The selection of antifreeze pumps and the matching of pipeline resistance for low temperature chiller is an issue involving multiple aspects, including the selection of antifreeze, the selection of pumps, the calculation of pipeline resistance, and system design, etc.

I. Selection of Antifreeze and Material Compatibility

In low-temperature environments, the selection of antifreeze is of vital importance. Antifreeze not only needs to meet the freezing point requirements at low temperatures, but also needs to take into account its compatibility with materials such as pump bodies, pipelines, and seals. For instance, ethylene glycol aqueous solution is widely used due to its excellent anti-freezing performance, but it is corrosive to certain materials (such as common carbon steel), so corrosion-resistant materials (such as 316L stainless steel, polytetrafluoroethylene, etc.) need to be selected. In addition, the viscosity of antifreeze will increase significantly at low temperatures, which may affect the operating efficiency of the pump. Therefore, it is necessary to select a low-viscosity grade or use a pump type suitable for high viscosity, such as a screw pump.

Ii. Pump Selection and Material Selection

The selection of pumps should take into account their performance in low-temperature environments. The materials of the pump body, pipes, seals, etc. should have good low-temperature toughness to avoid cold brittleness or cracking caused by low temperatures. For example, common carbon steel is prone to cold brittleness at low temperatures. Therefore, materials such as austenitic stainless steel (such as 316L) or nickel-based alloys (such as Inconel 625) should be selected. In addition, the sealing parts of the pump (such as nitrile rubber and fluorine rubber) should be selected based on the nature of the antifreeze to ensure the sealing performance.

Iii. Calculation of Pipeline Resistance and Head

Pipeline resistance is an important factor affecting pump selection. Pipeline resistance includes resistance along the way, local resistance, equipment resistance, etc. According to the information I have found, the specific frictional resistance of cold water pipelines is usually controlled within the range of 150 to 200 Pa/m, and the total resistance of the pipeline is generally within the range of 20 to 50 kPa. The head of the water pump needs to be calculated based on the system resistance, and a safety margin of 10% to 15% should be considered. For instance, the calculation of the head of a chilled water pump needs to comprehensively take into account the resistance of the chiller, pipeline resistance, and the resistance of the air conditioning terminal equipment, etc.

Iv. Anti-freezing Measures and System Design

To prevent pump body or pipeline blockage caused by liquid freezing at low temperatures, multiple anti-freezing measures need to be taken. For instance, install vent valves, slope designs, elastic element buffers, pressure relief devices, etc., to prevent damage caused by the freezing and expansion of liquids. In addition, the influence of the concentration and properties of antifreeze on the system circulation flow and resistance should be taken into account in the system design, and corrections should be made when necessary.

V. Comprehensive Selection and System Matching

In the selection of antifreeze pumps and the matching of pipeline resistance for low temperature chiller, multiple aspects such as the selection of antifreeze, the material and performance of the pump, the calculation of pipeline resistance, antifreeze measures and system design need to be comprehensively considered. Through systematic selection and design, the stable operation of low temperature chiller in low-temperature environments can be ensured.

Conclusion

The selection of the antifreeze pump and the matching of pipeline resistance for low temperature chiller is a multi-faceted issue, which requires comprehensive consideration of multiple aspects such as the selection of antifreeze, the material and performance of the pump, the calculation of pipeline resistance, antifreeze measures and system design. Through scientific selection and design, the stable operation of low temperature chiller in low-temperature environments can be ensured.