Vapor flow, resistance

If there is any contact or bond resistance present between the fin and tube or plate on the hot or cold fluid side, it is included as an added thermal resistance on the right side of Eq. 17.5 or 17.6. For a heat pipe heat exchanger, additional thermal resistances associated with the heat pipe should be included on the right side of Eq. 17.5 or 17.6 these resistances are evaporator resistance at the evaporator section of the heat pipe, viscous vapor flow resistance inside heat pipe (very small), internal wick resistance at the condenser section of the heat pipe, and condensation resistance at the condenser section. 

D. Rectification in vertical wetted wall column with turbulent vapor flow, Johnstone and Pigford correlation =0.0.328(Wi) Wi P>vP 3000 < NL < 40,000, 0.5 < Ns. < 3 N=, v,.gi = gas velocity relative to R. liquid film = — in film -1 2 " [E] Use logarithmic mean driving force at two ends of column. Based on four systems with gas-side resistance only, = logarithmic mean partial pressure of nondiffusing species B in binary mixture. p = total pressure Modified form is used for structured packings (See Table 5-28-H). 

The theoretical maximum suction lift at sea level for water (14.7 psi) (2.31 fi/psi) = 34 ft. However, due to flow resistance, this value is never attainable. For safety, 15 feet is considered the practical limit, although some pumps will lift somewhat higher columns of water. WTen sealing a vacuum condition above a pump, or the pump pumps from a vessel, a seal allowance to atmosphere is almost always taken as 34 feet of water. High suction lift causes a reduction in pump capacity, noisy operation due to release of air and vapor bubbles, vibration and erosion, or pitting (cavitation) of the impeller and some parts of the casing. (The extent of the damage depends on the materials of construction.)... 

D. E. Overcashier, T. W. Patapoff, and C. C. Hsu, Lyophilization of protein formulations in vials Investigation of the relationship between resistance to vapor flow during primary drying and small scale product collapse, J. Pharm. Sci., 88(7), 688 (1999). 

The water vapor flows from the sublimation front into the chamber and to the connection between chamber and condenser with a favorable small pressure drop there are no measurable flow resistances, e. g. between the shelves or the shelves and the chamber walls. 

Furthermore, the transplants are often packed in aluminum boxes, which are sealed by sterile filters permeable to water vapor. Even if the box can be designed with a negligible resistance to water vapor flow, the heat transfer is substantially reduced. 

Equation (1.24) tells us that only in the situation where C = °o (meaning that the flow resistance is equal to 0) will S = Sg,f. A number of helpful equations is available to the vacuum technologist for calculating the conductance value C for piping sections. The conductance values for valves, cold traps, separators and vapor barriers will, as a rule, have to be determined empirically. 

Analogous to sampling TIN with the filter pack method, sampling with a quartz- or glass-fiber filter followed by a sorbent can provide a relatively accurate measure of the total (i.e., vapor plus particle phase) concentration of specific PAH compounds. Such methodologies were reviewed by Lee et al. (73). Selection of a sorption medium for collection of vapor-phase PAHs is influenced by air-flow resistance, collection efficiency, breakthrough volume, the effort required to purify the medium for use, and the efficiency with which the PAH can be recovered from the sorbent. 

To operate SD at peq 0 j the condenser temperature Tco has to be smaller than given in the table as T < (how much smaller depends on the condenser configuration, i.e. to condense the vapor on the surface with a minimum of flow resistance and interference with permanent gas and water molecules). For Tco < in the table it is assumed that the equilibrium pressure of the ice on the condenser surface needs to be only 10% below peq 01. 

Pressure drop. Wet pressure drop on the tray is determined by the resistance of the aerated mass to vapor flow (Sec. 6.3.3). As the nature of the dispersion is different, one would expect a different mechanism to cause pressure drop in the spray regime. This has been confirmed by experiments (88,114). To date, not enough is known about the nature of this mechanism. 

Because of the flow resistance of the caps and risers in bubble-cap columns, there is a decrease in liquid depth as the liquid passes across the tray. Figure 16-4 shows an extreme example in which this liquid gradient is so great that only one out of the form bubble caps is operating normally. In general, the dimensionless ratio of total liquid gradient to pressure-drop head caused by the bubble-cap assembly should be less than 0.4 in order to ensure adequate vapor distribution, and, for single-pass crossflow trays, the rate of liquid flow across the tray should be less than 0.22 ft3/(sXft) diameter. 

Figure 8-5. Conductances and resistances involved in water vapor flow accompanying transpiration, as...

The flow resistance for the water vapor, frum the vials into the chamber, depends oo the mechaoical design of the vials and stoppers, In Rgtirc 5 [9], ihiee different foiiiis of stoppeis urc sliown witli tlicir relative resistance to I he water vapor flow compared with the vial without a stopper... 

---