Numerical investigation of heat-mass transfer characteristics of LiCl solution droplet in frost-prone ambient air

Optimizing the structure and operating mode of the heat source tower to enhance its heat transfer performance is beneficial for it to play a greater role in clean heating engineering. In this study, firstly, an improved closed-type heat source tower using a spray zone to replace the fin-tube heat exchanger in the traditional structure was proposed; next, a modified numerical model for the heat and mass transfer between anti-frost droplet and moist air in the improved structure was established; then, the heat and mass transfer mechanism between anti-frost droplet and moist air and the effects of moist air velocity and initial droplet diameter were studied. The results show that the convection effect and diffusion effect jointly dominate the mass transfer between the anti-frost droplet and moist air, and more than 90% of mass transfer resistance is concentrated on gas side; interfacial shear stress affects the mass transfer coefficient by thinning the concentration boundary layer on windward side of anti-frost droplet and influencing the quantity and intensity of vortices inside droplet; the mass transfer rates on both the windward and leeward sides of anti-frost droplet are promoted by interfacial shear stress, and the mass transfer rate on the leeward side of droplet is also enhanced by the returning moist air; when the moist air velocity is 0.2 m/s, the average mass transfer coefficient exhibits a quadratic functional relationship with time, however, as the moist air velocity and droplet diameter increase, the relationship between them gradually approaches linearity; finally, based on the research results, a Sh calculation model incorporating the effect of interfacial shear stress was established (R² = 0.99947).