Comparisons Using Methods of Continuum Mechanics and Monte Carlo at Differentially Pumped Chamber

Maxa, Jiří; Bílek,; Hlavatá,; Vyroubal, Petr; Lepltová,

doi:10.3849/aimt.01120

Cited by 15 publications

(14 citation statements)

References 4 publications

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“…The designed nozzle diameter was 1.5 mm, with 0.5 mm length and opening angle 12 • according to Daněk [4]. The next step was to calculate the appropriate shape and spot to place the probe with the thermocouple system [5,6], which is crucial to maximize the utilization of the cryogenic temperature within the supersonic flow [7][8][9][10].…”

Section: +1mentioning

confidence: 99%

Energy Harvesting Using Thermocouple and Compressed Air

Bayer

Maxa

Šabacká

2021

Sensors

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In this paper, we describe the possibility of using the energy of a compressed air flow, where cryogenic temperatures are achieved within the flow behind the nozzle, when reaching a critical flow in order to maximize the energy gained. Compared to the energy of compressed air, the energy obtained thermoelectrically is negligible, but not zero. We are therefore primarily aiming to maximize the use of available energy sources. Behind the aperture separating regions with a pressure difference of several atmospheres, a supersonic flow with a large temperature drop develops. Based on the Seebeck effect, a thermocouple is placed in these low temperatures to create a thermoelectric voltage. This paper contains a mathematical-physical analysis for proper nozzle design, controlled gas expansion and ideal placement of a thermocouple within the flow for best utilization of the low temperature before a shockwave formation. If the gas flow passes through a perpendicular shockwave, the velocity drops sharply and the gas pressure rises, thereby increasing the temperature. In contrast, with a conical shockwave, such dramatic changes do not occur and the cooling effect is not impaired. This article also contains analyses for proper forming of the head shape of the thermocouple to avoid the formation of a detached shockwave, which causes temperature stagnation resulting in lower thermocouple cooling efficiency.

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Section: +1mentioning

confidence: 99%

Energy Harvesting Using Thermocouple and Compressed Air

Bayer

Maxa

Šabacká

2021

Sensors

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“…The pressure and shock wave distribution in the primary path of the electron beam passing through the differentially pumped chamber has a great influence on the resulting image quality [ 1 , 2 , 3 ]. The environmental scanning electron microscope (ESEM) is one of the most promising tools for studying plant [ 4 , 5 , 6 ] and polymer [ 7 , 8 ] samples using special signal electron detectors [ 9 ], which were developed based on gas flow simulations.…”

Section: Introductionmentioning

confidence: 99%

Application of Prandtl’s Theory in the Design of an Experimental Chamber for Static Pressure Measurements

Šabacká

Neděla

Maxa

et al. 2021

Sensors

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Pumping in vacuum chambers is part of the field of environmental electron microscopy. These chambers are separated from each other by a small-diameter aperture that creates a critical flow in the supersonic flow regime. The distribution of pressure and shock waves in the path of the primary electron beam passing through the differentially pumped chamber has a large influence on the quality of the resulting microscope image. As part of this research, an experimental chamber was constructed to map supersonic flow at low pressures. The shape of this chamber was designed using mathematical–physical analyses, which served not only as a basis for the design of its geometry, but especially for the correct choice of absolute and differential pressure sensors with respect to the cryogenic temperature generated in the supersonic flow. The mathematical and physical analyses presented here map the nature of the supersonic flow with large gradients of state variables at low pressures at the continuum mechanics boundary near the region of free molecule motion in which the Environmental Electron Microscope and its differentially pumped chamber operate, which has a significant impact on the resulting sharpness of the final image obtained by the microscope. The results of this work map the flow in and behind the Laval nozzle in the experimental chamber and are the initial basis that enabled the optimization of the design of the chamber based on Prandtl’s theory for the possibility of fitting it with pressure probes in such a way that they can map the flow in and behind the Laval nozzle.

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“…The flow is influenced by the shape of the sample, pumping speed, and ESEM aperture diameter. The flow speed was simulated as described previously (Maxa, 2011(Maxa, , 2016.…”

Section: Environmental Scanning Electron Microscopementioning

confidence: 99%

Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation

Yang

Neděla²,

Runštuk³

et al. 2017

Atmos. Chem. Phys.

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Abstract. An environmental scanning electron microscope (ESEM) was used for the first time to obtain well-resolved images, in both temporal and spatial dimensions, of labprepared frost flowers (FFs) under evaporation within the chamber temperature range from −5 to −18 • C and pressures above 500 Pa. Our scanning shows temperature-dependent NaCl speciation: the brine covering the ice was observed at all conditions, whereas the NaCl crystals were formed at temperatures below −10 • C as the brine oversaturation was achieved. Finger-like ice structures covered by the brine, with a diameter of several micrometres and length of tens to 100 µm, are exposed to the ambient air. The brine-covered fingers are highly flexible and cohesive. The exposure of the liquid brine on the micrometric fingers indicates a significant increase in the brine surface area compared to that of the flat ice surface at high temperatures; the NaCl crystals formed can become sites of heterogeneous reactivity at lower temperatures. There is no evidence that, without external forces, salty FFs could automatically fall apart to create a number of sub-particles at the scale of micrometres as the exposed brine fingers seem cohesive and hard to break in the middle. The fingers tend to combine together to form large spheres and then join back to the mother body, eventually forming a large chunk of salt after complete dehydration. The present microscopic observation rationalizes several previously unexplained observations, namely, that FFs are not a direct source of sea-salt aerosols and that saline ice crystals under evaporation could accelerate the heterogeneous reactions of bromine liberation.

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Comparisons Using Methods of Continuum Mechanics and Monte Carlo at Differentially Pumped Chamber

Cited by 15 publications

References 4 publications

Energy Harvesting Using Thermocouple and Compressed Air

Energy Harvesting Using Thermocouple and Compressed Air

Application of Prandtl’s Theory in the Design of an Experimental Chamber for Static Pressure Measurements

Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation

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