Novel Approach to the Analysis of Fluctuations in Steady-State Nucleate Boiling

1994 ◽  
pp. 1741-1748 ◽  
Author(s):  
Eric W. Roth ◽  
J. S. Semura ◽  
L. C. Brodie ◽  
Erik Bodegom
Keyword(s):  
Steady State ◽  
Nucleate Boiling ◽  
Novel Approach

A novel approach for the estimation of the efficiency of steady-state fiber bed coalescence

2013 ◽  
Vol 104 ◽  
pp. 268-275 ◽  
Author(s):  
Dragan D. Govedarica ◽  
Radmila M. Šećerov Sokolović ◽  
Dunja S. Sokolović ◽  
Slobodan M. Sokolović
Keyword(s):  
Steady State ◽  
Novel Approach

Abstract 89: The Ventriculo-Ventricular Coupling Index: A Novel Approach to Assessing Biventricular Function

2012 ◽  
Vol 111 (suppl_1) ◽  
Author(s):  
Navin K Kapur ◽  
Mark J Aronovitz ◽  
Robert Blanton ◽  
Emily Mackey ◽  
Vikram Paruchuri ◽  
...  
Keyword(s):  
Heart Failure ◽  
Steady State ◽  
Left Ventricular ◽  
External Jugular Vein ◽  
Arterial Elastance ◽  
Left Heart Failure ◽  
Novel Approach ◽  
Coupling Index ◽  
Ventricular Efficiency ◽  
The Right

Bi-ventricular (Bi-V) function in primary pulmonary hypertension (PPH) or PH secondary to left heart failure (SPH) remains difficult to characterize. As a measure of ventricular efficiency, ventriculo-arterial coupling (VAC) is calculated as the ratio of effective arterial elastance (Ea) to end-systolic elastance (Ees). No measure currently assesses ventriculo-ventricular coupling (VVC). Therefore, we developed a novel catheter-based approach to quantify Bi-V function using pressure-volume loop (PVL) analysis and hypothesized that Bi-V VAC ratios, defined as the VVC index (VVCI), may discriminate PPH and SPH. Methods: Adult male mice (n=6/group) underwent constriction of the pulmonary artery (PAC) or thoracic aorta (TAC) to model PPH and SPH respectively. Sham-operated animals underwent a left thoracotomy. Closed chest simultaneous Bi-V catheterization was performed after 7 days in PPH and 10 weeks in SPH. Conductance catheters were used for right and left ventricular PVL analysis via the right external jugular vein and right common carotid artery under steady-state conditions and with variable preload. Results: Steady-state Bi-V PVL and changes in VAC ratios and the VVCI are shown below. In sham mice VAC ratios and the VVCI reflect optimal ventricular efficiency. In PPH, the VVCI is significantly increased, while in SPH, the VVCI is significantly decreased compared to controls. Conclusion: These results identify a novel method to quantify Bi-V function in mice and further show that the VVCI can distinguish PPH and SPH. These findings have important implications for examining cardiac function in preclinical and clinical studies of left- and right-sided heart failure.

Steady-State Behavior of a Three-Dimensional Pool-Boiling System

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Michel Speetjens
Keyword(s):  
Steady State ◽  
Model Problem ◽  
Separation Of Variables ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Electronics Cooling ◽  
Nucleate Boiling ◽  
Cooling Capacity ◽  
State Behavior ◽  
Steady State Behavior

Pool-boiling serves as the physical model problem for electronics cooling by means of phase-change heat-transfer. The key for optimal and reliable cooling capacity is better understanding of the conditions that determine the critical heat-flux (CHF). Exceeding CHF results in the transition from efficient nucleate-boiling to inefficient film-boiling. This transition is intimately related to the formation and stability of multiple (steady) states on the fluid-heater interface. To this end, the steady-state behavior of a three-dimensional pool-boiling system has been studied in terms of a representative mathematical model problem. This model problem involves only the temperature field within the heater and models the heat exchange with the boiling medium via a nonlinear boundary condition imposed on the fluid-heater interface. The steady-state behavior is investigated via a bifurcation analysis with a continuation algorithm based on the treatment of the model with the method of separation of variables and a Fourier-collocation method. This revealed that steady-state solutions with homogeneous interface temperatures may undergo bifurcations that result in multiple solutions with essentially heterogeneous interface temperatures. These heterogeneous states phenomenologically correspond with vapor patches (“dry spots”) on the interface that characterize transition conditions. The findings on the model problem are consistent with laboratory experiments.

Steady-State Safety Analysis of Ghana Research Reactor-1 With Low-Enriched-Uranium Core

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Edward Shitsi ◽  
Prince Amoah ◽  
Emmanuel Ampomah-Amoako ◽  
Henry Cecil Odoi
Keyword(s):  
Steady State ◽  
Research Reactor ◽  
Flow Instability ◽  
Argonne National Laboratory ◽  
Safety Analysis ◽  
Nucleate Boiling ◽  
Pressurized Water ◽  
Safety Margins ◽  
Water Reactors ◽  
Enriched Uranium

Abstract Research reactors all over the world are expected to operate within certain safety margins just like pressurized water reactors and boiling water reactors. These safety margins mainly include onset of nucleate boiling ratio (ONBR), departure from nucleate boiling ratio (DNBR), and flow instability ratio (FIR) in addition to the maximum clad or fuel temperature and saturation temperature or boing point of the coolant inside the core of the reactor. This study carried out steady-state safety analysis of the Ghana Research Reactor-1 (GHARR-1) with low enriched uranium (LEU) core. Monte Carlo N-particle (MCNP) code was used to obtain radial and axial power peaking factors used as inputs in the preparation of the input file of plate temperature code of Argonne National Laboratory (PLTEMP/ANL code), which was then used to obtain the mentioned safety parameters of GHARR-1 with LEU core in this study. The data obtained on the ONBR were used to obtain the initiation of nucleate boiling boundary data with respect to the active length of the reactor core for various reactor powers. The obtained results for LEU core were also compared with that of the high enriched uranium (HEU) core. The results obtained show that the 34 kW GHARR-1 with LEU core is safe to operate just as the previous 30 kW HEU core was safe to operate.

Steady-State Subcooled Nucleate Boiling on a Downward-Facing Hemispherical Surface

1998 ◽  
Vol 120 (2) ◽  
pp. 365-370 ◽  
Author(s):  
K. H. Haddad ◽  
F. B. Cheung
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Heat Transport ◽  
Bubble Dynamics ◽  
Flow Direction ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Flux

Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low-heat-flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high-heat-flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the increase observed in the critical heat flux in the flow direction along the curved heating surface.

The Departure From Nucleate Boiling in Rod Bundles During Pressure Blowdown

1970 ◽  
Vol 92 (4) ◽  
pp. 621-627 ◽  
Author(s):  
J. O. Cermak ◽  
R. F. Farman ◽  
L. S. Tong ◽  
J. E. Casterline ◽  
S. Kokolis ◽  
...  
Keyword(s):  
Steady State ◽  
Flux Distribution ◽  
Cross Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
Local Velocity ◽  
Heat Flux Distribution ◽  
Rod Bundles ◽  
Rod Bundle ◽  
Proper Allowance

Tests were performed in a high pressure heat transfer loop to determine the behavior of transient DNB during pressure blowdown in rod bundles. Water flowed along a 21 rod, 5-ft-long electrically heated rod bundle with a radially nonuniform heat flux distribution. Both steady-state and transient DNB tests were conducted over the following range of operating parameters: 1 Pressure—750 to 1500 psia; 2 Inlet temperature—480 to 540 deg F; 3 Mass velocity—1 × 106 to 3 × 106 lb/hr ft2; 4 Grid configurations—2. The data were analyzed using calculated subchannel local velocity and enthalpy as a function of time with proper allowance for the mixing and cross flow within the bundle. Results show that the inception of transient DNB during pressure blowdown can be predicted on the basis of steady-state data.

scholarly journals A novel approach to distinguish between enzyme mechanisms: quasi-steady-state kinetic analysis of the prostaglandin H synthase peroxidase reaction

2003 ◽  
Vol 372 (3) ◽  
pp. 713-724 ◽  
Author(s):  
Peter V. VRZHESHCH ◽  
Elena A. BATANOVA ◽  
Alevtina T. MEVKH ◽  
Sergei D. VARFOLOMEEV ◽  
Irina G. GAZARYAN ◽  
...  
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Catalytic Cycle ◽  
Prostaglandin H Synthase ◽  
Compound I ◽  
Novel Approach ◽  
Steady State Kinetic ◽  
Enzyme Intermediates ◽  
Prostaglandin H ◽  
State Kinetic

A method of analysis for steady-state kinetic data has been developed that allows relationships between key partial reactions in the catalytic cycle of a functioning enzyme to be determined. The novel approach is based on a concept of scalar and vector ‘kinetic connectivities’ between enzyme intermediates in an arbitrary enzyme mechanism. The criterion for the agreement between experimental data and a proposed kinetic model is formulated as the kinetic connectivity of intermediate forms of the enzyme. This concept has advantages over conventional approaches and is better able to describe the complex kinetic behaviour of prostaglandin H synthase (PGHS) when catalysing the oxidation of adrenaline by H2O2. To interpret the experimental data for PGHS, a generalized model for multi-substrate enzyme reactions was developed with provision for irreversible enzyme inactivation. This model showed that two enzyme intermediates must undergo inactivation during the catalytic cycle. These forms are proposed to be PGHS compound I and a compound I–adrenaline complex.

Sign in / Sign up

Export Citation Format

Share Document