High Temperature Heat Transfer Fluids

To provide a source of heat between 200 and 450 °C. High temperature oils, alkylated aromatics, mixture of diphenyl and diphenyl oxide, di- and triaryl ethers, molten salts, liquid sodium or patented fluids can provide sensible heat or latent heat. 

175 °C consider Dowtherm J 200 to 400 °C consider molten salt 275 °C consider Dowtherm A 310 °C consider Dowtherm G 

Usually a portion of the liquid is purged and replaced with fresh makeup. 

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Example 10-16. Heating Oil Using High Temperature Heat Transfer Fluid (used by permission of The Dow Chemical Co., reference [183] 197l)... 

A column was used to strip low-volatile materials from a high-temperature heat transfer fluid. During a maintenance procedure, water was trapped between two valves. During normal operation, one valve was opened and the hot oil came in contact with the cold water. The result was almost sudden vaporization of the water, followed by considerable damage to the column. Consider liquid water at 25°C and 1 atm. How many times does the volume increase if the water is vaporized at 100°C and 1 atm ... 

Now it is possible to achieve over 90% conversion of cis-decalin with 95% selectivity to trans-decalin with some zeolites at 200°C [Lai and Song, 1996]. trans-Decalin has substantially higher thermal stability at temperatures above 400°C [Song et al., 1992], Possible applications are high-temperature heat-transfer fluids and advanced thermally stable jet fuels. The advanced jet fuels can be used both as heat sinks and as fuels for high-Mach aircraft [Song et al., 1993, 1994 Harrison et al., 1995 Edwards et al., 1997]. 

I HE past ten years have seen a growing interest in the use of sodium and its alloys with potassium (NaK) as heat-transfer fluids. Although the main impetus in the development of these metals has come from the atomic energy program on power reactors, the experience gained is also applicable to the use of these metals as high-temperature heat-transfer fluids in other industries. 

In this chapter in Section 3.1 we consider mechanical drives. In Sections 3.2 and 3.3 furnaces and exchangers, condensers and reboUers are considered followed by fluidized bed with coil in the bed, Section 3.4 and static mixers. Section 3.5. Direct contact systems are considered next liquid-liquid. Section 3.6 gas-liquid cooling towers. Section 3.7 gas-liquid quenchers. Section 3.8 gas-liquid condensers. Section 3.9, and gas-gas thermal wheels. Section 3.10. Heat loss to the atmosphere is described in Section 3.11. Refrigeration, steam generation and high temperature heat transfer fluids are presented in Sections 3.12 to 3.14, respectively. Tempered heat exchange systems are considered in Section 3.15. 

Molten-salts are the preferred high-temperature heat-transfer fluid in the chemical industry... 

Seifert, W.F., Jackson, L.L., Sech, C.E. Organic Fluids for High Temperature Heat Transfer Systems, Chemical Engineering, Oct. 30, 1972, p. %. 

Most fluid-to-fluid heat transfer is accomplished in steady-state equipment, but thermal regenerators, in which a bed of solid shapes is alternately heated by a hot fluid and the hot shapes then used to warm a colder fluid, are also used, especially in high-temperature heat transfer. Cyclical unsteady-state processes such as these are not considered in this book. 

Liquid metals are u ed for high-temperature heat transfer, espedally in nuclear reactors. Liquid mercury, sodium, and a mixture of sodium and potassium called NaK are commonly used as carriers of sensible heat. Mercury vapor is also used as a carrier of latent heat. Temperatures of 1500 F and above are obtainable by using such metals. Molten metals have good specific heats, low viscosities, and high thermal conductivities. Their Prandtl numbers are therefore very low in comparison with those of ordinary fluids. 

The heat input may be direct heat input, for example, injected hot solids or hot recycled product fuel gas or indirect heat input, as by high-temperature heat transfer surfaces located in the fluid bed. 

HEXAFLUOROBENZENE The development of commercial routes to hexafluoroben2ene [392-56-3] included an intensive study of its derivatives. Particularly noteworthy was the development of high temperature lubricants, heat-transfer fluids, and radiation-resistant polymers (248). 

Methyl- and dimethylnaphthalenes are contained in coke-oven tar and in certain petroleum fractions in significant amounts. A typical high temperature coke-oven coal tar, for example, contains ca 3 wt % of combined methyl- and dimethylnaphthalenes (6). In the United States, separation of individual isomers is seldom attempted instead a methylnaphtha1 ene-rich fraction is produced for commercial purposes. Such mixtures are used for solvents for pesticides, sulfur, and various aromatic compounds. They also can be used as low freezing, stable heat-transfer fluids. Mixtures that are rich in monomethyinaphthalene content have been used as dye carriers (qv) for color intensification in the dyeing of synthetic fibers, eg, polyester. They also are used as the feedstock to make naphthalene in dealkylation processes. PhthaUc anhydride also can be made from m ethyl n aph th al en e mixtures by an oxidation process that is similar to that used for naphthalene. 

Operabihty (ie, pellet formation and avoidance of agglomeration and adhesion) during kiln pyrolysis of urea can be improved by low heat rates and peripheral speeds (105), sufficiently high wall temperatures (105,106), radiant heating (107), multiple urea injection ports (106), use of heat transfer fluids (106), recycling 60—90% of the cmde CA to the urea feed to the kilns (105), and prior formation of urea cyanurate (108). 

The half-pipe jacket is used when high jacket pressures are required. The flow pattern of a liquid heat-transfer fluid can be controlled and designed for effective heat transfer. The dimple jacket offers structural advantages and is the most economical for high jacket pressures. The low volumetric capacity produces a fast response to temperature changes. 

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