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

Abstract

<jats:sec> <jats:title content-type="abstract-subheading">Purpose</jats:title> <jats:p>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.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Design/methodology/approach</jats:title> <jats:p>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.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Findings</jats:title> <jats:p>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.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Practical implications</jats:title> <jats:p>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.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Originality/value</jats:title> <jats:p>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.</jats:p> </jats:sec>

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

“…In literature the results of experiments concerning time-dependent flow parameters during fluid flow in small gaps are rare. Several examples of works dealing with this topic are [5][6][7][8][9][10][11].…”

“…In the Trefftz method unknown solution to a differential equation is approximated by means of a linear combination of functions strictly satisfying the governing differential equation. In literature a lot of examples of using the Trefftz method for solving: direct [20][21][22], inverse [1][2][3][15][16][17][18][24][25][26], stationary [1][2][3]16,[18][19]24] and nonstationary [10,11,15,17,25,26] problems can be found.…”

Heat Transfer Coefficient Determination during FC-72 Flow in a Minichannel Heat Sink Using the Trefftz Functions and ADINA Software

“…The domain Ω 𝑀 ∪ Ω 𝐹 was divided into rectangular four-node elements. In each element, like in [43], the temperature was approximated by a linear combination of the basis functions which strictly satisfy the given differential equations, Equations ( 1) or (2), respectively: To analyze the heat transfer intensity, the local values of heat transfer coefficient on the surface between the heated foil and the boiling liquid were used. They were determined from the Robin boundary condition:…”

“…To date, the authors of the present work have studied heat transfer enhancement during flow boiling in one [38,39], two [40,41], or three minichannels [42] of rectangular cross-section and in an annular gap [7]. Most of the previous research focused on experiments conducted in the stationary state, although some of the latest works concerned time-dependent studies [41,43]. Based on the experimental data, analytical and analytical-numerical methods using the Trefftz functions, the heat transfer coefficient values on the heating surface contacting the fluid flowing in a minichannel were determined.…”

Comparison of the 1D and 2D calculation models used for determination of the heat transfer coefficient during flow boiling heat transfer in a minichannel

“…This method consists in transforming the inverse problem into a few direct problems by differentiation the measured quantity with respect to the identified quantity. Inverse problems can also be solved by the method based on the functions that strictly satisfy the governing equation, so-called Trefftz functions [24][25][26][27][28][29][30][31]. The approximate solution of a differential equation, in form a linear combination of the Trefftz functions, is fitted to the given boundary conditions.…”