Liquid moving/ pumping

Flow of the liquid past the electrode is found in electrochemical cells where a liquid electrolyte is agitated with a stirrer or by pumping. The character of liquid flow near a solid wall depends on the flow velocity v, on the characteristic length L of the solid, and on the kinematic viscosity (which is the ratio of the usual rheological viscosity q and the liquid s density p). A convenient criterion is the dimensionless parameter Re = vLN, called the Reynolds number. The flow is laminar when this number is smaller than some critical value (which is about 10 for rough surfaces and about 10 for smooth surfaces) in this case the liquid moves in the form of layers parallel to the surface. At high Reynolds numbers (high flow velocities) the motion becomes turbulent and eddies develop at random in the flow. We shall only be concerned with laminar flow of the liquid. 

Figure 8.5—Effect of the nature of the capillary inner wall on migration velocities If the inner wall has not been treated (glass or silica naturally have a negative polyanionic layer) the liquid is pumped from the anodic towards the cathodic reservoir. This is called the electro-osmotic flow. Thus an anion can move towards the cathode. Between pH 7 and 8. vE0S can increase by 35%. However, if the wall is coated with a nonpolar film (e.g. octadecyl) this flow does not exist.

Pumping Head—The energy required to raise water to the distribution elevation and overcome friction losses through pipe, valves, fittings and nozzles. It is expressed in feet of liquid the pump must move and is equal to the total friction loss, static head and pressure drop through the distribution system. 

Electrostatic charges are also generated when liquids move in contact with other materials, liquid or solid, eg, during pumping of gasoline. Serious industrial hazards caused by static in chemical and related fields have been described (28), and a study of accidents in the chemical industry revealed that 115 out of 1600 accidents, or 7%, were ascribed to static electricity (29) (see Plant safety). 

Moving-bed ion exchange. Ion-exchange resin particles are small spherical beads. These can be readily moved out of an ion-exchange column with up-flowing liquid and pumped with the liquid to another tank or column. Transport of resin is used in two types of uranium extraction processes, (1) the moving-bed type and (2) the continuous RIP type. 

In most colloid mills the feed liquid is pumped between closely spaced surfaces one of which is moving relative to the other at speeds of 50 m/s or more. In the mill shown schematically in Fig, 29.13 the liquid passes through the narrow spaces between the disk-shaped rotor and the casing. The clearances are adjustable down to 25 jum. Often cooling is required to remove the heat generated. The... 

Liquid-flow-modulated heat pipes have two separate wicking structures, one to transport liquid from the evaporator to the condenser and one that serves as a liquid trap. As the temperature gradient is reversed, the liquid moves into the trap and starves the evaporator of fluid. In addition to these liquid-vapor control schemes, the quantity and direction of heat transfer can also be controlled through internal or external pumps, or through actual physical contact with the heat sink. 

Pumps are used to move liquids. The pump inereases the pressure of the liquid. Water at 120°C and 3 bar is fed into a pump that has only 10% efficiency. The flowrate of the water is 100 kgmole/h and its outlet pressure from the pump is 84 bar. Using Peng-Robinson equation of state as a fluid package, determine the outlet temperature of the water. 

Fluids are often pumped hydrodynamically to exert the flow. Various pumps are used, including syringe pumps, peristaltic pumps, piezoelectric pumps, and gas-pressure-driven hydrodynamic pumps. In the case of hydrodynamic pumps, an inert gas is pressurized in the headspace of the vial containing the sample or carrier fluid. The force exerted by the gas on the liquid phase sustains flow of the liquid in the channel. When a liquid moves along the circular cross-section channel, the Poiseuille equation can be used to relate the... 

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