| Membrane separation has been widely used in biomedical related areas such as hemodialysis and hemopurification. The most commonly used membrane system is hollow fiber module whose configuration is similar to that of tube-shell heat exchanger. Investigations were mainly focused on the hollow fiber membrane preparation, mass transfer of hollow fiber modules and extending of its application. All the research work in this thesis will be explored around this topic.(1) Firstly, immersion precipitation is one of the most important methods for the production of hollow fiber membranes. In this paper dry-wet spinning technique was used during the preparation of dialysis hollow fiber membranes, three-component solution PAN/DMF/Water was chosen as the basic materials, PEG400 was chosen as the pore forming agent. The macro-morphology such as inner and outer diameter and wall thickness of the hollow fibers were observed by microscopy; the micro-morphology of the membrane surface and cross-section ware observed by SEM. The influence of some important spinning parameters such as spinning pressure, nonsolvency pressure, spinneret aperture and rolling rate were investigated. The appearance of some big bores in the hollow fiber surface was discussed based on phase transition theory. Some suggestions for avoiding the defects were presented and the optimized conditions for membrane formation were obtained.The results show that: the spinneret aperture is the key factor that determines the membrane macro-structure, the bigger the spinneret aperture the bigger the fiber size; the membrane inner ,outer diameter and it's wall thickness increase with the spinning pressure; the membrane inner ,outer diameter increase and the wall thickness decrease with the nonsolvency pressure; with proper spinneret aperture, spinning and nonsolvency pressure, satisfactory fibers were obtained.(2) Secondly, Mass transfer coefficient is an important parameter to evaluate the performance of hollow fiber modules. With the help of Matlab software, the shell-side flow field was simulated numerically under the condition of well developed fluid flow. The theoretical model considers the effects of both the inner wall of the module shell and the random distribution of the hollow fibers on the shell-side mass transfer performance. For different packing density of hollow fibers, the concentration field and the shell-side mass transfer coefficients of dialyzers were obtained with the concentration boundary conditions of constant wall flux and constant wall concentration which are similar to the boundary conditions often used in heat transfer problems. Also the influence of flow rate to the mass transfer coefficient was studied. It was found that, because of the random distribution of hollow fibers channel flow exists in the shell-side flow field, The mass transfer coefficient increases with flow rate. Different packing patterns of hollow fibers result in different mass transfer coefficient values. This effect comes out more remarkable when neglecting the module wall effect. By varying the packing density from 10% to 50%, mass transfer coefficient increases first and then decreases experiencing a maximum value. Comparing to that with no wall effect, we found that, the wall effect promotes the mass transfer in a relatively low packing density but comes to the contrary as the packing density getting higher.(3) Lastly the dialysis membrane separation process is used in the field of cryobiology, especially in the process of removal cryoprotective agents(CPA) from cryopreserved cells.The experimental setup was established successfully to study the factors that affect the osmolality change(residual CPA concentration) in the cell suspension. The experimental results show that: i) during the initial time period, the sudden decrease of the osmolality can be avoided by prepriming the dialysate side with sub-hypertonic CPA solution or hypertonic saline solution. ii) As the washing process goes on, the residual CPA decreases slower and the washing efficiency decreases, this problem can be solved by increasing the blood flow rate and the dialysate flow rate. Through experiments the optimum procedure for removing CPA was found which can decrease both the osmotic shock to the cells and the wahing time.Further more experiments of the removal of glycerol from cryopreserved RBCs were done using the novel hollow fiber module dialysis method and traditional centrifugal method. Using the new method the Freeze-Thaw-Wash(FTW) RBC count recovery(%) is 89.71±2.46 (Mean±SD), hemoglobin recovery(%) is 84.93±4.64, the free hemoglobin concentration (g/L) is 0.66±0.13, and the osmolality of the FTW RBC suspension(the residual glycerol concentration) is 340.33±20.56mOsm .There is no significant difference between the results of centrifugal method. All these results satisfy the requirements of the national quality standards for freeze-thaw-wash RBCs . It takes only 30-40 minutes to wash one unit of frozen RBCs using the new method, which is much less than the 2 hours of the centrifugal method. The results show that compared to the traditional centrifugal method, this method is more efficient and safe.An automated washing system was designed based on the above progress. It was demonstrated that the new device has great potential to be used in hospitals, blood centers and cell banks et.al.
|
PDF Full Text Request