| Droplet evaporation is not only a common physical phenomenon in daily life,but also widely exists in many engineering applications and product design,such as inkjet printing,biomedicine and thermal management of microelectronic devices.It is very important to understand the wetting and evaporation characteristics of fixed droplets.HFE7100 fluorinated liquid is a new type of highly volatile liquid,which has the advantages of low boiling point,no pollution and large evaporation latent heat.It has a good application prospect in aerospace and electronic equipment evaporative cooling,and has become a hot spot in the scientific research field.In this paper,the physical phenomena of droplet wetting and evaporation of HFE7100 are studied,and the evaporation mechanism is revealed,in order to promote the rapid and efficient utilization of HFE7100 in related fields.In this paper,the evaporation process of HFE7100 solid droplets was observed experimentally by controlling the substrate temperature and the substrate thermal conductivity as variables.The morphological characteristics were obtained by photographing the morphological evolution behavior of droplets during the whole evaporation process using the droplet shape analyzer,and the changes of contact angle,contact diameter and evaporation residual volume were recorded,and the variation laws of various parameters were analyzed;The wetting area during evaporation was photographed by digital video microscope,the wetting range was calculated,and the wetting characteristics of droplets were analyzed.The main conclusions of this paper are as follows:（1）The droplets show the same evaporation pattern at different substrate temperatures and substrate thermal conductivity.When the substrate temperature increases and the thermal conductivity of the substrate increases,there is an obvious curve change in the contact angle and contact line at the three-phase line during the evaporation process,and its value decreases with the passage of evaporation time until the evaporation is completed.It is judged that the droplet is always in the evaporation state of mixed mode.（2）When the substrate was heated from 20 ℃ to 40 ℃,the contact angle,contact diameter and wetted area changed significantly;As the substrate temperature increases,the droplet evaporation becomes more intense,especially when the substrate temperature changes from lower than the ambient temperature to higher than the ambient temperature;The evolution law of droplet volume in the instantaneous state directly reflects that the evaporation rate of droplets is accelerated,the evaporation time is reduced,and the mass loss rate and contact angle show nonlinear behavior.When the contact angle is low,the mass loss rate at different substrate temperatures can maintain a constant state.（3）When the substrate temperature is the same,the evaporation characteristics of droplets on different substrate thermal conductivity are quite different.The evaporation contact angle and contact diameter of droplets on low thermal conductivity substrates tend to be consistent with the increase of substrate temperature,while the relevant values of droplets on high thermal conductivity substrates change rapidly.According to the experimental results,it is concluded that the thermal conductivity of the substrate has a certain influence on the transient heat transfer and evaporation process of the droplets. |
