Contactless heat transfer measurement methods in processing units

Abstract

Contactless measurement of local values of heat transfer coefficient by two different methods is presented in this Ph.D. thesis. The first method, temperature oscillation (also known as TOIRT method), uses heat waves from heat sources that hit the measured wall and measure the surface temperature of the wall using an IR camera. By comparing the phases of the individual signals (generated heat waves and the measured surface temperature) it is possible to obtain information about the phase delay, which is directly related to the coefficient of heat transfer. I have validated the method experimentally when measuring the heat transfer coefficient between tube and flowing fluid in the tube and also numerically. Experimental measurements show results that are in agreement with the literature. The sensitivity analysis shows that this method is suitable for measuring the heat transfer coefficient in the range of 100 – 3000W=m2K with a reasonable error. After performing the verification experiments I applied the method to the measurement of geometries typical of proces engineering such as vessels equiped with impellers or reactors. However, these apparatuses do not have simple but very complex flows inside and this method has never been used for similar applications. The results of the measurement of the heat transfer coefficient at the bottom of the vessel equiped with impeller as well as on the wall of the vessel for various configurations and various impellers are presented. Data from the measurement of the heat transfer between the smooth wall and the perpendicular impinging jet are also presented. The results show good agreement with the literature except measurements on the wall of the vessel with the impeller, which show a different tendency. The second method, which I derived for the non-oscillatory change in the heat flux that falls on the measured wall, calculates the local values of the heat transfer coefficient from the temperature response of the wall to the step function in heat flux. The method of heat flux jump (HFJ) is described, analytically and numerically verified and sensitivity analysis showed that it is suitable for small values of heat transfer coefficient, up to approximately 1000 W=m2K. I have verified the method for measuring the heat transfer coefficient between a smooth wall and the impinging air jet with good agreement with the literature. In addition to the measurement method itself, this method can also be applied to adjust and improve the results of the TOIRT method or even to measure the distribution of incident heat flux on the measured wall. Both methods are very suitable for process engineering because they are fully contactless and do not require temperature measurement of the fluid between which heat transfer occurs. It is thus possible in this way to measure the heat transfer coefficient values in reactors with dangerous or toxic substances etc. Moreover, both methods are very fast in terms of both measurement and evaluation, and the new heat flux jump method is even faster.

Práce se zabývá metodami měření součinitele přestupu tepla a jejich aplikací na různé geometrie typické pro procesní inženýrství. Rešeršní část práce je zaměřena na teoretický základ přenosu tepla a přehled experimentálních metod. První praktická část práce je věnována aplikaci dynamické oscilační metody pro komplexní toky – míchání vsádky, míchání s usměrňovacím válcem nebo omezený impaktní proud. Druhá část je věnována vlastní nové dynamické metodě, která je teoreticky odvozena a následně analyticky, numericky a experimentálně ověřena. Po validaci metody následují další experimenty s více komplexními geometriemi. Metoda svou citlivostí především v nižších intenzitách přestupu tepla je tak velmi vhodná pro měření přestupu tepla mezi stěnou a plyny, kde se dají očekávat nižší přenosové součinitele.