Liquid thermometers applications

In filled thermometers the thermal expansion of a gas or a liquid is transmitted through a thin capillary tube to a bellows or helix, where the deformation indicates the temperature. The temperature range of filled thermometers is very wide, approximately -200 to +700 °C. They are extremely robust but are not very high in accuracy. The application is mainly for process instrumentation and as stand-alone control devices. 

Tn addition to the error due to the exposed stem, ordinary chemical thermometers of low cost are subject to errors due to irregularities in the bore and sometimes the scale graduations may not be very accurate. " It is therefore essential to check the thermometer at several temperatures against the melting points of pure solids or the boiling points of pure liquids as described below. The application of an exposed stem correction will of course be unnecessary if the thermometer is calibrated in this way. A calibration curve may then be drawn upon graph " paper from the data thus obtained. Temperatures at intervals of about 20° are marked as abscissae and the corrections to be added or subtracted as ordinates the points thus obtained are then connected by a smooth curve. The thermometer correction at any temperature may be read directly from the curve. 

Soft, silver white metal that melts in the hand (29.8 °C) and remains liquid up to 2204 °C (difference 2174 °C, suitable for special thermometers). Gallium is quite widespread, but always in small amounts in admixtures. Its "career" took off with the advent of semiconductors. Ga arsenide and Ga phosphide, which are preferential to silicon in some applications, have extensive uses in microchips, diodes, lasers, and microwaves. The element is found in every mobile phone and computer. Ga nitride (GaN) is used in UV LEDs (ultraviolet light-emitting diodes). In this manner, a curiosity was transformed into a high-tech speciality. 

Thermotropic cholesterics have several practical applications, some of which are very widespread. Most of the liquid crystal displays produced use either the twisted nematic (see Figure 7.3) or the supertwisted nematic electrooptical effects.6 The liquid crystal materials used in these cells contain a chiral component (effectively a cholesteric phase) which determines the twisting direction. Cholesteric LCs can also be used for storage displays utilizing the dynamic scattering mode.7 Short-pitch cholesterics with temperature-dependent selective reflection in the visible region show different colors at different temperatures and are used for popular digital thermometers.8... 

Gallium, like mercury, is liquid at room temperature, but unlike mercury is much less hazardous. Its most interesting use is as a visualization tool of soft tissues and bone lesions in radiography. Industrial applications include use in high temperature thermometers, metal alloys, and as a substitute for mercury in arc lamps. 

Mercury (Hg) Mercury is a silvery white liquid metal. Because of its high density, mercury is used in sphygmomanometers. It is also found in some thermometers. Before its toxic nature was fully understood, mercury compounds had been used in medical applications ranging from treatment of syphilis to constipation. Mercury alloys well with many other metals, and alloys containing mercury are known as amalgams. 

Mercury has been known for over 4000 years. Its chemistry has many unusual aspects that have resulted in extensive usage by mankind. Mercury is the only common metal that is liquid at room temperature. It is also one of the very few elements that is monoatomic in its vapor phase at low temperatures, an indication of the weak Intermolecular forces that are present in mercury. The element exhibits surprisingly different chemistry from its congeners zinc and cadmium, a feature that is probably a consequence of the poor shielding by electrons in the completely filled 4f and 5d sublevels. The metal is used in a number of applications, including thermometers, amalgams, and production of chlor-aUcali. 

Another interesting application of nanotubes is the nanothermometer (Fig. 3.7). A carbon nanotube (about 10p.m long and 75 nm in diameter) is filled wifh liquid gallium, which expands in the tube as the temperature increases. Therefore, the level of the gallium in the nanotube changes in proportion to temperature, similar to the mercury in a macroscale thermometer. This nanothermometer should be suitable for use in a wide variety of microenvironments. 

Commercial phenyltrichlorosilane, b.p. 195-205° (1072 g., 5.07 moles), and 1.0 g. of iron powder are placed in a 1-1. threenecked flask equipped with a magnetic stirrer, a thermometer, and a gas inlet tube 1.0 cm. in diameter, which extends well beneath the level of the liquid in the flask. A vigorous stream of chlorine is admitted through the gas inlet tube.f The temperature of the reaction mixture, initially at room temperature, rises spontaneously, and the flow of chlorine is adjusted so as to maintain the reaction mixture at 65-70°. No external application of heat is required. The chlorination is continued for approximately 6.5 hours, after which time the reaction mixture will have gained 190-200 g. in weight. The crude product is... 

The reflective wavelength of cholesteric liquid crystals varies according to temperature. Such an effect has been made useful in thermography. It has been applied in the diagnosis of cancers by displaying the skin temperature distribution. It has also been applied to test faults in integrated circuits. The applications also include thermometers and temperature warning indicators and non-destructive detection. 

The low melting point (234 K) of Hg results in its being a unique metal. Its high thermal expansion coefficient makes it a suitable liquid for use in thermometers, and it has widespread application in barometers, diffusion pumps and in Hg switches in electrical apparatus. An older use was in mirrors. Some other metals dissolve in mercury to give amalgams, their uses are varied, for example ... 

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