Longjian Li

Thermal interface materials are critical components for ensuring efficient heat dissipation in thermal management systems. The current research focus is to fabricate thermal interface materials (TIMs) that demonstrate high thermal conductivity while at low filler loadings. In this study, an aligned, thermally conductive skeleton was fabricated via the freeze casting method, utilizing carbon nanofibers (CNFs) and nickel (Ni) particles. This skeleton was subsequently infiltrated with silicone rubber (SR) to obtain the polymer composite. Within the aligned skeleton, CNFs and Ni particles are densely packed, with the Ni particles acting as conductive bridges between adjacent CNFs. This bridging effect facilitates a substantial enhancement in the overall thermal conductivity with only a minimal addition of Ni. By combining the skeleton’s microstructure with thermal performance, the effects of key parameters on thermal conductivity were systematically investigated. A maximum thermal conductivity improvement of 64.8% was achieved by hybridizing CNFs with a small amount of Ni (1.09 vol%) compared to the CNF-only counterpart. Furthermore, at a low total loading (8.02 vol% CNFs and 1.09 vol% Ni), the composite achieved a thermal conductivity of 3.30 W/(m·K). This value was 47.2% higher than that of a CNF-only TIM and 36.2% higher than that of a composite prepared by common freezing under the same filler composition. Additionally, the incorporation of Ni enhanced the composite’s thermal stability. Moreover, the composite exhibited a favorable combination of enhanced mechanical strength and excellent elasticity.

Heat transfer enhancement is always pursued in the industry to achieve high-performance and low-energy-consumption heat exchange devices and systems. For decades, various types of heat transfer-enhancing tubes with differing geometries and wall configurations have been developed. In this paper, the heat transfer and pressure drop characteristics of air inside an innovative heat transfer tube with regular wall dimples, namely a vortex-enhanced tube, which has a great application prospect in the gas–gas heat exchanger, are numerically studied with an experimentally validated model. The effects of the depth, axial pitch, and radial rotation angle of the dimple in the tube wall on the convective heat transfer coefficient and friction drag coefficient are comprehensively analyzed. Based on the Performance Evaluation Criteria (PEC) of the tubes, the optimal parameters of the vortex-enhanced tube are obtained. When Re ranges from 10,000 to 40,000, the comprehensive evaluation factor of the vortex-enhanced tube is 1.29 times higher than the smooth tube. Dimple pacing, dimple depth, and dimple helical angle of the optimal tube type are 8 mm, 6 mm, and 83°, respectively.

Accurate estimation of the thermal conductivity of porous materials is crucial for the modeling of heat transfer and energy consumption calculation in energy, aerospace, biomedicine and chemical engineering, etc. The series-parallel model is a simple and direct method and is usually used in the prediction of the effective thermal conductivity (ETC) of porous materials. In this work, the weighted coefficients of the series and parallel section were obtained based on the tortuosity of the porous materials. Then, the physical model of the ETC of the porous materials was established. Furthermore, the ETC of the porous materials was developed using the fractal model to calculate the pore cross-sectional area of the porous materials. Finally, quantitative analysis of the characteristic parameters, e.g., porosity, tortuosity, tortuous fractal dimension and pore diameter distribution, of the ETC of the porous materials was conducted. The results show that the proposed model can provide an accurate prediction of the ETC of porous materials.

Vapour chamber is a planar heat pipe and has been widely used in the thermal management of electronic device. In this work, a grooved aluminium vapour chamber was presented with a one-through cooling plate to develop a simplified and practicable battery liquid cooling system. The impact of filling ratio and tilting configuration on the thermal performance of vapour chamber was experimentally investigated. The results showed that the thermal resistance of the vapour chamber increased gradually with the increase in filling ratio, and there was a deterioration of the heat transfer in tilting configuration. However, the vapour chamber at 20% filling ratio had a better performance at positive tilting angle configuration compared with that at negative tilting angle configuration. Moreover, the temperature distribution of the heating surface is fairly uniform with the application of the vapour chamber. Despite the temperature rise of the cooling water in the cooling plate up to 3.8ºC, the minimum temperature difference of the heating surface could be kept within 1 ºC and the minimum thermal resistance could be kept within 0.075ºC/W. The results indicate that the temperature difference of the heating surface can be suppressed through the heat and mass transport of phases inside the vapour chamber.

Herein, a water‐limited sol–gel method is applied to fabricate microencapsulated phase change materials (MEPCMs) which have a sodium nitrate (NaNO₃) core and a titanium dioxide (TiO₂) shell. The MEPCM has a high melting temperature of 306.5 °C and a solidification temperature of 296.7 °C, which shows a potential usage as a high‐temperature compatible thermal storage medium for industrial waste heat recovery and concentrated solar power (CSP). The MEPCM is demonstrated to be thermally stable for 200 thermal cycles with a high latent heat of 135.3 J g⁻¹. The high‐temperature latent functional thermal fluid (HT‐LFTF) is prepared by dispersing the NaNO₃@TiO₂ MEPCMs into thermal oil. The test results show that MEPCMs provide an 18.4% effective thermal conductivity enhancement and 131.7% effective specific heat enhancement compared with base thermal oil. The rheological test indicates that the MEPCMs added in the thermal oil enhance the viscosity of the suspension and it increases with the MEPCM concentration. This work provides a new type of thermal oil–based functional thermal fluid containing high‐temperature MEPCM and paves the way for the application of LFTF in high‐temperature heat storage and transfer.

In this study, a new type of functional hybrid suspension for solar energy conversion and thermal energy storage was prepared by adding carbon nanotube (CNT) and microencapsulated phase-change material (MEPCM) into deionized water. MEPCM with octadecane as the core material and titania (TiO₂) as the shell material was synthesized by the sol–gel method. The MEPCMs were spherical particles with diameters of 2–4 μm, and the thickness of the shell was about 100 nm. The MEPCM achieved better thermal stability and thermal conductivity than the pure octadecane due to the TiO₂ shell. The melting and solidification latent heats of the MEPCM were about 154.24 and 154.26 J/g, respectively. The encapsulation efficiency of octadecane was calculated to be 65.84%. Most of all, the novel hybrid CNT and MEPCM suspensions exhibited remarkable dispersion stability owing to the stable reticular structure composed of CNT in the suspension. Compared with pure water, the thermal conductivity, specific heat of the MEPCM/CNT suspension improved by 34.48 and 43.57%, respectively and the photo-thermal conversion efficiency reached a high value of 86.0%. This work provided a new type of hybrid functional suspension towards direct absorption solar collector for solar energy conversion and storage.

Pseudo-potential lattice Boltzmann models have been widely applied in many multiphase simulations. However, most of these models still suffer from some drawbacks such as spurious velocities and untunable surface tension. In this paper, we aim to discuss the surface tension of a popular pseudo-potential model proposed by Kupershtokh et al., which has attracted much attention due to its simplicity and stability. The influence of a parameter on the surface tension in the model is analyzed. Based on the analysis, we proposed a method to adjust surface tension by changing the parameter in the model. However, the density distribution and the stability of the model also depend on the parameter. To adjust the surface tension independently, the pressure tensor modifying method is introduced and numerically tested. The simulation results show that, by applying the pressure tensor modifying method, the surface tension can be adjusted with little influence on the stability and density distributions.