Dongsheng Zhu

The investigation of thermal conductivity and energy storage properties of graphite/paraffin composites

Phase change materials (PCM) have been extensively scrutinized for their widely application in thermal energy storage (TES). Paraffin was considered to be one of the most prospective PCMs with perfect properties. However, lower thermal conductivity hinders the further application. In this letter, we experimentally investigate the thermal conductivity and energy storage of composites consisting of paraffin and micron-size graphite flakes (MSGFs). The results strongly suggested that the thermal conductivity enhances enormously with increasing the mass fraction of the MSGFs. The formation of heat flow network is the key factor for high thermal conductivity in this case. Meanwhile, compared to that of the thermal conductivity, the latent heat capacity, the melting temperature, and the freezing temperature of the composites present negligible change with increasing the concentration of the MSGFs. The paraffin-based composites have great potential for energy storage application with optimal fraction of the MSGFs.

Thermal Physics and Critical Heat Flux Characteristics of Al2O3–H2O Nanofluids

This study investigates the influence of the thermal physics of nanofluids on the critical heat flux (CHF) of nanofluids. Thermal physics tests of nanoparticle concentrations ranged from 0 to 1 g/L. Pool boiling experiments were performed using electrically heated NiCr metal wire under atmospheric pressure. The results show that there was no obvious change for viscosity and a maximum enhancement of about 5 to 7% for thermal conductivity and surface tension with the addition of nanoparticles into pure water. Consistently with other nanofluid studies, this study found that a significant enhancement in CHF could be achieved at modest nanoparticle concentrations (<0.1 g/L by Al2O3 nanoparticle concentration). Compared to the CHF of pure water, an enhancement of 113% over that of nanofluids was found. Scanning electron microscope photos showed there was a nanoparticle layer formed on the heating surface for nanofluid boiling. The bubble growth was photographed by a camera. The coating layer makes the nucleation of vapor bubbles easily formed. Thus, the addition of nanoparticles has active effects on the CHF.

Surface Tension and Viscosity of Aluminum Oxide Nanofluids

Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. Due to the importance of thermophysical property on the heat transfer behavior of fluids, the surface tension and viscosity of Al2O3‐H2O nanofluids were investigated. The tests of nanoparticle concentrations ranged from 0 g/l to 1 g/l. The measurements of surface tension and viscosity were equipments based on the maximum bubble pressure method and a capillary viscometer, respectively. The results showed that the surface tension and the viscosity of nanofluids are both highly dependent on the temperature, which is the same to those of water. Because the nanoparticle concentration studied in this work is very low, so there is no obvious change for the viscosity and a maximum enhancement only about 5% for surface tension is obtained at a concentration of 1 g/l.

Numerical Simulation on Thermal Energy Storage Behavior of SiC-H2O Nanofluids

Abstract Thermal energy storage plays an important role in a wide variety of industrial, commercial, and other applications when there is a serious mismatch between the supply and demand of energy. Latent heat storage with phase change materials is very attractive, because of its high-energy storage density and its isothermal behavior during the phase change process. Here, the heat transfer enhancement in a two-dimensional enclosure containing nanofluids is solved using Fluent 6.2 software. Starting with steady natural convention, the phase change behavior is simulated considering different volume fractions of the SiC-H2O nanofluids. The simulation results show that the freezing rate of nanofluids is enhanced due to the addition of nanoparticles. The higher the volume fraction is, the shorter the total freezing time. Adding 5% SiC nanoparticles into water, the total freezing time can be saved by 17.4%. The computation results show that adding nanoparticles is an efficient way to enhance the heat transfer in a latent heat thermal energy storage system.