For investigating condensation heat transfer characteristic inside flat tubes widely applied in air-cooled condenser in large power plant

a water cooled visualization condensation test system is designed and built for an indirect study on the flow regime of condensation process in a condenser. Base on the observed stratified flow regime

a theoretical model is built for condensation flow and heat transfer process including condensate water bath development on the arc wall and condensate film development on the other wall. Especially

for condensate film on the wall

a hyperbolic equation is proposed. Considering the convection and conservation characteristic in the equation

a solution algorithm for steady conservation equation is produced by combination of the conjugate gradient method

the Newton method and simulated annealing method

which can avoid the complex of traditional non-steady method. The visualization results indicate that the flow regime of condensation process is stratified flow regime and the corresponding theoretical calculation results indicate that the condensate film thickness on the wall is far less than condensate bath height

which is in the 1 mm order of magnitude

and leads to high condensation heat transfer coefficient. The results supply grounds for judging the onset position of freezing in flat tube under air cooling condition in power plant in winter.