Zimmermann, Matthias (2022)
Experimental Investigation of Nucleate Boiling on Microstructured and Smooth Surfaces.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00019673
Dissertation, Erstveröffentlichung, Verlagsversion
Kurzbeschreibung (Abstract)
In the last decade, the focus of boiling research has shifted towards micro- and nanostructures. Both structures improve the boiling process significantly compared to smooth surfaces. The interactions between fluid and surface, however, are very complex and not well understood. This impedes the development of universally applicable correlations that incorporate the influence of those complex structures, which would enable the construction of more efficient evaporators. In this thesis, a new experimental setup is constructed to enable boiling experiments at a large pressure, temperature, and heat flux range. FC-72, a refrigerant, and ethanol are chosen as boiling fluids. The boiling process is analyzed on various length scales using two different heater modules. A copper heater module is used to determine mean heat transfer coefficients and critical heat fluxes. An infrared transparent heater module is utilized to examine local heat transfer phenomena beneath growing bubbles. Two copper microneedle surfaces with a needle diameter of 1µm and different lengths of 10 and 20 µm are manufactured and characterized according to their roughness, their wetting, and wicking behavior. Two uncoated copper surfaces with different roughness are produced for comparison. The experimental data of the uncoated surfaces obtained with the new setup is validated by comparing the data to correlations and data published by other researchers. The two microstructured surfaces increase the heat transfer coefficients by a maximum factor of 2.8 compared to the smoother uncoated surface. The critical heat fluxes obtained for the microstructured surfaces, on the other hand, are reduced. Possible reasons are identified and analyzed, narrowing down the causes. This enabled the construction of an optimized, hierarchical surface, which shows higher critical heat fluxes than the uncoated surfaces. An increase in the heat transfer coefficient occurs at small system pressures, when using a smooth surface and ethanol as boiling fluid compared to FC-72. This is likely due to the formation of an evaporating microlayer, while the measurements using FC-72 show mostly contact line evaporation. These experiments also successfully verify the applicability of correlations distinguishing contact line and microlayer evaporation that were developed using generic non-isothermal dewetting experiments [127].
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2022 | ||||
Autor(en): | Zimmermann, Matthias | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Experimental Investigation of Nucleate Boiling on Microstructured and Smooth Surfaces | ||||
Sprache: | Englisch | ||||
Referenten: | Stephan, Prof. Dr. Peter ; Schnabel, Dr. Lena | ||||
Publikationsjahr: | 2022 | ||||
Ort: | Darmstadt | ||||
Kollation: | XIII, 146 Seiten | ||||
Datum der mündlichen Prüfung: | 22 Februar 2022 | ||||
DOI: | 10.26083/tuprints-00019673 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/19673 | ||||
Kurzbeschreibung (Abstract): | In the last decade, the focus of boiling research has shifted towards micro- and nanostructures. Both structures improve the boiling process significantly compared to smooth surfaces. The interactions between fluid and surface, however, are very complex and not well understood. This impedes the development of universally applicable correlations that incorporate the influence of those complex structures, which would enable the construction of more efficient evaporators. In this thesis, a new experimental setup is constructed to enable boiling experiments at a large pressure, temperature, and heat flux range. FC-72, a refrigerant, and ethanol are chosen as boiling fluids. The boiling process is analyzed on various length scales using two different heater modules. A copper heater module is used to determine mean heat transfer coefficients and critical heat fluxes. An infrared transparent heater module is utilized to examine local heat transfer phenomena beneath growing bubbles. Two copper microneedle surfaces with a needle diameter of 1µm and different lengths of 10 and 20 µm are manufactured and characterized according to their roughness, their wetting, and wicking behavior. Two uncoated copper surfaces with different roughness are produced for comparison. The experimental data of the uncoated surfaces obtained with the new setup is validated by comparing the data to correlations and data published by other researchers. The two microstructured surfaces increase the heat transfer coefficients by a maximum factor of 2.8 compared to the smoother uncoated surface. The critical heat fluxes obtained for the microstructured surfaces, on the other hand, are reduced. Possible reasons are identified and analyzed, narrowing down the causes. This enabled the construction of an optimized, hierarchical surface, which shows higher critical heat fluxes than the uncoated surfaces. An increase in the heat transfer coefficient occurs at small system pressures, when using a smooth surface and ethanol as boiling fluid compared to FC-72. This is likely due to the formation of an evaporating microlayer, while the measurements using FC-72 show mostly contact line evaporation. These experiments also successfully verify the applicability of correlations distinguishing contact line and microlayer evaporation that were developed using generic non-isothermal dewetting experiments [127]. |
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Alternatives oder übersetztes Abstract: |
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Status: | Verlagsversion | ||||
URN: | urn:nbn:de:tuda-tuprints-196738 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau 16 Fachbereich Maschinenbau > Fachgebiet für Technische Thermodynamik (TTD) |
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TU-Projekte: | DFG|SFB1194|TP C02 Stephan | ||||
Hinterlegungsdatum: | 30 Mai 2022 12:07 | ||||
Letzte Änderung: | 19 Aug 2022 09:13 | ||||
PPN: | 496550136 | ||||
Referenten: | Stephan, Prof. Dr. Peter ; Schnabel, Dr. Lena | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 22 Februar 2022 | ||||
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