Precision temperature control

The hydroxide process developed by BeH Telephone Laboratories (8,9) is used by most producers (11). It is usuaHy operated at higher pressures than the carbonate process and quartz is grown at faster rates. Less precise temperature controls are needed. 

Condensing Organic Va.por, The eutectic mixture of diphenyl and diphenyl oxide is an excellent vapor medium for precise temperature control at temperatures higher than those practical using steam. This mixture can achieve 315°C while holding pressure at 304 kPa (3 atm) absolute. In contrast, steam would require 10.6 MPa (105 atm) pressure. 

These systems, commercially known as Tberminol VP or Dowtherm A, differ from steam in some key areas which can result in operating problems unless handled properly in design (14). The low pressure—high temperature operation means that the AT/AP ratio at saturation is quite high for example, at 315°C the ratio is 25 times that of steam. This means that a pressure drop that would be nominal in a steam system (10 kPa (0.1 atm)), can not be tolerated if precise temperature control is needed. 

There are two predominant problems. First, there is the necessity to keep the plant in operation, which may vary from a non-essential service such as the comfort cooling of an infrequently used room, to the precise temperature control of an expensive or potentially dangerous process. The second problem is the time taken in transit, which might be as long as a year in parts of the world subject to excessive docks and custom delays. 

Fairly precise temperature control is required, since the reaction mixture begins to solidify at about —50°. 

Fast reactions usually require less precise temperature control, because often, but not invariably, they have low activation energies. The converse is true for very slow reactions. 

Yoon DS, Lee Y-S, Lee Y, Cho HJ, Sung SW, Oh KW, Cha J, Lim G (2002) Precise temperature control and rapid thermal cycling in a micromachined DNA polymerase chain reaction chip. J Micromech Microeng 12 813-823... 

The use is described of a process involving both hydrolysis and pyrolysis to recover caprolactam from nylon 6 used in carpet fibres. By means of precise temperature control and the use of a catalyst, nylon 6 can be isolated from the PP backing. The process has been developed by the National Renewable Resource Laboratory, and interest has been shown by AlliedSignal who are considering a cooperative research and development project. 

Accordingly, this direct route demands absolutely precise temperature control because overheating of the reaction media increases radical formation in an un-... 

Both the Departments of the Army and the Navy have used mineral-insulated band heaters for various superheating applications. For example, the Department of the Navy uses similar equipment to test chemical stability of components within artillery shells (AEA, 2001a). In addition to high watt densities, these heaters provide even temperature profiles and fairly precise temperature control. 

The authors noted the regeoselective character of this treatment - only one regioisomer was always isolated from the reaction mixture. Furthermore, a precise temperature control and solvent choice are decisive factors for the successful... 

For the purpose of this argument, however, let us say that the biphasic system appears to be needlessly complicated. The reason for this might be the need for precise temperature control, not always possible in the field. Separation of the phases is possible but problematic on a large scale. Contamination by the use of inorganic salts to insolubilize the polymer precludes injecting groundwater back into the ground. 

C- NMR was measured in the mode of 1H noise decoupling without NOE, using D2O sealed up in a capillary tube. All UV and NMR measurements were performed under precise temperature control. 

Ultrasonic Mainly gases of low molar mass Hj, N2. COj, He. Ar. A quartz crystal transducer transmits a sound wave through a sample of gas with a similar crystal used as the receiver. The velocity of the sound wave is proportional to the square root of the molar mass of the sample. The phase shift of the sound signal is measured by comparison with a reference signal. Precise temperature control is required. 1-10 Gas chromatography... 

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