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

摘要

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.