Rotational temperature measurements in DBDs operating at atmospheric pressure : a Raman spectroscopic study on CO2

Samenvatting

The aim of this study is to non-intrusively and in situ determine the rotational temperature inside an atmospheric pressure dielectric barrier discharge (DBD, 70 mm × 28 mm area, 1-3 mm gap, 1-1.5 mm two-sided quartz dielectric) in CO2. The discharge is used to study the reaction channels that accompany the dissociation of CO2 to CO, which is a key step in the storage of renewable energy in value-added hydrocarbons. The rotational temperature in the conditions under study is equivalent to the translational gas temperature, which is an important parameter for a better understanding of the chemistry in the reactor.A setup has been built to examine the feasibility of doing Raman spectroscopy inside the narrow discharge gap with a Nd:YAG laser (532 nm, 50 mJ/pulse, 10 Hz). The measured spectra show a strong linearity when presented in a Boltzmann plot, which proves a Maxwell-Boltzmann distribution of the occupation of the rotational energy levels and with that an equilibrium between the rotational and translational gas temperature.The final Raman spectrometer uses a similar laser (532 nm, 18 mJ/pulse, 10 Hz) and a reflective Bragg grating to filter out Rayleigh scattering and stray light with an attenuation of the central wavelength of up to 104 and a FWHM of 0.14 nm = 5 cm-1. The rotational temperature can be determined with an accuracy of 2%.In the conditions under study (200-1000 mbar, 0.180-1.56 slm CO2 flow rate, 29-53 W power input, 11 kV peak voltage @62.1 kHz (cw)) it is found that the gas temperature inside the 3 mm gap, 1 mm dielectric DBD (460-565 K) is well described by a heating theory, based on a balance between the power input and heat extraction by the reactor. Furthermore, the gas temperature shows a linear relation with the average apparent temperature of the outside wall of the reactor (362-413 K), as measured by an infrared camera. Both the power input and the wall temperature can be used to estimate the gas temperature with an accuracy of 2%.

Datum prijs	31 mrt. 2014
Originele taal	Engels
Begeleider	F.K. Brehmer (Afstudeerdocent 1), S. Welzel (Afstudeerdocent 2) & Richard A.H. Engeln (Afstudeerdocent 2)