Francisco, Oscar Augusto de AguiarByczynski, WiktorAkiba, KazuBertella, ClaudiaBitadze, AlexanderBrock, MatthewBulat, BartoszButton, GuillaumeBuytaert, JanDe Capua, StefanoCallegari, RiccardoCastellana, ChristineCatinaccio, AndreaCharrier, CatherineCharvet, ColetteCoco, VictorCollins, PaulaDegrange, JordanDumps, RaphaelFeito, Diego AlvarezFournel, FrankFreestone, JulianJedrychowski, MariuszLima, Vinicius FrancoTorreira, Abraham GallasHulsbergen, WouterHynds, DanielIzquierdo, Gonzalo ArnauJalocha, PawelJans, EddyJohn, MalcolmJurik, NathanLatham, ThomasLeflat, AlexanderCid, Edgar LemosLindner, RolfMapelli, AlessandroMathad, AbhijitMorris, AndyNoel, JeromeNomerotski, Andreide Oliveira, Ruivan Overbeek, MartijnParkes, ChrisPetagna, PaoloPorret, AlexandreRenaud, DenisRoeland, ErnoRomagnoli, GiuliaRouchouze, Ericde Roo, KristaSanders, FreekSchneider, ThomasSchindler, HeinrichSchmidt, BurkhardSchopper, AndreasScantlebury-Smead, LukeVan Stenis, MirandaSvihra, PeterTeissandier, BenoitTeissier, Jean-FrancoisThery, XavierThomas, EricVerlaat, BartWilliams, Mark R. J.2022-08-152022-08-152022-08-152022-09-1110.1016/j.nima.2022.166874https://infoscience.epfl.ch/handle/20.500.14299/190117WOS:000829830600004The LHCb VELO Upgrade I, currently being installed for the 2022 start of LHC Run 3, uses silicon microchannel coolers with internally circulating bi-phase CO2 for thermal control of hybrid pixel modules operating in vacuum. This is the largest scale application of this technology to date. Production of the microchannel coolers was completed in July 2019 and the assembly into cooling structures was completed in September 2021. This article describes the R & D path supporting the microchannel production and assembly and the motivation for the design choices, together with the achieved fluidic and thermal performance. The Thermal Figure of Merit of the microchannel coolers is measured on the final modules to be between 1.5 and 3.5 K cm(2) W-1, depending on glue thickness. The microchannel coolers constitute 18% of the total radiation length of the VELO and less than 2% of the material seen before the second measured point on the tracks. Microchannel cooling is well suited to the VELO implementation due to the uniform mass distribution, close thermal expansion match with the module components and resistance to radiation.Instruments & InstrumentationNuclear Science & TechnologyPhysics, NuclearPhysics, Particles & FieldsPhysicsmicrochannel coolingbi-phase co2silicon wafer bondingthermal figure of meritvelo upgradeprediction methodsco2 evaporationmodelheattubestext::journal::journal article::research article