Non-Linear Characteristics of Subcooled Water Flow Boiling CHFS Versus Outlet Subcoolings for Flow Velocities at Pressures in Various Tubes

2008 ◽  
Author(s):  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Flow Velocity ◽  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Twisted Tape ◽  
Outlet Pressure ◽  
Subcooled Water ◽  
Twisted Tapes ◽  
Non Linear ◽  
Bare Tube

Non-linear characteristics of the subcooled water flow boiling CHF versus outlet subcooling for a flow velocity with outlet pressure as a parameter in a horizontal or vertical tube with a twisted tape having flowing subcooled water was clarified using the existing databases expanding quite recently derived the CHF correlations based on two CHF mechanisms for the bare tubes with various inside diameters and length-to-diameter ratios for a flow velocity with outlet pressure as a parameter. The databases were applied measured using, the horizontal tubes with inside diameters of 8 and 12 mm, having length-to-diameter ratios of 6.25 and 4.17 respectively with twisted-tapes having a twist ratio of 2.0, for flow velocities of 7 and 10 m/s, at pressures ranging from 0.2 to 1.1 MPa. The nonlinear characteristics of subcooled water flow boiling CHFs for outlet subcoolings in the tubes having helically coiled 1 mm diameter wires of the coil pitches of 12, 24 and 36 mm, with flowing subcooled water of a flow velocity of 7 m/s at outlet pressures of 0.2, 0.3 and 1.1 MPa were investigated based on the subcooled water flow boiling CHF correlations for bare tubes previously derived. The following results were derived that (1) the non-linear characteristic of CHF versus outlet subcooling, for a horizontal or vertical tube having a twisted tape, divided into three regions for middle, transition, and high outlet subcooling was clarified. The characteristics were similar to that for a identical bare tube, with higher CHF values for middle and high outlet subcooling values respectively, and (2) the enhanced CHF values for middle and high outlet subcooling values being dependent on outlet pressuret and being independent of one respectively, were described by the same CHF correlations derived for a identical bare tube, with higher coefficients of the correlations depending on the tubes with twisted tapes of twist ratios.

Generalized Prediction for Subcooled Water Flow Boiling CHFs Versus Outlet Subcoolings for Flow Velocities at Outlet Pressures in Various Tubes

2004 ◽  
Author(s):  
Akira Sakurai ◽  
Katsuya Fukuda
Keyword(s):  
Flow Velocity ◽  
Water Flow ◽  
Flow Boiling ◽  
Hydrodynamic Instability ◽  
Vertical Tube ◽  
Spontaneous Nucleation ◽  
Outlet Pressure ◽  
Subcooled Water ◽  
Inside Diameter ◽  
Flow Velocities

The mechanisms and corresponding correlations for the subcooled water flow boiling CHFs for outlet subcoolings in a vertical tube having an inside diameter, D, and length-to-diameter, L/D, ratio for a flow velocity with outlet pressure as a parameter were previously clarified by the authors based on the existing flow boiling CHF data measured using the tubes having the diameters ranging from 0.4 to 12 mm, and the L/D ratios ranging from 2.4 to 96.6 for the flow velocities ranging from 5 to 130 m/s, at the pressures ranging from 0.34 to 17.2 MPa. Namely the CHF, qcr,sub, versus outlet subcooling, Δsub,out, for a flow velocity with outlet pressure as a parameter were divided into four regions for outlet subcoolings: first the CHF decreased down to minimum one (first region), secondly it increased up to maximum one (second region), thirdly it decreased down to minimum one (third region), and finally it again increased monotonously with an increase in outlet subcooling. The CHFs belonging to third region became significant with a decrease in diameter for the smaller tubes with diameters such as around 1 mm, and on the other hand, those almost disappeared with an increase in diameter for the larger tubes with the diameters such as around 9 mm. The CHFs belonging to second region significantly depending on the pressure and tube diameter, and those belonging to fourth region being almost independent of the pressure, and tube inside diameter, D, and length-to-diameter, L/D, ratio were well expressed by the unified subcooled water flow boiling CHF correlations representing the CHF resulting from the hydrodynamic instability, HI, and those representing the CHF resulting from the heterogeneous spontaneous nucleation, HSN, on the inside surface near the exit of heated tube respectively. In the present paper, the generalized evaluation of the maximum qcr,sub of the qcr,sub data belonging to 2nd region resulting from the HI unsolved before was realized solving the simultaneous equations consisted with the unified qcr,sub correlation representing qcr,sub resulting from the HI previously derived and the generalized correlation for the Δsub,out,max at corresponding qcr,sub,max newly derived.

Critical Heat Fluxes of Subcooled Water Flow Boiling Against Outlet Subcooling in Short Vertical Tube

2002 ◽  
Author(s):  
Koichi Hata ◽  
Toshiyuki Sato ◽  
Takeya Tanimoto ◽  
Masahiro Shiotsu ◽  
Nobuaki Noda
Keyword(s):  
Experimental Data ◽  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Heat Fluxes ◽  
Outlet Pressure ◽  
Subcooled Water ◽  
Wide Range ◽  
Inner Diameter ◽  
Flow Velocities

The critical heat fluxes (CHFs) of subcooled water flow boiling are systematically measured for the flow velocities (u = 4.0 to 13.3 m/s), the outlet subcoolings (ΔTsub,out = 3 to 129 K) and the outlet pressure (Pout = 800 kPa). The SUS304 test tubes of 3, 6, 9 and 12 mm in inner-diameter, d, and 33, 66, 99 and 133 mm in length, L, respectively for L/d = 11 are used. The CHFs first become lower and then become higher with the increase in subcooling. The CHFs for four different inner-diameters with L/d = 11 measured here become higher with the decrease in the diameter. CHF correlation for the latter increasing regime was given in non-dimensional form against average outlet subcoolings based on the experimental data. The correlation can describe not only the CHFs obtained in this work at the outlet pressure of 800 kPa but also the authors’ published CHFs (1284 points) for the wide range of Pout = 159 kPa to 1 MPa, d = 6, 9 and 12 mm, L = 49, 99 and 149 mm, ΔTsub,out = −4 to 130 K and u = 4.0 to 13.3 m/s within 15% difference for 50 K≤ΔTsub,out≤130 K and within +30 to −10% for 30 K<ΔTsub,out<50 K.

Critical Heat Fluxes of Subcooled Water Flow Boiling Against Outlet Subcooling in Short Vertical Tube

2004 ◽  
Vol 126 (3) ◽  
pp. 312-320 ◽  
Author(s):  
Koichi Hata ◽  
Masahiro Shiotsu ◽  
Nobuaki Noda
Keyword(s):  
Experimental Data ◽  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Heat Fluxes ◽  
Outlet Pressure ◽  
Subcooled Water ◽  
Wide Range ◽  
Inner Diameter ◽  
Flow Velocities

The critical heat fluxes (CHFs) of subcooled water flow boiling are systematically measured for the flow velocities (u=4.0 to 13.3 m/s), the outlet subcoolings (ΔTsub,out=3 to 129 K) and the outlet pressure Pout=800kPa. The SUS304 test tubes of 3, 6, 9 and 12 mm in inner-diameter, d, and 33, 66, 99 and 133 mm in length, L, respectively for L/d=11 are used. The CHFs first become lower and then become higher with the increase in subcooling. The CHFs for four different inner-diameters with L/d=11 measured here become higher with the decrease in the diameter. CHF correlation for the latter increasing regime was given in non-dimensional form against average outlet subcoolings based on the experimental data. The correlation can describe not only the CHFs obtained in this work at the outlet pressure of 800 kPa but also the authors’ published CHFs (1284 points) for the wide range of Pout=159kPa to 1 MPa, d=6, 9 and 12 mm, L=49, 99 and 149 mm, ΔTsub,out=−4 to 140 K and u=4.0 to 13.3 m/s within 15% difference for 50K⩽ΔTsub,out⩽140K and within −10 to +30% for 30K<ΔTsub,out<50K.

scholarly journals Critical Heat Fluxes of Subcooled Water Flow Boiling against Inlet Subcooling in Short Vertical Tube

2004 ◽  
Vol 47 (2) ◽  
pp. 306-315 ◽  
Author(s):  
Koichi HATA ◽  
Hirokazu KOMORI ◽  
Masahiro SHIOTSU ◽  
Nobuaki NODA
Keyword(s):  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Heat Fluxes ◽  
Subcooled Water

Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in a Short Vertical Tube Caused by Exponentially Increasing Heat Inputs

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Koichi Hata ◽  
Nobuaki Noda
Keyword(s):  
Water Flow ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Heat Fluxes ◽  
High Heating Rate ◽  
Subcooled Flow Boiling ◽  
Subcooled Water ◽  
Subcooled Flow ◽  
Inner Surface ◽  
High Heating

The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for the flow velocities (u=4.0–13.3m∕s), the inlet subcoolings (ΔTsub,in=68.08–161.12K), the inlet pressures (Pin=718.31–1314.62kPa), the dissolved oxygen concentrations (O2=2.94ppm to the saturated one), and the exponentially increasing heat inputs (Q0exp(t∕τ), τ=16.82msto15.52s) are systematically measured with an experimental water loop comprised of a pressurizer. The SUS304 tubes of the inner diameters (d=3mm, 6mm, 9mm, and 12mm), heated lengths (L=33.15–132.9mm), L∕d=5.48–11.08, and wall thickness (δ=0.3mm and 0.5mm) with the rough finished inner surface (surface roughness, Ra=3.18μm) are used in this work. The transient CHF data (qcr,sub=6.91–60MW∕m2) are compared with the values calculated by the steady state CHF correlations against inlet and outlet subcoolings. The transient CHF correlations against inlet and outlet subcoolings are derived based on the experimental data. The dominant mechanisms of the subcooled flow boiling CHF for a high heating rate are discussed.

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