During an experiment to measure the temperature of hot gas flowing through a large pipe with a small thermocouple located centrally in the pipe, the following data were obtained under the steady state conditions.
Velocity of gas in the pipe line, 4 m/s
Temperature of pipe wall, 400°C
Temperature indicated by the thermocouple, 580o C
Diameter of the thermocouple junction, 1.5 mm
Emissivity of the thermocouple, 0.3
Calculate the true gas temperature.
The convective heat transfer coefficient can be calculated from Nud = 0.5 <!--[if gte vml 1]>
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The property values may be used at 400°C and are: k = 49.72 ´ 10–3 W/m °C,
m = 32.68 ´ 10–6 kg/ms; r = 0.5224 kg/m3
Comment on the methods by which accuracy of the thermocouple reading can be improved.