Transpiration effect

B. 5-26-A Graphical comparisons experiments and correlations. [E,S] For spheres. Includes transpiration effects and changing diameters. [78] [146] p.222... 

Other processes that have increased importance at small length scales such as thermal creep (transpiration) and electrokinetic effects are also being considered for use in microcombustors. For example, transpiration effects are currently being investigated by Ochoa el al. [117] to supply fuel to the combustion chamber creating an in-situ thermally driven reactant flow at the front end of the combustor. 

McFarlane JC, Pfieeger T, Fletcher J. 1987b. Transpiration effect on the uptake and distribution of bromacil, nitrobenzene, and phenol in soybean plants. J Environ Qual 16 372-376. 

In the application of a gravimetric technique, (ii) to (viii) must be taken into account and also special attention must be given to the control and measurement of the adsorbent temperature and to the assessment of the buoyancy corrections. Thermal transpiration effects should be allowed for if volumetric or gravimetric measurements are made at low pressure. 

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. 

Mason and co-workers [149] have noted the importance of R-T transfer in the thermal transpiration effect, which describes the pressure gradient developing along a capillary at low pressures by virtue of a temperature difference. The theory has been utilized by several investigators (see Section VII.A.2). 

E,S] For spheres. Includes transpiration effects and changing diameters. 

The cryogenic adsorption system was specially developed to measure adsorption isotherms of H2 and D2. This system is equipped with a closed helium cycle two-stage Gifford McMahon refrigerator to operate under cryogenic conditions. The adsorption temperature can be kept constant within 0.03 K at 20 K. Adsorption isotherms are obtained by gas adsorption manometry. This method is based on the measurement of the gas pressure in a calibrated, constant volume, at a known temperature. The dead space volume was calculated from a helium calibration measurement at the temperature of interest. Thermal transpiration effect was calibrated according to the work by Takaishi and Sensui [41]. 

Transpiration is a process that involves loss of water vapour through the stomata of plants. The loss of water vapour from the plant cools the plant down when the weather is very hot, and water from the stem and roots moves upwards or is pulled into the leaves. When less water is available for the plants, dehydrated mesophyll cells release the plant hormone abscisic acid, which causes the stomatal pores to close and reduce the loss of water during release of oxygen and intake of carbon dioxide. Fig. 2.7 (a) shows the transpiration effect in plants with open and closed stomata. 

Fig. 2.7 (a) Transpiration effect in plants (b) AKZO NOBEL s Stomatex fabric based on transpiration effect. 

Experimentally, particularly with the McBain spring balances, some difficulties may be experienced. The tube containing the sample must be well immersed in the liquid nitrogen. Thermal transpiration effects can operate when radiation from the equipment above the sample can radiate energy and raise the temperature of the sample. Similarly, as the containing tube has the characteristics of a Dewer vessel (thermos flask) sufficient time should be allowed for thermal equilibration. The carbon sample may never reach 77 K but is a litde higher as experimental limitations become controlling factors. 

Chapter 10—Sick Occupational Illnesses—Occupational illnesses often do not occur in real time, but have a latency period before their manifestation. When illnesses arise where symptoms occur immediately, the acute results can often follow a cause scenario similar to that of an injury. But, when exposures to chemicals, radiation, noise, biological entities, or environmental extremes transpire, effects are often not immediate. The approach to prevention has to be addressed before the event. In this chapter, illnesses and their preventive approaches will be addressed by following a normal industrial hygiene approach to head off possible occupationally related illnesses. The emphasis is on identifying the potential hazards to health and how to best preclude them or protect your workforce from exposure. 

---