Transpiration apparatus

The detailed description of the apparatus and the experimental procedure were given by Kvande (1979). Figure 7.3 shows the main features of the transpiration apparatus. A standard Kanthal-wound furnace is located horizontally and can be moved back-and-forth along a tube made of Inconel 600 (an alloy consisting of 76% Ni, 15% Cr, and 9% Fe, and not reacting significantly with fluoride vapors at about 1000°C). The tube has an outer diameter 30 mm, an inner diameter 24.7 mm, and a length 1 m. 

The effect of zearalenone on crop development may be connected to its influence on the status and functioning of the photosynthetic apparatus (Koscielniak et al. 2008). The after-effects of zearalenone on the growth of soybean and wheat plants, net photosynthesis and transpiration rates, stomatal conductance, photochemical efficiency of photosystem 2 and on final seeds yield were determined. Modifications in leaf area were more pronounced in soybean than in wheat, and this tendency increases in successive developmental phases. The net photosynthesis was stimulated during the juvenile phase and during that of the final one by about 13.6% (average) in soybean plants. Stimulation of transpiration was also observed after... 

As shown previously (Section 14.7), thermal transpiration or thermomole-cular flow arises when gas is contained in two vessels at equal pressures but different temperatures and a connection is made between the vessels. A vacuum microbalance represents just such a system. The long tube surrounding the hang-down wire separates the sample, immersed in the coolant bath from the warm upper portion of the apparatus. With vacuum microbalances the effects of thermal transpiration are further exacerbated by the temperature gradient along the hang-down wire. 

Both the volumetric and gravimetric apparatus are subject to this effect. Data acquired at low pressures must be corrected for thermal transpiration. The continuous flow method is not subject to this phenomenon. 

Nitrogen adsorption in the submonolayer region (and hence at very low equilibrium pressures) was determined with the same apparatus but a transistor-type thermal conductivity gage (24) was used for pressure determination. As with the higher pressure runs, equilibrium was checked by taking desorption points at the very lowest pressures several hours were required to reach equilibrium. Where important, the measured pressure was corrected for the thermal transpiration effect. 

Figure 7.2. Schematic diagram of the isothermal part of the apparatus used for transpiration experiments.

Figure 7.3. Main features of the apparatus used for transpiration experiments. 1 - thermocouple, 2 - gas entrance, 3 - graphite tube, 4 - furnace, 5 - capillary openings, 6 - graphite shields, 7 - Kanthal heating, 8 - graphite boat, 9 - cold-finger, 10 - Inconel tube, 11 - gas exit.

Gas Exchange. CO2 assimilation and transpiration were measured using an open, flow-through apparatus and infrared gas analysis. Distilled H2O was continuously provided to the entire cut edge of the leaf disc enclosed in a Leaf Section Chamber (Analytical Development Co., Hoddesdon, U.K.). The vapor pressure deficit was maintained at 8.9 1.0 or 18.4 1.0 mbars. This corresponds to relative humidity levels of 72% and 42%, respectively. 

With this apparatus, Macbride showed that putrefying animal matters generate fixed air, although fixed air arrests their putrefaction and appears to make them fresh again. Foods also give out fixed air, which thus seems to be formed in digestion and absorbed by the blood, co be evacuated with the urine or by transpiration. Blood, sweat, and urine precipitate lime water (really due to the phosphates). ... 

Lister and McDonald [135] have described in detail the construction and calibration of low temperature ethylene adsorption apparatus. In measurements of such low pressures, two obvious risks must be considered namely the desorption of water and thermal transpiration. By heating the entire system for a short while, or by permanently keeping the system under vacuum, most of the adsorbed vapors from the glass walls should be removed. Otherwise the slowly desorbing vapors will increase the pressure in the system during adsorption measurements leading to erroneous results. When low pressure measurements are made on a gauge held at a different temperature from that part of the apparatus where the adsorption takes place, correction for thermal molecular flow also needs to be considered. To obtain accurate results Lister and McDonald prepared and used correction data. 

In gas-cleaning installation buildings, often there are so-called free flooded streams (Idelchik, 1968). They originate, for example, at an entry of a stream from a gas pipeline in the apparatus of much larger cross section already filled with gas. Thus, between an inducted stream of a basin (aerosol) and a mix in the apparatus, there are difficult contacts, where the result is quite often expressed in not design fall of aerosol corpuscles. The specified phenomenon not always is desirable. For example, in the scrubber of full transpiration used as the air conditioner, but not as the dust precipitator, the bottom part turns to the dry dust-collecting chamber. 

In wet apparatuses, heat-and-mass transfer that occur and their completeness depend on character and intensity of contact of phases. Technological calculation of the wet apparatus in the fullest aspect develops three independent calculations heat exchange between an irrigation water and medium in the apparatus, a mass transfer (absorption of gases and steams a liquid, liquid transpiration), and trapping of aerosol corpuscles [26-30]. 

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