The measurement of steam temperatures in power stations

摘要

Errors in steam-temperature measurement may occur because of: (a) Incomplete mixing of steam from different sources. (b) Variation in temperature over the cross-section of a steam pipe. (c) Difference in temperature between steam and thermometer pocket. (d) Difference in temperature between pocket and thermometer. (e) Slow response of the thermometer. (f) Inaccuracy in the measuring instrument. These sources of error have been considered theoretically and the results are given in a form suitable for application to practical cases. It is considered that two streams of steam entering a single pipe are thoroughly mixed in a distance of about 30 diameters. The temperature gradients in high-velocity steam in a well-lagged pipe are negligible except near the pipe wall. Errors of steam-temperature measurement using pockets can be made negligible by proper design, with the exception of errors due to time lag. Thermometers immersed in the steam have greatly reduced errors due to time lag. Confirmatory experimental work is described.