The influence of windows on infra-red temperature measurements for solids’ mass flow rate determination

• Published in: Flow measurement and instrumentation 2012-10, Vol.27, p.99-103
• Main Authors: Kato, M., Pugh, J.R., McGlinchey, D.
• Format: Article
• Language: English
• Subjects: Emissivity; Infra-red; Optical windows; Radiation; Transmissivity
• ISSN: 0955-5986; 1873-6998
• DOI: 10.1016/j.flowmeasinst.2012.04.012

Thermal mass flow meters can, in theory, be used in pneumatic conveying applications to provide a reliable monitoring of the mass flow rate of solids being transported in a stream of gas. Accurate measurement of temperature is necessary for the mass flow rate to be reliably determined. Direct measurement of temperature of particulate solids being conveyed pneumatically can be achieved, in principle, with the use of infra-red (IR) detectors. This has been done in previous work for the measurement of solids’ temperatures in a pneumatic conveying line where windows were employed. This paper investigates the influence of windows on the temperature measurement process. We investigate specifically the effect of dust deposited on the window surface in conjunction with the window temperature. The results show that if the window is not ideal, measurements of temperatures above the temperature of the window will be below actual, and measurement of target temperatures below the window temperature will be higher than actual. A simple assumption that a non-ideal window would attenuate the IR signal and result in lower temperature measurements is therefore, not valid. An analysis is offered that explains the results obtained. ► Study of the effect of window quality on infra-red temperature measurement. ► Both surface dust and temperature of the window affect the measurement of the solids temperature. ► Experimental results are in agreement with the theoretical analysis presented. ► Window temperature must be controlled for accurate measurement of solids mass flow.