Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with to the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

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.

Flow Boiling of R134a and R134a/Propane Mixtures at Low Saturation Temperatures Inside a Plain Horizontal Tube

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
A. Rabah ◽  
S. Kabelac
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Azeotropic Point ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Maximum Decrease

Local heat transfer coefficients for flow boiling of pure 1,1,1,2-tetrafluoroethane (R134a) and binary mixtures of propane (R290) and R134a were measured. The experimental setup employed a vapor heated plain horizontal tube (di=10mm, do=12mm, L=500mm). The measurements covered a wide range of saturation temperatures (233≤Ts≤278K), mass fluxes (100≤ṁ≤300kg∕m2s), qualities (0≤ẋ≤1), and concentrations (0≤z̃≤0.65). In the zeotropic region of R134a/R290 mixtures, the measured local heat transfer coefficient was found to show a maximum decrease by a factor of 2 relative to that for pure R134a. At the azeotropic point (65% R290), it was found to increase by a factor of 1.2. The measured local heat transfer coefficients for both R134a and R134a/R290 were compared with a number of correlations.

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

1999 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
High Resolution ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Density ◽  
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 in a wide range emphasizing on engine relevant conditions. A high resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained by a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled testplate measured with thermocouples were applied as boundary conditions in a heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hr referring to adiabatic wall temperatures in the presence of film cooling. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results of identical flow situations (constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf depending on the various parameters were recognized and quantified. 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.

Effects of Reynolds Number and Pressure Ratio on Leakage Loss and Heat Transfer in a Stepped Labyrinth Seal

2001 ◽  
Author(s):  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Operating Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Sealing Performance

The influence of Reynolds number and pressure ratio on the operating characteristics of a stepped labyrinth seal was experimentally determined. The geometries investigated represent designs of a stepped labyrinth seal typical for modern jet engines. Heat transfer and discharge measurements were obtained for two plane models with various seal clearances. The experiments covered a range of Reynolds numbers and pressure ratios. Independent variation of Reynolds number and pressure ratio was obtained by adjusting the back pressure at the seal exit for a given pressure ratio. Dimensionless discharge coefficients, describing the sealing performance, were derived from the measured leakage rates. Pressure ratio, Reynolds number, tip geometry and seal clearance all affected the sealing performance. Finite element calculations were employed to calculate the local heat transfer coefficients from the measured wall and gas temperatures. Averaging of the local values yielded mean heat transfer coefficients and mean Nusselt numbers. The heat transfer was mainly determined by the Reynolds number. Compressibility effects on the heat transfer were observed to be very small.

Heat Transfer During Near-Critical-Pressure Condensation of Refrigerant Blends

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Srinivas Garimella ◽  
Ulf C. Andresen ◽  
Biswajit Mitra ◽  
Yirong Jiang ◽  
Brian M. Fronk
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Region ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Wide Range

Heat transfer during condensation of refrigerant blends R404A and R410A flowing through horizontal tubes with 0.76 ≤ D ≤ 9.4 mm at nominal Pr = 0.8–0.9 was investigated. Local heat transfer coefficients were measured for the mass flux range 200 < G < 800 kg m−2 s−1 in small quality increments over the entire vapor–liquid region. Heat transfer coefficients increased with quality and mass flux, while the effect of reduced pressure was not very significant within this range of pressures. The heat transfer coefficients increased with a decrease in diameter. Correlations from the literature were not able to predict the condensation heat transfer coefficient for these fluids at these near-critical pressures over the wide range of tube diameters under consideration. A new flow-regime based model for heat transfer in the wavy, annular, and annular/wavy transition regimes, which predicts 91% of the data within ±25%, is proposed.

Effects of Reynolds Number and Pressure Ratio on Leakage Loss and Heat Transfer in a Stepped Labyrinth Seal

2001 ◽  
Vol 123 (4) ◽  
pp. 815-822 ◽  
Author(s):  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Operating Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Sealing Performance

The influence of Reynolds number and pressure ratio on the operating characteristics of a stepped labyrinth seal was experimentally determined. The geometries investigated represent designs of a stepped labyrinth seal typical for modern jet engines. Heat transfer and discharge measurements were obtained for two plane models with various seal clearances. The experiments covered a range of Reynolds numbers and pressure ratios. Independent variation of Reynolds number and pressure ratio was obtained by adjusting the back pressure at the seal exit for a given pressure ratio. Dimensionless discharge coefficients, describing the sealing performance, were derived from the measured leakage rates. Pressure ratio, Reynolds number, tip geometry, and seal clearance all affected the sealing performance. Finite element calculations were employed to calculate the local heat transfer coefficients from the measured wall and gas temperatures. Averaging of the local values yielded mean heat transfer coefficients and mean Nusselt numbers. The heat transfer was mainly determined by the Reynolds number. Compressibility effects on the heat transfer were observed to be very small.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

scholarly journals Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

2021 ◽  
Author(s):  
T. Vossel ◽  
N. Wolff ◽  
B. Pustal ◽  
A. Bührig-Polaczek ◽  
M. Ahmadein
Keyword(s):  
Heat Transfer ◽  
Contact Pressure ◽  
Local Heat Transfer ◽  
Casting Process ◽  
Local Heat ◽  
Air Gap ◽  
Gap Formation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).

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