Effects of Air Remnant on Temperature and Pressure in Medical Waste Sterilizer

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi:10.408/ 013 Trans Tech Publications, Switzerland Effects of Air Remnant on Temperature and Pressure in Medical Waste Sterilizer Dengchao Jin 1, a, Zhenbo Bao, b,hongjun Teng 3, c and Yang Li 4, d 1 Department of Mechanic and Electronic Engineering, Tianjin Agricultural University, Tianjin, China, Department of Mechanic and Electronic Engineering, Tianjin Agricultural University, Tianjin, China, Clinic, Tianjin Agricultural University, Tianjin, China, Department of Mechanic and Electronic Engineering, Tianjin Agricultural University, Tianjin, China, a dengchao.jin@gmail.com, b baozhenbo@sohu.com, c hongjun-teng@163.com, d liyang.tjac@gmail.com Keywords: Medical waste, Steam treatment,sterilizer, Air remnant, Antoine equation Abstract. The effects of air remnant on temperature and pressure in medical waste sterilizer were tested using the modern medical waste autoclave. The relations between air remnant, pressure and temperature in sterilizing chamber were also theoretically developed. Both results of theoretical calculation and test indicate that the air remnant in chamber has influence on both temperature and pressure in sterilizer, more air remnant will cause lower temperature at the same pressure in sterilizer chamber. The relationship between temperature and pressure in sterilizer was not Antoine style but a superimposed one, experimental results meet well with the theoretical calculation. Introduction Medical waste is hazardous because of its infectious nature, more and more attentions have been paid on how to manage and dispose it [1]. Steam treatment technology is one kind of non-incineration style. The principle of steam autoclave is moisture-heat sterilizing, the heat of steam can cause protein in the microbes to denaturalize, solidify and carbonize, which will eliminate the infection of pathogenic bacteria[]. How quickly the steam heat can transport and penetrate through medical waste and how well it can be distributed in sterilizing chamber becomes critical in this process. The air remnant in the chamber is an important factor affecting the heat transfer, removing the air by vacuum is an effective method to improve the heat transfer and penetrating performance [3]. The Antony style relations between air remnant, pressure and temperature were formulated by Tang xinjun[4]. In this study, the effects of air remnant under different pressure on temperature was experimentally verified, another style formulation on relations between air remnant, pressure and temperature in sterilizing chamber were also theoretically developed. Experimental method The experiment was conducted in medical waste steam sterilizer (Fig.1). Its schematic diagram is shown as Fig.. By setting different vacuum level or a different vacuum number (the vacuum number refers to alternately conducted number of vacuum and steam injection), different air residual amount in chamber was obtained. Under different residual air,the chamber temperature was measured and recorded.the experiment process was: for the first time, steam was directly injected into chamber without vacuum operation, until the chamber pressure reached the setting pressure value, temperature within the chamber was measured and recorded. Secondly, one pumping vacuum in different vacuum levels wers operated.after each vacuum, steam were injected into chamber untill chamber pressure All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-1/0/16,09:01:53)

2 1 Progress in Environmental Science and Engineering reached same as first one, studied the chamber temperature under different air remnant. Finally, vacuum operation was setted three times, each vacuum was 0.08Mpa, the chamber temperature was also recorded when it reached the same as setting pressure.there is four temperature measurement points. In test, the initial temperature of chamber each time was same before vacuum operation. To do this, a fan ventilation was used before experiment, to keep the chamber temperature 40 when each experiment was began Fig. 1 Medical waste sterilizer 1 sterilizer chamber filter 3 vacuum pump 4 temperature indicator 5 recorder 6 wire 7 thermocouple 8 steam valve Fig. Schematic diagram of experimental system Experimental results and analysis Experimental results. Under different vacuum level (and different vacuum times), when setting chamber pressure was 0.MPa, the chamber temperature after steam injected into the chamber are showed as table1. From the experimental results, it can be found that under the same chamber pressure, the greater of vacuum, the higher of chamber temperature. Tab. 1 Chamber temperature in different vacuum Vacuum once vacuum three times Degree of vacuum(mpa) Air residual rate (%) Temperature measurement points Temperature measurement points Temperature measurement points Temperature measurement points Average temperature (C) Experimental analysis. The mix gas within chamber can be considered air before the vacuum. According to Dolton's Law[5], P=P a + P g P a Partial pressure of air in the gas mixture, P g Partial pressure of steam in the gas mixture. Within the temperature and pressure of this experiment condition, the air in the gas mixture can be regarded as ideal gas, its state changes are shown in Figure 3. (1)

3 Advanced Materials Research Vols P 1,T 1,V,n initial state vacuum constant temperature P 1 ',T 1 ', V, n Fig. 3 State change of air in chamber Where, P 1 the atmospheric pressure, T 1 initial temperature, V 1 volume after spraying the steam into the sterilizer chamber, P the mixture gas pressure, T the mixture gas temperature. Due to poor heat transfer of air, the time required to reach temperature equilibrium should be very long, meanwhile, vacuum operation is very quickly, the air temperature inside the chamber should not drop much, but also not rise much. It could be considered as isothermal process, that is, the temperature of the gas in the chamber is kept constant before and after pumping vacuum. If the moles number of air inside the chamber is n before vacuum, the mole number of residual air within chamber is n' after the vacuum. By the ideal gas equation of state, it can be led: P 1 V=nRT 1 () P 1 'V=n'RT 1 (3) Where, V the chamber volume (m 3 ), P 1 the chamber pressure(mpa) before the vacuum (atmospheric MPa), P 1 ' the chamber pressure after the vacuum(mpa), T 1 the chamber temperature before and after the vacuum (K). From the above two equations, the next relationship can be obtained n' P ' = P1 (4) n After vacuum, steam came into chamber, but the moles number of residual air in chamber didn't change, as for as the temperature rised, the air partial pressure corresponding increased, therefore: P ' P = (5) T1 T Where, T the chamber temperature after steam spraying into chamber (K); P the partial pressure of air when the chamber temperature was T (MPa). From Formula 4 and 5, it can be found: / n PT 1 P = (6) n T1 We defined n'/n = P 1 '/P 1 as air residual rate here. If no air emissions, air residual rate n'/n=1. If the air are all drained out, air residual rate n'/n=0. The chamber setting pressure was 0.MPa. In the range of experimental temperature and pressure, the relation between the steam partial pressure P g (MPa) and T (K) can be expressed by Antoine equation: B lnpg = A (7) C+ T According to the data of references [6], A=9.3876, B=386.36, C=-45.47, when the chamber temperature was 40 before vacuum, T 1 =313.15K, P 1 =0.1013MPa. Combining with formula 4, 6 and 7, the relation of air residual rate, pressure and temperature in chamber was: n' P = T + exp( ) (8) n T inject steam isothermal process P,T,V, n' final state

4 14 Progress in Environmental Science and Engineering Fig. 4 Relation between temperature and air remnant in 0.3MPa Fig. 5 Relation between temperature and air remnant in 0.5Mpa Fig. 6 Relation between temperature and air remnant in 0.MPa Fig. 7 Relation between temperature and air remnant in 0.15MPa The comparing of experimental results and theoretical calculations results The comparing of experimental results and theoretical calculations results were shown in Fig.4 to Fig.7, it could be concluded that calculated results and experimental results met well. Conclusions From the calculated and experimental results, the conclusion can be drowned that: under a certain pressure, the higher the vacuum, the less residual air led to the higher temperature of chamber. The presence of air affected the nature of the mixture gas, causing the temperature of the mixture gas lower than that of pure steam. Acknowledgements This work was financially supported by Ministry of Science and Technology of China Project (10C ) and Tianjin Municipal Science and Technology Commission Project (10ZXCXSH03900).

5 Advanced Materials Research Vols References [1] Ruoyan Gai, Lingzhong Xu, Huijuan Li. Waste Management, Vol. 30(010): p [] Diaz L.F., Savage G.M., Eggerth L.L.,. Waste Management, Vol. 5(005): p [3] Stolze R., Kuhling J.,. Waste Management & Research, Vol. 7(009): p [4] Xinyun Tang, Ming Zhang, Haiquan Zhao. Acta Microbiologica Sinica, Vol. 30(003): p (In Chinese). [5] Geankoplis C J.Transport Processes and Unit Operation nd Ed, Allyn and Bacon,Inc.,1983. [6] Xinzhi Cheng. Chemical Engineering Thermodynamics. Beijing:Chemical Industry Press,011. (In Chinese).

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