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【Objective】 The Venlo-type greenhouse is commonly used in commercial horticulture due to its efficient space utilization and superior light transmission. This study investigates the impact of spire width on microclimate within such greenhouses under natural ventilation conditions. 【Method】 The study focused on multi-span glass greenhouses. We used experimental measurement and CFD modelling to simulate the variations in temperature and airflow in the greenhouse for various spire widths: 3.2 m JD3.2, 3.6 m JD3.6 and 4 m JD4 under natural ventilation conditions when the outdoor wind speed was 0 and 1 m/s, respectively. 【Result】 ① Comparing with measured temperature at different sampling points in the greenhouse reveals that the relative error of the simulated temperature ranged from 0.2% to 3.3%, ② Spire width had a significant effect on temperature distribution in the greenhouse. In particular, temperature increased upward in the greenhouses with the JD3.2 spire, while, in contrast, temperature increased downward in the greenhouses with the JD3.6 spire. ③ Regardless of the outdoor wind speed, greenhouses with JD3.2 spire had the best heat removal efficiency. The heat removal efficiency of JD3.6 and JD4 spire and the associated temperature distribution in the greenhouses was better when the outdoor speed was 0 m/s than when the outdoor wind speed was 1 m/s. 【Conclusion】 For all spire widths we compared under different working conditions, the greenhouse with JD3.2 spire work best for ventilating and cooling the greenhouse.

【Objective】 The geometry of side ventilation windows is an important design parameter of greenhouse and this paper investigates the impact of their aspect ratio on air circulation in terraced greenhouses. 【Method】 The study is based on butterfly windows of terraced greenhouses in Guangzhou, using numerical simulation and experimental data measured from a greenhouse (Window C). We modelled five aspect ratios and compared the numerical simulations with experimental data. Air circulation in the greenhouse is quantified using non-uniformity coefficients. 【Result】 The average errors between the simulated and measured temperature and wind speed are 2.48% and 8.76% respectively, and their associated root mean square errors are 1.10 ℃ and 2.1×10-3 m/s, respectively. Changes in the aspect ratio do not result in significant effect on average temperature in the greenhouses, but affect temperature variation noticeably. Among the five aspect ratios we compared, Window A gives the greatest average wind speed and highest wind uniformity coefficient. Compared with Window C, it increase average wind speed by 23% and the wind speed uniformity coefficient by 41%. 【Conclusion】 Our results show that reducing the aspect ratio of the side ventilation window as currently used by local farmers can effectively increase the uniformity of both temperature and wind speed in the greenhouse.

In order to study the inter flow of magnetic drive pump, the total flow field of magnetic drive pump was simulated with CFD software based on SST k-ω turbulence model, and the flow fields distribution rules of cooling channel were analyzed under different working conditions. The numerical results show that the internal flow of magnetic drive pump was disorganized under small flow condition, then the inter flow becomes gradually smooth with the increase in flux, at the same time, the area with low speed near the outlet of reflow hole and the pressure of the cool circulation channel become smaller. The pressure of cooling channel gradually decreases in flow process from deflector hole to reflow hole, and the area of low pressure is easily formed near the outlet of reflow hole.

In order to reveal the evolution law of heat transfer during phase change in a corrugated plate flow passage of a plate heat exchanger, a two-dimensional two-channel model was established to simulate the process of heat transfer during phase change in an unsteady flow passage. The results show that when the time was <3/5T, the average Nusselt number and average heat flux of the heat exchange wall surface decreased with time, the average temperature of the cold fluid outlet increased, the average temperature of the hot fluid outlet decreased, and the volume fraction of the gas phase was no higher than 0.2. When the time was >3/5T, the average Nusselt number and the average heat flux of the heat exchange wall, as well as the outlet average temperature of the cold and hot fluid, reached stability, while the volume fraction of the gas phase increased rapidly. During the whole heat transfer process, the change in Nusselt number and heat flux along the heat transfer wall surface was basically the same, and its value fluctuated along the wall surface, displaying extrema at the exit, entrance, and corrugated corner. The temperature of the heat exchange wall fluctuated and increased along the Y-axis, and began stabilizing after a time >3/5T. As time went on, the temperature gradient of the hot and cold fluid outlet and the temperature difference between the two sides of the heat exchange wall decreased, whereas the relative parameters of the heat flow inlet section of the corrugated passage reached stability before those of the cold flow inlet section. The whole simulation process fully reflects the heat transfer mechanism during phase change in a corrugated plate flow passage of a plate heat exchanger. [ABSTRACT FROM AUTHOR]