Numerical study on solar-driven methanol steam reforming reactor with multiple phase change materials

The multi-stage phase change material (PCM) fillings were proposed in the methanol steam reforming tube reactor driven by the parabolic-trough concentrated solar energy. Two-dimensional mathematical model of such surround filling reactor with numerical simulation was developed to evaluate its performance on eliminating the solar energy fluctuation. The effects of PCM with different thermophysical properties on chemical performance of the reactor were conducted when the sun is blocked. The optimal arrangement of multiple-stage PCMs was investigated and its performance under solar radiation fluctuations was investigated to improve the available latent heat of PCM and chemical performance of the reactor. The results showed that the PCM filling in the reactor significantly increased the time of methanol reforming reaction and improved the chemical performance when the heating by concentrated solar energy was ceased. PCM with lower phase change temperature and more latent heat could maintain the chemical reaction for a longer time. However, better chemical performance when PCM released latent heat could be achieved by PCM with higher phase change temperature. Compared to single PCM filling, Two-stage PCMs reached a maximum relative improvement in methanol conversion of 10.86%. Three-stage PCMs reached the maximum relative enhancement in methanol conversion of 11.36% compared to Two-stage PCMs. Under the cyclic and solar fluctuations, the multiple-stage PCMs reactor produced nearly twice as much hydrogen as that of the reactor without PCM. During a 6-h real solar radiation fluctuation, the multiple-stage PCMs reactor also have better methanol conversion. However, more than Three-stage PCMs arrangement improved the chemical performance of reactor only slightly.