Selection of High-temperature Synthetic Heat Transfer Fluids
2026-06-01
In the processing of chemical fibers and polymer materials, heat transfer fluid systems provide heating throughout the entire process from melt conveying to spinning and forming. The process temperatures range from 180℃ to 400℃, involving two heat transfer modes: liquid phase and gas phase. Improper selection will, in mild cases, accelerate fluid degradation and increase oil replacement frequency; in severe cases, it will cause coking and pipe blockage, spinning breakage and even full-line shutdown. The selection of high-temperature synthetic heat transfer fluids is not a simple temperature matching process, but a systematic assessment combining process characteristics, heat transfer modes, equipment precision and maintenance cycles.
1. Core Criterion: Process Temperature Determines the Upper Limit of Fluid Service Temperature
The maximum allowable operating temperature of the heat transfer fluid must be at least 10 to 20℃ higher than the actual process temperature, which is the basic principle for selection. Operation beyond the rated temperature will accelerate thermal cracking of the fluid: low-boiling substances generated will cause vapor lock in the system, while high-boiling condensates will form scale on pipe walls, triggering a vicious cycle of local overheating.
Based on temperature ranges, the applicable products for chemical fiber and polymer industries are divided into three categories:
- Medium-temperature range (below 280℃): Applied to acrylic spinning rolls (≤180℃), DTY texturing machine bobbins (≤220℃), BOPP/BOPET film production (≤280℃) and other working conditions. TUW-170, TUW-181, TUW-210 and TUW-240 medium & low temperature synthetic heat transfer fluids are recommended.
- High-temperature range (280℃ ~ 330℃): Covering direct polyester melt conveying (320-340℃), PBT/PTT/PC processing (320-330℃), PBS/PBAT synthesis (≤330℃) and other core processes. TUW-320, TUW-330, TUW-350D and TUW-1000 high-temperature liquid-phase heat transfer fluids are ideal choices.
- Ultra-high temperature range (330℃ ~ 400℃): For polyimide film production (300-400℃) and similar scenarios, TUW-400, a biphenyl-biphenyl ether blend applicable to both liquid and gas phases, is required.
2. Heat Transfer Modes: Matching Principles for Liquid Phase and Gas Phase
The choice between liquid-phase and gas-phase heat transfer in chemical fiber processes depends on temperature control accuracy and system design.Liquid-phase heat transfer systems feature low operating pressure and simple operation, making them the preferred option for most spinning processes. For typical liquid-phase working conditions such as direct polyester melt conveying pipelines, nylon spinning assemblies and polyester chip heating, hydrogenated terphenyl-based heat transfer fluids (e.g. TUW-350D) are highly recommended. At 350℃ liquid-phase operation, its vapor pressure is approximately one-fifth that of biphenyl-biphenyl ether mixtures at the same temperature, delivering lower system pressure and higher safety margin.
Gas-phase heat transfer is adopted for scenarios requiring high-precision temperature control, such as VK tubes for interlaced polyester filament production and high-speed FDY spinning assemblies. TUW-400 biphenyl-biphenyl ether mixtures can achieve a temperature control accuracy within ±1℃ via evaporation-condensation circulation in the gas phase. It should be noted that gas-phase systems demand superior sealing performance, and their operating pressure rises sharply with temperature increase. System pressure resistance shall be fully considered during design.
3. Process Segmentation: Selection Differences for Various Materials
Polyester fiber is the most widely used product in the chemical fiber industry. Its production chain, from PTA-MEG polycondensation to direct melt spinning, operates at 280℃ to 340℃. TUW-350D is recommended for liquid-phase service in direct synthetic fiber melt conveying pipelines, with a service life of up to 10 years. For melt pumps and spinnerets that operate at higher temperatures and bear concentrated thermal loads, TUW-400 is a better option, with a service life of around 6 years.
Biodegradable materials represent the fastest-growing segment in recent years. The maximum process temperature for PBS/PBAT synthesis and spinning is 330℃, which can be satisfied by TUW-350D and TUW-350. Strict operation below the rated temperature is necessary to prevent accelerated fluid aging caused by overheating.
Industrial yarn and film production cover a wide temperature spectrum. TUW-350D and TUW-1000 are suitable for polyester industrial yarn drawing ovens (≤300℃). For polyimide film production at temperatures up to 400℃, TUW-400 ultra-high temperature dual-phase heat transfer fluid is mandatory. PPS processing operates at 320-330℃. Apart from conventional high-temperature liquid-phase heat transfer fluids, special wide-temperature-range models including TUW-HVT/MVT/LVT can also be selected to meet differentiated requirements of different process sections.
4. Maintenance Cycle and Selection Economy
Selection shall not only focus on initial procurement cost, but also evaluate the full-lifecycle economy. Taking direct polyester melt conveying as an example, TUW-350D for liquid-phase use boasts a 10-year service life with minimal annual fluid replenishment. In contrast, fluids with insufficient thermal stability need replacement within 3 to 5 years. Combined with costs of pipeline cleaning and production downtime, the overall expense far exceeds the initial price gap. Regular fluid replacement schedules are essential for high-precision spinning equipment (such as FDY/POY spinning assemblies) to avoid spinning breakage and product quality fluctuations resulting from fluid deterioration.
The selection of high-temperature synthetic heat transfer fluids is essentially a systematic balance of process temperature, heat transfer mode, material properties and operation & maintenance costs. Temperature sets the upper limit, heat transfer mode defines the fluid type, process characteristics determine the specific model, and economic efficiency finalizes the decision. With precise selection, the heat transfer fluid system will serve as a reliable "heat power unit" for chemical fiber and polymer production lines.
Selection of High-Temperature Synthetic Heat Transfer Fluids
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