scholarly journals Entropy Generation Measurement in a Laminar Turbine Blade Boundary-Layer

1997 ◽  
Author(s):  
John D. Wallace ◽  
Mark R. D. Davies
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Rate ◽  
Turbine Blade ◽  
Entropy Generation ◽  
Transfer Rate ◽  
Surface Heat ◽  
Entropy Generation Rate ◽  
Blade Surface ◽  
Surface Heat Transfer

This paper demonstrates a method of calculating the entropy generation rate in an incompressible laminar turbine blade boundary-layer from measurements of surface heat transfer rate. It is shown that the entropy generated by fluid friction in an incompressible blade boundary-layer is significantly less than that generated by heat transfer at engine representative temperature ratios. The centre blade in a low-speed linear cascade is electrically heated and isolated from the airflow with a bypass valve. Upon opening the valve the blade is transiently cooled and thin film heat transfer gauges, painted on machinable glass ceramic inserts mounted into the surface of the blade, are used to record blade surface temperature and surface heat transfer rate signals; local Nusselt numbers are then calculated. Non-dimensional temperature distributions are derived across the boundary-layer using the blade surface heat transfer rate and a similarity condition. The equation describing the local entropy generation per unit volume is then integrated through the boundary-layer at each chordwise measurement point on the blade surface.

Effects of Rotation on Blade Surface Heat Transfer: An Experimental Investigation

1997 ◽  
Author(s):  
Roger W. Moss ◽  
Roger W. Ainsworth ◽  
Tom Garside
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Experimental Investigation ◽  
Turbine Blade ◽  
Time History ◽  
Surface Heat ◽  
Blade Surface ◽  
Surface Heat Transfer ◽  
Effects Of Rotation ◽  
Wake Passing

Measurements of turbine blade surface heat transfer in a transient rotor facility are compared with predictions and equivalent cascade data. The rotating measurements involved both forwards and reverse rotation (wake free) experiments. The use of thin-film gauges in the Oxford Rotor Facility provides both time-mean heat transfer levels and the unsteady time history. The time-mean level is not significantly affected by turbulence in the wake; this contrasts with the cascade response to freestream turbulence and simulated wake passing. Heat transfer predictions show the extent to which such phenomena are successfully modelled by a time-steady code. The accurate prediction of transition is seen to be crucial if useful predictions are to be obtained.

Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Film Cooling Performance for a Gas Turbine Blade

1998 ◽  
Author(s):  
Hui Du ◽  
Srinath V. Ekkad ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Film Cooling ◽  
Surface Heat ◽  
Blade Surface ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake

The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.

New Heat Transfer Gages for Use on Multilayered Substrates

1986 ◽  
Vol 108 (1) ◽  
pp. 153-160 ◽  
Author(s):  
J. E. Doorly ◽  
M. L. G. Oldfield
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Wind Tunnel ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Surface Heat ◽  
Basic Flow ◽  
Surface Heat Transfer ◽  
Vitreous Enamel ◽  
Coated Metal

The paper describes a technique which enables measurements of the surface heat transfer rate to be made using thin-film gages deposited on a vitreous enamel-coated metal model. It is intended that this will have particular application in rotating turbine test rigs, where it offers considerable advantages over present techniques. These include ease of manufacture, instrumentation, durability, and lack of interference with the basic flow. The procedures for gage calibration and measurement processing are outlined, and the results of wind tunnel tests which confirm that the method is both practical and accurate are described.

Non-similar solutions for mixed convection along a wedge embedded in a porous medium saturated by a non-Newtonian nanofluid

2014 ◽  
Vol 24 (7) ◽  
pp. 1471-1486 ◽  
Author(s):  
Ali J. Chamkha ◽  
M. Rashad ◽  
Rama Subba Reddy Gorla
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Surface Heat ◽  
Content Type ◽  
Transfer Rates ◽  
Surface Heat Transfer

Purpose – The purpose of this paper is to present a boundary layer analysis for the mixed convection past a vertical wedge in a porous medium saturated with a power law type non-Newtonian nanofluid. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt, Lewis number Le and the power law exponent n. The dependency of the friction factor, surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed. Design/methodology/approach – This general non-linear problem cannot be solved in closed form and, therefore, a numerical solution is necessary to describe the physics of the problem. An implicit, tri-diagonal finite-difference method has proven to be adequate and sufficiently accurate for the solution of this kind of problems. Therefore, it is adopted in the present study. Variable step sizes were used. The convergence criterion employed in this study is based on the difference between the current and the previous iterations. When this difference reached 10−5 for all the points in the η directions, the solution was assumed to be converged, and the iteration process was terminated. Findings – The results indicate that as the buoyancy ratio parameter (Nr) and thermophoresis parameter (Nt) increase, the friction factor increases whereas the heat transfer rate (Nusselt number) and mass transfer rate (Sherwood number) decrease. As the Brownian motion parameter (Nb) increases, the friction factor and surface mass transfer rates increase whereas the surface heat transfer rate decreases. As Le increases, mass transfer rates increase. As the power law exponent n increases, the heat and mass transfer rates increase. Research limitations/implications – The analysis is valid for natural convection dominated regime. The combined forced and natural convection dominated regimes will be reported in a future work. Practical implications – The approach used is useful in optimizing the porous media heat transfer problems in geothermal energy recovery, crude oil extraction, ground water pollution, thermal energy storage and flow through filtering media. Originality/value – The results of the study may be of some interest to the researchers of the field of porous media heat transfer. Porous foam and microchannel heat sinks used for electronic cooling are optimized utilizing the porous medium. The utilization of nanofluids for cooling of microchannel heat sinks requires understanding of fundamentals of nanofluid convection in porous media.

Natural Convective Boundary-Layer Flow Over a Vertical Cylinder Embedded in a Porous Medium Saturated With a Nanofluid

2012 ◽  
Vol 3 (3) ◽  
Author(s):  
Rama Subba Reddy Gorla ◽  
Waqar Khan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Porous Medium ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Vertical Cylinder ◽  
Surface Heat

In this paper, a boundary layer analysis is presented for the natural convection past a vertical cylinder in a porous medium saturated with a nanofluid. Numerical results for friction factor, surface heat transfer rate, and mass transfer rate have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt, and Lewis number Le. The dependency of the friction factor, surface heat transfer rate (Nusselt number), and mass transfer rate on these parameters has been discussed. The results indicate that as Nr, Nb, and Nt increase, the friction factor and heat transfer rate (Nusselt number) decrease. The mass transfer rate (Sherwood number) increases with Le, Nb, and Nt.

A Holistic Optimization of Convecting-Radiating Fin Systems

2002 ◽  
Vol 124 (6) ◽  
pp. 1110-1116 ◽  
Author(s):  
M. Sasikumar ◽  
C. Balaji
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Entropy Generation ◽  
Transfer Rate ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Fluid Temperature ◽  
Minimum Entropy ◽  
Maximum Heat ◽  
Unit System

A convecting-radiating fin array, which stands vertically outside of a horizontal rectangular duct, has been analyzed for various design constraints. Fully developed turbulent flow is considered inside the duct. This study takes into account the variation of fluid temperature along the duct, which has been ignored in most of the earlier studies. The one-dimensional governing equation for temperature distribution along the fin is solved for all the fins of the fin array and the total heat transfer rate per unit system mass, total entropy generation rate and optimum fin height based on maximum heat transfer rate per unit system mass are evaluated from the derived temperature profiles. These quantities are then correlated as functions of geometric and flow parameters for three types of fin profile. Optimum solutions are generated based on (i) maximum heat dissipation rate per unit system mass and (ii) minimum entropy generation rate. A procedure to combine these two optima in order to obtain a “holistic” optimum is also discussed.

Surface Heat Transfer Fluctuations on a Turbine Rotor Blade Due to Upstream Shock Wave Passing

1989 ◽  
Vol 111 (2) ◽  
pp. 105-115 ◽  
Author(s):  
A. B. Johnson ◽  
M. J. Rigby ◽  
M. L. G. Oldfield ◽  
R. W. Ainsworth ◽  
M. J. Oliver
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Shock Waves ◽  
Rotor Blade ◽  
Transfer Rate ◽  
Turbine Rotor ◽  
Surface Heat ◽  
Transfer Rates ◽  
Surface Heat Transfer ◽  
Turbine Rotor Blade

A theoretical model to explain observed rapid large-scale surface heat transfer rate fluctuations associated with the impingement of nozzle guide vane trailing edge shock waves on a transonic turbine rotor blade is described. Experiments were carried out in the Oxford Isentropic Light Piston Cascade Tunnel using an upstream rotating bar system to simulate the shock wave passing. High-frequency surface heat transfer and pressure measurements gave rapidly varying, large, transient signals, which schlieren photography showed to be associated with the impingement of passing shock waves on the surface. Heat transfer rates varying from three times the mean value to negative quantities were measured. A simple first-order perturbation analysis of the boundary layer equations shows that the transient adiabatic heating and cooling of the boundary layer by passing shock waves and rarefactions can give rise to high-temperature gradients near the surface. This in turn leads to large conductive heat transfer rate fluctuations. The application of this theory to measured fluctuating pressure signals gave predictions of fluctuating heat transfer rates that are in good agreement with those measured. It is felt that the underlying physical mechanisms for shock-induced heat transfer fluctuations have been identified. Further work will be necessary to confirm them in rotating experiments.

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