Experimental evidence supporting two-mechanism critical heat flux

Chiang, Tung‐Liang; Carlson, R.D.; Priemer, R.

doi:10.1016/0017-9310(82)90174-0

Cited by 8 publications

(7 citation statements)

References 4 publications

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“…The relationship of transition boiling temperature oscillations at high quality and the vertical oscillation of the wetting front is supported by the recent observations of France et al (1982). These investigators observed the transition boiling temperature oscillations recorded by two wall thermocouples at the same axial position but at different circumferential positions.…”

Section: Conclusion and Significancesupporting

confidence: 63%

A moving‐front transition boiling model

Kao

Weisman

1985

AIChE Journal

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In accordance with visual observations, a transition boiling model that assumes a quench front which alternately advances and retreats in the water flow direction, is proposed. With appropriate choice of a quench zone width and heat transfer rate when the surface is wet, the model predictions are in the same range as the observed temperature oscillations. SCOPEHeater wall temperature oscillations are characteristic of transition boiling. In flow boiling, the mechanism governing transition boiling depends on the volume fraction of vapor present. At high vapor volume fractions, annular flow occurs and a thin film of liquid is present on the wall during nucleate boiling. Transition boiling behavior at high volume fractions is governed by behavior in the region where this liquid film disappears.In accordance with visual observations and temperature measurements, it was postulated that at high vapor fractions the characteristic temperature fluctuations are caused by the vertical oscillation of the edge of the liquid film on the heater surface. The temperature oscillations computed from this moving front model were compared with experimental observations taken in a test section heated by hot mercury.The observed temperature oscillations were also used to estimate wetted area fractions during transition boiling. By relating these wetted area fractions to the aforementioned analytical model, a means for prediction of transition boiling heat transfer rates in the mercury-heated test section was developed. CONCLUSIONS AND SIGNIFICANCEThe present work strongly supports the assumption that transition boiling temperature fluctuations in flowing systems at high vapor fractions are caused by vertical oscillations of the wetting front. Not only is this model in accord with recent visual observations, but it leads to predictions of wall temperature oscillations whose magnitudes are in general agreement with measurements. Further, it explains the high crosscorrelation coefficient between temperature variations at the same axial elevation but different circumferential locations. The model also leads to heat transfer coefficient predictions which are in

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Section: Conclusion and Significancesupporting

confidence: 63%

A moving‐front transition boiling model

Kao

Weisman

1985

AIChE Journal

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“…The length of the wetted region thus periodically expands and contracts. The authors justified their conclusion by their visual observations and temperature oscillation data as well as the wall temperature measurements of France et al (1982).…”

Section: Introductionmentioning

confidence: 88%

Transition boiling heat transfer during reflooding transients

Weisman

Kao

1986

AIChE Journal

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“…They reported that the two CHF mechanisms are related to a flow structure change. According to France et al (1982) different hydrodynamic structures is a requirement of the postulate that two CHF mechanisms exist in the heat flux dependent and independent CHF regions.…”

Section: Introductionmentioning

confidence: 99%

“…Levitan and Lantsman (1975) and Levitan et al (1981) reported that flow turbulence increases with increase in tube diameter, therefore, precipitation of droplets on the liquid film at the wall occurs causing a higher value of q c (Figure 1). France et al (1982) investigated the critical heat flux in high pressure and forced convection. They reported that the two CHF mechanisms are related to a flow structure change.…”

Section: Introductionmentioning

confidence: 99%

A new correlation for the limiting quality of critical heat flux at low mass fluxes and low pressures

Yıldız

Bartsch

2004

Int. J. Energy Res.

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SUMMARYThe limiting quality (or limiting critical quality) was studied experimentally. We used a test section made of Inconel-600 with 8 mm OD, 170 mm length and 1 mm wall thickness. The experiments were carried out with water at up flow for mass fluxes from 100 to 400 kg m À2 s À1, at low pressures (1.0-7.0 bar) and subcoolings (up to 70 K). The limiting quality is characterized by a sharp drop of the critical heat flux (CHF) in a diagram CHF versus critical quality with fixed values of pressure and mass flux and with change of the inlet subcooling. It was observed that the limiting quality appeared in our experimental results. There is a disagreement in the literature on how this phenomenon occurs. According to the present study the limiting quality phenomenon takes place due to a change of CHF mechanisms between DNB and dryout in agreement with Doroshchuk's findings. Existent correlations from literature have been compared with the experimental data. However, no correlations agree with our data because of their different validity ranges. Therefore a new correlation for the limiting quality phenomenon is developed for a large range of pressure. Furthermore the critical heat flux is calculated via a heat balance in which the value of the limiting quality is included.

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Experimental evidence supporting two-mechanism critical heat flux

Cited by 8 publications

References 4 publications

A moving‐front transition boiling model

A moving‐front transition boiling model

Transition boiling heat transfer during reflooding transients

A new correlation for the limiting quality of critical heat flux at low mass fluxes and low pressures

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