Mechanisms of gas temperature variation of the atmospheric microwave plasma torch

Abstract

The gas temperature is a key parameter that affects the process of microwave plasma chemistry in industrial applications. Based on the molecular emission spectrometry of the A2Σ+→X2Πr electronic system of OH radicals, the gas temperature of the atmospheric air microwave plasma core at different absorbed microwave power levels, gas flow rates, gas humidities, and volume fractions of CO2 in air was analyzed. In the experiment, the absorbed microwave power, gas flow rate, gas humidity, and volume ratio of CO2 in air was varied from 560 to 1750 W, 10 to 24 l min−1, 30% to 95%, and 0% to 40%, respectively. Moreover, the axial gas temperature distribution of the plasma torch was measured. The experimental results showed that (i) the plasma gas temperature mainly ranged from 4000 to 7000 K, (ii) the plasma gas temperature rose with increasing absorbed microwave power but was hardly affected by the feeding gas flow rate, (iii) the plasma gas temperature decreased by ∼400 K for every 20% increase in the fraction of CO2 in air and decreased with increasing gas humidity, and (iv) the plasma torch gas temperature decreased along the axial direction. Due to the lack of a prevailing microwave discharge theory, an in-depth analysis of the mechanisms of gas temperature variation was performed based on the heat balance equation.

An atmospheric microwave plasma-based distributed system for medical waste treatment

“…Current traditional centralized waste treatment methods (e.g., open burning, incineration, and sanitary landfills) are prone to secondary transmission of medical waste during transfer (Jie et al 2021a , b ; Sarkodie and Owusu 2021 ; Jie et al 2022 ). These methods are becoming increasingly apparent as public awareness of environmental protection and resource recycling grows due to their potential risks, particularly to groundwater and soil (Ma et al 2017 ; Wang et al 2020a , b , c ; Chakraborty and Saha 2022 ).…”

“…Consequently, novel methods used in small and mobile medical waste devices, such as microwave heating and thermal (arc) plasma treatment techniques, have emerged in recent years (Mazzoni and Janajreh 2017 ; Samal 2017 ; Sanlisoy and Carpinlioglu 2017 ; Li et al 2020a , b ; Jie et al 2021a , b ; Li et al 2021 ; Bhatt et al 2022 ; Huang et al 2022 ; Pancholi et al 2022a ). Microwave heating is a green and environmentally friendly method and a substitute for traditional heating in batch treatments of various materials (Li et al 2021 ; Wang et al 2022 ).…”

“…Furthermore, the considerable heat loss under this high power inevitably induces electrode ablation, necessitating an additional cooling system for cooling the electrodes and the regular replacement of the electrodes. Contrary to arc plasmas, the microwave plasma torch can be ignited without an electrode in a length of ~ 30 cm under a low incident microwave power, typically from ~ 1 to ~ 3 kW (Jie et al 2021a , b , 2023 ). Additionally, our recent research has proven that microwave plasma can environmentally treat solid wastes and vitrify the residual ash into slag (Jie et al 2022 , 2023 ).…”

“…The microwave plasma obtains instantaneous high-temperature characteristics. Although the gas temperature of the microwave plasma torch, which ranges from 2000 to 9000 K, is lower than that of arc plasma (Huang et al 2020 ; Jie et al 2021a , b ), a high gas temperature on the order of magnitude of thousands of degrees is sufficient for treating medical waste. The interior temperature of the reaction chamber can be readily controlled during medical waste treatment by varying the number of microwave plasma torches.…”

Wide Bandgap Nanocoatings for Polymer Dielectric with Outstanding Electrical Strength

“…The methods used to promote dissipation of surface charges in polymer dielectrics and increase their flashover voltages mainly include doping modifications, [24][25][26] surface fluorination treatments [27][28][29] and plasma treatments. [30][31][32] However, although these schemes have provided good experimental results, they are still difficult to apply in engineering due to various problems, such as instability of the product after plasma treatment. [33,34] In addition, polymer carrier traps, which are a very important parameter of polymer dielectrics, directly determine the charge characteristics and electrical strengths of polymer dielectrics.…”