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.
Highlights
Introduction pte dMContinuous and reliable measurement of gas temperature in atmospheric pressure plasmas (APP) is critical for future applications in plasma medicine, food and agriculture as well as nanomaterials synthesis
The use of plasma-exposed microdroplets has important potential for delivering plasma-activated liquids and on-demand nanoparticles downstream over rapid timescales. Their chemistry, lifetime and transport will be sensitive to the gas temperature in the plasma. It is well-known that the addition of small quantities of electronegative gases, e.g. O2 or H2O, can increase the gas temperature in noble gas plasmas[2,42] and the possibility exists for accelerated gas heating as the droplet evaporation proceeds
Continuous gas temperature measurement in plasmas is important for many applications, for verifiable monitoring and control of plasmas for medical treatment
Summary
Continuous and reliable measurement of gas temperature in atmospheric pressure plasmas (APP) is critical for future applications in plasma medicine, food and agriculture as well as nanomaterials synthesis. Gas temperature increase in APPs is due to the high electron and particle collisionality of these systems.[1] Most chemical and combustion reactions are strongly dependent on gas temperature,[2] as are surface reactions and neutral radical distributions and their kinetics.[3,4] in many biomedical and material applications a controlled heat load is required for the treatment of heat sensitive surfaces e.g. wound tissue and polymers.[5] Issues such as feedback process control, process stability/repeatability, regulatory, or end-user approval, require a capability for inline monitoring of temperature and rapid response to fluctuations or thermal runaway
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