Publikacje

Abstract:

The article aims to explore boiling heat transfer in mini-channels with a rectangular
cross-section using various fluids (HFE-649, HFE-7000, HFE-7100, and HFE-7200). Temperature
measurements were conducted using infrared thermography for the heated wall and K-type ther-
mocouples for the working fluid. The 2D mathematical model for heat transfer in the test section
was proposed. Local heat transfer coefficients between the heated wall and the working fluid were
determined from the Robin condition. The problem was solved by means of the finite element
method (FEM) with Trefftz functions. The values of the heat transfer coefficient that were obtained
were compared with the results calculated from Newton’s law of cooling. The average relative
differences between the obtained results did not exceed 4%. The study included uncertainty analyses
for temperature measurements with K- and T-type thermocouples. Expanded uncertainties were
calculated using the uncertainty propagation and Monte Carlo methods. Precisely determining
the uncertainties in contact temperature measurements is crucial to ensure accurate temperature
data for subsequent heat transfer calculations. The results of the heat transfer investigations were
compared in terms of fluid temperature, heat transfer coefficients, and boiling curves. HFE-7200
consistently exhibited the highest fluid temperature and temperature differences at boiling incipience,
while HFE-7000 demonstrated the highest heat transfer coefficients. HFE-649 showed the lowest
heat transfer coefficients. The boiling curves exhibited a typical shape, with a notable occurrence
of ‘nucleation hysteresis phenomena’. Upon the analysis of two-phase flow patterns, bubbly and
bubbly-slug structures were observed.

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Investigations of Flow Boiling in Mini-channels: Heat Transfer Calculations with Temperature Uncertainty Analyses