the droplet bottom and causes a 10–25% enhancement in the heat transfer of the droplet. For droplets of the same bottom, the steam shearing effect is more significant with a larger droplet height.

► The growth of condensing water droplets in steam flow is measured.
► Droplet growth rate increases at larger steam flow velocities.
► Steam flow shearing causes an internal flow inside condensing droplets.
► The internal flow increases heat transfer of condensing droplets by 15–25%.
► A CFD model has been developed to simulate the flow and heat transfer of droplets.