The Experts below are selected from a list of 1092 Experts worldwide ranked by ideXlab platform
Magdalena Piasecka - One of the best experts on this subject based on the ideXlab platform.
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trefftz function based thermal solution of inverse problem in unsteady state flow boiling heat transfer in a minichannel
International Journal of Heat and Mass Transfer, 2017Co-Authors: Beata Maciejewska, Magdalena PiaseckaAbstract:Abstract The paper shows the results for flow boiling heat transfer in a 1.7 mm deep minichannel vertically oriented with FC-72 Fluorinert as a working fluid. The heated wall of the minichannel was formed with a thin Foil. Thermocouples mounted at 18 points monitored the Outer Foil surface temperature. All experimental parameters were controlled using data acquisition stations. The measurements were performed at 0.01 s intervals. The observations of the flow structures were carried out concurrently on the internal surface of the Foil contacting the fluid. The aim of the numerical calculations was to determine the heat transfer coefficient on the contact surface between the heated Foil and FC-72. The heat transfer coefficient was calculated with the use of the Robin boundary condition. To do that, the Foil and fluid temperatures and Foil temperature gradient had to be known. The Foil temperature was found by solving an unsteady-state two-dimensional inverse boundary problem with the use of the Trefftz method in time-space subdomains. A linear combination of Trefftz functions was used to approximate the Foil temperature. The unknown coefficients of the Trefftz function linear combination were determined by minimizing the functional. Error propagation in time and mean relative differences determined between the measured and computed heated Foil temperatures were presented.
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A numerical solution to an inverse unsteady-state heat transfer problem involving the Trefftz functions
'EDP Sciences', 2017Co-Authors: Beata Maciejewska, Magdalena PiaseckaAbstract:This paper shows the results concerning flow boiling heat transfer in an asymmetrically heated vertical minichannel. The heated element for FC-72 Fluorinert flowing in that minichannel was a thin Foil. The Foil surface temperature was monitored continuously at 18 points by K-type thermocouples from the Outer Foil surface. Fluid temperature and pressure in the minichannel inlet and outlet, current supplied to the Foil and voltage drop were also monitored. Measurements were carried out at 1 s intervals. The objective was to determine the heat transfer coefficient on the heated Foil–fluid contact surface in the minichannel. It was obtained from the Robin boundary condition. The Foil temperature was the result of solving the nonstationary two-dimensional inverse boundary problem in the heated Foil. Using the FEM combined with Trefftz functions as basis functions solved the problem. The unknown temperature values at nodes were calculated by minimising the adequate functional. The values of local heat transfer coefficients were consistent with the results obtained by the authors in their previous studies when steady-state conditions were analysed. This time, however, these values were analysed as time dependent, which facilitated observation of coefficient changes that were impossible to observe under the steady-state conditions
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Equalizing calculus in Trefftz method for solving two-dimensional temperature field of FC-72 flowing along the minichannel
Heat and Mass Transfer, 2014Co-Authors: Sylwia Hożejowska, Magdalena PiaseckaAbstract:The paper focuses on the numerical solution to two-dimensional temperature field of boiling liquid flowing along a vertical, asymmetrically heated minichannel with a rectangular cross-section. One of the walls of a minichannel is DC supplied single-sided enhanced Foil with mini-recesses distributed unevenly in the selected area. The parallel walls are made of glass panes for thermal insulation and they are intended for observation of the two-phase flow and the void fraction. The thin layer of thermosensitive liquid crystal paint on the Outer side of the Foil enabled to record two-dimensional temperature distribution of Outer Foil surface. The paper described computations based on Trefftz method for finding two-dimensional temperature field of boiling liquid flowing along the minichannel. The presented research is limited only to the liquid phase of the two-phase mixture observed in the minichannel. The velocity of liquid flowing through the minichannel is represented by a piecewise linear approximating function. To solve energy equation for liquid phase, Trefftz functions specially generated for this purpose were employed. Temperature field in the fluid was approximated by a linear combination of Trefftz functions. Equalizing calculus was applied to the Trefftz method to smooth temperature measurements and reduce measurement errors. Temperature at the interface between working fluid and Foil amounts to the saturation temperature. Temperature distribution in the Foil and the glass pane was also computed using proper Trefftz functions.
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Trefftz method for solving two-dimensional temperature field of boiling fluid flowing along the minichannel
EPJ Web of Conferences, 2013Co-Authors: Sylwia Hożejowska, Magdalena Piasecka, Leszek HożejowskiAbstract:The paper focuses on the numerical solution to two-dimensional temperature field of boiling liquid flowing along a vertical, asymmetrically heated minichannel with a rectangular cross-section. One of the walls of a minichannel is a DC supplied heating Foil. The parallel walls are made of glass panes for thermal insulation and for observation of the fluid flow and the void fraction. A thin layer of thermosensitive liquid crystal paint on the Outer side of the heating Foil enabled to record two-dimensional temperature distribution of Outer Foil surface. The paper presents computations based on Trefftz method for finding two-dimensional temperature field of boiling liquid flowing along the minichannel. The presented research is limited only to a liquid phase of the two-phase mixture observed in the minichannel. The velocity of liquid flowing through the minichannel is represented by a piecewise linear approximating function. To solve energy equation for liquid phase, Trefftz functions specially generated for this purpose were employed. Temperature field in the fluid was approximated by a linear combination of Trefftz functions. Temperature at the interface between working fluid and Foil amounts to the saturation temperature. Temperature distribution in the Foil and the glass pane was also computed using proper Trefftz functions.
Sylwia Hożejowska - One of the best experts on this subject based on the ideXlab platform.
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Equalizing calculus in Trefftz method for solving two-dimensional temperature field of FC-72 flowing along the minichannel
Heat and Mass Transfer, 2014Co-Authors: Sylwia Hożejowska, Magdalena PiaseckaAbstract:The paper focuses on the numerical solution to two-dimensional temperature field of boiling liquid flowing along a vertical, asymmetrically heated minichannel with a rectangular cross-section. One of the walls of a minichannel is DC supplied single-sided enhanced Foil with mini-recesses distributed unevenly in the selected area. The parallel walls are made of glass panes for thermal insulation and they are intended for observation of the two-phase flow and the void fraction. The thin layer of thermosensitive liquid crystal paint on the Outer side of the Foil enabled to record two-dimensional temperature distribution of Outer Foil surface. The paper described computations based on Trefftz method for finding two-dimensional temperature field of boiling liquid flowing along the minichannel. The presented research is limited only to the liquid phase of the two-phase mixture observed in the minichannel. The velocity of liquid flowing through the minichannel is represented by a piecewise linear approximating function. To solve energy equation for liquid phase, Trefftz functions specially generated for this purpose were employed. Temperature field in the fluid was approximated by a linear combination of Trefftz functions. Equalizing calculus was applied to the Trefftz method to smooth temperature measurements and reduce measurement errors. Temperature at the interface between working fluid and Foil amounts to the saturation temperature. Temperature distribution in the Foil and the glass pane was also computed using proper Trefftz functions.
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Trefftz method for solving two-dimensional temperature field of boiling fluid flowing along the minichannel
EPJ Web of Conferences, 2013Co-Authors: Sylwia Hożejowska, Magdalena Piasecka, Leszek HożejowskiAbstract:The paper focuses on the numerical solution to two-dimensional temperature field of boiling liquid flowing along a vertical, asymmetrically heated minichannel with a rectangular cross-section. One of the walls of a minichannel is a DC supplied heating Foil. The parallel walls are made of glass panes for thermal insulation and for observation of the fluid flow and the void fraction. A thin layer of thermosensitive liquid crystal paint on the Outer side of the heating Foil enabled to record two-dimensional temperature distribution of Outer Foil surface. The paper presents computations based on Trefftz method for finding two-dimensional temperature field of boiling liquid flowing along the minichannel. The presented research is limited only to a liquid phase of the two-phase mixture observed in the minichannel. The velocity of liquid flowing through the minichannel is represented by a piecewise linear approximating function. To solve energy equation for liquid phase, Trefftz functions specially generated for this purpose were employed. Temperature field in the fluid was approximated by a linear combination of Trefftz functions. Temperature at the interface between working fluid and Foil amounts to the saturation temperature. Temperature distribution in the Foil and the glass pane was also computed using proper Trefftz functions.
Beata Maciejewska - One of the best experts on this subject based on the ideXlab platform.
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trefftz function based thermal solution of inverse problem in unsteady state flow boiling heat transfer in a minichannel
International Journal of Heat and Mass Transfer, 2017Co-Authors: Beata Maciejewska, Magdalena PiaseckaAbstract:Abstract The paper shows the results for flow boiling heat transfer in a 1.7 mm deep minichannel vertically oriented with FC-72 Fluorinert as a working fluid. The heated wall of the minichannel was formed with a thin Foil. Thermocouples mounted at 18 points monitored the Outer Foil surface temperature. All experimental parameters were controlled using data acquisition stations. The measurements were performed at 0.01 s intervals. The observations of the flow structures were carried out concurrently on the internal surface of the Foil contacting the fluid. The aim of the numerical calculations was to determine the heat transfer coefficient on the contact surface between the heated Foil and FC-72. The heat transfer coefficient was calculated with the use of the Robin boundary condition. To do that, the Foil and fluid temperatures and Foil temperature gradient had to be known. The Foil temperature was found by solving an unsteady-state two-dimensional inverse boundary problem with the use of the Trefftz method in time-space subdomains. A linear combination of Trefftz functions was used to approximate the Foil temperature. The unknown coefficients of the Trefftz function linear combination were determined by minimizing the functional. Error propagation in time and mean relative differences determined between the measured and computed heated Foil temperatures were presented.
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A numerical solution to an inverse unsteady-state heat transfer problem involving the Trefftz functions
'EDP Sciences', 2017Co-Authors: Beata Maciejewska, Magdalena PiaseckaAbstract:This paper shows the results concerning flow boiling heat transfer in an asymmetrically heated vertical minichannel. The heated element for FC-72 Fluorinert flowing in that minichannel was a thin Foil. The Foil surface temperature was monitored continuously at 18 points by K-type thermocouples from the Outer Foil surface. Fluid temperature and pressure in the minichannel inlet and outlet, current supplied to the Foil and voltage drop were also monitored. Measurements were carried out at 1 s intervals. The objective was to determine the heat transfer coefficient on the heated Foil–fluid contact surface in the minichannel. It was obtained from the Robin boundary condition. The Foil temperature was the result of solving the nonstationary two-dimensional inverse boundary problem in the heated Foil. Using the FEM combined with Trefftz functions as basis functions solved the problem. The unknown temperature values at nodes were calculated by minimising the adequate functional. The values of local heat transfer coefficients were consistent with the results obtained by the authors in their previous studies when steady-state conditions were analysed. This time, however, these values were analysed as time dependent, which facilitated observation of coefficient changes that were impossible to observe under the steady-state conditions
Leszek Hożejowski - One of the best experts on this subject based on the ideXlab platform.
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Trefftz method for solving two-dimensional temperature field of boiling fluid flowing along the minichannel
EPJ Web of Conferences, 2013Co-Authors: Sylwia Hożejowska, Magdalena Piasecka, Leszek HożejowskiAbstract:The paper focuses on the numerical solution to two-dimensional temperature field of boiling liquid flowing along a vertical, asymmetrically heated minichannel with a rectangular cross-section. One of the walls of a minichannel is a DC supplied heating Foil. The parallel walls are made of glass panes for thermal insulation and for observation of the fluid flow and the void fraction. A thin layer of thermosensitive liquid crystal paint on the Outer side of the heating Foil enabled to record two-dimensional temperature distribution of Outer Foil surface. The paper presents computations based on Trefftz method for finding two-dimensional temperature field of boiling liquid flowing along the minichannel. The presented research is limited only to a liquid phase of the two-phase mixture observed in the minichannel. The velocity of liquid flowing through the minichannel is represented by a piecewise linear approximating function. To solve energy equation for liquid phase, Trefftz functions specially generated for this purpose were employed. Temperature field in the fluid was approximated by a linear combination of Trefftz functions. Temperature at the interface between working fluid and Foil amounts to the saturation temperature. Temperature distribution in the Foil and the glass pane was also computed using proper Trefftz functions.
Max L Blosser - One of the best experts on this subject based on the ideXlab platform.
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improving metallic thermal protection system hypervelocity impact resistance through design of experiments approach
40th AIAA Aerospace Sciences Meeting & Exhibit, 2002Co-Authors: Carl C Poteet, Max L BlosserAbstract:A design of experiments approach has been implemented using computational hypervelocity impact simulations to determine the most effective place to add mass to an existing metallic Thermal Protection System (TPS) to improve hypervelocity impact protection. Simulations were performed using axisymmetric models in CTH, a shock-physics code developed by Sandia National Laboratories, and validated by comparison with existing test data. The axisymmetric models were then used in a statistical sensitivity analysis to determine the influence of five design parameters on degree of hypervelocity particle dispersion. Several damage metrics were identified and evaluated. Damage metrics related to the extent of substructure damage were seen to produce misleading results, however damage metrics related to the degree of dispersion of the hypervelocity particle produced results that corresponded to physical intuition. Based on analysis of variance results it was concluded that the most effective way to increase hypervelocity impact resistance is to increase the thickness of the Outer Foil layer. Increasing the spacing between the Outer surface and the substructure is also very effective at increasing dispersion.
