Boiling heat transfer in vertical minichannels. Liquid crystal experiments and numerical investigations

The solution of the two-dimensional inverse heat transfer problem with the use of the FEM in combination with Trefftz functions

“…It is called "boiling front" and it shifts in the direction opposite to the liquid flow in the minichannel with the increase in the heat flux supplied to the heating surface [5,[9][10][11][12][13]. Figure 6 shows hue distribution on the foil surface during increasing heat flux, obtained with liquid crystal thermography, with a visible "boiling front" (BI).…”

“…The opposite side of the heating foil is covered with thermosensitive liquid crystals and covered by piece of glass. The application of liquid crystals thermography allows to observe changes in this foil surface temperature [5,[9][10][11][12][13]. Thermocouples K-type and pressure converters are installed on the inlet and outlet of the minichannel.…”

Investigation into flow boiling heat transfer in a minichannel with enhanced heating surface

“…During the calibration process, the water of the pre-set temperature is fed to the minichannel in the closed cycle in the supplementary degassed system with the heater equipped with autotransformer. The surface colour description for the determined temperature is performed similarly to the way described in [1], but instead of HSI hue, the colour description was used as its number. Custom-made software, developed in Delphi ver.…”

“…Flow structure observation is carried out simultaneously at the opposite side of the minichannel. The "boiling front" is identified as a sudden drop in the temperature of the heating surface following its rise, at constant EPJ Web of Conferences capacity of the internal heat source [1][2][3][4][5][6][7]. It moves upstream together with an increase in the heat flux.…”

“…The local heat transfer coefficient is determined with the use of the two-dimensional model of heat transfer through foil and glass [5]. Similarly to heating surface temperature measurement errors discussed in [1], the mean temperature measured using liquid crystal thermography error is estimated to be 0.9 K. A detailed discussion of heat flux and heat transfer coefficient errors can be found in [1]. For the selected settings: #4, #13 and #22 (see Fig.…”