Effect of Nanofluid on the Film Boiling Behavior at Vapor Film Collapse

2009 ◽  
Author(s):  
Takahiro Arai ◽  
Masahiro Furuya
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Direct Contact ◽  
Film Surface ◽  
Film Boiling ◽  
Vapor Film ◽  
Quenching Temperature ◽  
Steel Sphere ◽  
Film Collapse ◽  
Al2o3 Nanofluid

A high-temperature stainless-steel sphere was immersed into Al2O3 nanofluid to investigate film boiling heat transfer and collapse of vapor film. Surface temperature is referred to the measured value of thermocouples embedded into and welded onto a surface of the sphere. A direct contact between the immersed sphere and Al2O3 nanofluids is quantified by the acquired electric conductivity. The Al2O3 nanofluid concentration is varied from 0.024 to 1.3 vol%. A film boiling heat transfer rate of Al2O3 nanofluid is almost the same or slightly lower than that of water. A quenching temperature rises slightly with increased the Al2O3 nanofluid concentrations. In both water and Al2O3 nanofluid, the direct contact signals between the sphere and coolant were not detected before vapor film collapse.

Effect of Hydrated Salt Additives on Film Boiling Behavior at Vapor Film Collapse

2008 ◽  
Author(s):  
Takahiro Arai ◽  
Masahiro Furuya
Keyword(s):  
High Speed ◽  
Video Camera ◽  
Film Boiling ◽  
Vapor Film ◽  
Quenching Temperature ◽  
Steel Sphere ◽  
Digital Video Camera ◽  
Collapse Temperature ◽  
Test Film ◽  
Film Collapse

A high-temperature stainless-steel sphere was immersed into various salt solutions to test film boiling behavior at vapor film collapse. The film boiling behavior around the sphere was observed with a high-speed digital-video camera. Because salt additives enhanced condensation heat transfer, the observed vapor film was thinner. Surface temperature of the sphere was measured. Salt additives increased the quenching (vapor film collapse) temperature, because frequency of direct contact between sphere surface and coolant increased. Quenching temperature rises with increased salt concentration. The quenching temperature, however, approaches a constant value when the slat concentration is close to its saturation concentration. The quenching temperature is well correlated with ion molar concentration, which is a number density of ions, regardless of the type of hydrated salts.

Effect of Hydrated Salt Additives on Film Boiling Behavior at Vapor Film Collapse

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Takahiro Arai ◽  
Masahiro Furuya
Keyword(s):  
Salt Concentration ◽  
High Speed ◽  
Video Camera ◽  
Film Boiling ◽  
Vapor Film ◽  
Quenching Temperature ◽  
Steel Sphere ◽  
Digital Video Camera ◽  
Collapse Temperature ◽  
Film Collapse

A high-temperature stainless steel sphere was immersed into various salt solutions to investigate film boiling behavior at vapor film collapse. The film boiling behavior around the sphere was observed with a high-speed digital-video camera. Because the salt additives enhance the condensation heat transfer, the observed vapor film was thinner. The surface temperature of the sphere was measured. Salt additives increased the quenching (vapor film collapse) temperature because the frequency of direct contact between the sphere surface and the coolant increased. Quenching temperature increases with increased salt concentration. The quenching temperature, however, approaches a constant value when the salt concentration is close to its saturation concentration. The quenching temperature is well correlated with ion molar concentration, which is a number density of ions, regardless of the type of hydrated salts.

Destabilization of Film Boiling Due to Arrival of a Pressure Shock—Part I: Experimental

1981 ◽  
Vol 103 (3) ◽  
pp. 459-464 ◽  
Author(s):  
A. Inoue ◽  
S. G. Bankoff
Keyword(s):  
Heat Transfer ◽  
Horizontal Tube ◽  
Nucleate Boiling ◽  
Transient Heat Transfer ◽  
Film Boiling ◽  
Vapor Film ◽  
Pressure Shock ◽  
Transfer Rates ◽  
Vapor Explosions ◽  
Film Collapse

Transient heat transfer from an electrically-heated 3 mm o.d. horizontal tube, initially in subcooled film boiling, was measured immediately after passage of a shock wave of 1–5 × 105 N/m2 over-pressure. The fluids tested were Freon-113 and 95 percent ethanol-5 percent water at initially 0.5–2 × 105 N/m2 at 22–24° C. Transient heat transfer rates, averaged over 0.5–1 ms after vapor film collapse, ranged up to 20 times the steady-state value. The maximum transient flux occurred at supercritical contact temperatures, with frequently a minimum in the range of contact temperatures between the homogeneous nucleation and the critical temperature. Photography at 5000 frames/s showed apparently complete vapor film collapse within one or two frames, followed by re-establishment of film boiling in ∼1 ms, and eventually nucleate boiling in ∼100 ms. The surface temperature which gave the highest peak transient flux shifted appreciably with increasing shock pressure, which indicates some compressibility even after “contact” was made. Implications for vapor explosions are discussed.

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