Abstract

It is currently impossible to control irrigation at the level of a single plant. Even with drip irrigation, in which emitters could conceivably be placed on a plant-by-plant basis, there is no way to control the amount of water emitted according to the needs of the individual plants. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the water input for every plant in a farm (or field) could be optimized. Therefore, we are exploring the possibility of developing a microfluidic system that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. The principal aim is to show proof of concept by building and testing a prototype to produce data suggestive of the potential for multiple individually controllable microfluidic ports along a pressurized tube of water. Hence, in this study we perform experiments using a thermally actuated microvalve for irrigation in precision agriculture applications. The microvalve was manufactured using soft-lithography techniques, i.e., using polydimethylsiloxane (PDMS). The active microvalve was designed for a “normally open” configuration and consists of two layers: (1) a flow layer and (2) a control layer. The flow layer contains the water inlet, outlet, and the flow channels for passage of water. The control layer contains an enclosure (chamber) which expands upon heating, which in turn deforms a thin membrane into the flow layer and thus impedes (or reduces) the water flow rate in the flow layer. Both layers are bonded together and then on a glass substrate. The bonded PDMS microvalve and glass assembly is heated to different temperatures for enabling the actuation of the microvalve. Experiments were performed using two microvalves of identical design but with two different actuation fluids. The first design used the control chamber filled the air while the second design used the control chamber containing a Phase Change Material (PCM). Experiments were performed to determine the reduction of water flowrate as the membrane deforms with increase in temperature. Water flows into the inlet of the microvalve from a syringe barrel, with a hydrostatic pressure head of about 0.62 [m]. The water from the microvalve outlet was collected in a 10[ml] pipette. The results show that the water flowrate decreased as the temperature at the base of the microvalve was increased. There was a 60% and 40% reduction in the water flowrate through the microvalve design with control chamber containing air and PCM (phase change material) respectively.

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