With the development of the carrying capacity of cryogenic rocket, the requirement of propellant filling flow rate is also increasing. Cryogenic fluid conveying pipeline is an indispensable equipment in aerospace field, which is used in cryogenic propellant filling system. In the low-temperature fluid conveying pipeline, the low-temperature vacuum hose, because of its good sealing, pressure resistance and bending performance, can compensate and absorb the displacement change caused by thermal expansion or cold contraction caused by temperature change, compensate the installation deviation of the pipeline and reduce vibration and noise, and become an essential fluid conveying element in the low-temperature filling system. In order to adapt to the position changes caused by the docking and shedding motion of the propellant filling connector in the small space of the protective tower, the designed pipeline should have some flexible adaptability in both the transverse and longitudinal directions.

The new cryogenic vacuum hose increases the design diameter, improves the cryogenic fluid transfer capacity, and has flexible adaptability in both lateral and longitudinal directions.

Overall structure design of cryogenic vacuum hose

According to the use requirements and salt spray environment, the metal material 06Cr19Ni10 is selected as the main material of the pipeline. The pipe assembly consists of two layers of pipe bodies, internal body and external network body, connected by a 90° elbow in the middle. Aluminum foil and non-alkali cloth are alternately wound on the external surface of the internal body to construct the insulation layer. A number of PTFE hose support rings are set outside the insulation layer to prevent direct contact between the internal and external pipes and improve the insulation performance. The two ends of the joint according to the connection requirements, the design of matching structure of the big diameter adiabatic joint. An adsorption box filled with 5A molecular sieve is arranged in the sandwich formed between the two layers of tubes to ensure that the pipeline has a good vacuum degree and vacuum life at cryogenic. The sealing plug is used for the sandwich vacuuming process interface.

Insulating layer material

The insulation layer is composed of multiple layers of reflection screen and spacer layer alternately wound on the adiabatic wall. The main function of the reflector screen is to isolate the external radiation heat transfer. The spacer can prevent direct contact with the reflecting screen and act as flame retardant and heat insulation. The reflective screen materials include aluminum foil, aluminized polyester film, etc., and the spacer layer materials include non-alkali glass fiber paper, non-alkali glass fiber cloth, nylon fabric, adiabatic paper, etc.

In the design scheme, aluminum foil is selected as the insulation layer as the reflecting screen, and non-alkali glass fiber cloth as the spacer layer.

Adsorbent and adsorption box

Adsorbent is a substance with microporous structure, its unit mass adsorption surface area is large, by molecular force to attract gas molecules to the surface of the adsorbent. The adsorbent in the sandwich of cryogenic pipe plays an important role in obtaining and maintaining the vacuum degree of the sandwich at cryogenic. The commonly used adsorbents are 5A molecular sieve and active carbon. Under vacuum and cryogenic conditions, 5A molecular sieve and active carbon have similar adsorption capacity of N2, O2, Ar2, H2 and other common gases. Activated carbon is easy to desorb water when vacuuming in sandwich, but easy to burn in O2. Activated carbon is not selected as adsorbent for liquid oxygen medium pipeline.

5A molecular sieve was selected as the sandwich adsorbent in the design scheme.