Heat-transfer fluid

Heat transfer operations. Heat transfer fluids other than steam... 

Use a heat transfer fluid below its atmospheric boiling point if flammable. 

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). 

Aqueous solutions of propylene glycol display excellent antifree2e properties and are therefore valuable as low temperature heat-transfer fluids. For apphcations involving indirect food contact, heat-transfer fluids formulated with the USP grade product are preferred, since there could be inadvertent contact with a food product. These fluids are commonly used in the brewing and dairy industries as well as in refrigerated display cases in retail grocery stores. 

From empirical studies, values of b are known for many common heat-transfer fluids. Typical values for air and water are given in Table 2 (1 3). 

This implies that the LMTD or M I D as computed in equations 20 through 26 may not be a representative temperature difference between the two heat-transferring fluids for aU tubes. The effective LMTD or M ID would be smaller than the value calculated, and consequentiy would require additional heat-transfer area. The tme value of the effective M I D may be determined by two- or three-dimensional thermal—hydrauUc analysis of the tube bundle. Baffle—Tube Support PlateXirea. The portion of a heat-transfer tube that passes through the flow baffle—tube support plates is usuaUy considered inactive from a heat-transfer standpoint. However, this inactive area must be included in the determination of the total length of the heat-transfer tube. 

Table 1. Commercially Available Heat-Transfer Fluids...

Petro-Canada Oils. Petro-Canada manufactures three oils specially refined for use as heat-transfer fluids. Calflo EG is a semisynthetic, paraffinic heat-transfer fluid specifically developed for use in systems where incidental contact with food may result. Calflo AE is a saturated paraffinic oil containing inhibitors to minimise oxidation. Calflo HTE is a saturated paraffinic oil inhibited to minimise oxidation. 

Synthetic fluids are safe, noncorrosive, essentially nontoxic, and thermally stable when operated under conditions recommended by the manufacturers. Generally, these fluids are more expensive than petroleum oils, but the synthetics can usually be reprocessed to remove degradation products. There are several classes of chemicals offered permitting a wide temperature range of appHcation. Any heat-transfer fluid in use should be examined periodically to monitor degradation or contamination. 

Tetralin. Tetralin is a trade name of Du Pont for 1,2,3,4-tetrahydronapththalene [119-64-2] C qH 2- Tetralin, a derivative of naphthalene, is made by hydrogenating one ring completely and leaving the other unchanged. Tetralin is produced by several manufacturers and is one of the oldest heat-transfer fluids. Tetralin can be used both in Hquid- and vapor-phase systems. The normal boiling point is 207°C. 

Dowtherm Heat-Transfer Fluids. Dow Chemical Co. manufactures a family of heat-transfer fluids to meet differing appHcations. Dow Chemical also markets the Syltherm fluids produced by Dow-Coming Corp. Design and operating guidelines are offered in many of the company pubHcations describing the Dowtherm fluids. 

Therminol Heat-Transfer Fluids. Monsanto Chemical Co. manufactures a series of synthetic heat-transfer fluids that offer a wide operating temperature range. AH of these fluids, except for Therminol VP-1 and Therminol LT, are intended for Hquid-phase operation only. Monsanto also offers the two natural petroleum oil-based heat-transfer fluids discussed. 

Marlotherm Heat-Transfer Fluids. Two heat-transfer fluids are manufactured by HbIs America Madotherm S is a mixture of isomeric diben2ylben2enes intended for Hquid-phase systems, and Marlotherm L is a mixture of ben2yl toluenes that are suitable for both Hquid- and vapor-phase appHcations. Marlotherm L can be pumped readily at temperatures as low as —50° C and can be used in vapor-phase systems at temperatures from 290—350°C. The low temperature characteristics of Marlotherm enable it to be used in processes involving both heating and cooling. 

Therm alane Heat- Transfer Fluids. Coastal Chemical Co. manufactures three heat-transfer fluids intended for Hquid-phase systems. 

Some physical properties, such as heat capacity and thermal conductivity, are difficult to measure accurately at higher temperatures and error as great as 20% are common. For critical appHcations, consult the heat-transfer fluid manufacturer concerning methods that were employed for these measurements. 

Tdowtherm A. Heat Transfer Fluid, Dow Chemical Co., Midland, Mich. 

The dehydrogenation of 2-butanol is conducted in a multitube vapor-phase reactor over a zinc oxide (20—23), copper (24—27), or brass (28) catalyst, at temperatures of 250—400°C, and pressures slightly above atmospheric. The reaction is endothermic and heat is suppHed from a heat-transfer fluid on the shell side of the reactor. A typical process flow sheet is shown in Figure 1 (29). Catalyst life is three to five years operating in three to six month cycles between oxidative reactivations (30). Catalyst life is impaired by exposure to water, butene oligomers, and di-j -butyl ether (27). 

P). Otherwise the baffles should be located iaside the cod helix. A conventional jacket consists of a vessel outside the main vessel with a gap for the flow of heat-transfer fluid. Half-pipe jackets are usefld for high pressures up to 4 MPa (600 psi). They are better for Hquid than for vapor service fluids and can be easdy 2oned. Dimple jackets are suitable for larger vessels and process conditions up to 2 MPa (300 psi) and 370°C. Internal cods can be either hehcal or baffle cods (Fig. 34). 

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. 

Propylene Glycol. Propylene glycol, the second largest use of propylene oxide, is produced by hydrolysis of the oxide with water. Propylene glycol has very low toxicity and is, therefore, used direcdy in foods, pharmaceuticals (qv), and cosmetics, and indirectly in packaging materials (qv). Propylene glycol also finds use as an intermediate for numerous chemicals, in hydrauhc fluids (qv), in heat-transfer fluids (antifreeze), and in many other apphcations (273). 

Hydraulic and Heat-Transfer Fluids. HydrauHc fluids (qv) for high altitude supersonic aircraft and thermal exchange appHcations including solar panels employ fluids such as tetrakis(2-ethyIhexoxy)silane. These products have been marketed under the trade name Coolanol by Monsanto (see Heat-exchangetechnology). 

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