Membrane separation is carried out in a device where thin porous membranes are packaged to give a designed performance. The diffusion and microconvection(ultrafiltration) are main mechanisms for this type of separation devices. Unlike other separation schemes this method does not require phase change such as in distillation or evaporation. Hence the separation can usually be carried out at low temperatures and consquently is energy-saving as long as separation factor through the membrane is large enough. Three types of membrane materials, namely flat module, cartridge-type module and hollow fiber devices. Because of the conveniences of handling and its compact volume hollow fiber type modules are most favored. This type of hollow fiber modules finds many applications such as in artificial kidney, ultrafiltration devices and enzyme reactor. In the future more separation processes will utilize this type devices. Despite its wide applications understanding on the performance of hollow fiber reactor module is relatively poor. In other words, up to now only empirical approaches have been taken to improve the design of this device. There are many factors which can affect the performance, namely bundle diameter, fiber diameter, manifold design for inlet and outlet and flow rates among fibers. Also the distribution of dialysates among fibers is one of the parameters which can not be overlooked. In this thesis we have chosen to study the flow distribution among fibers in the inlet manifold, which can be utilized for better design of manifold.
The flow in the forehead of the hollow fiber reactor has mixed characteristics of the impinging jet and the manifold. It is difficult to analyze the flow characteristics only with experimental results. It is nearly impossible to obtain analytical solutions of the governing equations for the flow distribution in the hollow fiber reactor. In this study, we used computational analysis with appropriate boundary conditions. The computational results obtained in this study were confirmed the experiments. A new computational algorithm was developed. The flow distributions in the hollow fiber reactor with only one head, the types of which are cone(inclined head) and cylinderical (right angled head), were studied. The appropriateness of the Poisson equation for the calculation of the pressure was investigated. The effect of the backhead on the flow distribution in the fiber bundle was investigated. The flow distributions in the fiber bundle joined with double right-angled heads became more unified than joined with only one right-an angled head. The velocities at the edge region of the fiber bundle joined with two inclined heads became more slower than one inclined head. To investigate the appropriateness of computational algorithm experiments were carried out with the bundle made by the centrifugal force. The flow rate through one fiber was measured for the bundle joined with only one head. For the bundle joined with two heads, the continuous photographing of the appearance of dye on the manifold surface was taken.
The experimental results were well consistent with those of computation. If the height of the right-angled head was very low (small R4), the assumption that the surface of the bundle was continuous porous wall was not suitable for the computation. For the basic study on the efficiency of the hollow fiber reactor with nonuniform velocity distribution in the fiber bundle, the errors in measuring the local mass transfer rate using limiting current method was studied by computational analysis. The errors became larger as the discrepancy between the local electrodes. The efficiencies of a Graetz type mass transfer for the hollow fiber reactor with double right-angled heads were larger than those with double inclined heads.
