No abstract

A phase change material (PCM) has the characteristics of latent heat storage, controllable phase transition temperature (PTT), and chemical stability. It can naturally regulate the ambient temperature in a certain range and reduce the load of air conditioning operation. Therefore, it plays an important role in the field of energy-saving buildings, and the PTT of PCM is one of the decisive factors. In this paper, through analyzing PCM installed in solar buildings at various regions, a binary eutectic mixture (EM) was prepared from lauric acid (LA) and octadecanol (OD) by the method of mixed melting, and the PTT and enthalpy of the EM were 39.87 °C and 186.94 J/g, respectively. The PTT, latent heat, and EM ratio were determined by theoretical calculation, the step cooling curve, and DSC. FT-IR result shows that no chemical reaction occurs among the components of composites, and the molecular forces are uniform and stable. XRD results further proves that no other phases existed in the composites. Thermal cycles (500) and the TG test show that the EM has excellent thermal stability and heat resistance, which meets the engineering application. Due to the thermodynamic properties of the EM, it can be used in thermal cooling of electronic systems, building envelopes, and thermal storage in solar buildings to obtain a good energy-saving effect.

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.