The gasification of straw stalk in CO2 environment was studied by isothermal thermogravimetric analysis. The characteristics of rice straw and maize stalk gasification at different temperatures were examined under CO2 atmosphere. The relationship between reaction time and carbon conversion of two biomass chars was analyzed by the random pore model (RPM), and compared with the simulation of the shrinking core reaction model (SCRM). The results show that the random pore model is better to predict the experimental data at different temperatures. This means that the characteristics of pore structure for the influence of biomass chars gasification is well reflected by parameter ψ used in RPM. It indicates that the RPM can be applied to the comprehensive simulation of biomass chars gasification in CO2 environment.
A thickener that could address the phase separation problems of sodium acetate trihydrate (SAT) was determined by the gravity sedimentation method. Additionally, a hydrated salt nucleating agent to effectively reduce the supercooling of SAT was sought using the step‐cooling method. Combining these findings, a new SAT composite phase change material (SAT CPCM) was prepared. Additionally, a sample containing expanded graphite (EG) was prepared by melt blending to enhance the thermal conductivity. Our results show that a sample prepared with 1.5 % xanthan gum and 2 % sodium pyrophosphate decahydrate as a hydrated salt nucleating agent basically eliminates supercooling, its thermostability better than that of the composite phase change material using disodium hydrogen phosphate dodecahydrate. A sample with 6 % EG stays molten without leakage at a higher temperature and in the cooling test, the material‘s supercooling degree was only 1.1 °C. After 200 cooling‐heating cycles, the thermal stability was good, with high latent heats of 230.52 kJ/kg and thermal conductivities of 1.789 W(m ⋅ K) −1. This composite phase change material has great application potential in the field of low‐temperature heat storage.
Disodium hydrogen phosphate dodecahydrate (DHPD) is a kind of phase-change hydrated material that has been widely used in heat-storage technology, but it has the common problems of supercooling and phase-separation of hydrated salts, therefore, the addition of a nucleating and thickening agent is a traditional method to solve the above problems. In this paper, sodium carboxymethylcellulose (CMC) and xanthan gum (XG) are used to improve the supercooling and phase-separation properties of the hydrated phase-change salts. The phase transition characteristics and cycling stability are analyzed in detail with the solidification curve, DSC (differential scanning calorimetry), XRD (x-ray diffraction), TG (thermal gravimetry), and thermal cycling experiments. The thickening water absorption of CMC and XG decreases the supercooling properties of DHPD without the addition of the nucleating agents. The addition of 5%XG together with 2%CMC reduce the supercooling of DHPD to 1.6 °C. DSC analysis showed that the additions can adsorb the free water, decrease the evaporation of crystalline water, and remove the self-phase separation problems. The phase-change temperature and latent heat were 36.2 °C and 201.5 J/g, respectively. The supercooling degree of the modified DHPD was no more than 2 °C, showing its excellent thermal stability in the accelerated thermal cycle experiments.
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