Experimental investigation of water vapor condensation from flue gas in different rows of a heat exchanger model

Condensing heat exchangers (HE) are used in many applications because of their usability with different fluids and a wide operating range in terms of pressure, temperature and power. Despite that, the thermal design of condensing heat exchangers is still not optimized, due to the complexity of the condensation process and lack of related research. This paper presents results of experimental investigations of biofuel flue gas water vapor condensation on vertical tubes in different rows of a tube bundle in a crossflow. The effects of water vapor mass fraction, inlet flue gas temperature and the Reynolds number on heat transfer when the inlet cooling water temperature and flow rate are constant were analyzed. The results obtained showed that the main parameters which had the most influence on the condensation process were the water vapor mass fraction in the flue gas and its temperature at the inlet to the test section. In the range of inlet flue gas Reynolds numbers investigated, the Re effect on heat transfer was not as significant as the effect of the parameters indicated above. However, the Re number had some influence on the heat transfer variation along the inline tube bundle. A comparison of the average Nu number in the case of dry air with the experimentally determined average Nu number, even with low condensable gas mass fraction (6 %), showed that it increased considerably. A correlation was proposed, which helps to determine the average Nu number for the heat exchanger in the range of experiments performed.