An Improved Cluster-Renewal Model for the Estimation of Heat Transfer Coefficients on the Furnace Walls of Commercial Circulating Fluidized Bed Boilers

2004 ◽  
Vol 126 (6) ◽  
pp. 1040-1043 ◽  
Author(s):  
Animesh Dutta ◽  
Prabir Basu
Keyword(s):  
Heat Transfer ◽  
Circulating Fluidized Bed ◽  
Transfer Coefficients ◽  
Boiler Furnace ◽  
Heat Transfer Coefficients ◽  
Renewal Model ◽  
Solids Concentration ◽  
Wide Range ◽  
Using Data ◽  
Fluidized Bed Boilers

Using data from large CFB boilers, and taking average solids concentration, size and height of the boiler-furnace as variables, a correlation for fractional wall coverage has been developed. This correlation for wall coverage and several other refinements have been used to modify the cluster renewal model of heat transfer. Predicted heat transfer coefficients from this model, for a wide range of CFB boilers, show good agreements with those measured in these boilers.

An Improvement of Cluster-Renewal Model for Estimation of Heat Transfer on the Water-Walls of Commercial CFB Boilers

2003 ◽  
Author(s):  
Animesh Dutta ◽  
Prabir Basu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Thermal Boundary Layer ◽  
Circulating Fluidized Bed ◽  
Transfer Coefficients ◽  
Cfb Boiler ◽  
Heat Transfer Coefficients ◽  
Renewal Model ◽  
Solids Concentration ◽  
Gas Gap

Even though cluster renewal model appears to hold the ground for calculating heat transfer coefficients on water walls of a Circulating Fluidized Bed (CFB) boiler, there are certain parameters of this model including thickness of the gas-gap between the wall and the particle suspension, wall coverage, thermal boundary layer, cluster concentration, cluster velocity, dispersed phase convection are yet to be determined. Fractional wall coverage is the most important parameter among them. This paper presents a correlation of fractional wall coverage for commercial boilers based on the data from large CFB boilers where average solids concentration, size and height of the combustor were taken as variable. Data were deduced by applying cluster renewal model with recent findings on gas gap, thermal boundary layer, cluster concentration, cluster velocity to the reported heat transfer coefficients on four commercial CFB boilers. The improved cluster renewal model is validated against available data.

scholarly journals Mass and Heat Transfer Coefficients in Automotive Exhaust Catalytic Converter Channels

Catalysts ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 507
Author(s):  
Chrysovalantis C. Templis ◽  
Nikos G. Papayannakos
Keyword(s):  
Heat Transfer ◽  
Flow Reactor ◽  
Catalytic Converter ◽  
Reaction Rates ◽  
Cfd Model ◽  
Automotive Exhaust ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Mass And Heat Transfer

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two dimensional computational fluid dynamic (2-D CFD) model developed in Comsol Multiphysics, taking into account catalytic rates of a real catalytic converter. The effect of channel size and reaction rates on mass and heat transfer coefficients and the applicability of the proposed correlations at different conditions are discussed. The correlations proposed predict very satisfactorily the mass and heat transfer coefficients calculated from the 2-D CFD model along the channel length. The use of a one dimensional (1-D) simplified model that couples a plug flow reactor (PFR) with mass transport and heat transport effects using the mass and heat transfer correlations of this study is proved to be appropriate for the simulation of the monolith channel operation.

Heat Transfer in Rotating Serpentine Coolant Passage With Ribbed Walls at Low Mach Numbers

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Shang-Feng Yang ◽  
Je-Chin Han ◽  
Salam Azad ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Low Mach Number ◽  
Heat Transfer Coefficients ◽  
Rotation Numbers ◽  
Wide Range ◽  
Mach Numbers

This paper experimentally investigates the effect of rotation on heat transfer in typical turbine blade serpentine coolant passage with ribbed walls at low Mach numbers. To achieve the low Mach number (around 0.01) condition, pressurized Freon R-134a vapor is utilized as the working fluid. The flow in the first passage is radial outward, after the 180 deg tip turn the flow is radial inward to the second passage, and after the 180 deg hub turn the flow is radial outward to the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers up to 0.6 and Reynolds numbers from 30,000 to 70,000. Heat transfer coefficients were measured using the thermocouples-copper-plate-heater regional average method. Heat transfer results are obtained over a wide range of Reynolds numbers and rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Regional heat transfer coefficients are correlated with Reynolds numbers for nonrotation and with rotation numbers for rotating condition, respectively. The results can be useful for understanding real rotor blade coolant passage heat transfer under low Mach number, medium–high Reynolds number, and high rotation number conditions.

Heat Transfer for Forced Convection Past Coiled Wires

1990 ◽  
Vol 112 (4) ◽  
pp. 921-925 ◽  
Author(s):  
M. Dietrich ◽  
R. Blo¨chl ◽  
H. Mu¨ller-Steinhagen
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Measured Data ◽  
Subcooled Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Coil Geometry ◽  
Coil Diameter ◽  
Wide Range ◽  
Laminar And Turbulent Flow

Heat transfer coefficients were measured for forced convection of isobutanol in crossflow past coiled wires with different coil geometries. Flow rate and heat flux have been varied over a wide range to include laminar and turbulent flow for convective sensible and subcooled boiling heat transfer. To investigate the effect of coil geometry on heat transfer, the wire diameter, coil diameter, and coil pitch were varied systematically. The measured data are compared with the predictions of four correlations from the literature.

scholarly journals High-Resolution Measurements of Local Heat Transfer Coefficients From Discrete Hole Film Cooling

1999 ◽  
Vol 123 (4) ◽  
pp. 749-757 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
High Resolution ◽  
Film Cooling ◽  
Density Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Surface Patterns

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied over a wide range, emphasizing engine relevant conditions. A high-resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained from a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled test plate measured with thermocouples were applied as boundary conditions in this heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hf based on the difference between actual wall temperatures and adiabatic wall temperatures in the presence of film cooling. The hf data are given for an engine relevant density ratio of 1.8. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results for identical flow situations (i.e., constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf are recognized and quantified as the different ejection parameters are changed. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD codes in discrete hole film cooling.

Application of Advanced Experimental Techniques in the Development of a Cooled Turbine Nozzle

1996 ◽  
Author(s):  
H. K. Moon ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Major Elements ◽  
Fine Tuning ◽  
Experimental Techniques ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Wide Range ◽  
Cooling Design ◽  
Comparison Of The Results

In spite of very significant progress in analytical and numerical methods during recent years, experimental techniques are still essential tools for the development of cooled turbine nozzles. This paper describes the major elements of the development process for cooled turbine nozzles with a primary emphasis on advanced experimental heat transfer techniques. Thermochromic liquid crystals were used to measure the internal (coolant side) heat transfer coefficients of a practical vane cooling design which has a combination of different heat transfer augmenting devices. A comparison of the results and analytical predictions provided validations of existing correlations which were developed from the generic cases (usually one type of augmenting device). The overall cooling design was evaluated in a full-scale annular hot cascade which maintained heat transfer similarity. The freestream turbulence level was measured with an in-house developed heat flux probe. Cooling effectiveness distribution was evaluated from the surface metal temperatures mapped with an in-house developed wide range temperature pyrometer. The test results led to the fine-tuning of the nozzle vane cooling design.

Effects of Surface Roughness on Heat Transfer and Aerodynamic Performance of Turbine Airfoils

1997 ◽  
Author(s):  
N. Abuaf ◽  
R. S. Bunker ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Surface Finish ◽  
Local Heat Transfer ◽  
Surface Finishing ◽  
Transfer Coefficients ◽  
Average Roughness ◽  
Reynolds Analogy ◽  
Local Skin ◽  
Heat Transfer Coefficients ◽  
Wide Range

Aerodynamic flow path losses and turbine airfoil gas side heat transfer are strongly affected by the gas side surface finish. For high aero efficiencies and reduced cooling requirements, airfoil designs dictate extensive surface finishing processes to produce smooth surfaces and enhance engine performance. The achievement of these requirements incurs additional manufacturing finishing costs over less strict requirements. The present work quantifies the heat transfer (and aero) performance differences of three cast airfoils with varying degrees of surface finish treatment. An airfoil which was grit blast and Codep coated produced an average roughness of 2.33 μm, one which was grit blast, tumbled, and Aluminide coated produced 1.03 μm roughness, and another which received further post coating polishing produced 0.81 μm roughness. Local heat transfer coefficients were experimentally measured with a transient technique in a linear cascade with a wide range of flow Reynolds numbers covering typical engine conditions. The measured heat transfer coefficients were used with a rough surface Reynolds Analogy to determine the local skin friction coefficients, from which the drag forces and aero efficiencies were calculated. Results show that tumbling and polishing reduce the average roughness and improve performance. The largest differences are observed from the rumbling process, with smaller improvements realized from polishing.

Turbulent Flow in Closely-Pitched Internally Enhanced Tubes

2000 ◽  
Author(s):  
T. S. Ravigururajan ◽  
J. Srinivasan
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Helix Angle ◽  
Independent Study ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Parameters ◽  
Wide Range ◽  
Enhanced Tubes

Abstract General correlations are developed and verified for friction factor and heat transfer coefficients for single-phase turbulent flow in internally augmented tubes, with low pitch to height ratios. Data from existing investigations were collected for a wide range of tube parameters with e/d: 0.01 to 0.2; p/e: < 8; α/90: 0.2 to 1.0, and flow parameters; Re: 2000 to 250,000 and Pr: 0.66 to 37.6. The data were applied to a linear model to get normalized correlations that were then modified to approach smooth tube correlations, as the roughness variables became very small. The correlations predicted 92% of data from an independent study on microfin tubes within ± 30%. For closely-pitched enhanced tubes, the proposed correlations predict heat transfer/friction factor with better overall accuracy and are suitable for different types of internal enhancements. The heat transfer increases with decreasing p/e ratio and increasing helix angle. The effects of roughness height and pitch on both friction and heat transfer are similar to that experienced in traditional enhancement design (p/e > 8).

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