Steady-State and Stability Analysis of Natural Circulation With Fluids at Supercritical Pressure

2016 ◽  
Author(s):  
Francesco Carbone ◽  
Walter Ambrosini
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Stability Analysis ◽  
Natural Circulation ◽  
Supercritical Pressure ◽  
Research Centre ◽  
Working Fluid ◽  
Bhabha Atomic Research Centre ◽  
Transient Behaviour ◽  
Observed Behaviour

Natural circulation of CO2 at supercritical pressure is addressed in the present paper in order to assess the capabilities of linear and nonlinear analysis in-house codes developed for studying steady-state and transient behaviour of natural circulation loops. In past activities, the models have been developed, taking into account also the effect of the presence of heating structures, and have been equipped with a low diffusion numerical scheme, in order to minimise truncation error effects. In the present work, available heat transfer correlations were introduced in order to properly simulate heat transfer to supercritical fluids, though the present state-of-the-art in the field does not yet allow to reliably simulate relevant effects as the deteriorated of heat transfer occurring when buoyancy effects become dominant. The obtained transient and linear stability analysis codes were applied to published experiments performed at the Bhabha Atomic Research Centre in Mumbai, India, making use of carbon dioxide as working fluid. Both steady-state conditions and transient behaviour were addressed, obtaining interesting data in comparison to experimentally observed behaviour.

Thermal Performance of Water-Based Suspensions of Phase Change Nanocapsules in a Natural Circulation Loop

2013 ◽  
Author(s):  
C. J. Ho ◽  
Chi-Ming Lai
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Natural Circulation ◽  
Pure Water ◽  
Circulation Loop ◽  
Core Material ◽  
Working Fluid ◽  
Outer Diameter ◽  
Natural Circulation Loop ◽  
Water Based

Experiments were conducted to investigate the heat transfer characteristics of water-based suspensions of phase change nanocapsules in a natural circulation loop with mini-channel heat sinks and heat sources. A total of 23 and 34 rectangular mini-channels, each with width 0.8 mm, depth 1.2 mm, length 50 mm and hydraulic diameter 0.96 mm, were evenly placed on the copper blocks as the heat source and heat sink, respectively. The adiabatic sections of the circulation loop were constructed using PMMA tubes with an outer diameter of 6 mm and an inner diameter of 4 mm, which were fabricated and assembled to construct a rectangular loop with a height of 630 mm and a width of 220 mm. Using a core material of n-eicosane and a shell of urea-formaldehyde resin, the phase change material nanocapsules of mean particle size 150 nm were fabricated successfully and then dispersed in pure water as the working fluid to form the water-based suspensions with mass fractions of the nanocapsules in the range 0.1–1 wt.%. The results clearly indicate that water-based suspensions of phase change nanocapsules can markedly enhance the heat transfer performance of the natural circulation loop considered.

Effect of Twist Ratio on Heat Transfer Enhancement by Swirl Impingement

2019 ◽  
Author(s):  
Kishore Ranganath Ramakrishnan ◽  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Heat Transfer Enhancement ◽  
Experimental Work ◽  
Working Fluid ◽  
Transfer Enhancement ◽  
Average Heat ◽  
Twist Ratio ◽  
Single Jet

Abstract Steady state experimental work has been carried out to compare a conventional single jet of diameter 12.7mm with a swirling impinging jet. In this study swirl inserts with three different twist ratios 3, 4.5 and 6 were used to induce the swirling motion to the working fluid. The Reynolds number based on conventional impinging jet’s diameter is varied from 10000 to 16000. It is observed that with increase in twist ratio, the average heat transfer enhancement is reduced. However, with higher twist ratios more uniform distribution of heat transfer enhancement is observed.

Analysis of a Convection Loop for GFR Post-LOCA Decay Heat Removal

2004 ◽  
Author(s):  
Wesley C. Williams ◽  
Pavel Hejzlar ◽  
Pradip Saha
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Flow Regime ◽  
Natural Circulation ◽  
Heat Removal ◽  
Computer Code ◽  
Steady State Analysis ◽  
Decay Heat ◽  
Cooling Loops ◽  
State Analysis

A computer code (LOCA-COLA) has been developed at MIT for steady state analysis of convective heat transfer loops. In this work, it is used to investigate an external convection loop for decay heat removal of a post-LOCA GFR. The major finding is that natural circulation cooling of the GFR is feasible under certain circumstances. Both helium and CO2 cooled system components are found to operate in the mixed convection regime, the effects of which are noticeable as heat transfer enhancement or degradation. It is found that CO2 outperforms helium under identical natural circulation conditions. Decay heat removal is found to have a quadratic dependence on pressure in the laminar flow regime and linear dependence in the turbulent flow regime. Other parametric studies have been performed as well. In conclusion, convection cooling loops are a credible means for GFR decay heat removal and LOCA-COLA is an effective tool for steady state analysis of cooling loops.

Steady-State Behavior of a Two-Phase Natural Circulation Loop With Thermodynamic Nonequilibrium

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Dipankar N. Basu ◽  
Souvik Bhattacharyya ◽  
P. K. Das
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Control Parameters ◽  
Subcooled Boiling ◽  
Two Phase ◽  
State Behavior ◽  
Natural Circulation Loop ◽  
Steady State Behavior

A model to predict the steady-state behavior of a rectangular two-phase natural circulation loop has been proposed. The analysis employs a one-dimensional two-fluid model to identify various system parameters, with particular emphasis on the subcooled boiling region. The onset of two-phase region and point of net vapor generation and associated liquid temperatures and vapor qualities have been estimated using a few widely recognized correlations. Predicted results demonstrate that the consideration of subcooled boiling may have significant effect on system behavior, particularly around the transition regions. The interaction of saturated bubbles and subcooled liquid and associated change in heat transfer and frictional forces has been discussed in detail. Fluid stream has been observed to have different combinations of flow stream conditions at boiler exit and condenser inlet. Five probable combinations have been identified and a generalized working-regime map has been proposed on Nsub−NZu plane. Attempts have been made to identify the influence of various control parameters. A favorable sink condition (higher coolant flow rate or lower coolant entry temperature) has been found to be of particular importance to attain a wider operating range of wall heat flux and better heat transfer characteristics. A design map has been proposed to identify favorable operating condition in terms of control parameters to ensure complete condensation.

Steady State Parametric Modeling of Non-Conventional Loop Heat Pipes

2013 ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Heat Pipes ◽  
Parametric Model ◽  
Parametric Modeling ◽  
Working Fluid ◽  
Loop Heat Pipes

Loop Heat Pipes (LHPs) are used in many thermal management applications, especially for micro-electronics cooling, because of their ability to passively transport thermal energy from a source to a sink. This paper describes the development of a parametric model for a non-conventional LHP operating in steady state, employed to cool Light Emitting Diodes (LEDs). This device is comprised of a flat evaporator, and a finned circular loop wherein condensation and sub-cooling of the working fluid takes place. Unlike a conventional LHP, this device has no compensation chamber. In the mesh screen of the evaporator, the vapor flow entrains liquid and hence the quality of the two-phase mixture leaving the evaporator (xevap) is less than unity (unlike in a conventional LHP where saturated vapor leaves the evaporator). Since this lower quality (approximately 0.2) results in a smaller ratio of latent energy to sensible energy being removed by the condenser and sub-cooler respectively; the ratio of the length of the sub-cooler to condenser length is significantly larger. This results in more stable and controlled operation of the device. Mathematical models of the evaporator, the condenser and the sub-cooler sections are developed, and two closure conditions are employed in this model. For consistency and accuracy, some parameters in the model, such as the natural convection heat transfer coefficient (h o) and a few thermal resistances in the evaporator, are estimated empirically from test data on the device. The empirically obtained value of the heat transfer coefficient is in very good agreement with correlations from the literature. The parametric model accurately predicts the LED board temperature and other temperatures for a specific amount of thermal energy dissipated by the LEDs.

Natural Circulation of Lead-Bismuth in a One-Dimensional Loop: Experiments and Code Predictions

2002 ◽  
Author(s):  
P. Agostini ◽  
G. Bertacci ◽  
G. Gherardi ◽  
F. Bianchi ◽  
P. Meloni ◽  
...  
Keyword(s):  
Computational Study ◽  
Natural Circulation ◽  
Experimental Tests ◽  
Research Centre ◽  
Working Fluid ◽  
State Behavior ◽  
Post Test ◽  
Bismuth Alloy ◽  
Alloy Properties ◽  
And Behavior

The paper summarizes the results obtained by an experimental and computational study jointly performed by ENEA and University of Pisa. The study is aimed at assessing the capabilities of an available thermal-hydraulic system code in simulating natural circulation in a loop in which the working fluid is the eutectic lead-bismuth alloy as in the Italian proposal for Accelerator Driven System (ADS) reactor concepts. Experiments were performed in the CHEOPE facility installed at the ENEA Brasimone Research Centre and pre- and post-test calculations were run using a version of the RELAP5/Mod.3.2, purposely modified to account for Pb-Bi liquid alloy properties and behavior. The main results obtained by the experimental tests and by the code analyses are presented in the paper providing material to discuss the present predictive capabilities of transient and steady-state behavior in liquid Pb-Bi systems.

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