Abstract
Many studies have focused on the effect of surface wettability on condensation at the nanoscale, while few studies investigated the condensation process of water vapor below 450K. However, water vapor condensation below 450K is common and important in industrial fields. In this paper, molecular dynamics method is used to study the effect of surface wettability on the performance of water vapor condensation below 450K on a copper surface, and a comparison with the performance of water vapor condensation at 450K was performed. The results show that the heat transfer performance of vapor is not the same when condensing on a hydrophilic surface and on a hydrophobic surface. It’s found that lower temperature vapor requires more time in starting to condense on a hydrophobic surface, whose heat transfer efficiency first increases gradually and finally becomes constant. For the first time the process of vapor condensation on a hydrophobic surface was divided into three stages based on the changes in heat transfer efficiency, and the heat transfer performance of each stage was analyzed. The results show that a stronger surface wettability and higher vapor temperature improve the heat transfer performance during the condensation process. Moreover, the lower the vapor temperature is, the greater the impact of the wettability is on the heat transfer efficiency, and the vapor less easily condenses on a hydrophobic surface.
Highlights
Condensation is common in nature, and it is one of the most important heat transfer processes in power generation, desalination, heating, refrigeration, air conditioning, and other industrial fields
The results showed that lower vapor temperature had more difficulty in starting to condense on a hydrophobic surface
The results show that the higher the vapor temperature is, the higher the condensation rate and the heat transfer rate are, and at a certain vapor temperature, the condensation rate and the heat transfer rate for filmwise condensation are greater than those for dropwise condensation
Summary
Condensation is common in nature, and it is one of the most important heat transfer processes in power generation, desalination, heating, refrigeration, air conditioning, and other industrial fields. Condensation has been studied in depth as a branch of heat transfer research.. The modes of vapor condensation can be divided into dropwise condensation and filmwise condensation. The heat transfer efficiency of dropwise condensation is several orders of magnitude higher than that of filmwise condensation; it is important to develop ways to perform dropwise condensation. Its mechanism need to be studied thoroughly. Dropwise condensation is a multi-scale process that includes four stages: droplet nucleation, growth, coalescence, and departure.. The droplet formation process and mechanism at the initial nanoscale cannot be studied through traditional experimental means and simulation tools at the continuum level Dropwise condensation is a multi-scale process that includes four stages: droplet nucleation, growth, coalescence, and departure. The sizes of observed droplets range from micrometers to millimeters to centimeters, and numerous studies have investigated the size distribution and droplet development process. the droplet formation process and mechanism at the initial nanoscale cannot be studied through traditional experimental means and simulation tools at the continuum level
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