No abstract

Most of the current air compressors are driven by a slider-crank mechanism consisted of the crank, connecting rod, and piston. Complexity of this mechanism, however, restricts miniaturization of air compressors. In this study, a design based on a new mechanism, a hybrid of cross-slider and scotch-yoke mechanism, is adopted to develop an oil-free, light-weighted air compressor for portable medical devices. By eliminating the connecting rod, the mechanism has several advantages in addition to the obvious weight reduction due to the simpler mechanism such as the longer seal life of the seal between the piston and cylinder (so called Teflon cup) and reduced shaking forces. Cylinder pressure time history is obtained based on the ideal gas behavior and the isentropic process. Shaking forces and motor torque are calculated from the dynamics equation of the air compressor. The flow capacity curve of the air compressor is obtained by considering the effect of the clearance volume. An actual prototype was fabricated and tested to demonstrate the feasibility of proposed concepts.

Recently demand oxygen delivery (DOD) system has been preferred to continuous flow oxygen (CFO) method for long term oxygen therapy in patients with chronic obstructive pulmonary disease, since DOD system supplies oxygen during only inhalation and saves oxygen consumption. However, the oxygen saving ratio have not properly compared without considering fraction of inspired oxygen (FIO 2 ), though FIO 2 determines the efficacy of treatment. The purpose of this study was 1) to investigate the equivalence between the CFO method and a DOD system in terms of FIO 2 with considering dead space under various breathing parameters, 2) to propose and calculate the new effective oxygen saving ratio of the DOD method, 3) to compare FIO 2 obtained from calculation with that from experiment. The mathematical and experimental models of human respiratory system were developed. FIO 2 was calculated depending upon various breathing parameters and the new effective oxygen saving ratio was calculated to accurately compare oxygen saving consumption between the DOD and CFO method. Results of this study have shown that as supplied volume of oxygen increased, FIO 2 linearly increased. As beat per minute or tidal volume increased, FIO 2 decreased. The obtained FIO 2 between mathematical model and experiment showed errors less than 5% in CFO method and less than 11% in DOD method. Effective conserving oxygen ratios of the DOD system changed between 3.4 and 3.8, but had higher values when the volume of supplied oxygen was larger. In conclusion, CFO method had different equivalent values of FIO 2 depending on breathing parameters. Therefore it is appropriate to take into account of FIO 2 when considering performance of oxygen saving devices. The effective oxygen saving ratio proposed in this study may provide the new valuable index of oxygen saving of the DOD method while maintaining the same treatment effect compared with CFO method. In addition, the mathematical model developed in this study seems to predict FIO 2 similarly as obtained using experiment.