Experimental Investigation on Critical Heat Flux and Upstream-CHF with R-134a at high Pressures

Experimental Investigation on Critical Heat Flux and Upstream-CHF with R-134a at high Pressures | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Experimental Investigation on Critical Heat Flux and Upstream-CHF with R-134a at high Pressures Nikolai Rensch, Aurelian Florin Badea, Xu Cheng This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8777392/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 17 You are reading this latest preprint version Abstract An experimental study of the critical heat flux (CHF) in R-134a was performed in a vertical round tube with upward flow. The experiments were conducted in a wide pressure range from 1.10 MPa up to 3.98 MPa, corresponding to a reduced pressure of 0.27 to 0.98, respectively. The mass flux was varied between 300 kg/m²s and 2000 kg/m²s, while the local critical vapor quality ranged from − 3.43 to 0.69. The uniformly heated tube had an inner diameter of 10 mm and a heated length of 3000 mm and 1000 mm. The extensive experimental matrix resulted in a total of 500 CHF data points. At the onset of the boiling crisis, the wall temperature suddenly rises due to the poor heat transfer capability of the vapor phase compared to liquid. The temperature jump was less dramatic in the high subcritical pressure range, especially under dryout conditions. But the critical vapor quality, which marks the beginning of the boiling crisis, shifted to lower values and the CHF value decreased significantly with increasing pressure, especially near the critical pressure. During the experiments at reduced pressures of 0.95 and 0.98, the so-called upstream-CHF as well as the influence of the inlet subcooling and mass flux on its occurrence could be investigated. A possible explanation for the upstream-CHF phenomenon is the onset of homogeneous nucleation at a local wall temperature maximum, where the upstream-CHF point is located. CHF Upstream-CHF High pressure R-134a Experiment Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 21 Mar, 2026 Reviews received at journal 15 Mar, 2026 Reviews received at journal 13 Mar, 2026 Reviews received at journal 10 Mar, 2026 Reviews received at journal 10 Mar, 2026 Reviewers agreed at journal 08 Mar, 2026 Reviewers agreed at journal 08 Mar, 2026 Reviews received at journal 07 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers invited by journal 03 Mar, 2026 Editor assigned by journal 26 Feb, 2026 Submission checks completed at journal 04 Feb, 2026 First submitted to journal 03 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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The experiments were conducted in a wide pressure range from 1.10 MPa up to 3.98 MPa, corresponding to a reduced pressure of 0.27 to 0.98, respectively. The mass flux was varied between 300 kg/m\u0026sup2;s and 2000 kg/m\u0026sup2;s, while the local critical vapor quality ranged from \u0026minus;\u0026thinsp;3.43 to 0.69. The uniformly heated tube had an inner diameter of 10 mm and a heated length of 3000 mm and 1000 mm.\u003c/p\u003e \u003cp\u003eThe extensive experimental matrix resulted in a total of 500 CHF data points. At the onset of the boiling crisis, the wall temperature suddenly rises due to the poor heat transfer capability of the vapor phase compared to liquid. The temperature jump was less dramatic in the high subcritical pressure range, especially under dryout conditions. But the critical vapor quality, which marks the beginning of the boiling crisis, shifted to lower values and the CHF value decreased significantly with increasing pressure, especially near the critical pressure. During the experiments at reduced pressures of 0.95 and 0.98, the so-called upstream-CHF as well as the influence of the inlet subcooling and mass flux on its occurrence could be investigated. 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