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In order to gain a deeper knowledge of the heat and mass transfer processes in the case of starchy fruits and vegetables during microwave drying, we have conducted an experimental study based on a developed microwave apparatus for drying potato. The changes in the temperature, drying rate, moisture content, thermal parameters, moisture state and distribution of the potatoes samples during the microwave drying process were obtained. The results show that, according to the temperature changes of the samples dried at different microwave powers (600 W, 800 W, 1000 W), the microwave drying process can be divided into three stages: heating stage, constant temperature stage, and cooling stage. The moisture content reduction of the samples in the constant temperature stage accounted for more than 90% of the total reduction. Meanwhile, as the microwave drying process goes by, the thermal conductivity and thermal diffusivity of the samples both decrease first and then increase, while the volumetric heat capacity presents an opposite trend. Moreover, the range and amplitude of transverse relaxation time of the samples reduce over the drying time, which confirms the existence of massive, outward moisture-migration in the dried samples. The loss of the weakly bound water in the moisture-migration, which is closely related to the starch, has a significant effect on the heat and mass transfer in the dried samples. [ABSTRACT FROM AUTHOR]

The performance of an electronic radiator filled with metal foam with a porosity of 96% was studied. The effect of the factors including the flow rates, the pores per linear inch (PPI) and the numbers of fins was analyzed. The results show that the electronic radiator with metal foam reflects a stronger ability of the heat transfer compared to the electronic radiator without metal foam. With the increase in the flow rate between 10 L/h and 60 L/h, the heat transfer coefficient of both of the two electronic radiators will be improved, but it is also dependent on the number of fins. In this study, we find that the heat transfer coefficient first increases and then decreases with the number of fins. The optimum number is three. As for the effect of the PPI, the higher the PPI, the larger the heat transfer coefficient, while the pressure drop always increases with the flow rates' increase, the pores per linear inch (PPI) and the numbers of fins. [ABSTRACT FROM AUTHOR]

Droplet evaporation on rough substrates is ubiquitous in nature and has numerous technological applications, such as coating. To study the evaporation characteristics of nanodroplets on substrates with different rough structures, molecular dynamics simulations have been performed. Based on the Wenzel wetting model, three systems with different rough structures were constructed, in which the ratios of contact area (RCA) between substrates and nanodroplets were 33.3%, 50%, and 66.6%, respectively. The results indicate that the evaporation pattern of the nanodroplet in the system with RCA = 33.3% is the mixed mode, the evaporation pattern of the nanodroplet in the system with RCA = 50% is the constant-contact-radius mode, and the evaporation pattern of the nanodroplet in the system with RCA = 66.6% is the constant-contact-angle mode. Meanwhile, when the temperature of substrates (T) is suddenly raised from 0.67 to 0.83 ε/kB, followed by a corresponding rise in the temperature of nanodroplets, we find that temperature and evaporation rates of the nanodroplets increase with the increase in RCA in this period. Changes in RCA that lead to the changes in substrate wettability affect the heat transfer between nanodroplets and substrates. In particular, the more the substrate wettability, the higher the heat transfer efficiency. Moreover, the wettability of the substrate in the systems with RCA = 50% and 66.6% promotes the heat and mass transfer in the three-phase contact line region of the nanodroplets during the evaporation process, while the non-wettability of the substrate in the system with RCA = 33.3% suppresses the local heat and mass transfer. This work offers further knowledge of droplet evaporation on rough substrates, which, in turn, provides a reference for the process optimization of its technological applications. [ABSTRACT FROM AUTHOR]

Droplet nucleation and evaporation are ubiquitous in nature and many technological applications, such as phase-change cooling and boiling heat transfer. So far, the description of these phenomena at the molecular scale has posed challenges for modelling with most of the models being implemented on a lattice. Here, we propose an off-lattice Monte-Carlo approach combined with a grid that can be used for the investigation of droplet formation and evaporation. We provide the details of the model, its implementation as Python code, and results illustrating its dependence on various parameters. The method can be easily extended for any force-field (e.g., coarse-grained, all-atom models, and external fields, such as gravity and electric field). Thus, we anticipate that the proposed model will offer opportunities for a wide range of studies in various research areas involving droplet formation and evaporation and will also form the basis for further method developments for the molecular modelling of such phenomena. [ABSTRACT FROM AUTHOR]

• A heat and mass transfer model of droplet for artificial snow-making was established. • The critical droplet size for artificial snow-making under different environments was obtained. • The relationship between gas-liquid mass mixing ratio and snow-making density was studied, and the optimal gas-liquid mass mixing ratio suitable for artificial snow-making was obtained. This study investigates the heat and mass transfer of liquid droplets freezing in the process of artificial snow-making, and emphatically analyses the effects of droplet size, ambient temperature and relative humidity on the evaporative cooling and freezing of liquid droplets by establishing a theoretical model. On this basis, the critical droplet size for snow-making under different environmental conditions is obtained, and the accuracy of the droplet freezing model was verified by artificial snow-making experiments. Finally, by analyzing the density of artificial snow under different environmental conditions, the optimum gas-liquid mixing mass ratio (GLR) suitable for snow-making is obtained. The results show that the liquid droplets could be frozen under the action of self-evaporation and convection heat transfer with ambient. The time required for the droplet to be frozen completely shows a positive correlation with ambient temperature, relative humidity and droplet size. In the evaporation cooling stage, the droplet cooling rate increases with the decrease of ambient temperature, and in the phase transition stage, the time for the droplet resists the latent heat of phase transition increases with the increase of the droplet size. When the droplet size is smaller than the critical size for snow-making, the artificial snow can be achieved at a maximum temperature of 3 °C. The snow density decreases with the increase of GLR. And when the GLR is greater than 0.15, the snow density tends to be stable. [ABSTRACT FROM AUTHOR]