A Study on the Minimum Wetting Rate of Isothermal Films Flowing down on Outer Surface of Vertical Pipes.

Koizumi, Yasuo; Kodama, Yuki; Ohtake, Hiroyasu; Ueda, Tatsuhiro; Miyashita, Tohru

doi:10.1299/kikaib.65.3414

Cited by 6 publications

(8 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The frequency and the velocity of the large waves greatly varied with X until X  0.6 m and the variations of these became gentle after X  0.6 m. It is considered that a certain length, approximately 0.6 m in the experiments, is required for the large waves to grow and thereafter the growth calms down. (Koizumi et al, 1999) [DOI: 10.1299/mer.2014tep0006] © 2014 The Japan Society of Mechanical Engineers…”

Section: Resultsmentioning

confidence: 99%

“…9. Thus, the film near the exit end of a pipe where the CHF condition is encountered is more disturbed in the case of Ueda et al than in the case of Koizumi et al since a longer test pipe was used in the experiments of Ueda et al Therefore, it is suspected that the larger disturbance near the exit end of the test pipe resulted in the higher CHF in Ueda et al than in Koizumi et al (1999).…”

Section: Critical Heat Flux Of Film Flowmentioning

confidence: 98%

“…Since there exist many waves on the film and the dynamic pressure of the film fluctuates, the maximum value of the fluctuating dynamic pressure seems appropriate to be considered for the film breakup or the rewetting. Koizumi et al (1999) examined the MWR of the isothermal water film flowing down on the outer surface of pipes arranged vertically considering the importance of the relation between the MWR and the waves on the film surface. Hartley and Murgatroyd (1964) proposed the MWR  c correlation by assuming that the critical film thickness below which the film disrupts is given by the condition that the sum of the surface and the kinematic energy becomes minimum;…”

Section: Minimum Wetting Ratementioning

confidence: 99%

“…Fig. 1 State of Stagnation Point of Film at Front Edge of Dry-Patch (Koizumi et al, 1999) Koizumi et al (1999) measured the MWR by using the test facility shown schematically in Fig. 2.…”

Section: Analytical Model Of Mwrmentioning

confidence: 99%

“…The variation of the electric capacitance between the electric capacitance probe and the pipe surface on which the film flowed down was detected with 500 Hz to obtain the frequency of the large waves. (Koizumi et al, 1999) [DOI: 10.1299/mer.2014tep0006] © 2014 The Japan Society of Mechanical Engineers…”

Section: Analytical Model Of Mwrmentioning

confidence: 99%

See 4 more Smart Citations

Film flow on a wall and critical heat flux

Koizumi

2014

Mechanical Engineering Reviews

Self Cite

View full text Add to dashboard Cite

Since there were large waves on the film, the minimum wetting rate (MWR) was greatly affected by the waves. The contact angle of the film at the top edge of the stable dry-patch varied periodically synchronizing with the arrival of the waves. When the contact angle exceeded the maximum advancing contact angle, the top edge of the dry-patch began to move downward, i.e. the rewetting of the dry-patch was initiated. The MWR was properly given by considering the force balance at the top edge of the dry-patch that when the maximum of the dynamic pressure of the film fluctuating according to the waves exceeds the film holding force by surface tension corresponding to the maximum advancing contact angle. Many tiny bubbles were observed in the film in the falling film boiling and the upward flow boiling. The bubble generation in the film might create a dry-patch locally in the film. If the film flow coming to the dry-patch could not rewet it, the CHF condition occurred. In the falling film boiling, since the long film flow might have a larger disturbance of the film flow than the short film flow, the CHF of the long falling film boiling was higher than the CHF of the short falling film boiling. The disturbance of the film flow of upward flow boiling was larger than that of the falling film boiling. Thus, the CHF of the upward flow boiling was larger than the CHF of the falling film boiling. The CHF of those were predicted with a unique correlation except for the constant that expressed the difference of the degree of the disturbance of the film flow. The CHF of the flat mini-channels were also predicted well with the CHF correlation except for the constant. The constant, i.e. the CHF, was lower than of course the CHF of the upward flow boiling and also than the CHF of the falling film boiling. Since a wall effect due to the viscosity that suppressed the growth of the film flow disturbance was enhanced in the flat mini-channels, the disturbance of the film flow on the heat transfer surface was reduced and the CHF might become smaller. Correlations for the wavelength, the maximum film thickness and the wave velocity were introduced. The proposed correlations required only a film flow rate, physical parameters and geometrical dimensions. These values of the wave characteristics were required in the correlations of the MWR and the CHF. What is left toward the next step is to incorporate these characteristics of the waves with the MWR and CHF correlations.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Critical Heat Flux Of Film Flowmentioning

confidence: 98%

Section: Minimum Wetting Ratementioning

confidence: 99%

“…Fig. 1 State of Stagnation Point of Film at Front Edge of Dry-Patch (Koizumi et al, 1999) Koizumi et al (1999) measured the MWR by using the test facility shown schematically in Fig. 2.…”

Section: Analytical Model Of Mwrmentioning

confidence: 99%

Section: Analytical Model Of Mwrmentioning

confidence: 99%

See 3 more Smart Citations