Flow pattern transition instability during flow boiling in a single microchannel

Huh, Cheol; Kim, Jeongbae; Kim, Moo Hwan

doi:10.1016/j.ijheatmasstransfer.2006.07.027

Cited by 111 publications

(35 citation statements)

References 22 publications

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“…Zuber [15] suggested the following relationship for the mean bubble departure diameter OJ and bubble departure frequency f: (12) The bubble departure frequency obtained by using Zuber's [15] model and the experimentally measured values gives the same order of magnitude of 10--'. The departure diameter of the bubble in the microchannel was approximately half the hydraulic diameter, as shown in Fig.…”

Section: Bubblefrequencymentioning

confidence: 85%

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Elongated bubble behavior during flow boiling in a microchannel

2007

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Elongated bubble flow is a unique flow pattern that occurs during flow boiling in a microchannel. The incepted bubbles quickly grow to the channel size and form long elongated bubbles due to the confinement of the microchannel. The flow regimes and heat transfer coefficients in the microchannel are closely related to the elongated bubble behavior. Numerical and experimental investigations were performed to study the behavior of elongated bubbles and their effect on flow boiling. Elongated bubble growth in a lOu-um-diameter microchannel was calculated by using a two-zone model, while flow visualization of elongated bubble behavior was obtained with a high-speed CCD camera. Comparisons between the calculated results and experimental observations showed that the growth of the elongated bubble was governed by the evaporation of the thin liquid film that formed between the vapor core and the heated channel wall.

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Section: Bubblefrequencymentioning

confidence: 85%

“…I. A detailed description of the experimental apparatus, including the test section, can be found in Huh et al [12]. Deionized and degassed water was used as the working tluid.…”

Section: Thin Film Evaporation Modelfor Elongated Bubblesmentioning

confidence: 99%

Elongated bubble behavior during flow boiling in a microchannel

2007

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“…When the reaction temperature was further increased, the phasechange heat transfer had two types: one is that the flow resistance in the long microchannel results in the critical transport of the fluid; the other is that the critical boiling status can be attained in microchannel reactor in a short time. Alternating flow patterns of liquid phase and gasliquid phase produced periodic fluctuations of wall temperatures of the microchannel, pressure drops, and mass fluxes with large amplitudes at time intervals of milliseconds or seconds [27], which really affect the ester yields (Fig. 4).…”

Section: Discussionmentioning

confidence: 99%

Fast Esterification of Acetic Acid with Short Chain Alcohols in Microchannel Reactor

Yao

Zhang

et al. 2009

Catal Lett

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Microchannel reactor was used for the fast synthesis of acetic acid esters, including methyl acetate, ethyl acetate, n-propyl acetate and n-butyl acetate. Effects of the inner diameter of microchannel reactors, dosage of catalyst, residence time, reaction temperature and molar ratio of alcohol to acetic acid on yields of esters were studied in the p-toluene sulfonic acid-catalyzed homogeneous esterification of acetic acid with alcohols. Yields of acetic acid ester reached 74.0, 70.1, 97.2 and 92.2% when methanol, ethanol, n-propanol and n-butanol were used as the alcohols, respectively and the residence time was of 14.7 min.

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“…There is a waiting time for liquid to reach a high superheat to trigger the boiling heat transfer again. The above process is repeated in time sequence and the alternating liquid/twophase flow, or the liquid/two-phase/vapor flow, is sustained in heated microchannels, as reported by many investigators such as Wu and Cheng (2003), Chang and Pan (2007), Huh et al (2007), etc. Xu et al (2009 deals with flow instabilities in microchannels.…”

Section: Introductionmentioning

confidence: 99%

Seed bubbles trigger boiling heat transfer in silicon microchannels

Yang

2009

Microfluid Nanofluid

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The smooth channel surface of microsystems delays boiling incipience in heated microchannels. In this paper, we use seed bubbles to trigger boiling heat transfer and control thermal non-equilibrium of liquid and vapor phases in parallel microchannels. The test section consisted of a top glass cover and a silicon substrate. Microheater array was integrated at the top glass cover surface and driven by a pulse voltage signal to generate seed bubbles in time sequence. Each microheater corresponds to a specific microchannel and is located in the microchannel upstream. Five triangular microchannels with a hydraulic diameter of 100 lm and a length of 12.0 mm were etched in the silicon substrate. A thin platinum film was deposited at the back surface of silicon chip with an effective heating area of 4,500 9 1,366 lm, acting as the main heater for the heat transfer system. Acetone liquid was used. With the data range reported here, boiling incipience was not initiated if wall superheats are smaller than 15°C without seed bubbles assisted. Injection seed bubbles triggers boiling incipience and controls thermal non-equilibrium between liquid and vapor phases successfully. Four modes of flow and heat transfer are identified. Modes 1, 2, and 4 are the stable ones without apparent oscillations of pressure drops and heating surface temperatures, and mode 3 displays flow instabilities with apparent amplitudes and long periods of these parameters. The four modes are divided based on the four types of flow patterns observed in microchannels. Seed bubble frequency is a key factor to influence the heat transfer. The higher the seed bubble frequency, the more decreased non-equilibrium between two phases and heating surface temperatures are. The seed bubble frequency can reach a saturation value, at which heat transfer enhancement attains the maximum degree, inferring that a complete thermal equilibrium of two phases is approached. The saturation frequency is about a couple of thousand Hertz in this study.

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Flow pattern transition instability during flow boiling in a single microchannel

Cited by 111 publications

References 22 publications

Elongated bubble behavior during flow boiling in a microchannel

Elongated bubble behavior during flow boiling in a microchannel

Fast Esterification of Acetic Acid with Short Chain Alcohols in Microchannel Reactor

Seed bubbles trigger boiling heat transfer in silicon microchannels

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