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.

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.

scholarly journals Static and Motional Feedthrough Capacitance of Flexural Microresonator

2011 ◽  
Vol 2011 ◽  
pp. 1-6
Author(s):  
Wen-Teng Chang
Keyword(s):  
Silicon Carbide ◽  
Atmospheric Pressure ◽  
Network Analyzer ◽  
Reduced Pressure ◽  
Flexural Mode ◽  
Microelectromechanical System ◽  
Order Of Magnitude ◽  
Bode Plots

The present paper evaluates the static and motional feedthrough capacitance of a silicon carbide-based flexural-mode microelectromechanical system resonator. The static feedthrough capacitance was measured by a network analyzer under atmospheric pressure. The motional feedthrough was obtained by introducing various values into the modeling circuit in order to fit the Bode plots measured under reduced pressure. The static feedthrough capacitance was 0.02 pF, whereas the motional feedthrough capacitance of an identical device was about 0.2 pF, which is one order of magnitude larger than the static feedthrough capacitance.

Effect of Environmental Materials on Aqueous Corrosion of R7T7 Glass

1988 ◽  
Vol 127 ◽  
Author(s):  
N. Godon ◽  
E. Vernaz ◽  
J. H. Thomassin ◽  
J. C. Touray
Keyword(s):  
Atmospheric Pressure ◽  
Test Results ◽  
Aqueous Corrosion ◽  
Environmental Material ◽  
Environmental Materials ◽  
Activated Bentonite ◽  
Order Of Magnitude ◽  
Glass Specimen ◽  
Icp Analysis ◽  
Glass Behavior

ABSTRACTR7T7 glass behavior was investigated in contact with eleven different materials including smectites, bentonites, illites, granite and sand. The experiments were conducted at 90°C under atmospheric pressure with a 4 cm−1 SA/V ratio using two grams of material in double distilled water under static leaching conditions without renewal of the leachate. For each material a control test was conducted under the same conditions but without the glass specimen, as well as a series of tests on glass alone, without the environmental material. Kinetics studies lasting up to 364 days were performed on four selected materials.The test results (mass loss, ICP analysis of the leachates, SEM and TEM observations) showed relatively slight glass alteration in contact with sand, granite and one bentonite (i.e. the same order of magnitude as glass alone in deionized water), but greater alteration of glass in contact with all the other clays.The significant differences in glass behavior in contact with environmental materials can be accounted for by the behavior of the latter in solution: activated bentonite releases very large amounts of silicon and sodium into solution while smectite seems to remove silicon from solution.

Effect of Moisture Content on Mixing Air With Water-Liquid Flowing Through Inverted U-Tube for Power Plant Condenser Applications

2019 ◽  
Author(s):  
Khaled Yousef ◽  
Ahmed Hegazy ◽  
Abraham Engeda
Keyword(s):  
Water Vapor ◽  
Mass Flow ◽  
Static Pressure ◽  
Air Entrainment ◽  
Vapor Mixture ◽  
Flow Rates ◽  
Air Mass ◽  
Side Tube ◽  
Mass Flow Rates ◽  
Vapor Mass

Abstract Computational Fluid Dynamics (CFD) for air/water-vapor and water-liquid two-phase flow mixing with condensation in a vertical inverted U-tube is presented in this paper. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in air/water-vapor and water-liquid mixing flow when condensation is considered. Water-liquid flows upward-downward through the inverted U-tube while the air/water-vapor mixture is extracted from a side-tube just after the flow oriented downward. The CFD simulation is carried out for a side air/water-vapor mixture volume fraction (αm) of 0.2–0.7, water-vapor mass fraction (Xv) of 0.1–0.5 in the side air/water-vapor mixture and water-liquid mass flowrate (mw) of 2,4,6, and 8 kg/s. The present results reveal that, at lower air mass flow rate, no significant effect of Xv on the generated static pressure at the inverted U-tube higher part. However, by increasing the air mass flow rates, ma ≥ 0.001 at mw = 2 kg/s, and ma ≥ 0.00125 at mw = 4 kg/s, we can infer that the lowest static pressure can be attained at Xv = 0.1. This may be attributed to the increased vapor and air mass flow rates from the side tube which results in shifting the condensation from the tube highest part due to air accumulation. This leads to increasing the flow pressure and decelerating the water-liquid flow. Raising mw from 2 to 4 kg/s at the same vapor mass ratio results in a lower static pressure due to more condensation of water vapor. The turbulent intensity and kinetic energy starts to drop approximately at ma = 0.002 kg/s, and αm = 0.55–0.76 at mw = 2 kg/s for all Xv values but no noticeable change at mw = 4 kg/s occurs. These findings estimate the operational values of air and water mass flow rates for stable air entrainment from the side-tube. Increasing the air and vapor mass ratio over these values may block the evacuation process and fails the system continuance. Likewise more air entrainment from the side-tube will decelerate the water flow through the inverted U-tube and hence the flow velocity will decrease thereafter. Moreover, this study reveals that the inverted U-tube is able to generate a vacuum pressure down to 55.104 kPa for the present model when vapor condensation is considered. This generated low-pressure helps to vent an engineering system from the non-condensable gases and water vapor that fail its function if these are accumulated with time. Moreover, the water-liquid mass flow rate in the inverted U-tube can be used to sustain the required operating pressure for this system and extract the non-condensable gases with a less energy consuming system. The present CFD model provides a good physical understanding of the flow behavior for air/water-vapor and water-liquid flow for possible future application in the steam power plant.

Characterization of a Radiantly Driven Multistage Knudsen Compressor

2003 ◽  
Author(s):  
M. Young ◽  
Y. L. Han ◽  
E. P. Muntz ◽  
G. Shiflett
Keyword(s):  
Steady State ◽  
Atmospheric Pressure ◽  
Maximum Flow ◽  
Performance Model ◽  
Experimental Results ◽  
Maximum Pressure ◽  
Flow Rates ◽  
Micro Scale ◽  
Knudsen Compressors

Knudsen Compressors are meso/micro scale gas compressors/pumps based on thermal transpiration or thermal creep. The design of radiantly driven Knudsen Compressors is discussed, along with a model that was developed to understand their performance. Experimental pumping performances for Knudsen Compressors with one, two, five, and fifteen stage, radiantly driven cascades are also discussed. Temperature measurements across the transpiration membranes, for various pressures of Nitrogen, were obtained and compared to those predicted by the performance model. The results agree with the model to within 15% consistently under predicting the measured hot side temperature of the transpiration membrane. The pump-down curves, steady-state maximum pressure differences, and maximum flow rates produced by a single stage Knudsen Compressor were obtained. A variety of configurations were studied at pressures from 500 mTorr to atmospheric pressure. The experimental results agreed with the performance model’s predictions to within 20%.

Innovative Devices That Enable Variable Flow Systems for Energy Savings

2011 ◽  
Author(s):  
A. Keith Miller ◽  
John R. Bode ◽  
Robert Sachs ◽  
Kirt Jensen
Keyword(s):  
Energy Savings ◽  
Low Cost ◽  
Department Of Energy ◽  
Operating Life ◽  
Flow Rates ◽  
Variable Flow ◽  
The Past ◽  
The Us ◽  
Industrial Operations ◽  
Mechanical Devices

Over the past decade numerous studies both conducted by and authorized by the US Department of Energy Office of Industrial Technology have identified significant energy savings potential by adjusting flow rates to meet process demands. As much as 40% energy savings have been achieved when variable flow pumping systems were implemented in some DOE demonstration projects. To date, only a small fraction of the identified companies in various industries which can benefit in energy savings resulting from adjustable pumping flow rates have installed the requisite capabilities. One reason for the slow rate of adoption of variable pumping is that there are few commercially available methods for adjusting pump rates. Electronic Variable Frequency Drives (VFDs) are the most commonly implemented method of varying pump speeds, usually resulting in reduced operating life of the electric drive motors and sometimes in significant costs of plant modifications. Veritran Inc. with the support of Team Technologies, Inc. is developing low-cost mechanical devices for varying electric motor speeds without the large initial investment associated with VFDs nor the other detracting features of the need to install larger electric motors and reduced motor life expectancy. Veritran’s Infinitely Variable Transmissions (IVTs), such as SM-15IVT (www.veritraninc.com) are installed between the motor and the load, which allows for soft starts, and precise output set speeds, all under programmable microprocessor control. The amount of power demanded from the motor varies as the output speed of the transmission is changed or the load torque is changed. This paper will describe the engineering development that Veritran has been pursuing over the past decade of their novel IVTs, and will present some of the test data collected to date. Results will also be presented of systems analyses where IVTs are inserted into various industrial operations and significant energy savings result.

Variability and Corresponding Amplitude–Velocity Relation of Activity Propagating in One-Dimensional Neural Cultures

2007 ◽  
Vol 97 (5) ◽  
pp. 3597-3606 ◽  
Author(s):  
Shimshon Jacobi ◽  
Elisha Moses
Keyword(s):  
Linear Relation ◽  
Signal Propagation ◽  
Front Velocity ◽  
Multielectrode Arrays ◽  
One Dimensional ◽  
Neuron Activation ◽  
Velocity Relation ◽  
Order Of Magnitude ◽  
Chemical Stimuli

We investigate the propagation of neural activity along one-dimensional rat hippocampal cultures patterned in lines over multielectrode arrays. Activity occurs spontaneously or is evoked by local electrical or chemical stimuli, with different resulting propagation velocities and firing rate amplitudes. A variability of an order of magnitude in velocity and amplitude is observed in spontaneous activity. A linear relation between velocity and amplitude is identified. We define a measure for neuron activation synchrony and find that it correlates with front velocity and is higher for electrically evoked fronts. We present a model that explains the linear relation between amplitude and velocity, which highlights the role of synchrony. The relation to current models for signal propagation in neural media is discussed.

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