Modeling of the flow patterns and heat transfer in a turbulent bubbly polydispersed flow downstream of a sudden pipe expansion

2016 ◽  
Vol 101 ◽  
pp. 1251-1262 ◽  
Author(s):  
M.A. Pakhomov ◽  
V.I. Terekhov
Keyword(s):  
Heat Transfer ◽  
Flow Patterns ◽  
Pipe Expansion

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

Multiphase Flow in Circular and Triangular Pipes: Examining Flow Characteristics, Sand Erosion and Heat Transfer Via CFD and Experimental Work

2021 ◽  
Author(s):  
Ronald E. Vieira ◽  
Thiana A. Sedrez ◽  
Siamack A. Shirazi ◽  
Gabriel Silva
Keyword(s):  
Heat Transfer ◽  
Multiphase Flow ◽  
Experimental Work ◽  
Heat Exchangers ◽  
Flow Patterns ◽  
Cfd Simulations ◽  
Liquid Distribution ◽  
Circular Pipes ◽  
Sand Erosion ◽  
Sand Flow

Abstract Air-water two-phase flow in circular pipes has been studied by many investigators. However, investigations of multiphase flow in non-circular pipes are still very rare. Triangular pipes have found a number of applications, such as multiphase flow conditioning, erosion mitigation in elbows, compact heat exchanges, solar heat collectors, and electronic cooling systems. This work presents a survey of air-water and air-water-sand flow through circular and triangular pipes. The main objective of this investigation is to study the potential effects of triangular pipe geometry on flow patterns, slug frequency, sand erosion in elbows, and heat transfer in multiphase flow. Firstly, twenty-three experiments were performed for horizontal air-water flow. Detailed videos and slug frequency measurements were collected through circular and triangular clear pipes to identify flow patterns and create a database for these pipe configurations. The effect of corners of the triangular pipe on the liquid distribution was investigated using two different orientations of triangular pipe: apex upward and downward and results of triangular pipes were compared to round tubes. Secondly, ultrasonic wall thickness erosion measurements, paint removal studies, and CFD simulations were carried out to investigate the erosion patterns and magnitudes for liquid-sand and liquid-gas-sand flows in circular and triangular elbows with the same radius of curvature and cross-sectional area. Thirdly, heat transfer rates for liquid flows were also simulated for both circular and triangular pipe cross-sections. Although similar flow patterns are observed in circular and triangular pipe configurations, the orientation of the triangular pipes seems to have an effect on the liquid distribution and slug frequency. For higher liquid rates, slug frequencies are consistently lower in the triangular pipe as compared to the circular pipe. Similarly, the triangular elbow offers better flow behavior as compared to circular elbows when investigated numerically with similar flow rates for erosion patterns for both liquid-sand flow and liquid-gas-sand flows. Experimental and CFD results show that erosion in the circular elbow is about three times larger than in the triangular elbow. Paint studies results validated erosion patterns and their relations with particle impacts. Finally, heat transfer to/from triangular pipes is shown to be more efficient than in circular pipes, making them attractive for compact heat exchangers and heat collectors. This paper represents a novel experimental work and CFD simulations to examine the effects of pipe geometries on multiphase flow in pipes with several practical applications. The present results will help to determine the efficiency of utilizing triangular pipes as compared to circular pipes for several important applications and field operations such as reducing slug frequencies of multiphase flow in pipes, and reducing solid particle erosion of elbows, and also increasing the efficiency of heat exchangers.

Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

2018 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Klaus Helbig
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Time Step ◽  
Hot Air ◽  
Wide Range ◽  
Vortex Systems ◽  
Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

Investigation of Hydrodynamics and Heat Transfer Effects due to Light Guides in a Column Photobioreactor

2013 ◽  
Author(s):  
Caitlin Gerdes ◽  
Taylor N. Suess ◽  
Gary A. Anderson ◽  
Stephen P. Gent
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Mass Transfer ◽  
Temperature Distribution ◽  
Light Guide ◽  
Flow Patterns ◽  
Light Penetration ◽  
Algae Growth ◽  
Computational Fluid Dynamics Cfd ◽  
Light Guides

Proper light penetration is an essential design consideration for effective algae growth in column photobioreactors. This research focuses on the placement of light guides within a photobioreactor (PBR), and the effect they have on heat transfer, mass transfer, bubble and fluid flow patterns, and mixing. Studies have been done on a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with two light panels along the front and back of the PBR. A bubble sparger is placed along the center of the bottom length of the PBR with both height and width of 1.27 cm and a length of 33.02 cm. Different configurations and numbers of light guides (1.27 cm diameter) running horizontally from the front to the back of the PBR are modeled using the Computational Fluid Dynamics (CFD) software Star-CCM+. It is hypothesized that the addition of light guides will change the flow pattern but not adversely affect the heat or mass transfer of the carbon dioxide bubbles within the PBR. Potential concerns of light guide placement include inhibiting the flow of the carbon dioxide bubbles or creating regions of high temperature, which could potentially kill the algae. Benefits of light guides include increased light penetration and photosynthesis within the PBR. Five different light guide setups are tested with the carbon dioxide bubbles and water modeled as a turbulent multiphase gas-liquid mixture. The near wall standard k-epsilon two layer turbulence model was used, as it takes into account the viscosity influences between the liquid and gaseous phases. Eight different bubble volumetric flow rates are simulated. The bubble flow patterns, temperature distribution, Nusselt number, Reynolds number, and velocity are all analyzed. The results indicate square arrays of light guides give the most desirable velocity distribution, with less area of zero velocity compared to the staggered light guide setup. Temperature distribution is generally even for all configurations of light guides.

Computational Study of Gas Turbine Blade Cooling Channel

2010 ◽  
Author(s):  
R. S. Amano ◽  
Krishna Guntur ◽  
Jose Martinez Lucci
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Turbulence Models ◽  
Flow Patterns ◽  
Higher Order ◽  
Secondary Flows ◽  
Complex Flow ◽  
Cooling Performance ◽  
Cooling Channels

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.

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