An Experimental Investigation of Water Vapor Condensation from Biofuel Flue Gas in a Model of Condenser, (2) Local Heat Transfer in a Calorimetric Tube with Water Injection

In order for the operation of the condensing heat exchanger to be efficient, the flue gas temperature at the inlet to the heat exchanger should be reduced so that condensation can start from the very beginning of the exchanger. A possible way to reduce the flue gas temperature is the injection of water into the flue gas flow. Injected water additionally moistens the flue gas and increases its level of humidity. Therefore, more favorable conditions are created for condensation and heat transfer. The results presented in the second paper of the series on condensation heat transfer indicate that water injection into the flue gas flow drastically changes the distribution of temperatures along the heat exchanger and enhances local total heat transfer. The injected water causes an increase in the local total heat transfer by at least two times in comparison with the case when no water is injected. Different temperatures of injected water mainly have a major impact on the local total heat transfer until almost the middle of the model of the condensing heat exchanger. From the middle part until the end, the heat transfer is almost the same at different injected water temperatures.