| Since nitric oxide (NO) was identified as an important signal factor in organism in 1987, NO has got great attentions as a new technic to treat acute respiratory distress syndrome, high blood pressure, or other illnesses related to lung. Currently, the supply of NO for traditional medical applications has a potential risk caused by the formation of toxic nitric dioxide (NO2) due to the possible leakage of NO in tank. Therefore, it is necessary to provide an on-site and effective supply system of inhaled NO (INO) for patients and doctors. This paper investigates the characteristics of NO production induced by pulsed arc discharge in dry air at 1atm, and the performance of treatment equipment for respiratory distress. Some achievements are as follows: (1) The production of medical INO due to thermal plasma induced by arc discharge has been approved through analyzing the O3 formation mechanism due to silent discharge, the thermal balance kinetics, and the discharge types. Also a model of chemical reaction kinetics of NO production using pulsed arc discharges in dry air was developed with an approximate equation for theoretical calculation of concentration during the process. (2) The discharge conditions, under which NO was efficiently generated with a low NO2 concentration and NO2/(NO+NO2) ratio, were found through investigating the effects of the pulsed repetition rate, the gap between electrodes, and the materials of electrodes on the arc discharge by experiments. The discharge conditions were better than those currently used in the similar studies domestically and overseas as the NO2/(NO+NO2) ratio in our experiments was less than 13%, while that in the overseas studies was not less than 25%. The results showed that: the minimum ratio of NO2/(NO+NO2) was reached with a 3.5mm gap between the electrodes; the concentration of NO with needle-plate electrodes was higher than that with needle-needle electrodes, while the result was just reversed for the ratio of NO2/(NO+NO2). So electrodes made of different materials were better than those made of same materials, and the rod-plate electrodes were better than the rod-rod electrodes. Also, Mo as the plate electrode was better than others, and stainless steel was alternative for anode electrode material. (3) The air flow rate has been tested as an important factor affecting the stability of the concentration of NO, based on the experimental study on the effects of the direction, the air flow rate and the residence time on the concentration of NO, NO2 and the ratio of NO2/(NO+NO2). Under different directions of air flow, the results with air flow rate more than 2.5mL/m3 were reversed to those with air flow rate less than 2.5mL/m3. Therefore, stable concentration of NO and a lower ratio of NO2/(NO+NO2) could be obtained by adjusting the direction and magnitude of the air flow rate. (4) A small quantity of needless productions in pulsed arc discharge was deleted completely using catalytic reduction reactions. The catalysts for converting NO2 into NO and the operation conditions were obtained through experiments and theoretical calculation. It indicated that at certain temperature, small quantity of NO2, N2O and O3 generated by discharges could be effectively removed with Mo and W. (5) A sample INO system for clinical applications was designed based on the experimental and theoretical studies. The concentration of INO could vary from 0 to 200 mL/m3, and the ratio of NO2/NO less than 5% (NO2/NOx<4.7%) was reached, and the environmental noise was 45.7dB(A), which met the I level of the Standard of Environmental Noise of Urban Area, at the site with 1m departing from the machine. So the machine satisfied with the clinical applications request. Consequently, this system can be as a source of NO for medical treatment of respiratory distress (including severe acute respiratory distress syndrome, SARS).
|
PDF Full Text Request