Techniques of zone melting were applied to systems of organic compounds using a simple apparatus which allowed the passage of 18 molten zones through the sample during a single run.Spectrophotometric analysis indicated that the methyl violet concentration in naphthalene could be lowered to 1 p.p.m. by a single passage through the 18-zone column. Similarly, combustion of samples followed by counting of the CO2 in an ionization chamber showed that the concentration of carbon-14labeled naphthalene in benzoic acid could be lowered to less than one part per 10 million using this zone refiner.
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.
Thermal energy is a leading topic of discussion in energy conservation and environmental fields. Specifically for large-scale applications solar energy and concentrated solar power (CSP) systems use techniques that include thermal energy storage systems and phase change materials to harvest energy. However, on the smaller centimeter scale, there have been historically fewer investigations of these same techniques. The main goal of this paper is to investigate thermal energy storage (TES) as applied to a small scale system for thermal energy capture. Typical large-scale TES consists of a phase change material that usually employs a wax or oil medium held within a conductive container. The system stores the energy when the wax medium undergoes a phase change. In typical applications like buildings, the system absorbs and stores incoming thermal energy during the day, and releases it back to the surrounding environment as temperatures cool at night. This paper presents a new TES unit designed to integrate with a thermoelectric for energy harvesting application in small, cm-scale applications. In this manner, the TES serves as a thermal battery and source for the thermoelectric, even when originating power supply is interrupted. A unique feature of this TES is the inclusion of internal heat pipes. These heat pipes are fabricated from copper tubing and filled with working fluid, mounted vertically, and immersed in the wax medium of the TES. This transfers heat to the wax by means of thermal conductivity enhancement as an element of the heat pipe operation. This represents a first of its kind in this small-scale, thermal harvesting application. As tested, the TES rests atop a low temperature (60 °C) heat source with a heat sink as the final setup component. The heat sink serves to simulate thermal energy rejection to a future thermoelectric device. To measure the temperature change of the device, thermocouples are placed on either side of the TES, and a third placed on the heat source to ensure that the energy input is appropriate and constant. Heat flux sensors (HFS) are placed between the heat source and the TES and between the TES and heat sink to monitor heat transferred to and from the device. The TES is tested in a variety constructions as part of this effort. Basic design of the storage volume as well as fluid fill levels within the heat pipes are considered. Varying thermal energy inputs are also studied. Temperature and heat flux data are compared to show the thermal absorption capability and operating average thermal conductivities of the TES units. The baseline average thermal conductivity of the TES is approximately 0.5 W/mK. This represents the TES with wax alone filling the internal volume. Results indicate a fully functional, heat pipe TES capable of 8.23 W/mK.
This article investigates the use of advanced, high porosity thermally conductive foams and a thermal energy storage (TES) device for small scale thermal energy harvesting. In final application, it may be employed in various real world situations that include existing systems like thermoelectric generators (TEGs) and thermal scavenging systems that provide power output from freely available thermal sources. Experimental tests were conducted using various porosity metallic copper foams ranging from 85 % to 89 % porosity. Copper foams were selected to serve as the heat exchanger innards and examined for several key attributes. These included the ability of the foams to yield capillary action with working fluids like water or 3M™ HFE7200. Thermal energy absorption by the exchanger to the working fluid was also monitored. These results were compared to other exchangers based on capillary channel fabrication techniques as previously reported by the research team. Full characterization was based on operating temperature, measured thermal input, mass transfer rate, and heat transfer capability. Preliminary investigation of a matching, small-scale TES unit designed to integrate with the heat exchanger and a future thermoelectric for energy harvesting application was also conducted. Thermal storage was accomplished via solid-liquid phase change of a paraffin wax within the TES device forming a so-called “thermal battery.” In a final design, the TES includes what is defined by thermodynamics as heat pipes. The integrations of several heat pipes, made of copper tubing and filled with working fluid, mounted vertically and immersed in the wax medium will transfer heat to the wax by means of thermal conductivity and phase transition. This represents a first of its kind in this small-scale, thermal harvesting application. The specific tests performed in this initial work included one TES unit filled with a paraffin wax medium and a second that contained several copper vertically placed tubes surrounded by the paraffin wax. The overall thermal conductivity of the phase change medium (wax) was investigated for both constructions as was the ability of each to absorb thermal energy directly. Results indicated capillary action of the working fluid was possible via incorporation of copper foams within the heat exchanger. Maximum heat flux observed in exchanger tests was 0.27 kW/m2 given an operating temperature of 76.6 °C and 2.5W thermal input. Thermal storage tests indicated a maximum thermal capture rate of 0.91 W and phase change material thermal conductivity of 1.00 W/mK for the TES device constructed with copper tubing innards. This compared favorably to the baseline wax conductivity of approximately 0.32 W/mK. Future efforts will fully incorporate both the heat exchanger and matching TES device for a complete harvesting and thermal capture system. The ability of the exchanger to provide thermal energy for storage to the “thermal battery” will be monitored.
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