{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T00:57:39Z","timestamp":1760144259120,"version":"build-2065373602"},"reference-count":31,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2024,4,5]],"date-time":"2024-04-05T00:00:00Z","timestamp":1712275200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Plan Nacional de I + D","award":["ENE2016-79489-C2-1-P","ENE2016-79489-C2-1-P"],"award-info":[{"award-number":["ENE2016-79489-C2-1-P","ENE2016-79489-C2-1-P"]}]},{"name":"Ministerio de Econom\u00eda y Competitividad","award":["ENE2016-79489-C2-1-P","ENE2016-79489-C2-1-P"],"award-info":[{"award-number":["ENE2016-79489-C2-1-P","ENE2016-79489-C2-1-P"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper investigates non-invasive techniques for annular two-phase flow analysis, focusing on liquid film characterization to understand the interfacial phenomena that are crucial for heat and mass transfer. Limited methods allow the study of the temporal and spatial evolution of liquid film, such as Planar Laser-Induced Fluorescence (PLIF). However, this method possesses optical challenges, leading to the need for improved techniques to mitigate refraction and reflection, such as Refractive Index Matching (RIM). This study utilizes an experimental annular flow facility to analyze both RIM and non-RIM PLIF over a range of liquid Reynolds numbers from 4200 to 10,400. Three configurations\u2014PLIF RIM90, PLIF RIM40, and PLIF nRIM40\u2014are compared from both qualitative and quantitative perspectives. In the quantitative analysis, key variables of the liquid film are measured, namely mean film thickness, disturbance wave height, and frequency. Variations in the analyzed variables indicate minor deviations, which are not likely to be caused by the technique used. However, all three methodologies exhibited errors that are estimated to be within a maximum of 10%, with a mean value of approximately 8%.<\/jats:p>","DOI":"10.3390\/s24072317","type":"journal-article","created":{"date-parts":[[2024,4,5]],"date-time":"2024-04-05T08:27:52Z","timestamp":1712305672000},"page":"2317","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Comparison of Refractive Index Matching Techniques and PLIF40 Measurements in Annular Flow"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7028-9063","authenticated-orcid":false,"given":"Yago","family":"Rivera","sequence":"first","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]},{"given":"Dorian","family":"Bascou","sequence":"additional","affiliation":[{"name":"\u00c9cole Nationnale Sup\u00e9rieure d\u2019Arts et M\u00e9tiers, 75013 Paris, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2958-0558","authenticated-orcid":false,"given":"David","family":"Blanco","sequence":"additional","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9450-2479","authenticated-orcid":false,"given":"Lucas","family":"\u00c1lvarez-Pi\u00f1eiro","sequence":"additional","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"},{"name":"DEIOAC Departamento de Estad\u00edstica, Investigaci\u00f3n Operativa Aplicadas y Calidad, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2097-5089","authenticated-orcid":false,"given":"C\u00e9sar","family":"Berna","sequence":"additional","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"},{"name":"DEIOAC Departamento de Estad\u00edstica, Investigaci\u00f3n Operativa Aplicadas y Calidad, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4512-7991","authenticated-orcid":false,"given":"Jos\u00e9-Luis","family":"Mu\u00f1oz-Cobo","sequence":"additional","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9670-068X","authenticated-orcid":false,"given":"Alberto","family":"Escriv\u00e1","sequence":"additional","affiliation":[{"name":"IIE Instituto de Ingenier\u00eda Energ\u00e9tica, Universitat Polit\u00e9cnica de Valencia, 46022 Valencia, Spain"}]}],"member":"1968","published-online":{"date-parts":[[2024,4,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"112","DOI":"10.1016\/j.nucengdes.2019.03.008","article-title":"Characterization of the gas-liquid interfacial waves in vertical upward co-current annular flows","volume":"346","author":"Cuadros","year":"2019","journal-title":"Nucl. Eng. Des."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1016\/j.ijmultiphaseflow.2013.04.001","article-title":"Disturbance wave development in two-phase gas\u2013liquid upwards vertical annular flow","volume":"55","author":"Zhao","year":"2013","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.anucene.2018.07.016","article-title":"Prediction of rod film thickness of vertical upward co-current adiabatic flow in rod bundle","volume":"121","author":"Ju","year":"2018","journal-title":"Ann. Nucl. Energy"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"115336","DOI":"10.1016\/j.ces.2019.115336","article-title":"Study on the characteristics of interfacial waves in annular flow by image analysis","volume":"212","author":"Lin","year":"2020","journal-title":"Chem. Eng. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1016\/j.pnucene.2014.01.018","article-title":"Review of droplet entrainment in annular flow: Interfacial waves and onset of entrainment","volume":"74","author":"Berna","year":"2014","journal-title":"Prog. Nucl. Energy"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"64","DOI":"10.1016\/j.pnucene.2014.11.011","article-title":"Review of droplet entrainment in annular flow: Characterization of the entrained droplets","volume":"79","author":"Berna","year":"2015","journal-title":"Prog. Nucl. Energy"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"570","DOI":"10.1016\/j.ijmultiphaseflow.2010.03.004","article-title":"Time spatially resolved measurements of interfacial waves in vertical annular flow","volume":"36","author":"Belt","year":"2010","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1016\/j.ijmultiphaseflow.2019.07.013","article-title":"Simultaneous application of two laser-induced fluorescence approaches for film thickness measurements in annular gas-liquid flows","volume":"119","author":"Cherdantsev","year":"2019","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"3528","DOI":"10.1016\/j.nucengdes.2008.06.013","article-title":"Properties of disturbance waves in vertical annular two-phase flow","volume":"238","author":"Sawant","year":"2008","journal-title":"Nucl. Eng. Des."},{"key":"ref_10","first-page":"11","article-title":"Measurement of liquid holdup by using conductance probe sensor in horizontal annular flow","volume":"53","author":"Setyawan","year":"2019","journal-title":"J. Adv. Res. Fluid Mech. Therm. Sci."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3167775","DOI":"10.1109\/TIM.2022.3167775","article-title":"A Method to Suppress the Effect of Total Reflection on PLIF Imaging in Annular Flow","volume":"71","author":"Xue","year":"2022","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"845","DOI":"10.1007\/s00231-018-2465-5","article-title":"Study of spatiotemporally resolved temperature field and heat transfer in liquid film using PLIF","volume":"55","author":"Xue","year":"2019","journal-title":"Heat Mass Transf."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"111032","DOI":"10.1016\/j.expthermflusci.2023.111032","article-title":"Imaging and Investigation with Innovative PLIF40 for Improved Film Thickness Measurements in Annular Flow","volume":"150","author":"Xue","year":"2024","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"111769","DOI":"10.1016\/j.nucengdes.2022.111769","article-title":"Experiments in free falling and downward cocurrent annular flows\u2014Characterization of liquid films and interfacial waves","volume":"392","author":"Rivera","year":"2022","journal-title":"Nucl. Eng. Des."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"695","DOI":"10.1002\/aic.690200410","article-title":"Statistical characteristics of thin, wavy films. Part II: Studies on the substrate and its wave structure","volume":"20","author":"Chu","year":"1974","journal-title":"Am. Inst. Chem. Eng. J."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"695","DOI":"10.1002\/aic.690200410","article-title":"Statistical characteristics of thin, wavy films. Part III: Structure of the large waves and their resistances to gas flow","volume":"20","author":"Chu","year":"1975","journal-title":"Am. Inst. Chem. Eng. J."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1016\/j.ijheatfluidflow.2018.06.015","article-title":"Average liquid film thickness of annular air-water two-phase flow in 8 \u00d7 8 rod bundle","volume":"73","author":"Ju","year":"2018","journal-title":"Int. J. Heat Fluid Flow"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"103391","DOI":"10.1016\/j.ijmultiphaseflow.2020.103391","article-title":"X-ray measurements of thin liquid films in gas\u2013liquid pipe flow","volume":"131","author":"Kesana","year":"2020","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1016\/j.measurement.2019.06.027","article-title":"A new method for liquid film thickness measurement based on ultrasonic echo resonance technique in gas-liquid flow","volume":"146","author":"Wang","year":"2019","journal-title":"Measurement"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Rivera, Y., Bidon, M., Mu\u00f1oz-Cobo, J.-L., Berna, C., and Escriv\u00e1, A. (2023). A Comparative Analysis of Conductance Probes and High-Speed Camera Measurements for Interfacial Behavior in Annular Air\u2013Water Flow. Sensors, 23.","DOI":"10.3390\/s23208617"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"385","DOI":"10.1016\/j.ijmultiphaseflow.2010.01.003","article-title":"Studying disturbance waves in vertical annular flow with high-speed video","volume":"36","author":"Schubring","year":"2010","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"122","DOI":"10.1016\/j.ijmultiphaseflow.2014.07.009","article-title":"Analysis of spatial and temporal evolution of disturbance waves and ripples in annular gas\u2013liquid flow","volume":"67","author":"Alekseenko","year":"2014","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"271","DOI":"10.1007\/s12217-008-9028-1","article-title":"Investigation of Waves Interaction in Annular Gas\u2013Liquid Flow Using High-Speed Fluorescent Visualization Technique","volume":"20","author":"Alekseenko","year":"2008","journal-title":"Microgravity Sci. Technol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1007\/s00348-011-1200-5","article-title":"Application of a high-speed laser-induced fluorescence technique for studying the three-dimensional structure of annular gas\u2013liquid flow","volume":"53","author":"Alekseenko","year":"2012","journal-title":"Exp. Fluids"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"815","DOI":"10.1016\/j.ijmultiphaseflow.2010.05.007","article-title":"Planar laser-induced fluorescence (PLIF) measurements of liquid film thickness in annular flow. Part I: Methods and data","volume":"36","author":"Schubring","year":"2010","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"193","DOI":"10.1016\/j.ijmultiphaseflow.2019.06.002","article-title":"Structured planar laser-induced fluorescence (S-PLIF) for the accurate identification of interfaces in multiphase flows","volume":"118","author":"Charogiannis","year":"2019","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Cherdantsev, A., Bobylev, A., Guzanov, V., Kvon, A., and Kharlamov, S. (2023). Measuring liquid film thickness based on the brightness level of the fluorescence: Methodical overview. Int. J. Multiph. Flow, 168.","DOI":"10.1016\/j.ijmultiphaseflow.2023.104570"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"103549","DOI":"10.1016\/j.ijmultiphaseflow.2020.103549","article-title":"Liquid film thickness measurements on a plate based on brightness curve analysis with acute PLIF method","volume":"136","author":"Li","year":"2021","journal-title":"Int. J. Multiph. Flow"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"64","DOI":"10.1007\/s00348-020-2892-1","article-title":"Refractive index matching (RIM) using double-binary liquid\u2013liquid mixtures","volume":"61","author":"Helmers","year":"2020","journal-title":"Exp. Fluids"},{"key":"ref_30","unstructured":"Freeman, H. (1990). Machine Vision for Three-Dimensional Scenes, Academic Press."},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Patnaik, S., and Yang, Y.M. (2012). 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