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17 Dec Features of Gas and Liquid Phase HTF Systems

There are two kinds of heat transfer liquid (HTF) — gas phase HTF and liquid phase HTF. Which one to choose under specific situations? What are the features of gas phase and liquid phase HTF systems? Schultz will introduce to you in detail.

HTF, as heat transfer medium, can be divided into gas phase and liquid phase based on the boiling ranges. Synthetic HTF with a boiling point or azeotropy point can be used under the condition of gas phase, and it is called gas phase HTF. Gas phase HTF can also be used at liquid phase through pressurizing, so it can also be called gas/liquid phase HTF. Schultz S740 HTF is the gas/liquid phase HTF. Synthetic HTF with certain boiling ranges and mineral HTF that can only be operated at liquid phase are called liquid phase HTF. Schultz S750 is the liquid phase HTF. Most of HTF products on the market are liquid phase HTF and only a few are gas phase HTF.
There are two types of HTF heat transfer patterns because of different HTF phases, and they are gas phase heat transfer and liquid phase heat transfer.

The operating temperature of gas phase heat transfer system is the HTF saturation temperature, and the saturated gas works as heat transfer medium. The technological process of gas phase heat transfer is that HTF is heated to generate vapor which is transferred to heat consuming equipments and then cools down after letting out the latent heat, and the condensate flows back to the heating furnace by potential difference or use of reflux pump. The heat transfer between heating furnace and heat consuming equipments through gas phase is conducted in the mode of latent heat. This mechanism is called condensing heat transfer. The gas phase heat transfer system has even and constant heating temperature, and the temperature difference between inlet and outlet of heat consuming equipment can be controlled within a 1 to 2℃ range.

The operating temperature of liquid phase heat transfer system is lower than the HTF saturation temperature, and the heat transfer is based on liquid phase. The technological process is that HTF is heated by furnace and releases its heat to heat consuming equipments, and then flows back to heating furnace through the use of reflux pump. In this kind of heat transfer system, HTF provides heat to equipments in the state of sensible heat. The temperature difference between inlet and outlet of heat consuming equipment, depending on process requirements and reflux pump capacity, is usually in the range of 20 to 50℃.

In practice, consumers should choose the correct phase with proper HTF according to the operating temperature and temperature control accuracy. The features of liquid phase heat transfer system are low vapor pressure, high safety and more convenient to use, but in the process of heat transfer, the temperature change of HTF will cause temperature difference since it is sensible heat that HTF is carrying. The gas phase heat transfer is delivering HTF latent heat, compared with liquid phase heat transfer, which provides even and constant temperature. Therefore, it is good for situations where more stable operating temperature, higher temperature control accuracy and more temperature-sensitive heated medium are required.

The real advantage of HTF as heat transfer medium is liquid state form, but different features of gas and liquid phase heat transfer patterns fit in different heating systems. That’s why both can lead the market in turn for many years.