In this work, a CFD based design approach to improve fluidic stability of a cataract surgery system is presented. Cataract surgery is a procedure to remove hardened human lens (cataract) from the eye. Approximately two million cases of cataract surgery are done every year in the United States. The procedure starts with the incision of an aspiration port into the anterior chamber of the eye. The OD of the aspiration port is 0.9mm and is connected with vacuum pump and ultrasonic vibrator. After the incision, cataract is fragmented into small pieces using ultrasonic power. Finally, fragmented cataracts are extracted from the eye chamber using a vacuum pump. Current cataract surgery system has an issue of pressure surge followed by collapsing of the anterior chamber of the eye. In the extraction phase, often a big piece of cataract occludes the tip of the aspiration port to build up the pressure difference between the chamber and the pump. When the pressure difference reaches certain point the cataracts are abruptly pulled into the aspiration port. As a result of sudden displacement of cataract and the fluid from the chamber, pressure surges which causes eye chamber collapse. The collapsing of the chamber is not only dangerous to the organs in the anterior chamber such as cornea, but also it lifts the wall of posterior chamber and may damage the retina. Several different design concepts using mechanical and electrical feedback systems have been developed by Micro-Surgery Advanced Design Lab to improve fluidic stability of the system without significant influence upon the cycle time of the procedure. However, considering the size and precision required of the system and the complexity of the design parameters involved, feasibility test and design iterations using working prototypes may limit the possibility of finding an optimal solution to the design problem. In this work, a feasibility test method using computational flow analysis and bench-top simulation is proposed. In developing a design, it is suggested that the feasibility verification for the design concepts be divided into three different steps: CFD analysis, bench-top simulation and working prototype test. Each process filters the concepts before the concept is transferred to the next step and the results of each step are compared to improve the reliability. In CFD analysis, fluidic circuit is modeled to simulate the mechanisms of pressure surge and chamber collapse using CFDRC. Also, suggested design concepts are incorporated into the model to check the feasibility. In the interpretation of the results, the focus is on the estimation of time scale to see the validity of feedback system. Bench-top is an enlarged model of real eye and cataract surgery system. Dimensional analysis is used to design and interpret the result of the bench-top simulation. It has less flexibility in design changes than CFD analysis but easier to build and change than working prototypes because of the size. CFD analysis and bench-top simulation not only determine the initial feasibility of the design concept, but also it narrows down the design solution space to reduce the number of design iterations and save the time and cost for finding an optimal solution to the design problem.
DESIGN AND CFD ANALYSIS OF LIQUID RING VACUUM PUMP