The flow boiling heat transfer coefficient determination in a minichannel used the FEM combined with Trefftz functions

T Sobota,W Zima,S Łopata,Beata Maciejewska,Magdalena Piasecka,Kinga Strąk,S Grądziel

doi:10.1051/matecconf/201824001033

T Sobota, W Zima + Show 5 more

Open Access

https://doi.org/10.1051/matecconf/201824001033

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Abstract

The method of solving the inverse heat conduction problem, by means of the FEM with Trefftz-type basis functions, during flow boiling in a minichannel was shown. This basis functions were constructed with using the Hermite interpolation and Trefftz functions. The aim of the numerical calculations was to determine the local heat transfer coefficient on the basis of experimental data in a horizontally oriented minichannel. The refrigerant flowing along the minichannel (HFE-649 or HFE-7100) was heated by a thin enhanced plate by vibration-assisted laser texturing. The temperature on an outer smooth side of the plate was detected by means of infrared thermography. On the heated wall–fluid contact surface in the minichannel the heat transfer coefficient was obtained from the Robin boundary condition. It was assumed that the temperature distribution in the heated plate was described by the Poisson equation. The unknown values of temperature and temperature derivatives at nodes were computed by minimizing the functional which describes the mean square error of the approximate solution on the boundary and along common edges of neighbouring elements. The results were presented as the heated plate temperature and heat transfer coefficient versus the minichannel length.

Highlights

Heat transfer in small channels has been investigated intensively over the past years, for application as cooling electronic components
The experiments were recorded for two heat fluxes supplied to the heated plate under similar stable thermal and flow conditions
The results are presented as: the heated plate temperature measured by infrared thermography and the distance from the minichannel inlet - Fig. 3, the heat transfer coefficient and the distance from the minichannel inlet - Fig. 4, for two selected values of heat flux: 48 and 65 kW/m2

Summary

Introduction

Heat transfer in small channels has been investigated intensively over the past years, for application as cooling electronic components. The data from the experiments using several refrigerants were the basis for the analysis of steady-state flow boiling heat transfer in minichannels with smooth and enhanced heated surface performed by the authors of this paper in their previous works [7,8,9,10]. The numerical calculations involves determining the heat transfer coefficient by solving the boundary inverse heat conduction problem [11] using the FEM with the Trefftz functions and the Hermite interpolation [12]. These functions exactly satisfying the governing equation and are suitable for solving both direct and inverse problems. More information on the Trefftz function can be found in [13,14,15,16,17,18]

Experiment

Analysis and modelling

Results and discussion

Conclusions

Methods