Optimization of flue gas convective heat transfer with condensation in a rectangular channel

Abstract

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.

Optimization of flue gas turbulent heat transfer with condensation in a tube

“…Therefore, both the sensible and latent heat transfers were enhanced after optimization. In the optimization of the laminar convective heat transfer with vapor condensation [27], the total viscous dissipation after optimization only increased by 3.35%, while the total heat transfer rate increased by 31.67% and the condensing heat transfer rate increased by 29.26%. For the same heat transfer increment, the viscous dissipation increment for turbulent heat transfer with condensation was much larger than that for laminar convective heat transfer with condensation.…”

“…The thickness of the viscous sublayer for fully developed turbulent flow with Re = 10000 is 0.32 mm. Figure 3 shows that the distance between the vortex center and the tube surface was about 0.9 mm, which is about 3 times as the thickness of the viscous sublayer, while during optimization of the laminar convective heat transfer with vapor condensation [27], the vortices took up almost the entire flow channel, and the distance between the vortex center and the channel wall was half the height of the channel. For practical application, a series of small longitudinal vortex generators on the tube surface can be used to generate multiple longitudinal vortices, similar to the optimal flow, thereby enhancing the turbulent heat transfer with condensation.…”

“…Similar to laminar convective heat transfer with vapor condensation [27], entransy conservation equations will be established and the entransy dissipation expression deduced for turbulent heat transfer with condensation. Figure 1 shows the flue gas turbulent heat transfer with condensation in a vertical tube.…”

“…Similar to optimizing single-phase convective heat transfer [23][24][25], and laminar convective heat transfer with condensation [27], the optimization objective for the turbulent heat transfer with condensation is to determine the optimal velocity field that leads to the EED for given time-averaged viscous dissipation. Meanwhile, the flow and heat transfer are also governed by the continuity, time-averaged energy and species equations.…”

“…Moisture entransy and moisture entransy dissipation were defined. Song et al [27] defined entransy and entransy dissipation and deduced the field synergy equation for laminar convective heat transfer with vapor condensation. An optimal velocity field with multiple longitudinal vortices was obtained numerically.…”