Humidity-induced pressurization

Armstrong, I, Armstrong, W. and Beckett, P.M., 1992. Phragmites australis. Venturi- and humidity-induced pressure flows enhance rhizome aeration and rhizosphere oxidation. New Phytologist 120 107-207. 

FIGURE 7.16 Convective air flow due to thermal transpiration and humidity-induced pressurization. 

Humidity-induced pressurization is the result of vapor pressure differential between the leaf and atmosphere separated by a porous partition (plant cell membrane) (Figure 7.16). The total pressure will be greater on the more humid side. Humidity-induced diffusion is more important than thermal transpiration because it can be increased with temperature and can function at a constant temperature, as well as across temperature gradient (Armstrong et al., 1991a, 1991b). 

The relative importance of each of the processes described above is difficult to ascertain because all the processes function simultaneously and independently, and various interactive factors regulate each process. Humidity-induced pressurization is usually the most dominant process, regulating convective flows in many wetland plants. Species with cylindrical culms and linear leaves usually have internal pressurization potential (Brix et al., 1992) and may be able to grow in deeper water than species dependent on root oxygenation due to diffusion only (Brix et al., 1992). 

Mass flows mediated by thermal transpiration and humidity-induced pressurization require Knudsen s regime (i.e., pore diameter <0.1 pm). Static pressure in intercellular airspaces decreases... 

Armstrong, W. and P. M. Beckett. 1996. Pressurized aeration in wetland macrophytes some theoretical aspects of humidity-induced convection and thermal transpiration. Folia Geobot. Phytotaxinom. 31 25-36. Brix, H., B. K. Sorrell, P. T., Orr. 1992. Internal pressurization and convective gas flow in some emergent freshwater macrophytes. Limnol. Oceanogr. 37 1420-1433. 

Armstrong, W. and P. M. Beckett. 1996. Pressurized aeration in wetland macrophytes some theoretical aspects of humidity-induced convection and thermal transpiration. Folia Geobot. Phytotaxinom. 31 25-36. 

Another example of pressure-induced polymorphism is seen in the case of amiloride hydrochloride, where ball-milling Form-B causes a solid-state phase transformation into Form-A [43]. These workers deduced the phase relationship between two different pressure-induced polymorphs of the dihydrate, as well as the alternative route to one of those dihydrate forms that used the anhydrous form as the source material and effected the phase transformation through storage at high degrees of relative humidity storage. 

The moisture content of samples, in equilibrium, in the ESEM is varied at constant temperature (10°C), while lowering the pressure in the ESEM chamber from 9 torr to 2 torr. At the same time, relative humidity varies from 100% to 20%. The created chamber climate induces evaporation of the unbound (free) water in the cement paste (CP) samples without or with an embedded aggregate (to model simple concrete). It has been observed that curing conditions, sample age, water/cement (w/c) ratio, the presence of an aggregate, as well as the value of the RH, gives rise to different drying behaviour of the... 

Forced draft towers. Figure 9.17(f), locate the fan near ground level that requires simpler structural supports and perhaps lower noise level. A large space must be provided at the bottom for the air inlet. Because the air must make a 90° adjustment, the air distribution is poor. The humid air is discharged at a low velocity from the top of the tower and it tends to return to the tower, but the drift loss of water is less. The pressure drop on the discharge side of the fan that is less power demanding than that on the intake side of induced draft towers. 

The pressure induced by humidity in the intercellular airspaces is the difference in water vapor pressure inside and outside the leaf (Brix et al., 1992) ... 

The climate is determined by ambient temperature, wind speed, relative humidity, and (solar) radiation. Altitude can also be considered as a climate parameter the reduced ambient pressure induces physiological responses that enhance the risk for... 

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