Pool boiling of refrigerants over nanostructured and roughened tubes

Falling film boiling of refrigerants over nanostructured and roughened tubes: Heat transfer, dryout and critical heat flux

“…Data previously published of the falling film-boiling HTCs measured on a polished and roughened copper tube in R-134a at 5 °C and 25 °C [32] were thus referenced in this study, while new tests were conducted with a polished and roughened tube in R-245fa at 20 °C and included in this work to aid comparison across the entire range of conditions tested as well as further expand our understanding of plain tube falling film boiling. This study also builds upon previous work by the same authors on pool-boiling over nanostructured tubes [45], with those results at times used and referenced in this study.…”

“…Pool-boiling studies use the term CHF to indicate the peak heat flux that can be reached as wall superheats are increased before the heat flux collapses [57,58], as was done in our respective pool-boiling study reported on separately [45], as dryout due to a lack of liquid mass flow is not a mechanism present in pool-boiling.…”

RS–DFID Africa capacity-building initiative programme grant: harnessing unsteady phase-change heat exchange in high-performance concentrated solar power systems

“…Further efforts by the consortium focused on the pool boiling of refrigerants relevant to a wider range of applications, specifically R-134a (at 5 and 25°C) and R-245fa (at 20°C), and over a range of heat fluxes from 20 to 100 kW m −2 [29]. Specifically, Bock et al [29] investigated pool boiling over tubes with three surfaces: applying nanocoatings to polished copper using a layer-by-layer approach, a chemical oxidation process, which resulted in sharp copper oxide structures on the surface, and a commercial process known as nanoFLUX. Results from the study, including the equipment used, are shown in figure 8.…”

“…Building on the categorization work of the heat-transfer effects of pool boiling over a range of nanostructured tubes [29], the same authors extended their investigations into falling-film boiling. The authors used tubes, placed horizontally within a test chamber, with a thin film of refrigerant distributed along the length of the outside of the tubes.…”

Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review

“… 82 Heat transfer coefficient enhancements up to 200% demonstrated with commercial nanoFLUX coatings utilizing R-134a and R-245fa have primarily been attributed to increased nucleation sites, increased capillary pumping, and enhanced evaporation of wicked liquid beneath growing vapor bubbles. 83 The interesting phenomena of decreased wall superheat on increasing heat flux, termed ‘hookback’, has been shown with FC-72. 84 This is caused due to simultaneous activation of numerous submicron cavities and has been found to be dependent on the level of subcooling and the size-range of cavities.…”