Membrane module, parameters

Measurable Process Parameters. The RO process is relatively simple ia design. It consists of a feed water source, feed pretreatment, high pressure pump, RO membrane modules, and ia some cases, post-treatment steps. A schematic of the RO process is shown ia Figure 2a. 

Owiag to the variety of situations encountered ia RO appHcatioas, there is ao single analytical technique to predict membrane module performance. The module and the feed stream, along with the operatiag parameters, determine system performance. To predict module performance, a model that... 

The choice of the most suitable membrane module type for a particular membrane separation must balance several factors. The principal module design parameters that enter into the decision are summarised in Table 16.3. 

These equations describe an unheated transistor and were verified for a device with no backside etching (no membrane). The modelling parameters were provided by the manufacturer, whereas the value of the threshold voltage was taken from wafer map data. The channel length modulation parameter. A, had to be extracted from measurement data. The discrepancy between simulated and measured source-drain saturation current, fsd,sat> for a transistor embedded in the bulk silicon was less than 1%, which confirmed the vaHdity of the model assumptions. 

The second approach to concentration polarization, and the one used in this chapter, is to model the phenomenon by assuming that a thin layer of unmixed fluid, thickness S, exists between the membrane surface and the well-mixed bulk solution. The concentration gradients that control concentration polarization form in this layer. This boundary layer film model oversimplifies the fluid hydrodynamics occurring in membrane modules and still contains one adjustable parameter,... 

Table 14.2 Membrane module characteristics and physical parameters applied for calculation of the mass-transfer rates into and out of a sheet membrane [12-14, 33],...

Stage cut Parameter defined as the fractional amount of the total feed entering a membrane module that passes through the membrane as permeate. 

Choice and arrangement of the membrane module in a system is based on economic considerations with the correct engineering parameters being employed to achieve this. Some aspects to be considered are... 

The choice of module configuration as well as the arrangement of the modules in a system are based on economic considerations with correct engineering parameters being employed to achieve this economy, which include the type of separation problem, ease of cleaning, ease of maintenance, ease of operation, compactness of the system, scale, and the possibility of membrane replacement (13). Next, we will discuss these typical membrane modules. 

The permeate flux (7) is an important parameter in the design and economic feasibility analysis of the UF separation process. Hydrodynamics of membrane modules have an... 

To avoid major fouling and clogging problems, the nature of the feed to be treated has to be considered when hollow fiber modules are used. In the case of lumen to shell filtration, the inside diameter of the fiber is supposed to be at least 10 times the diameter of the largest species present in the feed. However, when the permeate flows from shell fo lumen, concentration and viscosity of the feed and the density of hollow fiber membrane per module may be critical parameters in the design process. Specific aeration or mixing requirements are necessary to keep the feed particles in suspension, and to avoid the clogging of the membrane module. 

In a general way, most of ceramic membrane modules operate in a cross-flow filtration mode [37] as shown in Figure 9.18. However, as discussed hereafter, a dead-end filtration mode may be used in some specific applications. Membrane modules constitute basic units from which all sorts of filtration plants can be designed not only for current liquid applications but also for gas and vapor separation, membrane reactors, and contactors, which represent the future applications of ceramic membranes. In liquid filtration, hydrodynamics in each module can be described as one incoming flow on the feed side Qp which results in two outgoing flows related to retentate Q, and permeate gp sides, respectively. The permeation flux J per membrane surface unit is directly calculated from Q. Two important parameters account for hydrodynamic working conditions of a module, one is the flow velocity, v, in the module calculated as the ratio of the incoming flow <2/ (mVs) by the hydraulic section of the module Q (m ), the other is the transmembrane pressure, P. ... 

A recent development of the secondary flow-enhanced membrane processes is the helical membrane module, which is characterized by a DNA helical-like spacer enveloped by polyester filter cloth with a pore size around 22 pm [31-33]. Figure 10.12 shows the schematics of the helical membrane spacers with different twisted helical angles. The main parameters of the helical membrane include the angles of twist of the spacer or membrane and the ratio of the membrane width to the length. 

Membrane module performance can to some degree be predicted as a function of operating parameters and feedwater characteristics. Calculation methods [40,41] exist for various membrane operating conditions, but computer modeling programs available from the membrane manufacturers have largely superseded these. These programs predict the performance of a membrane plant based on feedwater analysis and performance requirements. 

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