Performance of shape-stabilized phase change material wallboard with periodical outside heat flux waves

Numerical simulations were carried out to investigate the performance of shape-stabilized phase change material (SSPCM) wallboard with sinusoidal heat flux waves on the outer surface and compared with traditional building materials – brick, foam concrete and expanded polystyrene (EPS). One-dimensional enthalpy equation was solved using control volume-based implicit finite-difference scheme. Time lag (φ), decrement factor (f) and phase transition keeping time (ψ) of inner surface were applied to analyze the effects of PCM thermo-physical properties, inner surface convective heat transfer coefficient and thickness of SSPCM wallboard. The results showed that for SSPCM, there exist two flat segments within one wave length period of inner surface heat flux lines and it has larger time lag and lower decrement factor than those three ordinary building materials. It was found that melting temperature and thermal conductivity of SSPCM have little effects on φ, f and ψ, which is different from the case of temperature waves; for a certain outside heat flux wave, there exist critical values of latent heat of fusion and thickness of SSPCM above which the heat flux wave amplitude can be diminished to zero; inner surface convective heat transfer coefficient is one important factor which significantly influences the decrement factor; and the phase transition zone leads to small fluctuations of the original flat segments of inner surface heat flux line.

Research highlights
► Use Time lag φ, decrement factor f and phase transition keeping time ψ of inner surface to investigate SSPCM behavior under sinusoidal heat flux waves.
► Different from traditional materials, there exist two flat segments within the inner surface heat flux lines of SSPCM wallboard.
► Above critical values of latent heat and thickness of SSPCM, the outside heat flux wave may be fully “blocked” or “obstructed”.
► Compared with inside convective coefficient, thermal conductivity almost has no effects on heat wave propagation.
► Some behaviors of SSPCM under outside heat flux waves are different from those under outside temperature waves.