Visualization method phase change

If all mixtures reach equilibrium rapidly, both methods give identical results. For mixtures that do not reach equilibrium quickly, the second method is recommended, as with the titration method the change in the ratio of components during titration may occur too fast, not allowing sufficient time to visually recognize phase changes [33]. 

The simplest thermometers are bistate/phase change sensors. These low-cost nonelectric sensors can be crystalline solids that change from a solid to a liquid at a particular temperature or can be crayons, lacquers, pellets, or labels over a wide range of temperatures from 38 to 1,650°C (100-3,000°F). They offer a very inexpensive method for visual verification within about 1°F. 

The appearance of flow visualization methods [61, 62, 63, 64] has made possible the study of two-phase flows in flow field channels. These methods should be perfected considering the potential measurement artifacts introduced by the transparent element (change in thermal and current distribution, and flow field channel surface properties). Mathematical representations of the pressure drop in presence of two-phase flow will be needed to modify existing stack reactant flow distribution models [65]. 

The need of frequent calibration is of some inconvenience as compared with heat balance calorimeters. On the other hand, the method chosen permits the use of an uninsulated glassreactor and thus allows visual observation of phase changes, colour changes and mixing conditions. This is a distinct advantage for process development work. 

First-order phase transitions can be detected by various thermoanalytical techniques, such as DSC, thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) [31]. Phase transitions leading to visual changes can be detected by optical methods such as microscopy [3], Solid-solid transitions involving a change in the crystal structure can be detected by X-ray diffraction [32] or infrared spectroscopy [33], A combination of these techniques is usually employed to study the phase transitions in organic solids such as drugs. 

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