The heat transfer coefficients measuring methodology in partially transparent liquid solutions

Аuthors

Boboshina S. B., Poberegsky S. A., Cherepanov V. V.^*, Shirokova E. K.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: vvcherepanov@yandex.ru

Abstract

A detailed study and in-depth analysis of the thermophysical properties and characteristics of substances are necessary for the development and implementation of various materials in thermal activity using the method of short-term impacts to study the properties of partially transparent liquid solutions. The measurements are based on a theoretical model in which a small thickness metal film is in contact with two semi-infinite media. The irregular heat exchange mode use of the significantly reduces the measurement time to values of the order of ~10—4c. Express diagnostic methods involve direct contact of the test substance or liquid solution with the probe, while the measuring probe has low inertia, and also combines the functions of a source and receiver of heat. Small-sized sensors are used for measurements, they are dielectric substrates with resistive elements applied to them. Small-sized sensors are included in the branches of the bridge compensation scheme. Single rectangular voltage pulses with a duration of 40 ms were periodically given to the bridge with a frequency of 1 Hz from the pulse generator, such pulses have a minimal impact on the study object. The resistive element of the sensor was briefly heated after applying the pulse, then such a mode of electric currents in the branches of the bridge was selected with the help of additional ballast resistors, in which, despite the heating, the voltage (signal) on the diagonal of the bridge was zero. An oscilloscope was used to indicate the signal. The resistance value is recorded after balancing the bridge and the heat conductivity and thermal activity are calculated. The calculation is also based on the knowledge of the thermophysical characteristics of the etalon liquid and the value of the resistance in the interval between pulses. The heat conductivity resolution and thermal activity resolution depends on the uncertainty of the bridge compensation, which is 0.2 mV. The reliability of the method and its accuracy is established by comparing measurements results with the available in the open literature data.

Keywords:

liquid solutions, heat conductivity, short-term measurements, compensation scheme, irregular method

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