Experiments in Single-Phase Natural Circulation Miniloops With Different Working Fluids and Geometries

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Pietro Garibaldi ◽  
Mario Misale
Keyword(s):  
Experimental Data ◽  
Large Scale ◽  
Single Phase ◽  
Natural Circulation ◽  
Dynamical Behavior ◽  
Geometrical Parameters ◽  
Shear Stresses ◽  
Working Fluids ◽  
Fluid Velocities ◽  
Fluid Properties

The aim of this work is to analyze experimentally the influence of geometrical parameters and fluid properties on the thermal performances of rectangular single-phase natural circulation miniloops, which could be used for cooling of electronic devices. The present paper analyzes two experimental campaigns performed on two rectangular miniloops (ML1 and ML2), characterized by different heights, when two working fluids (water and FC43) are employed. The temperature trends are measured for different combinations of miniloop inclination and power, and the associated fluid velocities are calculated by means of an enthalpy balance. The experimental data are compared with Vijayan’s model, developed for large scale loops in steady-state conditions, corrected with a parameter that takes into account the loop inclination. The dynamical behavior is always stable. The time of the initial transient is long at high miniloop inclination (close to horizontal) and at low power, while the temperature overshoot grows up with increasing power and inclination. Results show that at the same power the velocity of FC43 is almost twice than that of water, but the thermal performances are worse because FC43 is characterized by low specific heat. Moreover, the velocities of the tallest miniloop are the lowest, probably because the enhancement of shear stresses overcomes the increase in buoyancy forces. For both fluids, the velocity grows almost linearly with power. Experimental data show a good agreement with the modified Vijayan’s model.

A Theoretical Evaluation of the Backfill Effect in Fracture of Gas Pressurized Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 47-53 ◽  
Author(s):  
G. Alpa ◽  
E. Bozzo ◽  
L. Gambarotta
Keyword(s):  
Experimental Data ◽  
Large Scale ◽  
Absorption Rate ◽  
Fracture Propagation ◽  
Simplified Model ◽  
Geometrical Parameters ◽  
Theoretical Evaluation ◽  
Rigid Particles ◽  
Pressurized Pipelines ◽  
Axial Fracture

The constraining action exerted by the soil surrounding pipelines, when an axial fracture propagates, has been analyzed through a simplified model. In order to avoid large-scale numerical computations, two main hypotheses have been assumed: (a) the deformed configuration of the fractured pipe has been considered as defined by two geometrical parameters; (b) the soil has been schematized as a cohesionless medium composed of rigid particles with friction. The energy absorption rate by soil during fracture propagation and the constraining forces on the pipe walls has been obtained as a function of the fracture speed and acceleration, of kinematic and geometric parameters and of the soil properties. Available experimental data give factors supporting the engineering evaluation of the backfill effect developed in the paper.

An Analytical and Experimental Study of Rotary-Vane Turbomachinery: Single-Phase Working Fluids

2008 ◽  
Author(s):  
A. Mehdizadeh ◽  
A. M. Mahmoud ◽  
S. A. Sherif ◽  
W. E. Lear
Keyword(s):  
Single Phase ◽  
Volume Ratio ◽  
Industrial Applications ◽  
Design Tool ◽  
Low Flow ◽  
Geometrical Parameters ◽  
Two Phase ◽  
Working Fluids ◽  
Positive Displacement ◽  
Air Compression

Rotary machines have played an important role for many years in refrigeration and air compression applications because of their inherent simplicity and reliability. They are also very attractive machines since as positive displacement devices; they are more suitable for low flow rates (low specific speeds). In this paper, the thermodynamic and fluid mechanic characteristics of a rotary-vane air-motor are analyzed. The optimum geometrical and operational characteristics of the machine are presented. Experiments are conducted to understand the working principles and operational constraints of the machine. This study also helps formulate design procedures that can be utilized to modify air-motors into optimized expanders for single-phase flow applications. The model has been used to evaluate geometrical parameters such as the optimum intake and exhaust port locations, their spreads and the geometric volume ratio, as well as evaluating performance parameters such as the work produced and the mechanical, isentropic and total efficiencies of the machine. It is anticipated in a follow-up study that the model developed will be the basis for an expander design tool that uses two-phase working fluids in relevant industrial applications.

Heat Transfer for Supercritical Flow With TRACE

2020 ◽  
Author(s):  
Jay Spore ◽  
Glenn Roth
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Critical Temperature ◽  
Single Phase ◽  
Supercritical Pressure ◽  
Significant Error ◽  
Heat Transfer Correlation ◽  
Supercritical Flow ◽  
Fluid Properties ◽  
Supercritical Flows

Abstract Flow regimes at water pressures above the critical pressure are characterized as supercritical flow. Supercritical flows have no phase change. The heat transfer from the wall to the fluid is single phase (there is no boiling or condensation). Experimental data indicate that for conditions that involve supercritical single-phase heat transfer, the Dittus-Boelter heat transfer correlation can be in significant error. A pseudo-critical temperature can be defined as a function of pressure for pressures that exceed the supercritical pressure. The pseudo-critical temperature is defined for heat transfer purposes as the temperature at which the specific heat peaks as the pressure is held constant. There is significant variation in fluid properties across the heat transfer boundary layer at temperatures near the pseudo-critical temperature. The large variation in properties is the reason for the failure of the Dittus-Boelter heat transfer correlation. Comparisons to experimental data indicate that the Mokry heat transfer correlation is a significant improvement over the Dittus-Boelter heat transfer correlation for single phase supercritical heat transfer. The Mokry correlation was chosen to be included into TRACE.

Numerical Investigation of Sloshing in a Tank: Statistical Description of Experiments and CFD Calculations

2010 ◽  
Author(s):  
Bogdan Iwanowski ◽  
Marc Lefranc ◽  
Rik Wemmenhove
Keyword(s):  
Experimental Data ◽  
Large Scale ◽  
Single Phase ◽  
Stokes Equations ◽  
Numerical Study ◽  
Point Of View ◽  
Navier Stokes ◽  
Two Phase ◽  
Statistical Point ◽  
Phase Liquid

Numerical study of liquid dynamics in an LNG tank is presented. The available data from large scale (1:10) sloshing experiments of 2D section of an LNG carrier reveal large scatter in recorded values of peak pressures. The experimental data is analysed from statistical point of view in order to obtain distributions of the pressure peaks. Then the entire experimental data record is reproduced numerically by CFD simulations and it is shown that pressure peaks obtained numerically display scatter of values as well. A statistical description of the numerically obtained record is provided and compared with description derived from the experimental data. The applied CFD code ComFLOW solves Navier-Stokes equations and uses an improved Volume of Fluid (iVOF) method to track movement of fluid’s free surface. Two different fluid models, single-phase (liquid+void) and two-phase (liquid+compressible gas) can be applied, the latter model being capable of simulating bubbles and gas entrapped in liquid. For low tank filling rate discussed in the paper (10%) the single-phase approach is sufficient. Comparison of statistical properties of experimental and numerical records is offered.

New correlations for wavy plate-fin heat exchangers: different working fluids

2014 ◽  
Vol 24 (5) ◽  
pp. 1086-1108 ◽  
Author(s):  
Morteza Khoshvaght Aliabadi ◽  
Faramarz Hormozi ◽  
Elham Hosseini Rad
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Cfd Simulation ◽  
Design Parameters ◽  
Geometrical Parameters ◽  
Working Fluids ◽  
Content Type ◽  
Simulation Results

Purpose – The main purpose of this paper is the generation of the heat transfer and pressure drop correlations by considering three working fluids, namely air, water, and ethylene glycol, for the wavy plate-fin heat exchangers (PFHEs). Design/methodology/approach – In order to present the general correlations, various models with different geometrical parameters should be tested. Because of the problems, such as difficult, long time, and costly fabrication of the wavy fins in experimental tests, computational fluid dynamics (CFD) calculations can be a useful method for the generation of the heat transfer and pressure drop correlations with eliminating the experimental problems. Hence, the effective design parameters of the wavy plate-fin, including fin pitch, fin height, wave length, fin thickness, wave amplitude, and fin length, and also their levels were recognized from the literature. The Taguchi method was applied to formulate the CFD simulation work. Findings – The simulation results were compared and validated with an available experimental data. The mean deviations of the Colburn factor, j, and Fanning friction factor, f, values between the simulation results and the experimental data were 3.74 and 9.07 percent, respectively. The presented air correlations and experimental data were in a good agreement, so that approximately 95 percent of the experimental data were correlated within ±12 percent. The j factor values varied for the different working fluids, while the f factor values did not sensibly change. Practical implications – The presented correlations can be used to estimate the thermal-hydraulic characteristics and to design of the compact PFHE with the wavy channels. Originality/value – This manuscript presents the new correlations for the compact PFHEs with the way channels by considering all the geometrical parameters and the working fluids with the different Prandtl numbers, 0.7, 7, and 150.

Asymmetry Investigation on Single Phase Flow in Inverted U-Tubes of Steam Generator Under the Condition of Natural Circulation

2010 ◽  
Author(s):  
Chuan Wang ◽  
Lei Yu
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Steam Generator ◽  
Mass Flux ◽  
Single Phase ◽  
Reverse Flow ◽  
Natural Circulation ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Outlet Temperature

In order to study the reverse flow characteristics in U-tubes of steam generator in the natural circulation case, the code RELAP5/MOD3.3 is used to model and calculate single-phase water flow for PWR under some typical operating conditions in the natural circulation case. The U-tubes of steam generator are classified according to their length and then are divided into different nodes and flow lines. The calculated results show that reverse flow exists in some inverted U-tubes of the steam generator, the natural circulation capacity of the primary coolant circuit system declines and the calculated net mass flux of the natural circulation accords with the experimental data. The traditional lumped parameter method can not simulate the reverse flow characteristics in inverted U-tubes and its result is much greater than the experimental data. When the steam generator outlet pressure is higher than inlet pressure, and gravitational pressure drop is lower than the total of frictional pressure drop and area change pressure drop, the reverse flow will occur. As to the nuclear power plant described in this paper, the mass flux of the shorter U-tubes drops more quickly and at last reverse flow will occur. The temperature distribution is uniform in inverted U-tubes, and it is almost identical with that of SG in secondary side. The occurrence of reverse flow can be judged by that whether the steam generator inlet temperature is lower than reactor outlet temperature obviously. It is indicated that reverse flow occurred in the U-tubes of the steam generator reduces the mass flux in the natural circulation system.

scholarly journals Experimental and Numerical Simulation Investigation of Single-Phase Natural Circulation in a Large Scale Rectangular Loop

2019 ◽  
Vol 45 (1) ◽  
pp. 17 ◽  
Author(s):  
A.R. Antariksawan ◽  
S. Widodo ◽  
M. Juarsa ◽  
S. Ismarwanti ◽  
D. Saptoadi ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Single Phase ◽  
Natural Circulation
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