Abstract: This paper focuses on the numerical determination of two-dimensional temperature fields in flow
boiling in an asymmetrically heated rectangular and vertical minichannel. One of the minichannel
walls is made of the DC supplied heating foil. The opposite wall is made of glass, which makes it
possible to observe the two-phase structure and void fraction. The external side of the heating foil,
coated with a layer of liquid crystals, is protected with a pane of glass. Thermosensitive liquid crystals
were used to detect two-dimensional temperature distribution of the heating foil. Direct and inverse
heat transfer problems that occur in flow boiling in a minichannel were solved using the methods
based on Trefftz functions. The selection of particular functions was dependent on the form of the
differential equation describing the heat transfer in solids (glass pane, heating foil) and in liquids.
These functions were used globally (in the classical Trefftz method) and as shape functions in the
FEM (FEMT) to find the two-dimensional temperature fields of the glass pane and the heating foil.
Solving these functions led to computing a direct heat transfer problem in the glass pane and an
inverse problem in the heating foil and the boiling liquid. Known foil and liquid temperature
distributions and gradients enabled the heat transfer coefficient on the foil-liquid contact to be
calculated from the Robin boundary condition. The results obtained using the numerical methods
described for single-phase flows ending in boiling incipience and for two-phase flows have been
summarized, compared and found to be similar.
