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.

Measurement of Heat Transfer in a 465t/h Circulating Fluidized Bed Boiler

2005 ◽  
Author(s):  
Yu Wang ◽  
Junfu Lu ◽  
Hairui Yang ◽  
Xinmu Zhao ◽  
Guangxi Yue
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Bulk Density ◽  
Fluidized Bed ◽  
Thermal Boundary Layer ◽  
Circulating Fluidized Bed ◽  
Transfer Coefficients ◽  
Cfb Boiler ◽  
Heat Transfer Coefficients ◽  
Solid Bulk

The study of heat transfer and thermal boundary layer in the combustor of a circulating fluidized bed (CFB) is important to the boiler design and operation. Both heat transfer coefficient between the solid-gas flow and the water-wall and the thickness of thermal boundary layer are key data to determine the amount and layout of the tube walls in a CFB furnace. A series of experiments was conducted on a 465t/h commercial CFB boiler, which operated at bed temperature between 850 and 900°C, and at superficial gas velocity between 5.2 to 5.9m/s. Local bed to water wall heat transfer coefficients and temperature profiles near the wall were measured at a set of test ports at different heights of the sidewall. In the same time, the local solid bulk density near the wall was also measured. Special tools such as heat flux probe, solid bulk density sampling probe and temperature probe were developed for the experiments and their structures were introduced. The experimental results were compared with the data from previous studies. Theoretical analysis of the factors that play important role in heat transfer in a CFB boiler was also performed. The relationship between heat transfer and thermal boundary layer was also discussed. Furthermore, a simple model correlating the local heat transfer coefficients with bulk density was developed.

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.

Darryl E. Metzger Memorial Session Paper: Comparison of Calculated and Measured Heat Transfer Coefficients for Transonic and Supersonic Boundary-Layer Flows

1995 ◽  
Vol 117 (2) ◽  
pp. 248-254 ◽  
Author(s):  
C. Hu¨rst ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Supersonic Boundary Layer ◽  
Nozzle Wall ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Three Dimensional Finite Element

The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U∞=230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 × 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent–divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number k–ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Laminar and Transitional Boundary Layer Structures in Accelerating Flow With Heat Transfer

1986 ◽  
Vol 108 (1) ◽  
pp. 116-123 ◽  
Author(s):  
K. Rued ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Pressure Gradients ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients ◽  
Layer Structures ◽  
Flow Heat

The accurate prediction of heat transfer coefficients on cooled gas turbine blades requires consideration of various influence parameters. The present study continues previous work with special efforts to determine the separate effects of each of several parameters important in turbine flow. Heat transfer and boundary layer measurements were performed along a cooled flat plate with various freestream turbulence levels (Tu = 1.6−11 percent), pressure gradients (k = 0−6 × 10−6), and cooling intensities (Tw/T∞ = 1.0−0.53). Whereas the majority of previously available results were obtained from adiabatic or only slightly heated surfaces, the present study is directed mainly toward application on highly cooled surfaces as found in gas turbine engines.

Buoyancy Driven Flow in Saturated Porous Media

2006 ◽  
Vol 129 (6) ◽  
pp. 727-734 ◽  
Author(s):  
H. Sakamoto ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Porous Medium ◽  
Saturated Porous Medium ◽  
Saturated Porous Media ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Bulk Medium

Measurements are reported of heat transfer coefficients in steady natural convection on a vertical constant flux plate embedded in a saturated porous medium. Results show that heat transfer coefficients can be adequately determined via a Darcy-based model, and our results confirm a correlation proposed by Bejan [Int. J. Heat Mass Transfer. 26(9), 1339–1346 (1983)]. It is speculated that the reason that the Darcy model works well in the present case is that the porous medium has a lower effective Prandtl number near the wall than in the bulk medium. The factors that contribute to this effect include the thinning of the boundary layer near the wall and an increase of effective thermal conductivity.

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Laser Doppler Velocimeter ◽  
Transfer Coefficients ◽  
Friction Coefficients ◽  
Heat Transfer Coefficients ◽  
Passage Vortex ◽  
Dimensional Boundary

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter (LDV). Friction coefficients obtained with the oil film interferometry (OFI) method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

The heat transfer coefficients of the heating surface of 300 MWe CFB boiler

2012 ◽  
Vol 21 (4) ◽  
pp. 368-376 ◽  
Author(s):  
Haibo Wu ◽  
Man Zhang ◽  
Qinggang Lu ◽  
Yunkai Sun
Keyword(s):  
Heat Transfer ◽  
Heating Surface ◽  
Transfer Coefficients ◽  
Cfb Boiler ◽  
Heat Transfer Coefficients

The Influence of Free Stream Turbulence on the Local Heat Transfer From Cylinders

1960 ◽  
Vol 82 (2) ◽  
pp. 101-107 ◽  
Author(s):  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Intensity ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients

Local heat-transfer coefficients and recovery factors are presented for three different cylinders in a two-dimensional subsonic air flow, with emphasis on the effect of screen-produced turbulence on these quantities. The increase in turbulent intensity so realized produced larger local heat-transfer coefficients, in a way dependent upon the location on the cylinders, through a direct increase in the heat transfer to the laminar boundary layer, through an earlier transition to turbulence, or through an alteration in the character of the separated flow. Alternatively, recovery factors were affected less, being invariant with respect to the turbulent intensity for attached boundary layer flow, but demonstrating large changes in those separated flow regions for which increased free stream turbulence produced substantial changes in the nature of the separated flow.

scholarly journals Heat transfer and skin-friction in channel with flow behind a cylinder

2021 ◽  
Vol 2088 (1) ◽  
pp. 012055
Author(s):  
N A Kiselev ◽  
A G Zditovets ◽  
Yu A Vinogradov
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Static Pressure ◽  
Thermal Imager ◽  
Transfer Coefficients ◽  
Reynolds Analogy ◽  
Friction Coefficients ◽  
Heat Transfer Coefficients ◽  
Smooth Model ◽  
Transfer Method

Abstract The paper presents the results of an experimental study of the parameters of the boundary layer, distribution of static pressure, heat transfer and friction coefficients of smooth surface located in the wake behind the cylinder in the channel. Cylinders of various diameters were placed in a slotted channel with a height of 30 mm on its axis. In all experiments, the flow velocity at the inlet was 50 m/s. The cylinder was made unheated. The friction coefficients of the smooth model were determined both from the velocity profile in the boundary layer and by direct weighing of the model on a one-component strain-gage balance. The local values of the heat transfer coefficients were determined by transient heat-transfer method using a thermal imager. The values of the heat transfer and friction coefficients in the wake behind the cylinder, referred to the values on the smooth wall in the undisturbed flow, varied in the range 1.15–1.65 and 1.3–1.75, respectively. The value of the Reynolds analogy factor for all cylinder diameters turned out to be less than unity.

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