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Summary The numerical simulation is effective to investigate the thermal performance of the packed bed latent heat thermal energy storage system which can provide more detailed information. There are three most commonly used numerical models developed based on the porous medium model: the continuous solid phase model, improved continuous solid phase model, and concentric dispersion model. The applicability of these models is compared by evaluating the variations of fluid temperature, temperature difference inside phase change material capsule, thermocline thickness, charging power, and computational time. The results show that the concentric dispersion model can accurately simulate the charging processes with a deviation of less than 5% between the results of the concentric dispersion model and experimental results. When the Bi is smaller than 1, the effect of the temperature gradient inside the capsule can be neglected and the continuous solid phase model shows a deviation less than 2%. When the Ste is smaller than 0.1, the sensible heat is negligible and the improved continuous solid phase model shows a deviation less than 2%. The computational time of the concentric dispersion model is generally 30% more than the other two models. [ABSTRACT FROM AUTHOR]

This work focuses on the problem of non-contact measurement for vegetables in agricultural automation. The application of computer vision in assisted agricultural production significantly improves work efficiency due to the rapid development of information technology and artificial intelligence. Based on object detection and stereo cameras, this paper proposes an intelligent method for vegetable recognition and size estimation. The method obtains colorful images and depth maps with a binocular stereo camera. Then detection networks classify four kinds of common vegetables (cucumber, eggplant, tomato and pepper) and locate six points for each object. Finally, the size of vegetables is calculated using the pixel position and depth of keypoints. Experimental results show that the proposed method can classify four kinds of common vegetables within 60 cm and accurately estimate their diameter and length. The work provides an innovative idea for solving the vegetable's non-contact measurement problems and can promote the application of computer vision in agricultural automation. [ABSTRACT FROM AUTHOR]

• A three-dimensional theoretical model for droplet freezing is proposed. • Crystallization kinetics is taken into the temporal and spatial thermodynamic analysis. • The dynamic behavior of ice-water phase front in recalescence stage is revealed. • Theoretical and experimental results show a good agreement. A three-dimensional (3-D) theoretical model is proposed to take the crystallization kinetics into the consideration of heat transfer, which allows for the description of the entire freezing process of a supercooled water droplet with the inclusion of the description of recalescence. The temporal evolution of the temperature and solid mass fraction at various stages during freezing are numerically studied, which shows a good agreement with the experimental results of the water droplet frozen in cold nitrogen gas stream. In particular, the ice-water phase front dynamics initiated from a single ice nucleation site is numerically investigated in recalescence stage, which shows that the ice-water phase front spreads over the entire water droplet with a diameter of 1.4 or 2.0 mm within about 16.0 or 23.0 ms governed by crystallization kinetics, leading to the drastic increase of the temperature and solid mass fraction of the droplet under the effect of thermodynamics. The present theoretical model can be useful to describe the dynamic behavior of ice crystallization in many other relevant cases. [ABSTRACT FROM AUTHOR]

• The non-uniform melting of an ice particle in free ascending has been investigated. • The effects of supercooling and superheating have been discussed. • The morphological variations of the melting ice particle have been obtained and analyzed. In order to achieve a thorough understanding of the flow and heat transfer characteristics of phase change slurry, melting process of a spherical ice particle during free ascending in resting water can provide fundamental knowledge. The motion of the ice particle is depicted by the momentum equation while the flow and heat transfer are described using the enthalpy-porosity model to take the phase change into account. The ascending and melting characteristics at different superheating degrees of water as well as supercooling degrees of the ice particle are investigated. The results show that the spherical ice particle first accelerates to the maximum velocity of approximately 0.04 m s−1 under the effect of buoyancy, and then gradually decelerates as the ice particle melts. The superheating degree of water has a significant influence on the movement and melting characteristics of the ice particle while the supercooling degree imposes negligible effect. The variations in morphology and the local heat transfer coefficient of the ice particle are obtained and analyzed. It is found that the local heat transfer coefficient on the surface of the ice particle significantly influences the morphology of the ice particle during melting, which appears as sphere, ellipsoid, barrel shape and oval shape, sequentially. [ABSTRACT FROM AUTHOR]

The eutectic mixture of lauric acid (LA) and stearic acid (SA) is a desirable phase change material (PCM) due to the constant melting temperature and large latent heat. However, its poor thermal conductivity has hampered its broad utilization. In the present study, pure LA, SA and the mixtures with various mass fractions of LA-SA were used as the basic PCMs, and 10 wt% expanded graphite (EG) was added to enhance the thermal conductivities. The phase change behaviors, microstructural analysis, thermal conductivities and thermal stabilities of the mixtures of PCMs were investigated by differential scanning calorimetry (DSC), scanning electronic microscope (SEM), transient plane source (TPS) and thermogravimetric analysis (TGA), respectively. The results show that the LA-SA binary mixture of mixture ratio of 76.3 wt%: 23.7 wt% forms an eutectic mixture, which melts at 38.99 °C and has a latent heat of 159.94 J/g. The melted fatty acids are well absorbed by the porous network of EG and they have a good thermal stability. Furthermore, poor thermal conductivities can be well enhanced by the addition of EG.