High-Resolution Measurements at Nucleate Boiling of Pure FC-84 and FC-3284 and Its Binary Mixtures

Abstract

In a special boiling cell, vapor bubbles are generated at single nucleation sites on top of a 20μm thick stainless steel heating foil. An infrared camera captures the rear side of the heating foil for analyzing the temperature distribution. The bubble shape is recorded through side windows with a high-speed camera. Global measurements were conducted, with the pure fluids FC-84 and FC-3284 and with its binary mixtures of 0.25, 0.5, and 0.75mole fraction. The heat transfer coefficient (HTC) in a binary mixture is less than the HTC in either of the single component fluid alone. Applying the correlation of Schlünder showed good agreement with the measurements (1982, “Über den Wärmeübergang bei der Blasenverdampfung von Gemischen,” Verfahrenstechnik, 16(9), pp. 692–698). Furthermore, local measurements were arranged with high lateral and temporal resolution for single bubble events. The wall heat flux was computed and analyzed, especially at the three-phase-contact line between liquid, vapor, and heated wall. The bubble volume and the vapor production rate were also investigated. For pure fluids, up to 50–60% of the latent heat flows through the three-phase-contact region. For mixtures, this ratio is clearly reduced and is about 35%.

Heat transfer mechanisms of a vapour bubble growing at a wall in saturated upward flow

“…Most of the heat is extracted at the location of the bubble foot as it expands rapidly over the heating strip surface, as is well known from experimental investigations by for example Moghaddam & Kiger (2009a) and Wagner & Stephan (2009). This will yield a high heat flux at the bubble foot, q , the location and value of which vary with time.…”

“…In a constant wall temperature boundary condition, the heat flux greatly increases when a bubble grows on the substrate, in order to keep the wall temperature constant. Lee et al (2003) <50 % R11 Constant T wall Demiray & Kim (2004) <12.5 % FC-72 Constant T wall Liao, Mei & Klausner (2004) a <30 % -- Myers et al (2005) 23 % FC-72 Constant heat flux Kim, Oh & Kim (2006) 44-360 % b R113 Constant T wall Wagner & Stephan (2009) 22 % FC-84/3284 Constant heat flux Moghaddam & Kiger (2009a) 16-29 % FC-72 Constant heat flux Gerardi et al (2009) ∼50-65 % Deionized water Constant heat flux Gerardi et al (2010) ∼100-115 % Deionized water Constant heat flux From these results, it appears that roughly 25 % of the heat required for bubble growth is accounted for by heat extracted from the wall. It also seems that the application of a constant wall temperature condition or constant heat flux condition yields roughly the same results.…”

Heat transfer coefficient and critical heat flux during nucleate pool boiling of water in the presence of nanoparticles of alumina, maghemite and CNTs

“…Of course, the superheating of the liquid in the present case is also the outcome of heat transfer from the wall. The ratio of heat extracted directly from the wall to the total heat required for evaporation has been reported as less than 50% by several researchers on pool boiling in saturated conditions; see, for example, Kim et al [42], Lee et al [43], Liao et al [44] and Wagner and Stephan [45]. One could argue that the presence of nanoparticles could transport heat away from the bubbles surface owing to the improved thermal conductivity of the working fluid.…”

Detection of liquid–vapor–solid triple contact line in two-phase heat transfer phenomena using high-speed infrared thermometry

“…In other words, we measure temperature beyond the surface to detect phases on the surface. This approach distinguishes DEPIcT from the now-estab- lished IR thermometry technique with IR-opaque heaters (Theofanous et al 2002;Wagner and Stephan 2009;Gerardi et al 2010), where the temperature measured is the temperature of the surface, which makes it hard to identify phases on the surface conclusively.…”