A normally-closed thermally-actuated Tesla microvalve was designed (using microfabrication/ soft-lithography techniques involving 3D Printed molds), assembled and tested. The motivation of the research work is to develop an array of microvalves for precise delivery of water to individual plants in a field (with the goal of developing smart irrigation systems for high value cash-crops in the agricultural sector). It is currently impossible to control irrigation-water application at the level of a single plant.&nbsp; If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the output of every plant in a farm field could be optimized (i.e., food-water-energy nexus in sustainability applications).&nbsp; The aim of this study is to develop and test a microfluidic system that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field.&nbsp;Two types of test fluids were leveraged for thermo-hydraulic actuation in this study: (a) Design-I: using air, and (b) Design-II: using Phase Change Material (PCM). The PCM used in this study is PureTemp29. The proposed approach enabled a simple and cheap design for microvalves that can be manufactured easily and are robust to weather conditions (e.g., when exposed to the elements in orchards and open fields). Other advantages include:&nbsp; safe &amp; reliable operation; low power consumption; can tolerate anomalous pressure loads/ fluctuations; simple actuation; affords easy control schemes; is amenable for remote control; provides long-term reliability (life-cycle duration estimated to be 3~5 years); can be mass produced and is low maintenance (possibly requiring no maintenance over the life time of operation).The microvalve layout integrates two different functionalities in a single layer: a flow region (consisting of microchannels and Tesla microvalves) and a control region (consisting of blind and micro-chambers that are separated from the microchannel by a thin membrane). The microfluidic chip is heated from below causing the working fluid to expand in volume in the microfluidic chamber (~100s of microns) causing the a flexible polymeric thin-membrane (~100 microns or less in thickness) to flex on the side. The device is microfabricated from Poly-Di-Methyl-Siloxane (PDMS) using soft lithography techniques (using a 3D Printed mold). The control chamber contains either air (thermo-pneumatic actuation) or PCM (thermo-hydraulic actuation involving repeated melting/ freezing of PCM). The flow region contains the flow channel (inlet and outlet ports, horizontal section and valve seat). The experimental results from testing the efficacy of the two types of micro-valves show significant reduction (for thermo-pneumatic actuation using air and for thermo-hydraulic actuation using PCM) in water flow rates for similar actuation conditions (i.e., heater temperature values). PCM design is expected to consume less power (lower OPEX) for long-term actuation but may have slower actuation speed and have higher manufacturing costs (CAPEX). Air actuation design is expected to consume more power (higher OPEX) for longer-term operation but may have faster actuation speeds and lower manufacturing costs (CAPEX).

Repurposed Tesla Microvalve Arrays for Smart Irrigation in Precision Agriculture Applications

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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