• Journal of Hydrogen and New Energy
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• v.35 no.4
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• pp.377-383
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• 2024

In this paper, the flow uniformity improvement and flow characteristic of the sensor condenser for a heat exchanger cleaning system were studied using response surface method and computational-fluid-dynamics. The design variable was defined as a shape for controllable sensor condenser area. The objective functions were defined as the improvement of flow uniformity in heat exchanger cleaning system tubes. The flow uniformity improvement and flow characteristic of optimum model was verified by numerical analysis and the reliability of the model was retained by comparison of numerical analysis and comparative analysis with the reference model.

• Journal of Sensor Science and Technology
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• v.9 no.3
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• pp.153-162
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• 2000

Triple points of high purity materials have been used to calibrate primarily the capsule-type platinum resistance thermometer (PRT) in the temperature range of the triple point of equilibrium hydrogen (13.8033 K) and water (273.16 K). In this work, triple points of Ne, $O_2$, Ar, Hg and $H_2O$ except for the triple point of equilibrium hydrogen were realized to establish the International Temperature Scale of 1990 (ITS-90). At each fixed point, two capsule-type PRTs, which were selected for the international comparison, were tested two times. The combined uncertainties of the realization of each triple point were calculated considering the type A and type B evaluation. In Korea Research Institute of Standards and Science, the combined standard uncertainties of the defining triple Points by the ITS-90 were estimated to about 0.18 mK for Ne, 0.14 mK for $O_2$, 0.14 mK for Ar, 0.24 mK for Hg and 0.11 mK for $H_2O$, respectively.

• Journal of Sensor Science and Technology
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• v.4 no.2
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• pp.37-44
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• 1995

A coprecipitation method was used for preparing Ca and Pt doped $SnO_{2}$-based material. Crystallite size and specific surface area were investigated by TEM, XRD and BET analysis. $SnO_{2}(Ca)/Pt$ based thick film devices were prepared by a screen printing technique for hydrocarbon gas detecting. Then the electrical and sensing characteristics of devices were investigated. As Ca and Pt addition, the crystal growth of $SnO_{2}$ was suppressed during calcining and sintering, and the sensitivity of $SnO_{2}(Ca)/Pt$ thick film to gas was enhanced. Also any difference in the sensing properties has to be attributed to the Pt and Au electrode. For the 2000 ppm $CH_{4}$, the sensitivity of $SnO_{2}(Ca)/Pt$ thick film devices were about 83% at an operating temperature of $400^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.21 no.6
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• pp.425-428
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• 2012

This paper presents the fabrication and characterization of graphene based hydrogen sensors. Graphene was synthesized by annealing process of Ni/3C-SiC thin films. Graphene was transferred onto oxidized Si substrates for fabrication of chemiresistive type hydrogen sensors. Au electrode on the graphene shows ohmic contact and the resistance is changed with hydrogen concentration. Nanoparticle catalysts of Pd and Pt were decorated. Response factor and response (recovery) time of hydrogen sensors based on the graphene are improved with catalysts. The response factors of pure graphene, Pt and Pd doped graphenes are 0.28, 0.6 and 1.26, respectively, at 50 ppm hydrogen concentration.

• Journal of Sensor Science and Technology
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• v.20 no.3
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• pp.168-171
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• 2011

Porous 3C-SiC(pSiC) samples with different pore diameters were prepared from poly crystalline N-type 3C-SiC by electrochemical anodization. The pSiC surface was chemically modified by the sputtering of Pd and Pt nano-particles as a hydrogen catalyst. Changes in resistance were monitored with hydrogen concentrations in the range of 110 ppm - 410 ppm. The variations of the electrical resistance in the presence of hydrogen demonstrated that Pd and Pt-deposited pSiC samples have the ability to detect hydrogen at room temperature. Regardless of the catalyst, the 25 nm pore diameter samples showed good response and recovery properties. However, the 60 nm samples showed unstable and slow response. It was found that the pore size affects the catalyst reaction and consequently, results in changes of the sensitivity to hydrogen.

• Journal of Sensor Science and Technology
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• v.19 no.2
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• pp.67-86
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• 2010

Hydrogen is emerging as clean fuel and important industrial raw materials. The hydrogen gas is not sensed by the human olfactory system, But the combustion characteristics of hydrogen is that the ignition is very easy, the propagation speed of the flame is very fast and explosion limits is a wide range of 4 %~75 %. Therefore it is extremely in danger, and the need for its leakage detection technologies is especially important in places such as a production, transportation, storage and usage. The hydrogen sensors are classified with ceramic type, semiconductor type, optical type, electrochemical type and so on. Hydrogen sensors and their technologies are reviewed in detail for materials, fabrication process, sensing characteristics, good point and faults, and production and utilization of sensors be discussed.

• Journal of Sensor Science and Technology
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• v.19 no.2
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• pp.87-91
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• 2010

Hydrogen gas sensors were fabricated using $PdO_x$ loaded with SWNTs. The nanoparticle powders of $SWNT_s-PdO_x$ composite were deposited on Si wafer substrates by a vacuum filtering deposition method. The fabricated sensors were tested against hydrogen gas. The composition ratio that exhibited the highest response to hydrogen gases was SWNTs : $PdO_x$ = 98 : 2 in wt% ratio at operating temperature of about $150^{\circ}C$. The response and recovery times were shorter than 1.0 min. in presence of 1000 ppm hydrogen.

• Journal of Sensor Science and Technology
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• v.18 no.4
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• pp.269-273
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• 2009

In this paper, a study on a portable hydrogen alarm system based on the palladium coated single mode fiber sensor has been reported. The fabricated hydrogen sensor exhibited 0.14 dB, 0.41 dB and 0.54 dB optical intensity variation when it was exposed by the nitrogen and hydrogen mixed gas containing 0.5 %, 1 % and 4 % of the hydrogen concentration, respectively. The fabricated sensor exhibited 20 second of response time and 120 second of recovery time for 4 % hydrogen containing gas. The fiber optics layout and software algorithm for detection of hydrogen leakage have been presented. The implanted portable hydrogen alarm system successfully generated an alarm signal when a 4 % hydrogen containing gas was leaked out.

• Journal of Sensor Science and Technology
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• v.18 no.3
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• pp.222-225
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• 2009

This paper describes the fabrication and characteristics of Schottky micro hydrogen sensors for high temperatures by using polycrystalline(poly) 3C-SiC thin films grown on Si substrates with thermal oxide layer using APCVD. Pd/poly 3C-SiC Schottky diodes were made and evaluated by I-V and C-V measurements. Electric current density and barrier height voltage were $2{\times}10^{-3}A/cm^2$ and 0.58 eV, respectively. These devices could operate stably at about 400 $^{\circ}$. The characteristics of implemented sensors have been investigated in terms of sensitivity, linearity of response, response rate, and response time. Therefore, from these results, Pd/poly 3C-SiC Schottky devices have very high potential for high temperature $H_2$ sensor applications.

• Journal of Sensor Science and Technology
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• v.29 no.6
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• pp.399-406
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• 2020

Pd nanogap hydrogen sensors were developed using an elastomeric substrate and operated through an on-off mechanism. A 10 nm thick Pd thin film was formed on a polydimethylsiloxane (PDMS) substrate, and 50% of the physical strain was applied in the longitudinal direction to fabricated uniform nanogaps. The initial concentration of the hydrogen gas for the PDMS/Pd films was controlled, and subsequently, the on-off switching response was measured. We found that the average nanogap was less than 50 nm, and the Pd nanogap hydrogen sensors operated over a wide range of temperatures. In particular, the sensors work properly even at a very low temperature of -40℃ with a fast response time of 2 s. In addition, we have investigated the relative humidity and annealing effects.