Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 100251

100251 - Design, Fabrication and Testing of a Novel Thermally-Actuated Tesla Valve (Tatv): A Hybrid Microvalve 

Conventional technologies that are deployed in contemporary irrigation systems need improvement, especially for precise metering of water to individual plants. In this study, a novel thermally-actuated hybrid microvalve was designed, fabricated, assembled, and tested using soft lithography-based approaches to develop microfluidic platforms which enable precise delivery of water volumes to individual plant for precision agriculture application (other applications include hydroponics and deep-space missions). The modified design integrates the “normally open and closed” hybrid configurations of Tesla Valves with a thermo-pneumatic actuator microfabricated in-situ - that modulates the diodicity of the microvalve apparatus in the microfluidic chip. Here, diodicity (Di) is defined as the ratio of flow rate in the forward direction to that of the reverse direction (for a constant value of pressure drop that is imposed on a microvalve device).The results from the study successfully demonstrated the operation of an array of Tesla Valves that are normally open in forward direction and marginally closed in reverse direction at room temperature (i.e., with Di > 1, the flow resistance values were different when the inlet and outlet ports were swapped). When the microfluidic chip was heated (at steady state conditions with a nominal temperature of ~30°C), the diodicity virtually vanished (i.e., Di ≈ 1) resulting in both reverse and forward directions being normally open (or having the same flow resistance – irrespective of the flow direction).

Microvalves can be categorized as “active” (that require external power sources for actuation and control) and “passive” (that do not require extrinsic power sources for modulation or control of flow rates). Of the different types of passive microvalves, a niche set can be identified that gained popularity in the literature – consisting of no-moving-parts (NMP) microvalves. These unique miniaturized microvalve architectures (i.e., passive microvalves) do not have any equivalent counterparts (in the conventional sense) for valves that are typically deployed for engineering applications on a bigger scale (i.e., on the mezo-scale). Examples of NMP valve architectures include Tesla Valve and Capillary-Burst valves.  These NMP microvalves were primarily developed for various fixed configurations – i.e., either as a “normally open” state or “normally closed” state before they are actuated to change their normal state [14]. Realizing a leak proof microvalve has also been an enigma in the microfluidics literature, since only a few microvalve architectures enable absolutely leak-proof operation (such as “ice-valve”) while the vast majority of microvalves are “leaky” [15].

Microvalves can be categorized based on their mode of operation and also their mechanism (or method) of actuation. Based on the mode of operation (or actuation scheme), microvalves can be divided into either normally open or normally closed valves [16]. The normally open state refers to the configuration where the fluid flow is unimpeded as a default state and there is no external or internal impedance imposed explicitly on the fluidic system. The normally closed state refers to the condition when the fluid flow is impeded explicitly by the microvalve in the default state (and the impedance is reduced or modulated or eliminated upon actuation of the microvalve). The actuation mechanisms for microvalves can include: membrane deformation [17], piezoelectric devices [18], magnetic fields (or electro-magnetic actuation) [19], electric fields (e.g., electrostatic actuation) [20], thermal stimulation [21,22,23], bi-stable actuators [24], and smart-materials-based actuators (e.g., shape-memory alloys or “SMAs”) [14].

In this study, a hybrid microvalve (similar to a Tesla Valve configuration) was developed and tested using soft lithography-based approaches. The microvalve integrates the “normally open and closed” hybrid configurations of Tesla Valves with a thermo-pneumatic (thermal-hydraulic) actuator microfabricated in-situ - that modulates the flow rates and diodicity of the microvalve.

Presenting Author: Ashok Thyagarajan TAMU

Presenting Author Biography: PhD student at TAMU

Authors:

Jonghyun Lee TAMU
Ashok Thyagarajan TAMU
Debjyoti Banerjee Texas A&M University