Thermocouple error correction for measuring the flame temperature with determination of emissivity and heat transfer coefficient

Abstract

Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.

An experimental and numerical investigation of heat transfer distribution of perforated plate burner flames impinging on a flat plate

“…The reason for this is that at lower z/d, the premixed cone tip with highest temperature is very close to the impingement plate and a further increase in the distance of location of this premixed cone tip from the impingement plate would result in flame with significantly lower temperature impinging the plate. A typical variation of flame temperature is reported in our previous work [17]. Furthermore, with the increase in Re, the inner premixed cone length increases and therefore the distance of the premixed cone tip (reaction zone) from the impingement plate decreases.…”

Variations in non-thermal NO formation pathways in alcohol flames

“…Corrections for radiative losses were conducted in accordance with [32,33] , accounting for variations in radiation to the burner surface. The porous plug surface temperature was measured using an IR thermometer, with all measured surface temperatures between 100 and 200 °C.…”

Combustion characteristics of premixed propane flame with added H 2 and CO on a V-shaped impinging burner

“…The uncorrected temperature data were used to distinguish the discrepancy of the change of flame geometry. The estimated radiation correction is about 250 C. The actual temperature could thus be more than 300 C greater than the uncorrected temperature [33]. We define the peak flame temperature as the maximum temperature measured in the entire combustion field.…”