Application of the 2-D Trefftz Method for Identification of Flow Boiling Heat Transfer Coefficient in a Rectangular MiniChannel

Mirosław Grabowski,Krzysztof Płaczkowski,Beata Maciejewska,Sylwia Hożejowska,Mieczysław E. Poniewski

doi:10.3390/en13153973

Mirosław Grabowski, Krzysztof Płaczkowski + Show 3 more

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https://doi.org/10.3390/en13153973

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Abstract

The study presents the experimental and numeric heat transfer investigations in flow boiling of water through an asymmetrically heated, rectangular and horizontal minichannel, with transparent side walls. A dedicated system was designed to record images of two-phase flow structures using a high-speed video camera with a synchronous movement system. The images were analyzed with Matlab 2019a scripts for determination of the void fraction for each pattern of two-phase flow structures observed. The experimental data measured during the experimental runs included inlet and outlet temperature, temperature at three internal points of the heater body, volume flux of the flowing water, inlet pressure, pressure drop, current and the voltage drop in the heater power supply. The flows were investigated at Reynolds number characteristic of laminar flow. The mathematical model assumed the heat transfer process in the measurement module to be steady-state with temperature independent thermal properties of solids and flowing fluid. The defined two inverse heat transfer problems were solved with the Trefftz method with two sets of T- functions. Graphs were used to represent: the boiling curves, the local void fraction values, the boiling heat transfer coefficients and the errors of both of them for selected mass fluxes and heat fluxes.

Highlights

A growing necessity of transferring very high heat fluxes from both miniaturized industrial equipment and home appliances generates demand for mini- or micro-scale cooling devices.Some cooling systems require low pumping power and low Reynolds numbers for the flow [1,2,3]
Flow boiling heat transfer, which is characteristic of high heat transfer coefficients, appears to be the appropriate solution
The determination of the heat transfer coefficient requires knowledge of the parameters of the boiling fluid flowing in the minichannel

Summary

Introduction

A growing necessity of transferring very high heat fluxes from both miniaturized industrial equipment and home appliances generates demand for mini- or micro-scale cooling devices. Some cooling systems require low pumping power and low Reynolds numbers for the flow [1,2,3] In such cases, flow boiling heat transfer, which is characteristic of high heat transfer coefficients, appears to be the appropriate solution. The determination of the heat transfer coefficient requires knowledge of the parameters of the boiling fluid flowing in the minichannel. Energies 2020, 13, 3973 transfer problems when the governing equation, domain, boundary conditions and physical properties of the material are known When any of these elements is unknown, we must deal with an inverse heat conduction problem—IHCP. High sensitivity to uncertainty of incoming data are a characteristic feature of many engineering inverse problems. Two sets of T-functions were applied to calculate: (a) two-dimensional temperature distributions of the heating copper block and the boiling water, (b) heating copper block temperature gradients, and (c) the heat transfer coefficient at the contact surface copper block–flowing fluid

Experimental Facility

Mathematical Model and Numeric Solution

Results and Discussion

Conclusions

Methods