Physical mechanisms of heat transfer during single bubble nucleate boiling of FC-72 under saturation conditions-I. Experimental investigation

Moghaddam, Saeed; Kiger, Ken

doi:10.1016/j.ijheatmasstransfer.2008.08.018

Cited by 111 publications

(49 citation statements)

References 42 publications

(82 reference statements)

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“…These results are in agreement with the numerical work by Son et al (1999). Recent work by Moghaddam and Kiger (2009) showed similar results for FC-72.…”

Section: Figsupporting

confidence: 92%

Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

Kandlikar

2010

Heat Transfer Engineering

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Recent literature indicates that under certain conditions the heat transfer coefficient during flow boiling in microchannels is quite similar to that under pool boiling conditions. This is rather unexpected as microchannels are believed to provide significant heat transfer enhancement under single-phase as well as flow boiling conditions. This paper explores the underlying heat transfer mechanisms and illustrates the similarities and differences between the two processes. Formation of elongated bubbles and their passage over the microchannel walls have similarities to the bubble ebullition cycle in pool boiling. During the passage of elongated bubbles, the longer duration between two successive liquid slugs leads to wall dryout and a critical heat flux that may be lower than that under pool boiling conditions. A clear understanding of the similarities and differences will help in overcoming some of these limiting factors and in developing strategies for enhancing heat transfer during flow boiling in microchannels.

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“…These results are in agreement with the numerical work by Son et al (1999). Recent work by Moghaddam and Kiger (2009) showed similar results for FC-72.…”

Section: Figsupporting

confidence: 92%

Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

Kandlikar

2010

Heat Transfer Engineering

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“…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.…”

Section: Overview Of Heat Transfer Mechanisms Proposed In Boilingmentioning

confidence: 99%

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

Baltis

Geld

2015

J. Fluid Mech.

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The aim of this study is to provide a better insight into the heat transfer mechanisms involved in single bubble growth in forced convection. In a set-up with vertical upflow of demineralized water under saturation conditions special bubble generators (BGs) were embedded at various positions in the plane wall. Power to a BG, local mean wall temperature and high-speed camera recordings from two viewing angles were measured synchronously. An accurate contour analysis is applied to reconstruct the instantaneous three-dimensional bubble volume. Interface topology changes of a vapour bubble growing at a plane wall have been found to be dictated by the rapid growth and by fluctuations in pressure, velocity and temperature in the approaching fluid flow. The camera images have shown a clear dry spot under the bubbles on the heater surface. A micro-layer under the bubble is experimentally shown to exist when the bubble pins to the wall surface and is therefore dependent on roughness and homogeneity of the wall. The ratio of heat extracted from the wall to the total heat required for evaporation was found to be around 30 % at most and to be independent of the bulk liquid flow rate and heat provided by the wall. When the bulk liquid is locally superheated this ratio was found to decrease to 20 %. Heat transfer to the bubble is also initially controlled by diffusion and is unaffected by the convection of the bulk liquid.

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“…Natural convection is driven by density differences in the liquid and since the temperature difference decreases with the enhance surface, the driving force for natural convection is weaker. Even small changes in bubble formation, departure and frequency have been shown to cause significant changes of the single phase convection mechanism for a single bubble [3]. Hence, the enhanced single phase convection heat transfer could be expected to come from the strong convection caused by the agitation of the vapor bubbles inside of the porous coatings and by the increase in the number of nucleate sites.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…The use of high resolution experimental techniques, for instance: micro fabricated heater devices with integrated temperature sensors, micro-heater arrays and high speed infrared cameras by researchers such as Stephan and Kern [1], Demiray and Kim [2], Moghaddam and Kiger [3] have been of great importance to recent advancements in the understanding of the mechanisms of nucleate boiling heat transfer. These studies have been able to discern and quantify the effect and interactions of different heat transfer mechanisms, such as; transient conduction, single phase micro convection and micro-layer evaporation and have therefore contributed greatly to the understanding of the boiling phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Boiling heat transfer on a dendritic and micro-porous surface in R134a and FC-72

Furberg

Palm

2011

Applied Thermal Engineering

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A visualization study was conducted with the aim of deepening the understanding of the boiling mechanism in a dendritic and microporous copper structure for enhanced boiling heat transfer. The unique structure has earlier been shown to enhance heat transfer in pool boiling applications as well as in convective boiling in both small and large channels. Pool boiling tests were conducted in R134a and in the dielectric fluid FC-72 and were visualized with a high speed imaging system. Data on bubble size, bubble frequency density, heat transfer coefficient and the latent and sensible heat flux contributions were collected and calculated at heat flux varying between 2 and 15 W/cm 2 . The enhanced surface produces smaller bubbles and sustains a high bubble frequency density in both fluids, even at low heat flux. An enhanced latent heat transfer mechanism of up to 10 times, compared to that of a plain reference surface, is the main reason for the improved boiling heat transfer performance on the enhanced surface. The data also suggests that the high nucleation bubble frequency density leads to increased bubble pumping action and thus enhancing single phase convection of up to 6 times. The results in this study highlight the importance of both two and single-phase heat transfer within the porous structure. KEYWORDS

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Physical mechanisms of heat transfer during single bubble nucleate boiling of FC-72 under saturation conditions-I. Experimental investigation

Cited by 111 publications

References 42 publications

Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

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

Boiling heat transfer on a dendritic and micro-porous surface in R134a and FC-72

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