CHF in Vertical Round Tubes With Uniform Heat Flux

Volume 3 ◽  
2004 ◽  
Author(s):  
W. Jaewoo Shim ◽  
Ji-Su Lee
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
World Literature ◽  
Average Error ◽  
Uniform Heat Flux ◽  
New Correlation ◽  
Uniform Heat ◽  
System Pressure ◽  
Data Points ◽  
Parameter Ranges

In recent years it is well known that models based on the local condition hypothesis give significant correlations for the prediction of CHF (Critical Heat Flux), using only few local variables. In this work, a study was carried out to develop a generalized CHF correlation in vertical round tubes with uniform heat flux. For this analysis, a CHF database that composed of over 10,000 CHF data points, which were collected from 12 different sources, was used. The actual data used in the development of this correlation, after the elimination of some questionable data, consisted of 8,951 data points with the following parameter ranges: 0.101 ≤ P (pressure) ≤ 20.679 MPa, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.03 ≤ L (length) ≤ 4.97 m, 0.11 ≤ qc (CHF) ≤ 21.42 MW/m2, and −0.87 ≤ Xe (exit qualities) ≤ 1.58. The result of this work showed that regardless of various flow patterns and regimes that exist in the wide flow conditions, the prediction of CHF can be made accurately with few major local variables: the system pressure (P), tube diameter (D), mass flux of water (G), and true mass flux of vapor (GXt). The new correlation was compared with 5 well-known CHF correlations published in world literature. The new correlation can predict CHF within the root mean square error of 13.44% using the heat balance method with average error of −1.34%.

Critical Heat Flux in Tubes With Cosine Axial Heat Flux

2005 ◽  
Author(s):  
W. Jaewoo Shim ◽  
Joo-Yong Park ◽  
Ji-Su Lee ◽  
Dong Kook Kim
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flux Distribution ◽  
Average Error ◽  
Uniform Heat Flux ◽  
Heat Flux Distribution ◽  
Uniform Heat ◽  
System Pressure ◽  
Data Points

In this study a method to predict CHF (Critical Heat Flux) in vertical round tubes with cosine heat flux distribution was examined. For this purpose a uniform correlation, based on local condition hypothesis, was developed from 9,366 CHF data points of uniform heat flux heaters. The CHF data points used were collected from 13 different sources had the following parameter ranges: 1.01 ≤ P (pressure) ≤ 206.79 bar, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.0254 ≤ L (length) ≤ 4.966 m, 0.11 ≤ qc (CHF) ≤ 21.42 MW/m2, and −0.87 ≤ X (exit qualities) ≤ 1.58. The result of this work showed that the uniform CHF correlation could be used to predict CHF accurately in a non-uniform heat flux heater for wide flow conditions. Furthermore, the location, where CHF occurs in non-uniform heat flux distribution, can also be determined accurately with the local variables: the system pressure (P), tube diameter (D), mass flux of water (G), and true mass flux of vapor (GXt). The new correlation predicted CHF with cosine heat flux, 297 data points from 5 different published sources, within the root mean square error of 12.42% and average error of 1.06% using the heat balance method.

Generalized CHF Correlation With Uniform Heat Flux for Annulus

2005 ◽  
Author(s):  
Sung-Woo Lee ◽  
Dong-Kook Kim ◽  
W. Jae-Woo Shim
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
World Literature ◽  
Average Error ◽  
Uniform Heat Flux ◽  
Outer Diameter ◽  
Good Prediction ◽  
New Correlation ◽  
Inner Diameter ◽  
True Mass

A new generalized CHF (Critical Heat Flux) correlation was suggested for water flow in uniformly heated Annulur tubes. The parametric ranges of experimental CHF data used for present analysis were as follows: 0.540< P (pressure) < 15.146 MPa, 197.77 < G (mass flux) < 653.52 kg/m2s, I.D (inner diameter) = 9.54 mm, O.D (outer diameter) = 19.4 mm, L (length) = 1.84 m, 75.48 < Inlet subcooling < 358.78 kJ/kg, 490.48 < qc (CHF) < 1775.89 KW/m2, and 0.120 < Xe (exit qualities) < 0.536. The new correlation was based on local condition hypothesis, and therefore consisted of the local variables such as tube diameter, pressure, mass flux of water and true mass fraction of steam. In addition, HBM (Heat Balance Method) that leads to the more accurate prediction of CHF than DSM (Direct Substitution Method) was used in developing the correlation. The new correlation was compared with 5 existing CHF correlations that showed comparatively good prediction in world literature. The new correlation predicted CHF better than the other ones with average error of −1.03% and root mean square error of 11.91%.

CHF for Uniformly Heated Vertical Tube Under High Pressure Conditions

2002 ◽  
Author(s):  
W. Jaewoo Shim ◽  
Joo-Yong Park
Keyword(s):  
High Pressure ◽  
Mass Flux ◽  
Flow Instability ◽  
Vertical Tube ◽  
Average Error ◽  
New Correlation ◽  
Data Points ◽  
Parameter Ranges ◽  
Two Parameters ◽  
True Mass

In this study, a total of 2,870 high pressure (70 bar ≤ P ≤ 206 bar) data points of critical heat flux (CHF) in uniformly heated round vertical tube for water were collected from 5 different published sources. The data consisted of following parameter ranges: 28.07 ≤ G (mass flux) ≤ 10,565.03 kg/m2s, 1.91 ≤ D (diameter) ≤44.68 mm, 40 ≤L (length) ≤4966 mm, 0.14 ≤qc (CHF) ≤ 9.94 MW/m2, and −0.85 ≤X (exit qualities) ≤ 1.22. With these data a comparative analysis is made on available correlations, and a new correlation is presented. The new high pressure CHF correlation, as in the low and medium pressure cases of earlier studies, comprised of local variables, namely, “true” mass quality, mass flux, tube diameter, and two parameters as a function of pressure only. This study reaffirms our earlier findings that by incorporating “true” mass quality in the local condition hypothesis, the prediction of CHF under these conditions can be obtained quite accurately, overcoming the difficulties of flow instability and buoyancy effects that are inherent in the phenomena. The new correlation predicts the CHF data significantly better than those currently available correlations, with average error 0.12% and rms error 13.52% by the heat balance method.

Flow Resistance Characteristics of a Specific Fuel RP-3 in Helical Tubes at Supercritical Pressure With Uniform Heat Flux

2017 ◽  
Author(s):  
Nan Zhang ◽  
Yanchen Fu ◽  
Haoran Huang ◽  
Jie Wen ◽  
Nigeer Te
Keyword(s):  
Heat Flux ◽  
Friction Factor ◽  
Mass Flux ◽  
Flow Resistance ◽  
Flow Characteristics ◽  
Supercritical Pressure ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Uniform Heat ◽  
Helical Tubes

The flow resistance characteristics of aviation kerosene RP-3 in horizontal helical tubes at the supercritical pressure under heating condition are investigated. Both pressure drop and friction factor were examined under uniform heat flux of 50kW/m2−300kW/m2, mass flux from 786kg/m2s to 1375kg/m2s, and helical diameter from 20mm to 40mm. The influence of viscous factors on the resistance is analyzed to explore flow characteristics in a helical tube and provide a reference for the design of heat exchangers. Friction factor decreases with the increase of heat flux at low inlet temperatures 323K and 423K. It is explained that the viscosity changes more dramatically than the density. When the fluid inlet temperature is 523K and the fluid mean temperature Tb is close to pseudo-critical temperature, frictional flow resistance becomes significantly larger Tpc due to huge variations in thermal properties in the radical direction. The effect of centrifugal force makes the friction factor decline slowly. The friction factor goes up with the enlargement of mass flux when Tb>0.81Tpc. This phenomenon is caused by the larger radial velocity gradient under the large mass flux. Different helical diameters play the leading roles for the bending flow in the tubes.

Experimental Investigation of Critical Heat Flux in Microchannels for Flow-Field Probes

2009 ◽  
Author(s):  
Ali Kos¸ar ◽  
Yoav Peles ◽  
Arthur E. Bergles ◽  
Gregory S. Cole
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
Thermal Condition ◽  
Average Error ◽  
New Correlation ◽  
Hydraulic Conditions ◽  
Data Points ◽  
Heated Length

Critical heat flux (CHF) of water in circular stainless steel microchannels with inner diameters ranging from ∼127μm to ∼254 μm was investigated. Forty-five CHF data points were acquired over mass velocities ranging from 1,200 kg/m2s to 53,000 kg/m2s, heated lengths from 2 cm to 8 cm, and exit qualities from −0.2 to 0.15. Most of the exit qualities fell below 0.1. It was found that CHF conditions were more dependent on mass velocity and heated length than on exit thermal condition. The results were also compared to six CHF correlations, with a mean average error ranging from 22% to 261.8%. A new correlation was proposed to better predict the critical heat flux data under the thermal-hydraulic conditions studied in this investigation. In developing the correlation, 319 data points were added from two previous studies.

Analysis for a Generalized CHF Correlation in Uniformly Heated Vertical Round Tubes

2003 ◽  
Author(s):  
W. Jaewoo Shim ◽  
Joo-Yong Park ◽  
Ohyoung Kim
Keyword(s):  
Mass Flux ◽  
Mass Fraction ◽  
Empirical Models ◽  
Data Sets ◽  
Square Root ◽  
System Pressure ◽  
Data Points ◽  
Preliminary Study ◽  
Parameter Ranges ◽  
True Mass

For empirical models based on the local condition hypothesis, few important parameters give significant correlations on the prediction of CHF (Critical Heat Flux). This work is a preliminary study to develop a generalized CHF correlation in uniformly heated vertical round tubes for water. For this analysis, a total of 8,912 CHF data points from 12 different published sources were used. This database consisted of following parameter ranges: 0.101 ≤ P (pressure) ≤ 20.679 MPa, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.03 ≤ L (length) ≤ 4.97 m, 8.5 ≤ L/D ≤ 792.26, −609.33 ≤ Inlet subcooling ≤ 1,655.34 kJ/kg, 0.11 ≤ qc (CHF) ≤ 21.41 MW/m2, and −0.85 ≤ Xe (exit qualities) ≤ 1.58. Five representative CHF data sets at pressure conditions of 0.101, 5.001, 10, 16 and 20 MPa were selected, analyzed, and compared to evaluate the effects of parameters on the CHF. It has revealed that the major variables which influenced the CHF, other than the system pressure (P), were tube diameter (D), mass flux of water (G), and local true mass fraction of vapor (Xt). Square root of GXt and square root of D were the significant parameters that showed strong parametric trends of the data sets. The results of this study have reaffirmed the feasibility that an advanced generalized CHF correlation for uniformly heated vertical round tubes can be found.

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