Abstract
Experimental measurements are compared with theoretical predictions for heat and mass transfer from hot and highly humid air (130°C, 0-15 wt% of water vapor content) to horizontal cooling tubes (30°C). The Reynolds number range is 2 800-9 000. Heat- and mass-transfer coefficients are measured under conditions with and without condensation present by using a newly developed condensate collector. It is found that the convective heat transfer and mass transfer are enhanced by 68% and 28% respectively by increasing the water vapor content in the air flow from 0 to 15 wt%. Mass transfer data fits well with Rose's equation and heat transfer data are shown to give 20-30% higher values than the prediction. This means that the analogy between heat and mass transfer does not hold under condensation conditions. This phenomenon is explained qualitatively by considering that the water vapor is consumed faster than the thermal energy in the separated flow region on the rear side of the tubes, due to the value of Pr/Sc being greater than unity.
