FLOW PHENOMENA IN POST-DRYOUT HEAT TRANSFER

1993 ◽  
Vol 7 (1-4) ◽  
pp. 271-325
Author(s):  
Mamoru Ishii
Keyword(s):  
Heat Transfer ◽  
Flow Phenomena

Heat Transfer and Flow Phenomena in a Swirl Chamber Simulating Turbine Blade Internal Cooling

1998 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani ◽  
H.-K. Moon ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Internal Cooling ◽  
Vortex Pairs ◽  
Nusselt Numbers ◽  
Swirl Chamber ◽  
Flow Phenomena ◽  
Energy Balances

Heat transfer and fluid mechanics results are given for a swirl chamber whose geometry models an internal passage used to cool the leading edge of a turbine blade. The Reynolds numbers investigated, based on inlet duct characteristics, include values which are the same as in the application (18000–19400). The ratio of absolute air temperature between the inlet and wall of the swirl chamber ranges from 0.62 to 0.86 for the heat transfer measurements. Spatial variations of surface Nusselt numbers along swirl chamber surfaces are measured using infrared thermography in conjunction with thermocouples, energy balances, digital image processing, and in situ calibration procedures. The structure and streamwise development of arrays of Görtler vortex pairs, which develop along concave surfaces, are apparent from flow visualizations. Overall swirl chamber structure is also described from time-averaged surveys of the circumferential component of velocity, total pressure, static pressure, and the circumferential component of vorticity. Important variations of surface Nusselt numbers and time-averaged flow characteristics are present due to arrays of Görtler vortex pairs, especially near each of the two inlets, where Nusselt numbers are highest. Nusselt numbers then decrease and become more spatially uniform along the interior surface of the chamber as the flows advect away from each inlet.

Effects of Interfacial Interactions Between Fluid and Solid Wall on Microscale Flows

2006 ◽  
Author(s):  
Xingang Liang
Keyword(s):  
Heat Transfer ◽  
Solid Wall ◽  
Mean Free Path ◽  
Characteristic Size ◽  
Interfacial Interactions ◽  
Interfacial Effects ◽  
Flow And Heat Transfer ◽  
Microscale Flow ◽  
Flow Phenomena ◽  
Microscale Flows

This work discusses the interfacial effects on flow and heat transfer at micro/nano scale. Different from bulk cases where interfaces can be simply treated as a boundary, the interfacial effects are not limited to the interface at microscale but extend into a significant, even the whole domain of the flow and heat transfer field when the characteristic size of the domain is close to the mean free path (MFP) of fluid particles. Most of microscale flow phenomena result from interfacial interactions. Any changes in the interactions between the fluid and solid wall particles could affect the flow and heat transfer characteristics, such as flow and temperature profiles, friction coefficient. The interactions depend on many parameters, such as the force between fluid and solid wall particles, microstructure of interfaces. The flow and heat transfer features does not only depend on the fluid itself, but also on the interaction with the solid wall because the interface impact can go deep inside the flow. Same fluid, same channel shape but different wall materials could have different flow characters.

Heat Transfer in an Upper Convected Maxwell Fluid with Fluid Particle Suspension

2015 ◽  
Vol 7 (3) ◽  
pp. 369-386 ◽  
Author(s):  
K. Vajravelu ◽  
K. V. Prasad ◽  
S. R. Santhi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Differential Equations ◽  
Dust Particle ◽  
Maxwell Fluid ◽  
Fluid Temperature ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Ucm Fluid ◽  
Flow Phenomena

AbstractAn analysis is carried out to study the magnetohydrodynamic (MHD) flow and heat transfer characteristics of an electrically conducting dusty non-Newtonian fluid, namely, the upper convected Maxwell (UCM) fluid over a stretching sheet. The stretching velocity and the temperature at the surface are assumed to vary linearly with the distance from the origin. Using a similarity transformation, the governing nonlinear partial differential equations of the model problem are transformed into coupled non-linear ordinary differential equations and the equations are solved numerically by a second order finite difference implicit method known as the Keller-box method. Comparisons with the available results in the literature are presented as a special case. The effects of the physical parameters on the fluid velocity, the velocity of the dust particle, the density of the dust particle, the fluid temperature, the dust-phase temperature, the skin friction, and the wall-temperature gradient are presented through tables and graphs. It is observed that, Maxwell fluid reduces the wall-shear stress. Also, the fluid particle interaction reduces the fluid temperature in the boundary layer. Furthermore, the results obtained for the flow and heat transfer characteristics reveal many interesting behaviors that warrant further study on the non-Newtonian fluid flow phenomena, especially the dusty UCM fluid flow phenomena.

Thermodynamic Analysis of Freezing and Melting Processes in a Bed of Spherical PCM Capsules

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
David MacPhee ◽  
Ibrahim Dincer
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Flow Rate ◽  
Present Model ◽  
Spherical Geometry ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Main Mode ◽  
Solidification Temperature ◽  
Flow Phenomena

The solidification and melting processes in a spherical geometry are investigated in this study. The capsules considered are filled with de-ionized water, so that a network of spheres can be thought of as being the storage medium for an encapsulated ice storage module. ANSYS GAMBIT and FLUENT 6.0 packages are used to employ the present model for heat transfer fluid (HTF) past a row of such capsules, while varying the HTF inlet temperature and flow rate, as well as the reference temperatures. The present model agrees well with experimental data taken from literature and was also put through rigorous time and grid independence tests. Sufficient flow parameters are studied so that the resulting solidification and melting times, exergy and energy efficiencies, and exergy destruction could be calculated. All energy efficiencies are found to be over 99%, though viscous dissipation was included. Using exergy analysis, the exergetic efficiencies are determined to be about 75% to over 92%, depending on the HTF scenario. When the HTF flow rate is increased, all efficiencies decrease, due mainly to increasing heat losses and exergy dissipation. The HTF temperatures, which stray farther from the solidification temperature of water, are found to be most optimal exergetically, but least optimal energetically. The main reason for this, as well as the main mode of loss exergetically, is due to entropy generation accompanying heat transfer, which is responsible for over 99.5% of exergy destroyed in all cases. The results indicate that viewing the heat transfer and fluid flow phenomena in a bed of encapsulated spheres, it is of utmost importance to assess the major modes of entropy generation; in this case from heat transfer accompanying phase change.

Measurements of Diabatic Flow in an Annulus With an Inner Rotating Cylinder

1962 ◽  
Vol 84 (2) ◽  
pp. 97-104 ◽  
Author(s):  
K. M. Becker ◽  
Joseph Kaye
Keyword(s):  
Heat Transfer ◽  
Axial Flow ◽  
Rotating Cylinder ◽  
Electrical Machine ◽  
Second Phase ◽  
Radial Temperature ◽  
Transfer Data ◽  
Adiabatic Flow ◽  
Wide Range ◽  
Flow Phenomena

The present paper is part of the second phase of an investigation of the phenomena and variables which control the rate of heat transfer in the air gap of a rotating electrical machine. Experimental data for diabatic flow in an annulus are summarized and compared with the results of previous studies. The data are examined in terms of the types of flow processes occurring in an annulus, and it is found that the results for diabatic flow clearly confirm those obtained for adiabatic flow in showing the existence of three, and possibly four, modes of flow in this annulus. These modes are: (1) Laminar flow; (2) laminar-plus-Taylor-vortexes flow; (3) turbulent flow; (4) turbulent-plus-vortexes flow. The heat-transfer data were subdivided into the following two limiting cases and one general case: Case A. Axial flow with zero rotation. Case B. Rotation of inner cylinder with zero axial flow. Case C. General case of combined axial flow and rotation. The heat-transfer data from this study and of previous investigations were correlated in terms of Reynolds number and Taylor number over a wide range of these variables in terms of fairly simple equations. Radial temperature profiles in the annular gap were measured for the diabatic flow and aided in the understanding of the different flow phenomena in the annulus with an inner rotating cylinder.

Conceptual Design and Cooling Blade Development of 1700°C Class High-Temperature Gas Turbine

2005 ◽  
Vol 127 (2) ◽  
pp. 358-368 ◽  
Author(s):  
Shoko Ito ◽  
Hiroshi Saeki ◽  
Asako Inomata ◽  
Fumio Ootomo ◽  
Katsuya Yamashita ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Gas Turbine ◽  
Conceptual Design ◽  
Thermal Efficiency ◽  
Internal Cooling ◽  
Closed Cycle ◽  
Steam Consumption ◽  
Flow Phenomena ◽  
High Temperature Gas

In this paper we describe the conceptual design and cooling blade development of a 1700°C-class high-temperature gas turbine in the ACRO-GT-2000 (Advanced Carbon Dioxide Recovery System of Closed-Cycle Gas Turbine Aiming 2000 K) project. In the ACRO-GT closed cycle power plant system, the thermal efficiency aimed at is more than 60% of the higher heating value of fuel (HHV). Because of the high thermal efficiency requirement, the 1700°C-class high-temperature gas turbine must be designed with the minimum amount of cooling and seal steam consumption. The hybrid cooling scheme, which is a combination of closed loop internal cooling and film ejection cooling, was chosen from among several cooling schemes. The elemental experiments and numerical studies, such as those on blade surface heat transfer, internal cooling channel heat transfer, and pressure loss and rotor coolant passage distribution flow phenomena, were conducted and the results were applied to the conceptual design advancement. As a result, the cooling steam consumption in the first stage nozzle and blade was reduced by about 40% compared with the previous design that was performed in the WE-NET (World Energy Network) Phase-I.

scholarly journals The Effect of Incident Wake Conditions on the Mean Heat Transfer of an Airfoil

1991 ◽  
Vol 113 (3) ◽  
pp. 412-418 ◽  
Author(s):  
K. Dullenkopf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Initial Conditions ◽  
Turbine Blades ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Average Technique ◽  
Experimental Base ◽  
Flow Phenomena ◽  
Inclination Angles ◽  
Wake Passing

The flow phenomena of wakes shed by upstream blade rows is a well-known problem in turbomachinery, which influences blade forces, vibrations, losses, and heat transfer. With respect to the heat load to turbine blades, this problem becomes even more complex because of the interaction between wake, potential flow, and the boundary layer along the surface of the airfoil. Experimentally evaluated mean heat transfer coefficients obtained under different unsteady initial conditions are reported. The heat transfer measurements have been carried out in the cascade test facility at the ITS in Karlsruhe, using a rotating bar wake generator placed upstream of the cascade to simulate the wake passing process. The variation of the wake parameters includes different wake passing frequencies, cascade inlet Reynolds numbers, and wake inclination angles. In addition, the relevant parameters of the unsteady wake have been measured by means of a fixed hot-wire anemometer using the ensemble-average technique. The results are compared to those from the literature for the wake of a cylinder in crossflow. They also serve as experimental base for parallel theoretical analyses.

scholarly journals Impinging jets – a short review on strategies for heat transfer enhancement

2018 ◽  
Vol 32 ◽  
pp. 01013
Author(s):  
Ilinca Nastase ◽  
Florin Bode
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Short Review ◽  
Great Difficulty ◽  
Impinging Jets ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Small Scale ◽  
Strong Shear ◽  
Flow Phenomena

In industrial applications, heat and mass transfer can be considerably increased using impinging jets. A large number of flow phenomena will be generated by the impinging flow, such as: large scale structures, large curvature involving strong shear and normal stresses, stagnation in the wall boundary layers, heat transfer with the impinged wall, small scale turbulent mixing. All these phenomena are highly unsteady and even if nowadays a substantial number of studies in the literature are dedicated, the impinging jets are still not fully understood due to the highly unsteady nature and more over due to great difficulty of performing detailed numerical and experimental investigations.

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