Time-dependent study of boiling heat transfer coefficient in a vertical minichannel

Purpose The purpose of this paper is to determine the time-dependent heat transfer coefficient during FC-72 flow boiling in a 1.7-mm-deep vertical and asymmetrically heated minichannel. Design/methodology/approach The temperature of the minichannel heated wall was recorded continuously with the use of thermocouples. The heat transfer coefficients for the subcooled and saturated boiling regions at the heated wall–fluid contact surface were calculated from the Robin boundary condition. Both the wall and fluid temperatures were obtained from the solution of the inverse nonstationary problems in two adjacent domains: the heated wall and flowing fluid. The FEM with Trefftz-type basis functions was applied to solve the inverse problem. Findings The obtained time-dependent heat transfer coefficient in subcooled boiling achieved rather low values, whereas in saturated boiling, the coefficient was the highest at the channel inlet. The boiling curves were plotted to illustrate the results. Practical implications The results of experiments are the best source of information for the design of minichannel cooling systems used for thermoregulation of components and heat exchangers. High-tech minichannel heat exchangers are applied in various industrial applications as microelectronics devices, gas turbines, internal combustion engines, nuclear reactors, X-ray sources and organic rankine cycle (ORC) modules. Originality/value In the study, the Trefftz functions for the nonstationary Fourier–Kirchhoff equation with the factor describing void fraction were determined and then used to construct the time-dependent basis functions in FEM.

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

MATEC Web of Conferences ◽

10.1051/matecconf/201824001033 ◽

2018 ◽

Vol 240 ◽

pp. 01033

Author(s):

Magdalena Piasecka ◽

Kinga Strąk ◽

Beata Maciejewska

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Heat Conduction Problem ◽

Flow Boiling ◽

Inverse Heat Conduction Problem ◽

Basis Functions ◽

Heated Wall ◽

Heated Plate ◽

Plate Temperature

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.

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Heat transfer coefficient determination using the FEM with time-dependent Trefftz-type basis functions in subcooled flow boiling in a minichannel

MATEC Web of Conferences ◽

10.1051/matecconf/201824001024 ◽

2018 ◽

Vol 240 ◽

pp. 01024

Author(s):

Beata Maciejewska ◽

Magdalena Piasecka

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Flow Boiling ◽

Local Heat Transfer ◽

Thin Foil ◽

Local Heat ◽

Basis Functions ◽

Time Dependent ◽

Flowing Fluid

Results concerning flow boiling heat transfer in a vertical minichannel of 1.7 mm depth were shown. The channel was asymmetrically heated by a thin foil. Its surface temperature was recorded continuously in points by thermocouples. Measurements were carried out in 0.01 s intervals. The objective of the numerical calculations was to determine the heat transfer coefficient on the heated foil–fluid contact surface in the minichannel from the Robin boundary condition. Both the foil and fluid temperatures were the result of solving the nonstationary two-dimensional problem in the foil and flowing fluid. The problem was solved by using the FEM combined with Trefftz-type basis functions. The values of the time-dependent local heat transfer coefficient were presented and discussed.

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Time-Dependent Heat Transfer Calculations with Trefftz and Picard Methods for Flow Boiling in a Mini-Channel Heat Sink

Energies ◽

10.3390/en14071832 ◽

2021 ◽

Vol 14 (7) ◽

pp. 1832

Author(s):

Magdalena Piasecka ◽

Sylwia Hożejowska ◽

Beata Maciejewska ◽

Anna Pawińska

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Heat Sink ◽

Flow Boiling ◽

Time Dependent ◽

Heated Wall ◽

Trefftz Method ◽

Mini Channels ◽

The Heat Transfer Coefficient

The intensification of heat transfer using two-phase boiling flow in mini-channels is widely used to dissipate the high heat fluxes in miniaturized electronic devices. However, the process itself is not fully recognized and still requires experimental studies and developing computation methods appropriate for them. The main aim of this work was the mathematical modeling of time-dependent heat transfer process in FC-72 flow boiling in a mini-channel heat sink with five parallel mini-channels of 1 mm depth. Channels have an asymmetrically heated wall while its outer temperature was measured by infrared thermography. The opposite wall of the mini-channels was transparent, helping to record flow patterns due to a high-speed digital camera. The objective of the numerical calculations was to determine the heat transfer coefficient on the wall-fluid contact surface from the Robin boundary condition. The problem was solved using methods based on the Trefftz-type functions. Three mathematical methods were applied in calculations: the FEM with Trefftz type basis functions, the Classical Trefftz Method, and the Hybrid Picard-Trefftz Method. The results were compared with the values of the heat transfer coefficient obtained from theoretical correlations from the literature.

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The heat transfer coefficient determination with the use of the Beck-Trefftz method in flow boiling in a minichannel

EPJ Web of Conferences ◽

10.1051/epjconf/201818002099 ◽

2018 ◽

Vol 180 ◽

pp. 02099 ◽

Cited By ~ 1

Author(s):

Kinga Strąk ◽

Beata Maciejewska ◽

Magdalena Piasecka

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Boiling Heat Transfer ◽

Transfer Problem ◽

Heat Conduction Problem ◽

Flow Boiling ◽

Inverse Heat Conduction Problem ◽

Heated Wall ◽

Trefftz Method

In this paper, the solution of the two-dimensional inverse heat transfer problem with the use of the Beck method coupled with the Trefftz method is proposed. This method was applied for solving an inverse heat conduction problem. The aim of the calculation was to determine the boiling heat transfer coefficient on the basis of temperature measurements taken by infrared thermography. The experimental data of flow boiling heat transfer in a single vertical minichannel of 1.7 mm depth, heated asymmetrically, were used in calculations. The heating element for two refrigerants (FC-72 and HFE-7100, 3M) flowing in the minichannel was the plate enhanced on the side contacting with the fluid. The analysis of the results was performed on the basis of experimental series obtained for the same heat flux and two different mass flow velocities. The results were presented as infrared thermographs, heated wall temperature and heat transfer coefficient as a function of the distance from the minichannel inlet. The results was discussed for the subcooled and saturated boiling regions separately.

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Simulation and experimental analysis of heat transfer characteristics in the plate type heat exchangers using TiO2/water nanofluid

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-05-2018-0191 ◽

2019 ◽

Vol 29 (4) ◽

pp. 1343-1362 ◽

Cited By ~ 19

Author(s):

Ataollah Khanlari ◽

Adnan Sözen ◽

Halil İbrahim Variyenli

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Heat Exchangers ◽

Working Fluid ◽

Heat Transfer Characteristics ◽

Content Type ◽

Plate Heat ◽

Overall Heat Transfer Coefficient ◽

Transfer Characteristics

PurposeThe plate heat exchangers (PHE) with small size but large efficiency are compact types of heat exchangers formed by corrugated thin pressed plates, operating at higher pressures when compared to most other traditional exchangers. This paper aims to analyze heat transfer characteristics in the PHE experimentally and numerically.Design/methodology/approachComputational fluid dynamics analysis has been used to simulate the problem by using the ANSYS fluent 16 software. Also, the effect of using TiO2/water nanofluid as working fluid was investigated. TiO2/water nanofluid had 2% (Wt/Wt) nanoparticle content. To improve solubility of the TiO2nanoparticles, Triton X-100 was added to the mixture. The results have been achieved in different working condition with changes in fluid flow rate and its temperature.FindingsThe obtained results showed that using TiO2/water nanofluid improved the overall heat transfer coefficient averagely as 6%, whereas maximum improvement in overall heat transfer coefficient was 10%. Also, theoretical and experimental results are in line with each other.Originality/valueThe most important feature which separates the present study from the literature is that nanofluid is prepared by using TiO2nanoparticles in optimum size and mixing ratio with surfactant usage to prevent sedimentation and flocculation problems. This process also prevents particle accumulation that may occur inside the PHE. The main aim of the present study is to predict heat transfer characteristics of nanofluids in a plate heat exchanger. Therefore, it will be possible to analyze thermal performance of the nanofluids without any experiment.

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Flow Boiling Study in Mini-Channels

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B ◽

10.1115/icnmm2006-96048 ◽

2006 ◽

Cited By ~ 1

Author(s):

Francesc Madrid ◽

Nadia Caney ◽

Philippe Marty

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Test Section ◽

Heat Exchangers ◽

Flow Boiling ◽

Two Phase ◽

Mini Channels ◽

Vapour Quality ◽

The Heat Transfer Coefficient

Mini-channel heat exchangers improve thermal performance in comparison to conventional macro-channel heat exchangers, being highly efficient, compact and requiring low fluid mass. However, classical correlations for two-phase flow in macro-channels fail in predicting the heat transfer coefficient in mini-channels. Therefore, new studies are needed in order to provide better knowledge on flow boiling phenomena in confined spaces. The proposed paper presents an experimental study on two-phase vertical flow boiling in mini-channels. The aim of this work is to determine the heat transfer coefficient and to study the pressure drop in a mini-channel heat exchanger (hydraulic diameter of 840μm) in order to obtain better understanding of the flow boiling mechanisms. A vertical upward flow test section is connected to a primary HFE-7100 circuit. A preheater imposes a given sub-cooled fluid temperature or a given two-phase vapour quality at the inlet. Downstream in the test loop, the fluid is condensed and pumped again into the test section. The pressure drop and the heat transfer coefficient in the test section have been measured for a variety of conditions. Different heat flux, inlet vapour quality and mass flow rate values have been tested. For the heat transfer coefficient, a correlating model is proposed as a function of the superficial velocity. This parameter appears to be much more appropriate than the vapour quality or the mass flow rate for dry-out occurrence prediction. A single critical velocity value has been found.

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The heat transfer and instabilities results during the onset of flow boiling in minichannels

E3S Web of Conferences ◽

10.1051/e3sconf/201912801016 ◽

2019 ◽

Vol 128 ◽

pp. 01016

Author(s):

Beata Maciejewska ◽

Magdalena Piasecka ◽

Artur Piasecki

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Flow Boiling ◽

Thin Foil ◽

Time Dependent ◽

Flow Boiling Heat Transfer ◽

Boiling Incipience ◽

The Heat Transfer Coefficient ◽

Heated Element

The paper discusses the results of flow boiling heat transfer in minichannels obtained on the basis of time-dependent experiments. The main interest of the work was to investigate the occurrence of the accompanying instabilities during the boiling incipience. The essential part of the experimental standwas a test section with two minichannels, each of 1.7 mm depth. The heated element for FC–72flowing along the minichannels was a thin foil. In the tested minichannel, the temperature of the outer surface of the foil was measured due to thermoelements. The onset of flow boiling in minichannels was induced by increasing the heat flux supplied to the heater. The main aims of the investigation were to determine the heat transfer coefficient by means of the FEM with time—dependent Trefftz–type basis functions based on the Hermite interpolation and to recognize dynamic instabilities during boiling incipience. The results were illustrated as: the heat transfer coefficient, the mass flow rate and the inletpressure versustime and as boiling curves.

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