SCIENCE CHINA Technological Sciences, Volume 60 , Issue 5 : 668-677(2017) https://doi.org/10.1007/s11431-016-9001-x

Thermal performances of non-equidistant helical-coil phase change accumulator for latent heat storage

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  • ReceivedDec 1, 2016
  • AcceptedJan 11, 2017
  • PublishedApr 10, 2017


Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material (PCM) temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperature distribution was also confirmed by simulation results.


This work was supported by the National Natural Science Foundation of China (Grant No. 51576187) and Fundamental Research Funds for the Central Universities (Grant No. WK2090130016).


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  • Figure 1

    (Color online) Schematic diagram of the helical-coil phase change heat accumulator.

  • Figure 2

    Variation of the temperature difference and the heat transfer area per length during the charging process.

  • Figure 3

    Liquid fraction of different helical-coil tubes with different coil number proportion.

  • Figure 4

    Grid of the helical-coil heat accumulator used for the simulations.

  • Figure 5

    Comparisons of the outlet temperature and the liquid fraction obtained from the two grids. (a) Outlet temperature; (b) liquid fraction.

  • Figure 6

    Comparisons of the temperature distribution between the equidistant helical-coil phase change heat accumulator and the non-equidistant one in the simulation.

  • Figure 7

    Comparison of the heat storage capacity between the equidistant helical-coil phase change heat accumulator (unoptimized) and the non-equidistant one (optimized) in the simulation.

  • Figure 8

    (Color online) Main structure of the experimental system.

  • Figure 9

    (Color online) Locations of the thermocouples and the structures of the equidistant and non-equidistant helical-coil phase change heat accumulator.

  • Figure 10

    Comparison of the structure between these two kinds of helical-coil tube. (a) Equidistant helical-coil tube; (b) non-equidistant helical-coil tube.

  • Figure 11

    Temperature variation of the equidistant heat accumulator (a) and the non-equidistant heat accumulator (b).

  • Figure 12

    Temperature distributions of the two kinds of the helical-coil heat accumulator and comparison of heat storage capacity.

  • Table 1   Thermophysical properties of the paraffin in this study

    Thermophysical properties


    Density ρ (kg/m3)


    Thermal conductivity k (W/(m K))


    Heat capacity cp (kJ/(kg K))


    Dynamic viscosity μ (Pa S)


    Latent heat Q (J/kg)


    Thermal expansion coefficient (K−1)


  • Table 2   Locations of the thermocouples (unit: cm)































  • Table 3   Different kinds of working conditions

    Temperature of the hot fluid (°C)

    Flow rate of the hot fluid (L/h)













  • Table 4   Degree of the optimization

    Flow rate L/h

















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