Measurement and Analysis for Rewetting Velocity Under Post-BT Conditions During Anticipated Operational Occurrence of BWR

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Sibamoto Yasuteru ◽  
Maruyama Yu ◽  
Nakamura Hideo
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Present Model ◽  
Flow Direction ◽  
Water Flow Rate ◽  
High Water ◽  
Falling Film ◽  
Loss Of Coolant Accident ◽  
Order Of Magnitude ◽  
Series Of Experiments

A series of experiments was performed for rewetting phenomena on dried-out fuel rod surfaces under post-boiling transition (post-BT) conditions with high-pressure and high-water flow rate simulating anticipated operational occurrences of a BWR. An analytical model for rewetting velocity, defined by a propagation velocity of a quench front, has been developed on the basis of the experimental results. The rewetting for the post-BT condition is characterized by the faster propagation of the quench front than that for reflood phase conditions during a postulated large-break loss-of-coolant accident. In order to provide an explanation of this characteristic, the present analytical model took an effect of a precursory cooling into account by modifying the existing correlation by Sun et al. (1975, “Effects of Precursory Cooling on Falling-Film Rewetting,” ASME J. Heat Transfer, 97, pp. 360–365), which is based on a one-dimensional analysis in a flow direction during the reflood phase. The present model demonstrates that the precursory cooling can significantly increase the rewetting velocity by more than an order of magnitude. Applying the experimental correlation developed in the separately conducted experiment into the heat transfer coefficient in the present model at a wet and a dry region with precursory cooling, our data of the rewetting velocity as well as the wall temperature profiles for the variable flow rates are successfully predicted.

Measurement and Analysis for Rewetting Velocity Under Post-BT Conditions During Anticipated Operational Occurrence of BWR

2009 ◽  
Author(s):  
Yasuteru Sibamoto ◽  
Yu Maruyama ◽  
Hideo Nakamura
Keyword(s):  
Analytical Model ◽  
Present Model ◽  
Flow Direction ◽  
Water Flow Rate ◽  
High Water ◽  
Loss Of Coolant Accident ◽  
Measurement And Analysis ◽  
Order Of Magnitude ◽  
Series Of Experiments ◽  
The Heat Transfer Coefficient

A series of experiments was performed for rewetting phenomena on dryed-out fuel rod surfaces under post-BT (Boiling Transition) conditions with high-pressure and high-water flow rate simulating anticipated operational occurrences of a BWR. An analytical model for rewetting velocity, defined by a propagation velocity of a quench front, has been developed on the basis of the experimental results. The rewetting for the post-BT condition is characterized by the faster propagation of the quench front than that for reflood phase conditions during a postulated large-break loss-of-coolant accident. In order to provide an explanation of this characteristic, the present analytical model took an effect of a precursory cooling into account by modifying the existing correlation by Sun-Dix-Tien [1] which is based on a one-dimensional analysis in a flow direction during the reflood phase. The present model demonstrates that the precursory cooling can significantly increase the rewetting velocity by more than an order of magnitude. Applying the experimental correlation developed in the separately conducted experiment into the heat transfer coefficient in the present model at a wet and a dry region with precursory cooling, our data of the rewetting velocity as well as the wall temperature profiles for the variable flow rates are successfully predicted.

Effect of Precursory Cooling on Falling-Film Rewetting

1975 ◽  
Vol 97 (3) ◽  
pp. 360-365 ◽  
Author(s):  
K. H. Sun ◽  
G. E. Dix ◽  
C. L. Tien
Keyword(s):  
Atmospheric Pressure ◽  
Present Model ◽  
Front Velocity ◽  
Falling Film ◽  
Vapor Mixture ◽  
Thin Slab ◽  
Flow Rates ◽  
Variable Flow ◽  
Order Of Magnitude ◽  
Hot Surface

An analytical model for falling-film wetting of a hot surface has been developed to account for the effect of cooling by droplet-vapor mixture in the region immediately ahead of the wet front. The effect of precursory cooling is characterized by a heat transfer coefficient decaying exponentially from the wet front. Based on the present model, the wet front velocity, as well as the temperature profile along a thin slab, can be calculated. It is demonstrated that the precursory cooling can increase the wet front velocity by an order of magnitude. Existing experimental data with variable flow rates at atmospheric pressure are shown to be successfully correlated by the present model.

The Effect of Turbulator Lean on Heat Transfer and Friction in a Square Channel

2003 ◽  
Author(s):  
Ronald S. Bunker ◽  
Sarah J. Osgood
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Standard Form ◽  
Bulk Flow ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Lean Angle ◽  
Series Of Experiments

An experimental study has been performed to investigate the convective heat transfer coefficients and friction factors present in square cooling passages with non-normal, or leaned turbulators. The standard form of turbulated channels used in virtually all turbine vanes and blades is that of nearly square turbulators, or rib rougheners, cast in an orthogonal orientation to the channel surface. While turbulators may be oriented at an angle to the bulk flow direction, the projection of the turbulator is still normal to the cast surface. Non-orthogonal lean angle presents an additional variable which may be used to improve or optimize performance, a factor hitherto not investigated. The present study has performed a series of experiments measuring both detailed heat transfer coefficient distributions and friction factors within a square channel with flow Reynolds numbers up to 400,000. Turbulator lean angles of 45, 22.5, 0, −22.5, and −45-degrees to the surface normal have been tested with a turbulator configuration of 45-degree orientation to the bulk flow, pitch-to-height ratio of 10, and height-to-hydraulic diameter ratio of 0.1. Results show up to a 20% reduction in heat transfer capability, and as much as 30% increase in friction factor. The local distributions of heat transfer are also more variable with lean angle. The conclusion is made that normal turbulators provide the best overall performance.

A semi-analytical model of heat transfer and pressure drop in annular flow regime for flow boiling in a horizontal microtube at uniform heat flux

2020 ◽  
Vol 44 (3) ◽  
pp. 362-384
Author(s):  
Amen Younes ◽  
Ibrahim Hassan ◽  
Lyes Kadem
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Regime ◽  
Analytical Model ◽  
Annular Flow ◽  
Present Model ◽  
Flow Boiling ◽  
Uniform Heat Flux ◽  
Two Phase

A semi-analytical model for predicting heat transfer and pressure drop in annular flow regime for saturated flow boiling in a horizontal microtube at a uniform heat flux has been developed based on a one-dimensional separated flow model. More than 600 two-phase heat transfer, 498 two-phase pressure drop, and 153 void fraction experimental data points for annular flow regime were collected from the literature to validate the present model. The collected data were recorded for various working fluids, R134a, R1234ze, R236fa, R410a, R113, and CO2, for round macro- and microsingle horizontal tubes with an inner diameter range of 0.244 mm ≤ Dh ≤ 3.1 mm, a heated length to diameter ratio of 90 ≤ Lh/Dh ≤ 2000, a saturation temperature range of –10 ≤ Tsat ≤ +50 °C, and liquid to vapor density ratios in the range 6.4 ≤ ρf/ρg ≤ 188. The model was tested for laminar and turbulent flow boiling conditions corresponding to an equivalent Reynolds number, 1900 ≤ Reeq ≤ 48 000, and confinement number, 0.27 ≤ Cconf ≤ 3.4. Under the annular flow regime, the present model predicted the collected data of the heat transfer, pressure drop, and void fraction with mean absolute errors (MAE) of 18.14%, 23.02%, and 3.22%, respectively.

Study on Enhancement of Sub-Cooled Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

2002 ◽  
Author(s):  
Yasuo Koizumi ◽  
Tomoyuki Suzuki ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Water Flow ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Water Flow Rate ◽  
Flow Region ◽  
High Water ◽  
Water Velocity ◽  
Rate Region

The influence of particle introduction into a subcooled water flow on boiling heat transfer and critical heat flux (CHF) was examined. When the water velocity was low, the particles crowded on the bottom wall of the flow channel and flowed just like sliding on the wall. When the water velocity was high, the particles were well dispersed in the water flow. In the non-boiling region, the heat transfer was augmented by the introduction of the particles into the water flow. As the introduction of the particles were increased, the augmentation was also increased in the high water flow rate region. However, it was independent upon the particle introduction rate in the low water flow rate region. The onset of boiling was delayed by the particle inclusion. The boiling heat transfer was enhanced by the particles. However, it was rather decreased in the high heat flux fully-developed-boiling region. The CHF was decreased by the particle inclusion in the low water flow region and was not affected in the high water flow region.

Experimental Study on Thermal Characteristics of Finned Coil LHSU Using Paraffin as Phase Change Material

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Guansheng Chen ◽  
Nanshuo Li ◽  
Huanhuan Xiang ◽  
Fan Li
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Phase Change ◽  
Phase Change Material ◽  
Water Flow ◽  
Water Flow Rate ◽  
Thermal Characteristics ◽  
Heat Transfer Fluid ◽  
Latent Heat Storage ◽  
Change Material

It is well known that attaching fins on the tubes surfaces can enhance the heat transfer into and out from the phase change materials (PCMs). This paper presents the results of an experimental study on the thermal characteristics of finned coil latent heat storage unit (LHSU) using paraffin as the phase change material (PCM). The paraffin LHSU is a rectangular cube consists of continuous horizontal multibended tubes attached vertical fins at the pitches of 2.5, 5.0, and 7.5 mm that creates the heat transfer surface. The shell side along with the space around the tubes and fins is filled with the material RT54 allocated to store energy of water, which flows inside the tubes as heat transfer fluid (HTF). The measurement is carried out under four different water flow rates: 1.01, 1.30, 1.50, and 1.70 L/min in the charging and discharging process, respectively. The temperature of paraffin and water, charging and discharging wattage, and heat transfer coefficient are plotted in relation to the working time and water flow rate.

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