Continuous gas temperature measurement of cold plasma jets containing microdroplets, using a focussed spot IR sensor

Abstract

Controlling gas temperature via continuous monitoring is essential in various plasma applications especially for biomedical treatments and nanomaterial synthesis but traditional techniques have limitations due to low accuracy, high cost or experimental complexity. We demonstrate continuous high-accuracy gas temperature measurements of low-temperature atmospheric pressure plasma jets using a small focal spot infrared sensor directed at the outer quartz wall of the plasma. The impact of heat transfer across the capillary tube was determined using calibration measurements of the inner wall temperature. Measured gas temperatures varied from 25 °C–50 °C, increasing with absorbed power and decreased gas flow. The introduction into the plasma of a stream (∼105 s−1) of microdroplets, in the size range 12 μm–15 μm, led to a reduction in gas temperature of up to 10 °C, for the same absorbed power. This is an important parameter in determining droplet evaporation and its impact on plasma chemistry.

Influence of aerosol injection on the liquid chemistry induced by an RF argon plasma jet

“…Moreover, aerosol injection into the plasma effluent results in a significant temperature decrease of a treated sample from 102 • C to 59 • C (input power 30 W) and from 73 • C to 48 • C (20 W) after 1 min treatment and a distance of 2 mm [23]. A decrease of the gas temperature by 10 • C via the introduction of micro droplets confirming our results has been reported recently [24]. Since, a thorough understanding of the physics and the chemistry of this modular source is desired to determine future key points for an application both in the biomedical and in the technological scenario.…”

Plasma Damage Control: From Biomolecules to Cells and Skin

“…The high demand for alternative wound healing therapies and antibiotic-free treatments has resulted in the development of various atmospheric pressure plasma jets (APPJs) and the enhancement of reactive species generation. − This study takes previous research a step further, presenting plasma-tailored wound therapy where drugs in the form of an aerosol are locally applied together with the plasma, and their topical penetration is accordingly promoted. Aerosol introduction in the plasma effluent in general decreases the temperature of the treated object; introduced droplets evaporate in effluent having a cooling effect on the treated target (approximately 25 °C during 1 min plasma treatment). Moreover, aerosol droplets in the effluent change the plasma chemistry and can limit the flux of UV plasma radiation toward the target.…”

Detecting trace methane levels with plasma optical emission spectroscopy and supervised machine learning

“…The gas temperature in the plasma during normal operation was estimated using a trace 0.1% N 2 admixture to generate test spectra for comparison with temperature dependent synthetic spectra generated by Specair software. For operation flow rates >2 slm, average gas temperatures were ∼335 K. Estimated confidence limits arising from the fitting are ±50 K. Other recent measurements using an IR probe on a similar capillary He plasma indicate maximum gas temperature of <323 K and standard error levels of 2 K [25]. The capillary outlet was a large distance (∼100 cm) from the plasma to minimise atmospheric impurity back-diffusion and the system was initially conditioned to remove background impurities, over 21 days, using a 100% He plasma and exterior infra-red heating while monitoring the reduction of spectral impurity bands.…”