A Thermally Actuated Microvalve for Irrigation in Precision Agriculture Applications

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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Experimental Study on Thermal Characteristics of Finned Coil LHSU Using Paraffin as Phase Change Material

Journal of Heat Transfer ◽

10.1115/1.4035321 ◽

2017 ◽

Vol 139 (4) ◽

Cited By ~ 1

Author(s):

Guansheng Chen ◽

Nanshuo Li ◽

Huanhuan Xiang ◽

Fan Li

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Phase Change ◽

Phase Change Material ◽

Water Flow ◽

Water Flow Rate ◽

Thermal Characteristics ◽

Heat Transfer Fluid ◽

Latent Heat Storage ◽

Change Material

It is well known that attaching fins on the tubes surfaces can enhance the heat transfer into and out from the phase change materials (PCMs). This paper presents the results of an experimental study on the thermal characteristics of finned coil latent heat storage unit (LHSU) using paraffin as the phase change material (PCM). The paraffin LHSU is a rectangular cube consists of continuous horizontal multibended tubes attached vertical fins at the pitches of 2.5, 5.0, and 7.5 mm that creates the heat transfer surface. The shell side along with the space around the tubes and fins is filled with the material RT54 allocated to store energy of water, which flows inside the tubes as heat transfer fluid (HTF). The measurement is carried out under four different water flow rates: 1.01, 1.30, 1.50, and 1.70 L/min in the charging and discharging process, respectively. The temperature of paraffin and water, charging and discharging wattage, and heat transfer coefficient are plotted in relation to the working time and water flow rate.

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Using a Novel Phase Change Material-Based Cooling Tower for a Photovoltaic Module Cooling

Journal of Solar Energy Engineering ◽

10.1115/1.4044890 ◽

2019 ◽

Vol 142 (2) ◽

Cited By ~ 1

Author(s):

Nasrin Abdollahi ◽

Masoud Rahimi

Keyword(s):

Surface Temperature ◽

Phase Change ◽

Phase Change Material ◽

Output Power ◽

Water Flow ◽

Flow Rate ◽

Cooling Tower ◽

Water Flow Rate ◽

Helical Tube ◽

Change Material

Abstract This paper presents an experimental investigation on a hybrid solar system, including a water-based photovoltaic (PV) solar module and a phase change material (PCM)-based cooling tower, for cooling of the module. Elimination of heat from the PV module was performed by the use of water in the back of the panel. The PCM-based cooling tower was used as a postcooling system. A composite oil consisting of 82 wt% coconut oil and 18 wt% sunflower oil has been used as a novel phase change material in the cooling tower. The helical tubes of the cooling tower were fabricated in two different curvature ratios of 0.054 and 0.032. The experiments were performed at three different water flow rates of 11.71, 16.13, and 19.23 mL/s. The cooling performance evaluation was carried out using the average surface temperature and output power of the photovoltaic panel. The results indicated that diminution of the average PV surface temperature relative to the reference temperature was 34.01 and 32.36 °C at a water flow rate of 19.23 mL/s for the cooling systems with helical tube curvature ratios 0.054 and 0.032, respectively. Furthermore, the highest electric output power was achieved for the cooling system with a helical tube curvature ratio of 0.054 at a water flow rate of 19.23 mL/s.

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A Thermally Actuated Microvalve for Smart Irrigation in Precision Agriculture Applications

10.1115/fedsm2021-65899 ◽

2021 ◽

Author(s):

Alaba Bamido ◽

Debjyoti Banerjee

Keyword(s):

Precision Agriculture ◽

Soft Lithography ◽

Large Field ◽

Cfd Simulations ◽

Manufacturing Costs ◽

Pneumatic Actuation ◽

3D Printed ◽

Thermally Actuated ◽

Control Layer

Abstract A normally-open thermally-actuated 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 application of irrigation-water at the level of a single plant. 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). The aim of this study is to develop and test a microfluidic system (consisting of a microvalve array) that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. Two types of test fluids were leveraged for thermo-hydraulic actuation of the microvalves developed 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: safe and 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 consists of two layers: a flow layer and a control layer. The control layer is heated from below and contains a microfluidic chamber with a flexible polymeric thin-membrane (200 microns in thickness) on top. 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 layer 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 a 60% reduction (for thermo-pneumatic actuation using air) and 40% reduction (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). Computational Fluid Dynamics (CFD) simulations were performed to investigate the effect of flowing water (in the microfluidic channel) on the average absolute pressure and temperature of air in the actuation chamber. The CFD simulations were performed using a commercial tool (Ansys™ 2019R1®). The results from the CFD simulations are presented in this study.

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