Critical-Heat-Flux and Flow-Pattern Observations for Low-Pressure Water Flowing in Tubes

1967 ◽  
Vol 89 (1) ◽  
pp. 69-74 ◽  
Author(s):  
A. E. Bergles ◽  
R. F. Lopina ◽  
M. P. Fiori
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Slug Flow ◽  
Complex Function ◽  
Choked Flow ◽  
Flux Data ◽  
Pressure Water ◽  
Electrical Probe ◽  
Inlet Conditions

This paper summarizes the results of an investigation of the critical-heat-flux condition for bulk boiling of water in uniformly heated round tubes where the inlet conditions were subcooled and exit pressures were below 100 psia. Choked flow was found to be prevalent under these conditions. The critical heat flux is shown to be a complex function of both local and inlet conditions. Detailed flow-pattern observations were made with an electrical probe. Many of the trends in the critical-heat-flux data can be related to the flow-pattern instability caused by slug flow.

scholarly journals Influence of the Flow Pattern on Critical Heat Flux

2014 ◽  
Vol 27 (5) ◽  
pp. 571-576
Author(s):  
Goshi YAMASHINA ◽  
Noriko NAKAMURA ◽  
Takeyuki AMI ◽  
Hisashi UMEKAWA ◽  
Mamoru OZAWA
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux

Flow Behavior and Flow Boiling Heat Transfer in Thin-Rectangular Mini-Channels

2008 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Tomonari Yamada
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Liquid Slug ◽  
Flux Condition

Boiling heat transfer of thin-rectangular channels of the width of 10 mm has been examined. The height of the flow channel was in a range from 0.6 mm to 0.4 mm. Experimental fluid was water. Bubbly flow, slug flow, semi annular flow and annular flow were observed. The flow pattern transition agreed well with the Baker flow pattern map for the usual sized flow path. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments. At the critical heat flux condition, the heat transfer surface was covered by liquid slug, a large bubble pushed away the liquid slug, a dry area was formed on the heat transfer surface and then liquid slug came around to cover the heat transfer surface again. This process repeated rapidly. Following this observation, a heat transfer surface temperature calculation model at the critical heat flux condition was proposed. The calculated result re produced the experimental result.

Critical Heat Flux in Microchannels With an Adjustable Inlet Orifice

2012 ◽  
Author(s):  
Brent A. Odom ◽  
Carlos A. Ortiz ◽  
Patrick E. Phelan
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Cooling Capacity ◽  
Hydraulic Diameter ◽  
Low Flow ◽  
Two Phase ◽  
Mass Fluxes ◽  
Inlet Conditions

The benefits of eliminating instabilities in two-phase microchannel flow with inlet orifices come with costs. This study describes the tradeoffs between microchannels with and without inlet orifices, focusing on results from critical heat flux data obtained for various orifice sizes and mass fluxes. An adjustable inlet orifice controlled with a micrometer was placed in front of an array of 31 parallel microchannels each with a hydraulic diameter of 0.235 mm and a length of 1.33 cm. For mass fluxes ranging from 186 kg m−2 s−1 to 847 kg m−2 s−1, critical heat flux (CHF) data were obtained for 7 different orifice sizes. For low flow rates that provided a low quality saturated inlet condition, the difference in CHF values was found to be minimal between open and almost closed orifice conditions. The smallest orifice achieved a CHF value of 5 W cm−2 less than the largest orifice size for a mass flux of 186 kg m−2 s−1, and 7 W cm−2 less for a mass flux of 433 kg m−2 s−1. For mass fluxes higher than 433 kg m−2 s−1, subcooled conditions were present at the orifice inlet, and the highest CHF values occurred with an orifice hydraulic diameter of 35 percent of fully open. For the higher mass flux cases, orifice sizes in the range of 1.8 percent to 28 percent of fully open caused CHF to occur at lower values than less restrictive orifice sizes. This was due to loss of cooling capacity from rapid pressure drop through the orifice. Slightly higher average channel pressures also decrease the refrigerant’s latent heat of vaporization. For the orifice sizes from 35 to 70 percent of unrestricted flow, a very minimal increase in pressure drop over fully open inlet conditions occurred and the general trend was higher CHF values. Very small inlet orifices are beneficial for steady state conditions that do not approach CHF; however, overly restricting the flow at the inlet to microchannels reduces cooling capacity significantly and will cause early onset of CHF. A slightly restrictive inlet orifice will increase CHF.

A compilation of rod array critical heat flux data sources and information

1974 ◽  
Vol 30 (1) ◽  
pp. 20-35
Author(s):  
E.D. Hughes ◽  
Ip Ka-Lam ◽  
A.N. Baker ◽  
M.W. Carbon
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Data Sources ◽  
Flux Data ◽  
Rod Array

D121 Influence of the Flow Pattern on Critical Heat Flux

2012 ◽  
Vol 2012 (0) ◽  
pp. 111-112
Author(s):  
Goshi Yamashina ◽  
Takaho Takeuchi ◽  
Noriko Nakamura ◽  
Takeyuki Ami ◽  
Hisashi Umekawa ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux
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