a b s t r a c tThermodynamically limited processes make waste heat abundant in availability. An Organic Rankine Cycle (ORC) steam powered micro system designed to scavenge waste heat from various sources (transportation, industries or solar) is presented. The key boiler component is fabricated and characterized in this work. The system design has been inspired by the various efforts implemented in development of micro heat recovery devices and engines. The complete system consists of three individual micro components (1) boiler, (2) free piston expander and (3) superheater. Specifically, design, fabrication techniques, test setup and results of the miniaturized boiler are presented in this paper. A key design feature of the boiler is the inclusion of capillary channels for fluid flow from the surrounding reservoirs to the heated area. The pressurized steam is created by the boiler as a result of phase transformation of the working fluid. This pressurized steam can be utilized to drive another MEMS device (PZT membranes, turbines, thermoelectric, etc.) to generate power. In this upgraded boiler design, radial capillary channels and a thin film glass steamdome were considered to improve the operating efficiency. These inclusions enhanced capillary flow, energy absorption via phase change, mass flow rate and operating pressure. The power inputs of 1.8 W and 2.7 W were selected to simulate and characterize the boiler performance based on real-world waste heat source temperatures. For these power inputs, the maximum power absorption efficiency demonstrated by the boiler via phase change of the working fluid was approximately 88%. The peak operating pressure demonstrated by the boiler was 8.5 kPa. These thermally efficient characteristics of the boiler make it a potential future device for waste heat scavenging.
Hydrogen sulfide (H2S) is rapidly emerging as a biologically significant signaling molecule. In recent studies, sulfide level in blood or plasma has been reported to be in the concentration between 10 and 300 μM suggesting it acts in various diseases. This work reports progress on a new Lab-on-a-Chip (LOC) device for these applications. The uniquely designed, hand-held device uses advanced liberation chemistry that releases H2S from liquid sample and an electrochemical approach to detect sulfide concentration from the aqueous solution. The device itself consists of three distinct layers of Polydimethylsiloxane (PDMS) structures and a three electrode system for direct and rapid H2S concentration measurement. In this work specifically, the oxidation of sulfide at the gold (Au) and platinum (Pt.) electrodes has been examined. This is the first known application of electrochemical H2S sensing in an LOC application. The analytical utility and performance of the device has been assessed through direct detection using chronoamperometry (CA) scan and cyclic voltammetry (CV). An electrocatalytic sulfide oxidation signal has been recorded for sulfide concentration range vs, Ag/AgCl at different pH buffers at the trapping chamber. The calibration curve in the range 1 μM to 1 M was obtained using this electrode setup. The detection limit was found to be 0.1 μM. This device shows promise for providing fast and inexpensive determination of H2S concentration in aqueous samples.
Hydrogen sulfide (H2S) detection is an important capability for applications that range from environmental to biomedical use. In medical application, hydrogen sulfide may be an effective marker for various cardiovascular diseases. This work reports progress on H2S detection using a unique lab-on-a-chip device designed specifically for both environmental and biomedical applications. The chip consisted of three distinct layers of PEO/PDMS structures which have been bonded using various techniques including Reactive Ion Etching (RIE). First layer consisted of capillary channels to organize the flow of the sample. Also, liberation of the sulfide took place at this layer. The second layer was a H2S selective membrane. The third layer consisted of trapping chamber where trapped H2S samples were withdrawn for the quantification of H2S concentration. Fabrication of the first layer was accomplished using photolithography technique. Specifically, the chip incorporated unique design features and operation with advanced liberating chemistry that effectively released H2S from aqueous solutions introduced to the device. Mixture of poly-dimethylsiloxane-ethylene oxide polymeric (PDMS-b-PEO) and polydimethylsiloxane (PDMS) was cast on Su8 mold which produced super hydrophilic channels that allowed liquid flow via capillary action. The chip has been both fabricated and characterized as reported in this work. For each sample, 150 μL of the reaction volume was loaded in an HPLC vial and analyzed by a Shimadzu Prominence HPLC equipped with fluorescence detection and an eclipse XDB-C18 column. Sulfide transfer increased steadily at a rate of approximately 2% per minute until peaking at approximately 60% at 30 minutes. Percent transfer data show that sulfide diffused into the trapping chamber in a reproducible manner and that it was stable once it reached its peak at 30 minutes. Characterization and testing of the fully assembled device indicates significant promise and utility. Additional improvements may be made by optimizing parameters such as the decreasing ratio of the chamber volumes to the membrane area and the membrane thickness. The performance of this microfludic device was attributed to hydrophilic surface of PEO/PDMS, strong bonding of the chip using 3M transfer tape and well suited PDMS membrane that allow selective diffusion of hydrogen sulfide.
Hydrogen sulfide (H2S) bioavailability and exogenous hydrogen sulfide therapy regulate numerous disease states including inflammation, cancer, cardiovascular, neurological and gastrointestinal diseases. This proposed work investigates and demonstrates new H2S detection techniques well suited to disease detection through a Lab on a Chip (LOC) approach. Currently, a novel chip has been designed to detect the level of H2S present in the blood. A unique LOC device has various parts which serve specific purposes. Three layers, liberation layer, silicone membrane and the trapping layer were bonded and integrated with electrodes at trapping layer. The micro-fabricated liberation layer was coated with the sulfide liberation buffer. The liberated gas was then passed via a highly selective polymer membrane and then collected at the final chamber for its quantification. The electrochemical detection was made possible at this chamber using boron doped nanocrystalline diamond electrode (BDUNCD) electrode. Detection using bare electrode has been investigated. This research specifically highlights the optimization of the sensor integrated lab on the chip device to detect sulfide in biological range in a water based sample. The limit of detection was shown to be 0.1 μM. In general, results showed that detection of H2S using this method was less labor intensive, fast and achievable with low cost.
This paper presents the detailed fabrication and baseline operational characterization of a miniature device capable of recovering waste heat for power. Waste heat to power is the process of scavenging heat from a large process as a result of mechanical inefficiencies and using that heat to generate useful power. To address this waste heat to power recovery approach, a MEMS based microboiler has been investigated in this work which is capable of capturing waste heat. The microboiler consists of a micro fabricated boilerplate and a steamdome. The boilerplate has been designed with capillary channels capable of driving fluid flow from the surrounding reservoirs to the heated surface, thus eliminating the need of an electrically powered flow pump. The working fluid undergoes phase change inside the enclosed central steamdome attached atop the boilerplate. This pressurized vapor can be made available to another MEMS device such as PZT membrane capable of generating mechanical or electrical power. In this way, the discarded heat from the larger process can be utilized to generate power output. In contrast to the previous work, a thick acrylic steamdome has been replaced with a thin glass steamdome to minimize premature condensation of vapor due to heat loss via large mass. The tests were performed on the microboiler with the input powers of 1.8 W and 2.7 W and the comparisons of the results were carried out using a simulation model. The average temperatures at the top of the boilerplate were 106° C and 144° C for the power inputs of 1.8 W and 2.7 W, respectively. The available powers at the top of the boilerplate via heat conduction were 1.14 W and 1.72 W for the power inputs of 1.8 W and 2.7 W for the supplied powers of 1.8 W and 2.7 W, respectively. With these known available power throughputs and the heat of vaporization of the future working fluid, the calculated maximum mass flow rates were 13.6 mg/s and 9.12 mg/s, respectively.
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