Turbulent Subcooled Boiling Flow—Experiments and Simulations

2001 ◽  
Vol 124 (1) ◽  
pp. 73-93 ◽  
Author(s):  
R. P. Roy ◽  
S. Kang ◽  
J. A. Zarate ◽  
A. Laporta
Keyword(s):  
Prandtl Number ◽  
Axial Velocity ◽  
Liquid Velocity ◽  
Laser Doppler Velocimeter ◽  
Transfer Model ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Subcooled Boiling ◽  
Dual Sensor ◽  
Boiling Flow

Experiments and simulations were carried out in this investigation of turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall only was heated. The measurements used, simultaneously, a two-component laser Doppler velocimeter for the liquid velocity field and a fast-response cold-wire for the temperature field, and a dual-sensor fiberoptic probe for the vapor fraction and vapor axial velocity. In the numerical simulation, the two-fluid model equations were solved by the solver ASTRID developed at Electricite´ de France. Wall laws for the liquid phase time-average axial velocity and temperature were developed from the experimental data, and the turbulent Prandtl number in the liquid was determined from the wall laws. The wall laws and turbulent Prandtl number were used in the simulations. The wall heat transfer model utilized the measured turbulent heat flux distribution in the liquid. Results from the simulations were compared with the measurements. Good agreement was found for some of the quantities while the agreement was only fair for others.

Heat transfer in a turbulent channel flow with square bars or circular rods on one wall

2015 ◽  
Vol 776 ◽  
pp. 512-530 ◽  
Author(s):  
S. Leonardi ◽  
P. Orlandi ◽  
L. Djenidi ◽  
R. A. Antonia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Prandtl Number ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Smooth Wall ◽  
Roughness Elements ◽  
Smooth Channel

Direct numerical simulations (DNS) are carried out to study the passive heat transport in a turbulent channel flow with either square bars or circular rods on one wall. Several values of the pitch (${\it\lambda}$) to height ($k$) ratio and two Reynolds numbers are considered. The roughness increases the heat transfer by inducing ejections at the leading edge of the roughness elements. The amounts of heat transfer and mixing depend on the separation between the roughness elements, an increase in heat transfer accompanying an increase in drag. The ratio of non-dimensional heat flux to the non-dimensional wall shear stress is higher for circular rods than square bars irrespectively of the pitch to height ratio. The turbulent heat flux varies within the cavities and is larger near the roughness elements. Both momentum and thermal eddy diffusivities increase relative to the smooth wall. For square cavities (${\it\lambda}/k=2$) the turbulent Prandtl number is smaller than for a smooth channel near the wall. As ${\it\lambda}/k$ increases, the turbulent Prandtl number increases up to a maximum of 2.5 at the crests plane of the square bars (${\it\lambda}/k=7.5$). With increasing distance from the wall, the differences with respect to the smooth wall vanish and at three roughness heights above the crests plane, the turbulent Prandtl number is essentially the same for smooth and rough walls.

Modelling of the Near-Wall Liquid Velocity Field in Subcooled Boiling Flow

2005 ◽  
Author(s):  
Franz Ramstorfer ◽  
Bernd Breitscha¨del ◽  
Helfried Steiner ◽  
Gu¨nter Brenn
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Subcooled Boiling ◽  
Test Channel ◽  
Boiling Flow ◽  
Near Wall

The subject of the present work is the modelling of the liquid streamwise flow velocity in the two-phase boundary layer in subcooled boiling flow under the influence of the vapor bubbles. Subcooled boiling flow experiments were carried out in a horizontal test channel in order to investigate the interaction between the bubbles and the liquid phase. The heater surface was located at the bottom of the test channel. The near-wall liquid flow velocity was measured using a two-component laser-Doppler anemometer. Based on the experimental data a model is proposed to describe the impact of the gaseous phase on the motion of the liquid in the subcooled boiling regime. It was observed that the axial velocity profiles near the wall follow a logarithmic law similar to that used in turbulent single-phase flow over rough surfaces. Based on this finding it is suggested to model the influence of the bubbles on the liquid flow analogously to the effect of a surface roughness. The correlation developed for an equivalent surface roughness associated with the bubbles yields good agreement of the modeled axial velocity profiles with the experimental data.

A Mechanistic Model for Predicting Subcooled Boiling Flow

2003 ◽  
Author(s):  
G. H. Yeoh ◽  
J. Y. Tu
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Group Model ◽  
Subcooled Boiling ◽  
Boiling Flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.

Subcooled Boiling Flow Heat Transfer From Plain and Enhanced Surfaces in Automotive Applications

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Franz Ramstorfer ◽  
Helfried Steiner ◽  
Günter Brenn ◽  
Claudius Kormann ◽  
Franz Rammer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Transfer Model ◽  
Subcooled Boiling ◽  
Cooling Systems ◽  
Porous Coatings ◽  
Transfer Rates ◽  
Boiling Flow

The requirement for the highest possible heat transfer rates in compact, efficient cooling systems can often only be met by providing for a transition to subcooled boiling flow in strongly heated wall regions. The significantly higher heat transfer rates achievable with boiling can help keep the temperatures of the structure on an acceptable level. It has been shown in many experimental studies that special surface finish or porous coatings on the heated surfaces can intensify the nucleate boiling process markedly. Most of those experiments were carried out with water or refrigerants. The present work investigates the potential of this method to enhance the subcooled boiling heat transfer in automotive cooling systems using a mixture of ethylene-glycol and de-ionized water as the coolant. Subcooled boiling flow experiments were carried out in a vertical test channel considering two different types of coated surfaces and one uncoated surface as a reference. The experimental results of the present work clearly demonstrate that the concept of enhancing boiling by modifying the microstructure of the heated surface can be successfully applied to automotive cooling systems. The observed increase in the heat transfer rates differ markedly for the two considered porous coatings, though. Based on the experimental data, a heat transfer model for subcooled boiling flow using a power-additive superposition approach is proposed. The model assumes the total wall heat flux as a nonlinear combination of a convective and a nucleate boiling contribution, both obtained from well-established semiempirical correlations. The wall heat fluxes predicted by the proposed model are in very good agreement with the experimental data for all considered flow conditions and surface types.

A wall heat transfer model for subcooled boiling flow

2005 ◽  
Vol 48 (19-20) ◽  
pp. 4161-4173 ◽  
Author(s):  
Helfried Steiner ◽  
Alexander Kobor ◽  
Ludwig Gebhard
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Wall Heat Transfer ◽  
Subcooled Boiling ◽  
Boiling Flow

Velocity Field in Turbulent Subcooled Boiling Flow

1997 ◽  
Vol 119 (4) ◽  
pp. 754-766 ◽  
Author(s):  
R. P. Roy ◽  
V. Velidandla ◽  
S. P. Kalra
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Liquid Flow ◽  
Single Phase ◽  
Laser Doppler Velocimeter ◽  
Subcooled Boiling ◽  
Boiling Flow ◽  
Phase Liquid ◽  
Single Phase Liquid Flow ◽  
Two Fluid

The velocity field was measured in turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall was heated. A two-component laser Doppler velocimeter was used. Measurements are reported in the boiling layer adjacent to the inner wall as well as in the outer all-liquid layer for two fluid mass velocities and four wall heat fluxes. The turbulence was found to be inhomogeneous and anisotropic and the turbulent kinetic energy significantly higher than in single-phase liquid flow at the same mass velocity. A marked shift toward the inner wall was observed of the zero location of the axial Reynolds shear stress in the liquid phase, and the magnitude of the shear stress increased sharply close to the inner wall. The near-wall liquid velocity field was quite different from that in single-phase liquid flow at a similar Reynolds number. Comparison of the measurements with the predictions of a three-dimensional two-fluid model of turbulent subcooled boiling flow show reasonably good agreement for some quantities and a need for further development of certain aspects of the model.

Turbulent Heat Transport in a Perturbed Channel Flow

1999 ◽  
Vol 121 (2) ◽  
pp. 322-325 ◽  
Author(s):  
C. U. Buice ◽  
J. K. Eaton
Keyword(s):  
Boundary Layer ◽  
Prandtl Number ◽  
Heat Transport ◽  
Channel Flow ◽  
Eddy Viscosity ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Turbulent Heat ◽  
Turbulence Structure ◽  
Turbulent Prandtl Number

The recovering boundary layer downstream of a separation bubble is known to have a highly perturbed turbulence structure which creates difficulty for turbulence models. The present experiment addressed the effect of this perturbed structure on turbulent heat transport. The turbulent diffusion of heat downstream of a heated wire was measured in a perturbed channel flow and compared to that in a simple, fully developed channel flow. The turbulent diffusivity of heat was found to be more than 20 times larger in the perturbed flow. The turbulent Prandtl number increased to 1.7, showing that the turbulent eddy viscosity was affected even more strongly than the eddy thermal diffusivity. This result corroborates previous work showing that boundary layer disturbances generally have a stronger effect on the eddy viscosity, rendering prescribed turbulent Prandtl number models ineffective in perturbed flows.

Heat Transfer in the Accelerated Fully Rough Turbulent Boundary Layer

1981 ◽  
Vol 103 (1) ◽  
pp. 153-158 ◽  
Author(s):  
H. W. Coleman ◽  
R. J. Moffat ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Pressure Gradient ◽  
Turbulent Heat Flux ◽  
Test Surface ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number

Heat transfer behavior of a fully rough turbulent boundary layer subjected to favorable pressure gradients was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Stanton numbers and profiles of mean temperature, turbulent Prandtl number, and turbulent heat flux are reported. Three equilibrium acceleration cases (one with blowing) and one non-equilibrium acceleration case were studied. For each acceleration case of this study, Stanton number increased over zero pressure gradient values at the same position or enthalpy thickness. Turbulent Prandtl number was found to be approximately constant at 0.7–0.8 across the layer, and profiles of the non-dimensional turbulent heat flux showed close agreement with those previously reported for both smooth and rough wall zero pressure gradient layers.

scholarly journals Numerical study of turbulent cavitating flows in thermal regime

2017 ◽  
Vol 27 (7) ◽  
pp. 1487-1503 ◽  
Author(s):  
Eric Goncalves ◽  
Dia Zeidan
Keyword(s):  
Prandtl Number ◽  
Transport Equation ◽  
Thermal Regime ◽  
Numerical Study ◽  
Temperature Drop ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Cavitating Flows ◽  
Content Type

Purpose The aim of this work is to quantify the relative importance of the turbulence modelling for cavitating flows in thermal regime. A comparison of various transport-equation turbulence models and a study of the influence of the turbulent Prandtl number appearing in the formulation of the turbulent heat flux are proposed. Numerical simulations are performed on a cavitating Venturi flow for which the running fluid is freon R-114 and results are compared with experimental data. Design/methodology/approach A compressible, two-phase, one-fluid Navier–Stokes solver has been developed to investigate the behaviour of cavitation models including thermodynamic effects. The code is composed by three conservation laws for mixture variables (mass, momentum and total energy) and a supplementary transport equation for the volume fraction of gas. The mass transfer between phases is closed assuming its proportionality to the mixture velocity divergence. Findings The influence of turbulence model as regard to the cooling effect due to the vaporization is weak. Only the k – ε Jones–Launder model under-estimates the temperature drop. The amplitude of the wall temperature drop near the Venturi throat increases with the augmentation of the turbulent Prandtl number. Originality/value The interaction between Reynolds-averaged Navier–Stokes turbulence closure and non-isothermal phase transition is rarely studied. It is the first time such a study on the turbulent Prandtl number effect is reported in cavitating flows.

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