Study and visualization of droplet entrainment from a polymer plate heat exchanger

Dropwise condensation and condensate droplet entrainment at the downstream end of a fully polymer compact heat exchanger made of PolyVinyliDene-Fluoride (PVDF) were studied for gas (air-steam) mixtures with a relatively high concentration of noncondensables. At high gas velocities, condensate drops may be taken away by the gas stream. These droplets may cause erosion of downstream equipment, and may reduce their heat and mass transfer performance. Experiments were conducted for various gas and coolant inlet temperatures, various air-steam mass flow rates and various inlet relative humidities. The main parameter affecting heat and mass transfer has been identified (inlet concentration). The main parameter affecting droplet entrainment is found to be the Weber number, We = ¿condv2 g,outdplate/ s, with a length scale dplate that has been explored in a dedicated experiment. It is found that in practical applications, droplet entrainment can be avoided by keeping the Weber number less than 1