Effect of humidification of combustion products in the boiler economizer with spiral geometry

In light of rising fuel prices and climate change in recent decades, improving the performance of heat recovery equipment such as boiler economizers is critical. Currently, numerical work is being done to improve the performance of the economizer with spiral geometry by humidifying combustion products. Simulations are performed using the finite volume method (FVM) and, in three cases, in a two-dimensional, steady, single-phase, and turbulent condition. In the first case, water vapor condensation and liquid water spray are not considered. In the second case, the impact of water vapor condensation is considered, and the effect of liquid water spray is not considered. In the third case, the water vapor condensation and the liquid water spray are simultaneously considered. Experimental correlation relations are used to predict the condensation rate in the second and third cases. The results are presented and discussed in the form of Nusselt number, convection heat transfer coefficient (h), outlet temperature, and heat transfer rate for different inlet temperatures of combustion products. Moreover, velocity, pressure, temperature contours, and velocity vectors are obtained and analyzed. The results showed that the cold-water outlet temperature in the third case was 2.85% higher than in the first case. In addition, a maximum improvement of 1.39% in the third case is obtained compared to the second case. Also, the heat transfer rate in the third case is improved by 8.2% compared to the first case and by 3.9% compared to the second case. The proposed method in the present work can be used to predict the effect of liquid water spray on the performance of boiler economizers.