Zhonghao Rao

Thermal Properties of Paraffin Wax-based Composites Containing Graphite

Abstract The paraffin/graphite composite phase change materials (PCMs) for battery thermal management system (BTMS) were prepared in thermostatic water bath. X-ray diffraction test shows that there is no chemical reaction between the paraffin and the graphite. The energy storage properties of the paraffin/graphite composite PCMs were characterized by Differential scanning calorimetry. The total latent heat was reduced with the increasing of the mass fraction of graphite. As the PCMs must have high thermal conductivity and be insulated, the proposed mass fraction of graphite is 20 wt% and the total latent heat is 89.6% as great as that of the pure paraffin, which may be the best for BTMS.

Thermal Management with Phase Change Material for a Power Battery under Cold Temperatures

A 3-D module of power battery thermal management unit with phase change material is formulated. The cold start-up time of air heating is 4.2 times of phase change material heating from 243.15 to 283.15 K. The temperature difference decreases from 9.9 to 4.6°C when the thermal conductivity of the phase change material increases to five times. The heat transports from the domain near an electrode can reheat the domain away from the electrode and make the thermal energy distributing more even inside the battery. A well-designed thermal management system with phase change material is positive for power battery applying under cold temperature.

Dissipative particle dynamics study of nano-encapsulated thermal energy storage phase change material

The nano-encapsulated phase change materials (PCM), which have several good thermophysical properties, were proposed as potential for thermal energy storage. Various PCM have been widely researched on micro and macro perspective by experimental and simulated methods to form a bridge between the microstructure and macroscale properties of the nano-encapsulated PCM. In this study, the dissipative particle dynamics (DPD) simulation method was used to investigate the mesoscopic morphologies and evolution mechanisms of the nano-encapsulated PCM. The coarse-grained and Flory–Huggins-type models were used to obtain the molecular structures and interaction parameters. The results showed that the nano-encapsulated PCM can be fabricated by using n-docosane as a core material and styrene (St), ethyl acrylate (EA) and allyloxy nonyl-phenoxy propanol polyoxyethylene ether ammonium sulfate (DNS-86) as shell materials. The core–shell structures failed to fabricate with excess surfactant and shell materials. The preliminary optimized encapsulation rate of the core material could be useful for the design and experiment of the nano-encapsulated PCM.

Simulation of heat dissipation with phase change material for cylindrical power battery

AbstractIn order to better understand the heat dissipation performance of power battery for electrical vehicles, a three-dimensional model based on phase change material (PCM) cooling for individual cylindrical battery cell has been developed. The model takes into account the effects of unsteady heat generation, internal conduction and external natural convection to investigate the temperature response and distribution. The simulation results showed that the PCM with thermal conductivity higher than 0·8 W m−1 K−1 can be used for keeping the maximum temperature below 50°C in a battery cell under a constant heat generation rate of 170 000 W m−3. The unsteady discharge simulated results demonstrated that the heat transfer coefficient was another important factor for heat transfer enhancement. The PCM based power battery thermal management system indicated effective cycle application because the PCM can store most of the thermal energy during discharge and release it to the outer air during charge or non-star...

Dissipative particle dynamics and experimental study of alkane-based nanoencapsulated phase change material for thermal energy storage

The nanoencapsulated phase change materials (PCM) for thermal energy storage have received much attention recently. In order to understand the morphologies and structure evolution of nanoencapsulated PCM, dissipative particle dynamics (DPD) simulation coupled with an experimental method was performed in this paper. The coarse-grained models of the alkane-based nanoencapsulated PCM system were constructed and the PCM nanocapsules were prepared by using n-octadecane as a core material, and methyl methacrylate (MMA) and methyl acrylate (MA) as shell materials. The results showed that the nanoencapsulated PCM with a shell–core structure were successfully fabricated by DPD simulation. The average diameter of the prepared PCM capsules by using the experimental method is 48.80 nm. The latent heat and melting temperature of the prepared nanoencapsulated PCM is 86.13 kJ·kg−1 and 20.60 °C. The alkane content in the prepared nanoencapsulated PCM is 41.59%. The DPD simulation method was confirmed to benefit the development of nanotechnology in thermal energy storage.

Molecular dynamics simulations of phase transition of n-nonadecane under high pressure

The phase transition behavior of n-nonadecane under high pressure was investigated with molecular dynamics (MD) simulations method. A simplified model with amorphous structure and periodic boundary conditions in constant-temperature, constant-pressure ensemble was used in this study. The results showed that the whirling and molecules motion of n-nonadecane chains were restrained by the high pressure. The simulated phase transition temperature of n-nonadecane under high pressure is higher than that under atmospheric pressure. The order parameter of n-nonadecane decreases with the increase in temperature. The simulations reveal that MD is an effective method to understand the phase transition of alkane-based phase change materials on molecular and atomic scale.

Exfoliated graphite/paraffin nanocomposites as phase change materials for thermal energy storage application

Abstract Nanofluid paraffin based composites were prepared as phase change materials for thermal energy storage applications by dispersing exfoliated graphite (EG) into paraffin with intensive ultrasonic irradiation without any dispersants. Under intensive ultrasonic irradiation, EG was stripped as exfoliated graphite micro/nanoplatelets (EGP). The influence of EGP as heat diffusion promoters on improving thermal properties of paraffin was evaluated. As measured by a laser flash technique, the thermal conductivity of paraffin/EGP composites at room temperature increases with increasing EG mass fraction. After suspended in a water bath for 72 h, EGP still has good dispersion in melting paraffin. All the characteristic Fourier transformation infrared spectral peaks of paraffin and paraffin/EGP composites were observed. These paraffin/EGP composites show a good thermal reliability. Their heating and cooling rates are significantly improved upon the addition of EGP. Hence, the use of EGP is effective to improve thermal conductivity of paraffin with acceptable reduction in its latent heat storage capacity.

Temperature response of a high power lithium-ion battery subjected to high current discharge

Abstract Commercial LiFePO4 batteries were tested with several discharge currents (15, 20, 25, 30 and 35 A). Five k-type thermocouples were placed at the surface of each battery to evaluate the temperature distribution and electrochemical behaviour. The experiment showed that the maximum surface temperature reached 76·5°C when the current was 35 A, and the time of the maximum test temperature over 50°C was 84·42% of the total time. Supported by ANSYS software based on the implicit finite difference, the chemical reaction around the electrode, especially in anode, was more active than other places, which appeared to be higher temperature. To design a successful battery thermal management system, it is needful to study the battery temperature distribution and electrochemical behaviour. Statistical studies indicate that the maximum deviation between experimental and simulated values of the temperature distribution is ±10%.

Enhanced photo-H 2 production by unsaturated flow condition in continuous culture

A biofilm photobioreactor under unsaturated flow condition (BFPBR-U) is proposed using a polished optical fiber as the internal light source for photo-H2 production in continuous culture. The main chamber was filled with spherical glass beads to create the reaction bed and the cells were immobilized to form a biofilm under unsaturated flow condition obtained by pumping substrate solution over a packing bed at a rate to create a thin fluid film and injecting the argon to maintain the gas phase space. The effects of operational conditions, including flow rate and influent substrate concentration, on the photo-H2 production performance were investigated. The unsaturated flow conditions eliminated the inhibition caused by high organic loading rate and enhanced light transmission efficiency, leading to an improvement in the photo-H2 production performance.

Thermal Properties of Paraffin/Nano-AlN Phase Change Energy Storage Materials

The phase change energy storage materials based on paraffin/nano-aluminum nitride were prepared in this study. The thermal stability of the composite materials was determined by differential scanning calorimeter, simultaneous thermogravimetry analysis-differential thermal analysis, and X-ray diffraction techniques. The results of differential scanning calorimeter and X-ray diffraction showed that the thermal performance and structure of the composite materials are stable. The change of latent heat is accredited for thermal energy storage. The thermogravimetry analysis-differential thermal analysis revealed that 3 wt% nano-aluminum nitride added into paraffin increases the flash point by at least 10°C.