Inlet pressure fluctuation characteristics of coiled adiabatic capillary tubes

Inlet pressure fluctuations were found during the experiments for coiled adiabatic capillary tubes in a one-pass-through type test facility. The fluctuation takes place when the inlet temperature rapidly changes from one point to another. Measured temperature distribution along the tube length showed that this phenomenon may be caused by the variation of flash point location in the capillary tube which leads to the pressure variation wave propagating upstream. Further experiments showed that the pressure fluctuation for coiled capillary tubes is much more prominent than for straight ones; the inlet pressure fluctuation is weak for small coil-diameter capillary tubes; with the increasing of the preset inlet pressure and decreasing of target inlet temperature, the fluctuation amplitude decreases; the pressure fluctuation amplitude at the inlet of parallel coiled capillary tubes is much lower than that of the single one and it needs less time to be stabilized which indicates the advantages of using parallel capillary tubes. The inlet pressure fluctuation in an actual air-conditioner system is found weaker than in the one-pass-through test facility.

► We found pressure fluctuations at the inlet of coiled adiabatic capillaries when the inlet temperature changes rapidly.
► The inlet pressure fluctuation for coiled capillaries is more prominent than that for straight ones.
► For higher preset inlet pressure and lower target inlet temperature, the inlet pressure fluctuation amplitude is lower.
► The fluctuation amplitude of parallel tubes is lower than the single tube and needs less time to be stabilized.
► The variation of flash location in the capillary may cause pressure variation wave leading to the fluctuation.