EFFECT OF RELATIVE HUMIDITY ON CHARACTERISTICS OF HUMAN SALIVA RESIDUE

The study of the evaporation dynamics and residual characteristics of saliva droplets on surfaces is of significant importance for health monitoring and epidemic prevention, especially in the context of epidemic transmission studies. Saliva, as one of the primary transmission mediums, may carry pathogens through the residuals left during the evaporation process. Understanding the evaporation dynamics of saliva droplets is crucial for controlling virus transmission and predicting environmental impacts. This study combines experiments and numerical simulations to systematically investigate the effect of relative humidity on the residual characteristics of micrometer-sized saliva droplets. Under controlled environmental humidity conditions ranging from 20% to 90%, the evaporation process of saliva droplets is monitored experimentally. The numerical model integrates multiple physical factors, such as temperature, humidity, and droplet size, to accurately predict the distribution of biological particles in the saliva. Under different relative humidity conditions, the evolution of the residual morphology of saliva droplets during evaporation is carefully recorded, including the shape, size of the residual liquid, and migration characteristics of biological particles. The experimental results reveal the two-stage feature of the droplet evaporation process and further analyze the formation of four distinct regions. As relative humidity increases, the width of the ``coffee ring'' increases, while its height decreases, and at higher humidity, the droplet fails to completely dry, showing significant residual liquid characteristics. Numerical simulation results show that a large number of particles migrate to the droplet edge and the gas-liquid interface, which explains the formation of the edge protein membrane observed in the experiments. Through a comprehensive analysis of the three-dimensional morphological changes and chemical composition, this study proposes the physical mechanism of ``coffee ring'' formation and discusses its dependence on environmental humidity. This research provides a theoretical basis for a deeper understanding of the transmission mechanism of viruses through saliva droplets on surfaces and offers experimental and simulation support for related public health studies. These findings can provide important data support and theoretical reference for future infectious disease control measures.