Temperature measurements, radiation effect

The temperature for methane and butane calculated with the isothermal model is a factor 1.4 times greater than the average temperature measured by Lihou and Maund (1982) in their small-scale tests, although higher local maximum temperatures were measured. In this model, combustion is stoichiometric, thus leading to very high fireball temperatures which, in turn, lead to high radiation emissions. Effective surface emissions measured experimentally were one-half the value calculated from this model, because combustion is not stoichiometric and emissivity is less than unity. 

A temperature measuring device indicates the temperature of its sensor, which is supposed to be, but is not necessarily, the temperature of Che medium that the sensor is in contact with. When a thermometer (or any other temperature measuring device such as a thermocouple) is placed in a medium, heat transfer takes place between the sensor of the thermometer and the medtum by convection until the sensor reaches the temperature of the medium. But when tlie sensor,is surrounded hy surfaces that arc at a different temperature than the fluid, ra diaition exchange also takes place between the sensor and the surrounding surfaces. When the heat transfers by convection and radiation balance each other, the sensor indicates a temperature that falls between the fluid and surface temperatures. Below we develop a procedure to account for the radiation effect and to determine the actual fluid temperature. 

Placing the sensor in a radiation shield without interfering with the fluid flow also reduces the radiation effect. The. sensors of temperature measure men devices used outdoors must be protected from direct sunlight since the radiation effect in that case is sure to reach unacceptable levels. 

The radiation effect in temperature measurements can be properly accounted for by... 

Since temperature measurements are required over such a wide range and diversity of situations, a large number of different types of thermometers with varying levels of accuracy and convenience have been developed over the years. Those most frequently used are based on the expansion of a gas, liquid or solid on changes in electrical resistance on the thermoelectric effect on changes in the thermal radiation of a system on changes in the thermal (Johnson) noise of electrical resistors on changes... 

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