Xiaoguang Zhang

Polyethylene glycol/Cu/SiO2 form stable composite phase change materials: preparation, characterization, and thermal conductivity enhancement

Novel form-stable composite phase change materials (FS-CPCMs) of polyethylene glycol (PEG)/Cu/SiO2 were prepared by adding Cu powder to PEG and SiO2 via the ultrasound-assisted sol–gel method. This method ensured the uniform distribution of Cu powder in the FS-CPCMs, thus providing an important method to develop composite phase change materials (CPCMs) with a high thermal conductivity. The FS-CPCMs were characterized by various techniques. The results showed that the FS-CPCMs remained in the solid state without leakage above the melting point of PEG. The XRD and FTIR results indicated that no new chemical bond was formed between the constituents of FS-CPCMs: Cu, PEG, and SiO2. The DSC and TGA analyses showed that the FS-CPCMs had an optimum phase-change temperature, a high enthalpy of phase change, an excellent thermal stability, and a good form-stable performance. The thermal conductivity was 0.431 W m−1 K−1 for 3.45 wt% Cu powder in the FS-CPCMs, an increase of 49.13% compared to pure PEG.

Preparation and thermal properties of phase change materials based on paraffin with expanded graphite and carbon foams prepared from sucroses

Carbon foam/expanded graphite composite (CEC) was prepared from a sucrose-expandable graphite resin using a thermal foaming method. This CEC was impregnated through its pores with paraffin to obtain a paraffin/carbon foam/expanded graphite composite (PCEC). In the case of CECs, when the amount of added expandable graphite reached 10 wt% to 15 wt%, the microstructure of the CEC was damaged because of the expansion in volume of the expandable graphite. Fourier transform infra-red spectroscopy and X-ray diffraction analysis of PCECs showed that there was no chemical interaction between the paraffin and CECs. With an increase in the amount of expandable graphite in CECs, the adsorption capacity of paraffin and the latent heat first showed an increase and then decreased. The heat transfer capability of the paraffin was truly improved by the CECs. The processes for the preparation of the CECs and PCECs were environmentally friendly, convenient, and inexpensive. The PCECs, with good thermal properties and chemical stabilities, are suitable for low temperature (40–50 °C) thermal energy storage applications.

Thermal behavior of composite phase change materials based on polyethylene glycol and expanded vermiculite with modified porous carbon layer

An innovative way to enhance the thermal conductivity of composite phase change materials (PCMs) is by carbonizing the carbohydrate-coated mineral substrate to modify its porous structure. Here, we study the effect of introducing different amounts of carbonized starch acting as a filler for enhancing the thermal conductivity of the shape-stabilized composite PCMs (ss-CPCMs) based on polyethylene glycol (PEG) and modified expanded vermiculite (MEV). The experimental exploration of the thermal behavior of composite PCMs has been explored sufficiently in depth. The MEV is shown by SEM images to tightly adhere to the carbon layer and to be composed of a dense micropore structure. Results from DSC indicate that the latent heat of the PEG/MEV ss-CPCMs gradually decreases with the increase of carbon layer mass fraction. Results obtained from FT-IR and TGA show that PEG/MEV ss-CPCMs exhibit good chemical and thermal stabilities. The thermal conductivity of the PEG/MEV ss-CPCMs increases with the carbon layer mass fractions and reaches up to 1.94 times that of PEG/EV ss-CPCMs. The PEG/MEV ss-CPCMs result in a promising material for applications in energy-efficient buildings due to its excellent thermal properties, ideal thermal conductivity and good chemical and thermal stability.