Hydrogen measuring techniques

Thomas and Rice [/. Appl. Mech., 40, 321-325 (1973)] applied the hydrogen-bubble technique for velocity measurements in thin hquid films. DureUi and Norgard [Exp. Mech., 12,169-177 (1972)] compare the flow birefringence and hydrogen-bubble techniques. 

Reference Growth process Hydrogen content (at. %) Deposition temperature (°C) ED(eV) D0(cm2/sec) Measurement technique... 

The foregoing analysis of free-convection heat transfer on a vertical flat plate is the simplest case that may be treated mathematically, and it has served to introduce the new dimensionless variable, the Grashof number, which is important in all free-convection problems. But as in some forced-convection problems, experimental measurements must be relied upon to obtain relations for heat transfer in other circumstances. These circumstances are usually those in which it is difficult to predict temperature and velocity profiles analytically. Turbulent free convection is an important example, just as is turbulent forced convection, of a problem area in which experimental data are necessary however, the problem is more acute with free-convection flow systems than with forced-convection systems because the velocities are usually so small that they are very difficult to measure. Despite the experimental difficulties, velocity measurements have been performed using hydrogen-bubble techniques [26], hot-wire anemometry [28], and quartz-fiber anemometers. Temperature field measurements have been obtained through the use of the Zehnder-Mach interferometer. The laser anemometer [29] is particularly useful for free-convection measurements because it does not disturb the flow field. 

A number of other techniques hold potential. Hydrogen manometry, where the hydrogen is extracted from the sample and its volume precisely measured, is an absolute technique. It requires, however, large samples (e.g., 4 g of garnet for the pyrope cahbration of Bell et al., 1995). It is, therefore, a bulk sample, and could only be useful in smdies of stmcturally incorporated trace amounts of water if there was absolutely no doubt that there was no contribution to the hydrogen measured from water present in fluid inclusions, in cracks, as adsorbed water, or in alteration minerals. 

Various refinements to these direct measurement techniques have been proposed. Substances such as glucose or potassium hydrogen phthalate, which are completely oxidized during the normal 5-day period of the BOD test, may be used as test substances to check the experimental technique of the BOD method used [24] (Eqs. 4.32 and 4.33). 

The first group is characterized by electrodeposition of copper at an overpotential of 550 my (potential at which there is no hydrogen evolution or hydrogen evolution was below the sensitivity of the measurement technique). 

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