Micro-membrane pump

Micro membrane pumps with thermo-pneumatic actuators for the conveyance of gases or liquids are mounted in housings made from chemically and ftiermally resistant polymers (PSU or PEEK) for an extended lifetime (Figure 4, right side). 

Figure 4. Micro cell container (PMMA) and micro membrane pump housing (PSU).

The field of liquid pumps for process engineering applications is huge and its discussion is certainly not within the scope of this book. However, small pumps in the range of a few watts of power consumption are an issue in many portable applications. Therefore, an example of a pump of the smallest scale is shown below. It is a micro-membrane pump from the KNF Neuberger Company with a flow capacity of 50 cm min at atmospheric pressure. The pump is able to provide a maximum pressure of 2 bar for a power consumption of 0.66 W (Figure 8.1). 

External energy sources for active mixing are, for example, ultrasound [22], acoustic, bubble-induced vibrations [23,24], electrokinetic instabilities [25], periodic variation of flow rate [26-28], electrowetting induced merging of droplets [29], piezoelectric vibrating membranes [30], magneto-hydrodynamic action [31], small impellers [32], integrated micro valves/pumps [33] and many others, which are listed in detail in Section 1.2. 

The channels, which had catalyzed electrodes on the surfaces, were covered with Nafion 112 (thickness 50 pm, equivalent weight 1,100 gmoF, ionic conductivity 0.083 S cm" ) to provide ionic conductivity between the anode and the cathode. The Nafion membrane was pressed with a glass plate to avoid solution leakage (Fig. 3.4a). Voltage-current measurements were performed at room temperature with a mass flow control system of fuel and oxidant as shown in Fig. 3.4b. The fuel and oxidant solutions were supplied to the electrodes with the micro-syringe pumps from the outlet of each channel. The flow rate of both the fuel and oxidant solutions was 80 pL miu". Composition of the fuel solution was 2M methanol solution... 

Figure 8.1 Micro-membrane liquid pump NF-5M from KNF Neuberger (photograph courtesy of KNF Neuberger).

More than 100 micro structured devices are listed on the homepage of the pChemTec consortium [24]. The devices cover physical applications such as flow distribution, mixing, heat transfer, phase transfer, emulsification and suspension, as well as chemical applications such as chemical and biochemical processing. Some separation units such as membrane separation and capillary electrophoresis are also offered. Control devices such as valves, micro pumps for product analysis and mass flow controllers supplement the catalog. 

Millipore Corporation, XX8140000) consisted of a membrane holder (Pellicon), a 4 gallon per minute rotary vane pump (Procon) and the membranes themselves. The filters were either 0.45 micron micro-porous (Durapore) or 100,000 NMWL ultrafiltration membranes. All tubing and connections were 1/2 inch. A manifold flow bypass was attached to the pump so fluid could be introduced into the filtration system without a sudden surge of pressure buildup (Bulletin AB822, Millipore Corporation). In all cases, 5 square feet of membrane were used. 

For gases or volatile liquids a very small quantity of sample is introduced with a micro-syringe to a kind of reservoir linked to the ionization chamber via a very narrow channel. Under the effect of a high vacuum that is maintained in the reservoir, the compound is sucked up and vaporized. This procedure is known as a molecular leak or molecular pumping. For continuous monitoring of gases and volatile compounds in the vapour state or dissolved in a liquid such as water, the sample can be diffused through a porous membrane. 

The electrolysis of sucrose was performed in a filter press cell (micro-flow cell, electro-cell AB) (Figure 21.19). The working electrode was platinum deposited electrochemically on a titanium plate. The counter electrode was a plate of stainless steel. The two compartments of the cell were separated by an ion-exchange membrane (Nation 423). A part of this membrane immersed in a saturated potassium sulfate permitted to connect by capillarity the MSE. The electrolyte in the cell was circulated by an external peristaltic pump (1 cm3 min-1) and passed through a reservoir (100 cm3). 

The principle of a purely osmotically controlled drug delivery was disclosed some 15 years ago [147]. The so-called elementary osmotic pump consists of a core containing the drug (and if necessary an osmotic agent) and a CA semipermeable membrane with a micro-orifice drilled usually by a laser beam. Drug release is activated by the transport of water through the semipermeable... 

Inorganic arsenic oxyanions, frequently present as environmental pollutants, are very toxic for most micro-organisms. Many microbial strains possess genetic determinants that confer resistance. In bacteria, these determinants are often found on plasmids, which has facilitated their smdy to the molecular level. Bacterial plasmids conferring arsenic resistance encode speciflc efflux pumps able to extrude arsenic from the cell cytoplasm, thus lowering the intracellular concentration of the toxic ions. Recently, apparently similar arsenic membrane transport proteins have been found with yeast, plants, and animals (8,9) (see Sec. V, below). 

Reports are also available on CO2 selective membrane reactors for WGS reaction. Zou et al. [40] first time synthesized polymeric C02-selective membrane by incorporating fixed and mobile carriers in cross-linked poly vinyl alcohol. Micro-porous Teflon was used as support. They used Cu0/Zn0/Al203 catalyst for low temperature WGS reaction. They investigated the effect of water content on the CO2 selectivity and CO2/H2 selectivity. As the water concentration in the sweep gas increased, both CO2 permeability and CO2/H2 selectivity increased significantly. Figure 6.18 shows the influence of temperature on CO2 permeability and CO2/H2 selectivity. Both CO2 permeability and CO2/ H2 selectivity decrease with increasing reactimi temperature. After the catalyst activation, the synthesis gas feed containing 1% CO, 17% CO2, 45% H2 and 37% N2 was pumped into the membrane reactor. They are able to achieve almost 100% CO conversion. They also developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. 

For these experiments, in order to protect the cells from environmental shear stress, an 5 p.m thin membrane made of alginate and poly-L-lysine was created around the immobilized micro-carrier [31]. The movement of microcapsules with immobilized chromatophores was observed microscopically in a glass microtube (d = 700 pm 1 = 5 cm) with the magnetic field conduit embedded in the wall. The experimental setup is presented in Figure 32.4. Fluid (L-15 medium) velocities applied were in the range from 1.6 to 6.4mm/s and corresponded to the predicted operational fluid velocities of the biosensor [11]. Fluid flow was provided by microsyringe pump (LabTronix, USA). 

Reservoir with membrane (micro- and macroencapsulation, coated solids, laminates, and large devices) Reservoir without membrane (hollow fibers, porous solids and foams, gels, osmotic pumps)... 

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