Simulation of night-time condensation on cucumber leaves in single slope solar greenhouse

Condensation on cucumber leaves provides a necessary condition for pathogen infection. However, it could be costly to monitor the condensation of all leaves in a greenhouse. Therefore, the CFD model for the spatial and temporal distribution of leaf microclimate, condensation on leaf surface and the indoor microclimate of single-slope solar greenhouse under closed-film condition at night was studied. In order to simplify the input parameters, the boundary condition variables of the model were reduced to 5 h^‑1, which were outdoor solar radiation intensity, outdoor air temperature (T_a), outdoor relative humidity (RH), outdoor average wind speed per hour and soil temperature at 0.5 m depth, without affecting the simulation performance of the model. According to the verification of the measured and simulated values of each microclimate parameter inside greenhouse, the results show that the mean absolute error (MAE) of T_a in 12 h was 1.47°C. The MAE of RH in 12 h was 1.95%. The absolute error (AE) of leaf wetness duration (LWD) between simulated and measured value was less than 1 h. In the study of spatial distribution simulation, the MAE of T_a was 0.31°C and the MAE of RH was 1.05%. The simulation result of condensation distribution on leaves within 12 h at night were tested. The true positive rate (TPR), true negative rate (TNR), false positive rate (FPR), false negative rate (FNR) and accuracy (ACC) of the model were 0.89, 0.99, 0.01, 0.28 and 0.9, respectively. This paper provided a reference for early warning model of disease based on the temporal and spatial distribution characteristics of microclimate in solar greenhouse.