The solid-liquid phase transition process is of significant importance the widely usage of phase change material (PCM), including in thermal energy storage and maintaining working temperature. In this paper, a phase change lattice Boltzmann (LB) model has been established to investigate the effects of inclining angle on the melting process in a cavity filled with PCM, considering three kinds of heat flux distribution: uniform distribution, linear distribution and parabolic symmetry distribution. The simulations results show that for all the heat flux distributions, the slight clockwise rotation of cavity is able to accelerate the melting process. Furthermore, when more heat is transported into the cavity through the middle part (parabolic symmetry distribution) or bottom part (linear distribution), the effects of cavity clockwise rotation on temperature field are more than that of anticlockwise rotation.

It is well known that a phase transition from liquid to vapor occurs in the thermal boundary layer adjacent to a nanoparticle that has a high temperature upon irradiation with a high-power laser. In this study, the mechanism by which the evaporated layer adjacent to a laser-irradiated nanoparticle can grow as a bubble was investigated. The pressure of the evaporated liquid volume due to heat diffusion from the irradiated nanoparticle was estimated using a bubble nucleation model based on molecular interactions. The bubble wall motion was obtained using the Keller-Miksis equation. The density and temperature inside the bubble were obtained by solving the continuity and energy equations for the vapor inside the bubble. The evaporation of water molecules or condensation of water vapor at the vapor-liquid interface and the homogeneous nucleation of vapor were also considered. The calculated bubble radius -time curve for the bubble formed on the surface of a gold particle with a diameter of 9 nm is close to the experimental result. Our study reveals that an appropriate size of the evaporated liquid volume and a large expansion velocity are important parameters for the formation of a transient nano-sized bubble. The calculation result suggests that homogeneous condensation of vapor rather than condensation at the interface occurs.

Polyalcohols such as neopentyl glycol (NPG) undergo solid-state crystal transformations that absorb/release sufficient latent heat. These solid-solid phase change materials (PCM) can be used in practical thermal management applications without concerns about liquid leakage and thermal expansion during phase transition. In this paper, microcapsules of NPG encapsulated in silica shell were successfully synthesized with the use of the emulsion technique. The size of the microcapsules was in the range of 0.2–4 μm, and the thickness of the silica shell was about 30 nm. It was found that the endothermic event of the phase change behavior of these NPG-silica microcapsules was initiated at around 39 °C and the latent heat was about 96.0 J/g. A large supercooling of about 43.3 °C was observed in the pure NPG particles without shell. The supercooling of the NPG microcapsules can be reduced to about 14 °C due to the heterogeneous nucleation sites provided by the silica shell. These NPG microcapsules were added into heat transfer fluid PAO to enhance its heat capacity. The effective heat capacity of the fluids can be increased by 56% by adding 20 wt. % NPG-silica microcapsules.

Structural phase transformations from wurtzite to a graphite-like phase and from wurzite to a tetragonal phase in ZnO and GaN nanowires under tensile loading cause significant changes in thermal conductivity. Molecular dynamics simulations are carried out to investigate the effect of deformation and the phase transformations on the thermal conductivity of [0001]-oriented GaN nanowires. The calculation of conductivity at each state of the nanowires is based on the equilibrium Green-Kubo approach with quantum correction. Under tensile loading, initially wurtzite-structured wires transform into a tetragonal structure, causing the thermal conductivity to decrease as the strain increases. Unloading of the transformed wires is associated with a reverse transformation from the tetragonal structure to the wurtzite structure. Opposite to what is observed during the forward transformation during loading, the thermal conductivity increases as the strain decreases in the unloading process. However, during the reverse transformation, the nanowires consist of both tetragonal regions and wurtzite-structured regions. Such intermediate states are not observed during the loading process. Phonon scattering at the interfaces between the wurtzite and tetragonal regions during unloading causes the thermal conductivity of the nanowires to be lower compared with that during loading.

Polyalphaolefins (PAOs) are widely implemented for electronics cooling. However, they have a low thermal conductivity. Adding nanoparticles to a PAO can significantly improve the thermal properties of the coolant. In this paper, the thermal performance of phase change materials (PCM) fluids with reduced supercooling in the phase transition was studied in a microchannel heat sink, and compared with that of the pure PAO. A test loop was designed and fabricated to test the synthesized PCM fluids. The PCM fluid with uncoated PCM particles has a 36% higher heat transfer coefficient than the pure PAO. The heat transfer coefficient of a silver coated PCM coated was also higher than of the pure PAO but lower than of the uncoated PCM. The thermal resistance of the uncoated PCM fluid was about 20% lower that of the PAO fluid at the same pumping power, despite the PCM fluid’s higher viscosity. Pumping tests run for several hours showed no effect on particle accumulation or settling within the heat transfer loop.

We present a short review of recent simulation work concerning heat transfer between nanoparticles and a suspending fluid. The role of numerical simulation in understanding such phenomena at a qualitative and quantitative level is emphasized. We discuss in particular the role of interfacial resistance, that of local curvature effects, and the possibility of achieving high temperatures inside the particles without creating a liquid vapor phase transition (boiling) in the surrounding fluid. Our present understanding on nanofluid conductivity from simulation studies is also discussed.

The use of phase-change materials for latent heat storage is a new type of environmentally-friendly energy-saving technologies. Molten salts, one kind of phase-change materials, which have high latent heats, and whose phase transition temperatures match the high temperatures of heat engines, are the most widely used high-temperature phase-change heat storage materials. However, the heat transfer at solid/liquid phase interface belongs to Micro/Nanoscale Heat transfer, lots of the thermal properties of molten salt at melting point is difficult to test. In this investigation, based on the theory that the thermal conductivity can be determined by measuring the speed of the propagation of the solid/liquid phase interface during phase change, a set of system is developed to investigate the thermal conductivity of molten salts at liquid/solid phase transformation point. Meanwhile, mathematical calculation is applied to intuitively simulate the melting and solidifying process in the phase change chamber, by which the error could be analyzed and partly corrected and the result precision could also be increased. And a series of verification experiments have been performed to estimate the precision and the applicability of the measuring system to evaluate the feasibility of the method and measuring system. This research will pave the way to the follow-on research on heat storage at high temperature in industry.