Research On The Theory Of Heat Mass Transfer In Steam Sterilizing Treatment Process For Medical Waste

Medical waste is one of the most important wastes which can do great harm to the environment. Many countries had the rigorous ordain to the classified collection, deposition, transportation and management of medical wastes, and plunged a great deal of manpower, material resources into the technical research.Recently, medical waste steam treatment technique drawn more and more attentions for its low investment and low treatment cost, and how to decide the sterilizing time was the key step of the process. The sterilizing time includes thermal death time and heat penetrate time, the thermal death time was determined by the characteristics of the microbe, the heat penetrate time was related to the heat and mass transfer. The research on the heat and mass transfer of the steam sterilization to determine the heat penetrate time, was of important practice worth.The medical wastes were classified into two kind of materials, dense and porous media. The dense media sterilization belonged to the external sterilization, in which only heat transfer was considered. The good sterilization effect can be obtained easily when the surface reached the sterilization temperature. The heat transfer model for dense media was used to calculate the penetrate time. The results show that the heat penetrate time was very short for this kind of media (The heat penetrate time of the plastic of 1mm thick was 0.054s, at 120℃). At the same time, the affect of the air was analyzed and it was found that the more air remained in the system, the longer of the heat penetrate time.In order to obtain good sterilization effect for porous media, not only the surface but also the inside must be remained in sterilization temperature for some time. The sterilization process for this kind of materials was complex in which the heat and mass transfer were included. The condensation of the steam in the pores of media made the process more complicated and difficult to analyze. The heat and mass transfer in porous media in the process of steam sterilization were analyzed in our work and the moisture diffusion and thermal mass diffusion coefficient's relationship with the content of the moisture and temperature was obtained. The results show that the heat penetrate time of the B-D paper of 10 mm thick was about 150 s at 120℃, which was much longer than the dense media's.