Computational Modeling and Field Evaluation of an Innovative Solar Updraft Aeration System for Aquaculture in the Developing World

Throughout the Asia Pacific region, fish farming is a vital and growing source of food security and economic activity. Since 1970, aquaculture has maintained an average annual growth rate of 8.7% in the region. Currently, almost 90% of global aquaculture production currently takes place in Asia Pacific and over 20 million people are employed in the sector. This growth has been associated with a large increase in family-run backyard aquaculture and integrated agriculture-aquaculture reservoirs in areas like rural Vietnam. However, yields in those rural ponds have typically been low. This is largely due to lack of aeration systems, which introduce oxygen into the pond water and allow for greater stocking densities, healthier fish, and greater yields. Aeration systems typically are not employed in these remote communities due to high capital costs, lack of access to reliable electricity, and prohibitive maintenance costs. To address this need, a low-cost solar-thermal aeration system for implementation in resource-constrained settings was devised. The system consists of a metallic solar collector and a heat transfer column, which induces convective circulation in the water by dissipating heat to the cooler, deeper layers of the pond. As a result of the circulation produced by the device, oxygen generated by phytoplankton at the top of the pond is distributed throughout the water column, preventing oxygen losses to the atmosphere due to surface supersaturation and increasing the overall pond oxygen content. This paper presents the system models developed to validate the concept, including a Computational Fluid Dynamics (CFD) model and a diel Dissolved Oxygen (DO) simulation model. These models, when used in conjunction, can estimate the increase in DO to be expected by the introduction of passive aeration device. These models were tailored to represent two target test ponds in Bac Ninh, Vietnam. To calibrate the models, instrumentation measured relevant parameters including DO and water temperatures at various depths, wind speed, ambient air temperature, and solar irradiance. A description of the mechanical design, construction and installation of two full-scale prototypes is then discussed, and field results for the first month post-implementation are analyzed. The model and experimental results indicate that the device can improve the DO content at deep levels of the ponds (i.e. oxygen-depleted regions) and has the potential to improve aquaculture productivity in resource-constrained settings.