Liquid head driving force

The pressure at point A in Fig. 10.4 was 13 psig. This means that the pressure drop in the vapor line from the stripper, back to the fractionator, was 3 psig. In order for the unstripped jet fuel, to flow out of the lower-pressure fractionator, and into the higher-pressure stripper, it had to overcome this 3-psig pressure difference. The 16-ft elevation difference between the draw-off nozzle on the fractionator and the stripper inlet provided the necessary liquid head driving force. 

The liquid head driving force of 16 ft, or 4 psi, shown in Fig. 10.4, is actually not all available to overcome the higher stripper pressure. The frictional loss of the piping used to feed the stripper should be subtracted from the liquid head driving force. In the jet fuel example presented above, this frictional loss was neglected. 

Raising the steam flow to the stripper increased the pressure drop in the overhead vapor line from 3 to 5 psi. The pressure at point A in Fig. 10.4 then increased from 13 to 15 psig. The 4-psi pressure head driving force was not sufficient to overcome the 5-psi pressure drop of the stripper s overhead vapor line. The unstripped jet fuel could no longer flow out of the fractionator and into the stripper, and the liquid level in the stripper was lost. 

Refrigeration, like dilution, reduces the vapor pressure of the material being stored, reducing the driving force (pressure differential) for a leak to the outside environment. If possible, the hazardous material should be cooled to or below its atmospheric pressure boiling point. At this temperature, the rate of flow of a liquid leak will depend only on liquid head or pressure, with no contribution from vapor pressure. The flow through any hole in the vapor space will be small and will be limited to breathing and diffusion. 

The overall driving force for mass transfer is AT = Pg—Pi, where Pi is the concentration of oxygen in the liquid phase expressed as an equivalent partial pressure. For the experimental conditions, T/ 0 due to the fast, liquid-phase reaction. The oxygen pressure on the gas side varies due to the liquid head. Assume that the pressure at the top of the tank was 1 atm. Then Tg = 0.975 atm since the vapor pressure of water at 20°C should be subtracted. At the bottom of the tank, 1.0635 atm. The logarithmic mean is appropriate AT =1.018 atm. Thus, the transfer rate was... 

A special condition called slack flow can occur when the gravitational driving force exceeds the full pipe friction loss, such as when a liquid is being pumped up and down over hilly terrain. Consider the situation shown in Fig. 7-5, in which the pump upstream provides the driving force to move the liquid up the hill at a flow rate of Q. Since gravity works against the flow on the uphill side and aids the flow on the downhill side, the job of the pump is to get the fluid to the top of the hill. The minimum pressure is at point 2 at the top of the hill, and the flow rate (Q) is determined by the balance between the pump head (Hp = — w/g) and the frictional and gravitational resistance to flow on the uphill side (i.e., the Bernoulli equation applied from point 1 to point 2) ... 

Capillary viscometers have been widely used in determining the viscosity of Newtonian fluids. In these viscometers, the driving force is usually the hydrostatic head of the test liquid itself, although, application of external pressure is also used in order to increase the range of measurement and allow non-Newtonian behavior to be studied. In operation, the efflux time of a fixed volume of test liquid is measured, from which the kinematic viscosity is calculated. 

Pressure-Difference Driving Force. The effect of a l- xm polycarbonate microporous filter on basal and augmented delivery in the controlled-release micropump due to a pressure difference is shown in Figure 3. As the pressure difference was lowered (i.e., as the liquid level dropped in the falling head permeameter) the basal flow rate was reduced to less than 0.2 mL/day (pressure difference, approximately 0.8 cm H20). At this basal rate, operation with a 100-U/mL reservoir becomes practical. More importantly, the degree of augmentation was increased to more than 10 X from the... 

Reboiler circuits may set tower elevations. A thermo-syphon reboiler requires enough liquid static head to provide a driving force so that the reboiler will work properly. This head determines the circulation ratio and the amount of vapor returned to the tower, thereby setting the entire tower gradient. Reboiler circuits must be considered with pump NPSH considerations as they set the tower elevation. 

Many towers have a bottom draw-off pump. NPSH requirements usually elevate the tower above the reboiler s minimum height, thereby increasing the static heads in the reboiler s vertical legs and the driving force in the circuit. With increased tower height it is worthwhile to check the reboiler circuit to see if liquid and return line sizes can be reduced. 

The H2 dimension can be greater than H. The minimum liquid level static head above the bottom tangent line can also be taken into account as an additional driving force. Because of the predictable and very simple piping, a safety factor of much less than two can be owed. (In the above equations 288 = 144 (safety factor). 

When the reboiler sump level is very low, there is little driving head to force liquid into the reboiler, and circulation rate is low. The little liquid entering the reboiler is essentially totally vaporized. Since there is little liquid head to suppress the boiling point, the liquid preheat zone is small and nucleate boiling begins almost immediately. A mist flow zone is formed above the nucleate boiling zone, where the... 

For some gas-liquid reactions, it is advantageous to use a very tall reactor rather than one that is shorter but larger in diameter. With a tall bubble column, the hydrostatic head increases the driving force for gas absorption at the bottom, and this effect plus the increase in gas residence time permits a greater fraction of the reactant gas to be absorbed. A tall reactor also requires less space for installation. Other factors to consider are the increased work of compression, though the work does not go up in proportion to the depth, and the effect of hydrostatic head on the volumetric gas... 

It is commonly accepted that the basic driving force underlying the FFC process is a differential aeration cell. Filaments are normally quite thin and shallow but can reach a length of several hundred millimeters. Two different regions of the progressing filaments can be observed the liquid filled active head and a tail of corrosion products. In their active head, filaments carry an acidic solution of the metal cations and the initiating anions [170]. 

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