Moliya Nurmalisa

This study validated the CO₂ distribution predicted by a computational fluid dynamics model considering CO₂ absorption by photosynthesis in a chamber and greenhouse. The effect of photosynthesis with CO₂ emission from a perforated tube remains not fully understood, although previous studies on CO₂ distribution in greenhouses have been conducted. Moreover, comparisons between CO₂ concentration measurement and simulation were obtained in the chamber and greenhouse model. Cases with open and closed side vents of the greenhouse showed that closed side vents have slightly more even of CO₂ concentration than those with open side vents inside the greenhouse. In contrast, the coefficient of variance (CV) of CO₂ inside the plant, open (8.8%) and closed (8.7%) side vents, induced almost no significant improvement. Additionally, cases of a rainy- and sunny-day model showed that photosynthetically active radiation possibly compensated CO₂ absorption through photosynthesis to be low at low light (rainy day) and higher at high light (sunny day). Nonetheless, the variability of CO₂ concentration inside the plant between rainy and sunny days determined almost no significant difference. Thus, this research shows characteristics of CO₂ distribution, assessing photosynthesis and the variability of CO₂ concentration that leads to the efficiency of CO₂ enrichment in the greenhouse.

A numerical simulation was performed to predict the distribution and uniformity of the airflow in a newly developed photosynthesis chamber. It is a semi-closed hanging-type chamber with three exhaust fans placed at the top to maintain airflow. The chamber's bottom (area: 0.55 m²) is fully opened for outside air inflow. For model validation, we measured both horizontal and vertical air velocity inside the chamber. After model validation, multiple sizes of transparent plates were applied just below the top of the chamber to investigate the effect of the plates on the uniformity of airflow. The simulation's results showed a diminishing stagnant area at the higher part of the plant, reaching a more uniform airflow distribution, with a Coefficient of Variation (CV) of 9.1% (full plate), 12.2% (half plate placed near the fans), 50.9% (without a plate), 45.5% (half plate placed on the opposite side of the fans), and 44.0% (small plate placed opposite with the fans). From simulation results, mounting a full-size transparent plate and a half-size one near the fans can significantly help to produce uniformair velocity distribution at the plant canopy.

Predictive numerical simulation of airflow uniformity in canopy plants could provide a suitable environment for plant growth. A numerical investigation of airflow in a photosynthesis chamber was conducted using the Computational Fluid Dynamics (CFD) model. This research-validated the numerical model with measurements performed in a bare bottom open chamber. The chamber has bottom openings with three exhaust fans on the roof. After model validation, airflow patterns and their uniformity were evaluated in different fan arrangements and doubled air volume rates. The obtained results showed that a more uniform airflow distribution was observed with increasing the fan’s air volume rate (0.0187, 0.0172, and 0.0177 m³s⁻¹), particularly fan in the middle position and diagonally position inside the plant with coefficients of variation of 14.36%, 9.3% and 10%, respectively. Moreover, increasing the fan’s air volume rate and moving the fan positions to the middle and diagonally can significantly help produce uniform air velocity distribution inside the plant.