Transient gas viscosity measurement using tunable diode laser absorption spectroscopy

An experimental study of pressure distribution nonlinearity in a circular micro-tube

“…The experimental setup, shown in Fig. 1, is similar to that used for our previous research [17], but with a different laser source (EP200-DM-B01-PM) and a compatible current controller (Newport Model 505) and temperature controller (Newport Model 8000). This laser source is used because it provides operating wavelengths corresponding to strong CO 2 absorption lines around 2000 nm, compared with the much weaker lines near 1577 nm used in the previous study.…”

“…(3). The detailed measurement procedures of integral absorbance were discussed in our previous research paper [17]. The absorbance measurement in the current research was performed at a range of known controlled conditions, with the important parameters presented in Table 1.…”

“…Intermediate transitions were also used for measurements at median pressure conditions. These transition lines are chosen because they allow the lowest possible current modulation at a reasonable temperature, which helps minimize the mode-structure influence on absorbance uncertainty mentioned in Gao et al [17]. 4, is measured by removing the absorption peak from each spectrum and fitting a fifthorder polynomial to the sloped background signal in Fig.…”

“…The technique of TDLAS, which is a laser-based diagnostic tool providing non-intrusive measurements of gas concentration and temperature [3,18,20], is applied in this paper. A previous gas viscosity measurement technique using TDLAS was presented in Gao et al [17], and the current paper focuses on the investigation of nonlinearity of pressure distributions. While the apparatus is similar to that used in the work of Gao et al [17], the earlier study measures the transient time of gas flow establishment in HC-PCF and relates this time to the viscosity coefficient of the gas, while the current paper investigates the steadystate flow under a pressure gradient to determine the nonlinearity of the spatial pressure distribution.…”

“…It is to be expected that hollow core photonic crystal fibers will find significant use in the future for gas sensing applications, because they have the advantages of immunity to electromagnetic interference, corrosion resistance, allowing remote sensing [24] and convenient deployment of laser light, as shown by previous applications [12,17,21,22,32]. As such, it will be necessary to have a full understanding of the flow through these devices, and having a method for determining the pressure distributions in these fibers is needed.…”