HTFS Heat Transfer and Fluid

The book by Walker (Appendix D, 1982) has a guide to the literature of heat transfer in book form and describes the proprietary services HTFS (Heat Transfer and Fluid Services) and HTR1 (Heat Transfer Research Inc.). 

Heat Transfer and Fluid Flow Service (HTFS), 73 266... 

Ucon HTF-500. Union Carbide Corp. manufactures Ucon HTE-500, a polyalkylene glycol suitable for Hquid-phase heat transfer. The fluid exhibits good thermal stabHity in the recommended temperature range and is inhibited against oxidation. The products of decomposition are soluble and viscosity increases as decomposition proceeds. The vapor pressure of the fluid is negligible and it is not feasible to recover the used fluid by distiHation. Also, because the degradation products are soluble in the fluid, it is not possible to remove them by filtration any spent fluid usuaHy must be burned as fuel or discarded. The fluid is soluble in water. 

Organic HTFs oxidize when heated in the presence of air. This starts at about 150°C and the rate increases with temperature. Heat transfer fluid manufacturers usually recommend a blanket of an inert gas such as nitrogen or argon on the expansion tank to prevent oxidation. This inert gas can also be utilized to pressurize the system in case the fluid will be utilized above its boiling point or the net positive suction head (NPSH) of the pump needs to be elevated. 

On the other hand, solid-like glass frozen products require a thermal treatment oriented toward recrystallization. This thermal treatment calls for precise freezing and rewarming cycles which are difficult to achieve when using direct expansion. (See Chapter 1.) In order to address these problems most modern freeze-dryers are fitted with a shelf cooling and heating system using a heat transfer fluid or HTF. 

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