Search

【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.

Water jet scouring technology is extensively applied in marine engineering, harbor maintenance, river training, and various other fields, showcasing a broad spectrum of potential applications. However, achieving a comprehensive understanding of the transient sand scouring characteristics of water jets remains challenging due to the inherent complexity of the coupled flow structure involving submerged jets and environmental fluids, along with the intricate dynamics of two-phase flow. This study, rooted in numerical simulation and experimental validation, introduces pulse characteristics into a submerged jet. A thorough investigation is conducted to explore the transient sand scouring characteristics and sand transport laws of the submerged jet under diverse working conditions. The results of this study revealed that the main reason for the asymmetry of the sand pit morphology is not the non-uniform distribution of sand grains, but more likely caused by turbulence effects. Simultaneously, within the initial 0.25 s of the pulse cycle, suspended sediment resulting from the pulsed jet in the preceding cycle gradually transports to the dune and its surrounding areas. Subsequently, from 0.25 s to 0.5 s, sediment on both sides of the pit's bottom undergoes movement and amalgamation with the sediment that remained unsettled during the previous cycle. The findings reveal that higher jet velocities significantly enhance sediment suspension, migration, and redeposition, leading to deeper erosion and the rapid formation of the sand pit's outline within 2 s. Additionally, the jet velocity and the impact distance are identified as critical factors influencing erosion depth and sediment dynamics. These insights advance the understanding of erosion mechanisms driven by pulsed jets, highlighting their impact on sediment transport processes. The research findings provide important guidance for dredging and ocean engineering fields and offer a theoretical basis for improving the understanding of submerged jet scouring mechanisms. [ABSTRACT FROM AUTHOR]

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]