Solution to External and Internal Heat and Mass Transfer Problems for Closed Two-Phase Thermosyphon

The paper presents the results of the analytical study of heat and mass transfer processes with the use of a two-phase closed thermosyphon (TPCT). The article gives a mathematical description of heat and mass transfer process in a TPCT, the description being done in the form of a system of differential equations of mass, momentum and energy conservation, complemented by single-valuedness conditions in the form of equations of heat and material balance, as well as boundary conditions. We determined the values of heat-transfer coefficients to the outer surface of the evaporator and from the outer surface of the condenser by solving the external problem considering the conditions of the flow around the thermosyphon by the flue gas stream. Wherein, for the heated tank solution and the section of the furnace mixing chamber, the systems of the conservation equations of mass, momentum, and energy were also used considering their specificity and corresponding boundary conditions. Thus, we identified the heat and mass transfer conditions in the thermosyphon under conditions as close as possible to the real ones. We applied a numerical finite element method to solve internal and external problems and obtained a numerical solution for the axisymmetric problem of natural convection in a cylindrical TPCT with heat-conducting walls. We took into consideration the conditions of heat transfer with the surrounding medium, which approximates the results of calculations to real conditions. The article presents some results of calculations, in particular: distribution of velocities and temperatures in the furnace mixing chamber (the evaporator zone); change of the mean values of heat transfer coefficients along the length of the thermosyphon; temperature distribution along the length of the thermosyphon on its internal and external surface. The results of the calculations indicate a high efficiency of the TPCT in solving the problem of heating the working solutions with the heat of flue gases for industrial production conditions.

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