Conservation equations of sensible entarnsy and latent entransy are established for flue gas convective heat transfer with condensation in a rectangular channel and the entransy dissipation expression is deduced. The field synergy equation is obtained on the basis of the extremum entransy dissipation principle for flue gas convective heat transfer with condensation. The optimal velocity field is numerically obtained by solving the field synergy equation. The results show that the optimal velocity field has multiple longitudinal vortices, which improve the synergy not only between the veloctiy and temperature fields but also between the velocity and vapor concentration fields. Therefore, the convective heat and mass transfers are significantly enhanced. Flow with multiple longitudinal vortices close to the optimal velocity field can be generated by discrete double-inclined ribs set in the rectangular channel. The numerical results show that the total heat transfer rate in the discrete double-inclined rib channel increases by 29.02% and the condensing heat transfer rate increases by 27.46% for Re = 600 compared with the plain channel. condensation, entransy, entransy dissipation, field synergy, longitudinal vortex Citation:Song W M, Meng J A, Li Z X. Optimization of flue gas convective heat transfer with condensation in a rectangular channel.

To effectively solve the problem of recovery and utilization of flue gas desulfurized gypsum (FGDG), a new method for preparing SO2 gas by adding a mixture of FGDG and pyrite into a boiling furnace and utilizing its high-temperature waste heat is proposed. Using the FactSage 6.1 Reaction module and the Equilib module, the pyrolysis behavior of FGDG with pyrite and the release characteristics of SO2 gas were studied. The effects of FeS2 addition, temperature, and ventilation flow rate on the decomposition of FGDG and the change in gas behavior were studied by thermogravimetric mass spectrometry and settling furnace (SF) experiments. In addition, the activation energies of the chemical reactions were determined by the Kissinger method, the Kissinger–Akahira–Sunose method, and the Flynn–Wall–Ozawa method. The results show that between 100 and 200 °C, mainly the loss process of CaSO4·2H2O crystal water from FGDG occurred. At 570 °C, FeS2 primarily undergoes self-decomposition. Between 820 and 1000 °C, the decomposition product of FeS2 reductively decomposes CaSO4. The average activation energy for the chemical reaction is 298.44 ± 8.83 kJ/mol. A lower pressure and ventilation and a higher FeS2 addition and temperature are beneficial for the reduction and decomposition of FGDG and for the increase in SO2 concentration. Therefore, in this study, the feasibility of adding FeS2 to reduce and decompose FGDG to prepare SO2 was preliminarily verified. The technology proposed in this article may shed some light on the recovery and high-value utilization of FGDG.

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Conservation equations for sensible and latent entransy are established for flue gas turbulent heat transfer with condensation in a tube, and the entransy dissipation expression is deduced. The field synergy equation is obtained on the basis of the extremum entransy dissipation principle for flue gas turbulent heat transfer with condensation. The optimal velocity field is numerically obtained by solving the field synergy equation. The results show that the optimal velocity field contains multiple longitudinal vortices near the tube surface. These improve the synergy not only between the velocity and temperature fields but also between the velocity and vapor concentration fields. Therefore, the turbulent heat and mass transfers are significantly enhanced. condensation, entransy, entransy dissipation, field synergy, longitudinal vortex Citation:Song W M, Meng J A, Li Z X. Optimization of flue gas turbulent heat transfer with condensation in a tube.