Vapor binding

Kettle reboilers are generally assumed to require neghgible pressure drop. It is important to provide good longitudinal liqmd flow paths within the shell so that the hquid is uniformly distributed along the entire length of the tubes and excessive local vaporization and vapor binding are avoided. 

Select 3-in. nozzle, head loss less than 0.00035 ft (negligible). Use large nozzle to ensure free drainage of unit and no vapor binding in oudet line. Actually a 1-in. connection would safely carry the liquid flow with a head of about 0.08 ft of liquid. A condenser must be free draining and capable of handling surges. 

Figure 10-119. Dry-wall vapor-binding limitation. (Used by permission Fair, J. R. Chemical Engineering, July 8, 1963. McGraw-Hill, Inc. All rights reserved.)...

Vapor binding, or air lock, is another common cause of household radiator malfunction. Often, the vapor accumulating in the radiator is CO,2, rather than air. The C02 originates from the thermal decomposition of carbonates in the boiler. Regardless, air and C02 form a noncondensable vapor in the radiator. These noncondensables mix with the steam in the radiator. The noncondensables then reduce the concentration of the steam, by dilution. The diluted steam has a lower partial pressure than pure steam. The lower the partial pressure of the steam, the more difficult it is to condense. As the rate of condensation of the steam drops, so does the heat radiated by the radiator. 

The turbine impeller of Figure 7.10(h) rotates in a case of uniform diameter, as in Figure 7.12(j). As Figure 7.4(a) demonstrates, turbine pump performance resembles that of positive displacement types. Like them, turbines are essentially self-priming, that is, they will not vapor bind. 

Horizontal tube evaporators may be susceptible to vapor-binding, and foaming liquids cannot usually be handled. The short tube variety is seldom used today except for preparation of boiler feed water. The kettle-type reboiler is frequently used in chemical plant applications for clean fluids. 

Fig. 7.2. OFET and drain current-drain voltage plot, current in amperes, voltage (negative) in volts, gate voltages 0-100 V in 20 V increments, for a diphenylbithio-phene oligomer on Si/SiO2. The depiction of the vapor binding is for the intended use of the OFET as a sensor...

Improperly sized condensate return headers result in overpressurization of the return system, venting of excessive amount of vapor, vapor binding of condensate pumps, faulty steam trap operation, and water hammer. The following factors should be considered ... 

In one debutanizer, the ability to condense the overhead product was lost. Investigation showed that a nitrogen-purged instrument had been recently installed. The nitrogen had accumulated in the top of the condenser shell, and gas blanketed the water-cooled tubes. A vent on the top of the condenser shell was opened, and condenser capacity was restored. Note that a small amount of really noncondensable gas can effectively vapor bind a shell-and-tube condenser. 

If this non-condensable is not removed from the channel head, then my clients have observed (over a period of days, not hours) a progressive loss in heat transfer capacity. The proof that this is a buildup of non-condensables is that briefly blowing the condensate seal restores heat transfer capacity. The CO increases the tube-side heat transfer film resistance, rather similar to a temporary fouling deposit. I call this vapor binding. 

Air leaking into the surface condenser results in vapor binding. This causes an increase in the shell-side heat transfer thermal resistance. In effect, the steam does not make good contact with the exterior of the surface condenser tubes. This vapor-binding effect often appears to the operators as if the tubes are fouled with cooling-water deposits. 

This has nothing to do with the effect on the partial pressure of water due to air leaks. It is really "fouling" of the exterior of the tubes with air. I know this is complex, but it is all explained and quantified in the literature. This problem is best described by the term vapor binding. 

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