Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry

2000 ◽  
Vol 122 (2) ◽  
pp. 314-320 ◽  
Author(s):  
Stefan Busam ◽  
Axel Glahn ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Operating Conditions ◽  
Chamber Wall ◽  
Test Facility ◽  
Detailed Knowledge ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Dimensional Parameter ◽  
Secondary Air

Increasing efficiencies of modern aero-engines are accompanied by rising turbine inlet temperatures, pressure levels and rotational speeds. These operating conditions require a detailed knowledge of two-phase flow phenomena in secondary air and lubrication oil systems in order to predict correctly the heat transfer to the oil. It has been found in earlier investigations that especially at high rotational speeds the heat transfer rate within the bearing chambers is significantly increased with negative effects on the heat to oil management. Furthermore, operating conditions are reached where oil coking and oil fires are more likely to occur. Therefore, besides heat sources like bearing friction and churning, the heat transfer along the housing wall has to be considered in order to meet safety and reliability criteria. Based on our recent publications as well as new measurements of local and mean heat transfer coefficients, which were obtained at our test facility for engine relevant operating conditions, an equation for the internal bearing chamber wall heat transfer is proposed. Nusselt numbers are expressed as a function of non-dimensional parameter groups covering influences of chamber geometry, flow rates and shaft speed. [S0742-4795(00)02202-X]

Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry

1999 ◽  
Author(s):  
Stefan Busam ◽  
Axel Glahn ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Operating Conditions ◽  
Chamber Wall ◽  
Test Facility ◽  
Detailed Knowledge ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Dimensional Parameter ◽  
Secondary Air

Increasing efficiencies of modern aero-engines are accompanied by rising turbine inlet temperatures, pressure levels and rotational speeds. These operating conditions require a detailed knowledge of two-phase flow phenomena in secondary air and lubrication oil systems in order to predict correctly the heat transfer to the oil. It has been found in earlier investigations that especially at high rotational speeds the heat transfer rate within the bearing chambers is significantly increased with negative effects on the heat to oil management. Furthermore, operating conditions are reached where oil coking and oil fires are more likely to occur. Therefore, besides heat sources like bearing friction and churning, the heat transfer along the housing wall has to be considered in order to meet safety and reliability criteria. Based on our recent publications as well as new measurements of local and mean heat transfer coefficients, which were obtained at our test facility for engine relevant operating conditions, an equation for the internal bearing chamber wall heat transfer is proposed. Nusselt numbers are expressed as a function of non-dimensional parameter groups covering influences of chamber geometry, flow rates and shaft speed.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Vaporization Heat Transfer in a Small Diameter Closed Two-Phase Thermosyphon

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Andrea Padovan ◽  
Stefano Bortolin ◽  
Marco Rossato ◽  
Sauro Filippeschi ◽  
Davide Del Col
Keyword(s):  
Heat Transfer ◽  
Small Diameter ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Input Power ◽  
Operating Conditions ◽  
Internal Diameter ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Vaporization Heat

This paper deals with vaporization heat transfer in a small diameter closed two-phase thermosyphon with a long evaporator and a short condenser, filled with water as operating fluid. The internal diameter of the evaporator is equal to 6.4 mm and the length-to-diameter ratio at the evaporator is equal to 166. A similar geometry is commonly used in vacuumed tube solar collectors. In the present investigation, the input power to the evaporator is provided by means of an electrical resistance wire wrapped around the external wall of the tube, while a water jacket is built at the condenser to reject the heat. The performance of the thermosyphon is described by using the wall temperature and the overall thermal resistance for different operating conditions: input power at the evaporator, cooling water temperature at the condenser, and inclination of the thermosyphon (30 deg, 60 deg, and 90 deg tilt angle to the horizontal plane). The present experimental data cover a range of heat flux between 1700 and 8000 W/m2 and saturation temperature between 28 °C and 72 °C. The vaporization heat transfer coefficients are compared with some correlations for closed two-phase thermosyphons displaying large disagreement. A new correlation is presented, which accurately predicts the present experimental values and other data by independent labs taken in closed two-phase thermosyphons, varying geometry and operating fluid (water, R134a, and ethanol).

Parametric Study of Convective Heat Transfer Coefficients at the Tire Surface

1980 ◽  
Vol 8 (3) ◽  
pp. 37-67 ◽  
Author(s):  
A. L. Browne ◽  
L. E. Wickliffe
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal State ◽  
Convective Heat Transfer Coefficient ◽  
Operating Conditions ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract Analyses have shown that the thermal state of a tire is influenced by both the size of and variation in the value of the convective heat transfer coefficient at the tire surface. In the work reported here, a test facility was constructed to permit the determination of convective heat transfer coefficients under a broad range of operating conditions. Data were obtained to show the effects of air speed, boundary layer thickness and turbulence level, humidity, tire surface contamination, tire surface roughness and unevenness, and tire surface wetness on convective heat transfer coefficients. The significance of these results to tire power loss is discussed.

scholarly journals Turbine Airfoil External Heat Transfer Measurement in a Hot-Cascade

1997 ◽  
Author(s):  
Luzeng J. Zhang ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
External Heat ◽  
Operating Conditions ◽  
Test Facility ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
External Heat Transfer ◽  
Heat Transfer Coefficients

Detailed knowledge of local external heat transfer around a turbine airfoil is critical for an accurate prediction of metal temperature and component life. This paper discusses the results of measurements of the local gas side heat transfer coefficient distribution which were performed in an annular gas turbine vane hot-cascade test facility and provides comparisons with analytical predictions. The steady state tests were performed at simulated engine operating conditions. The tests were conducted on an internally cooled airfoil with the intent to provide close to uniform coolant temperature at the mid-span of the airfoil and also to obtain a high heat flux through the wall, minimizing uncertainty. Internal coolant side heal transfer coefficients were measured through calibration tests outside the cascade by a wire heater. A calibrated infrared pyrometer was used to provide detailed airfoil surface local temperatures and the corresponding external heat transfer coefficients. The airfoil was instrumented with a number of thermocouples for both calibration and temperature measurement. A 12% freestream turbulence was generated by a turbulence grid upstream of the test cascade. The static pressure measured over the test vane agreed well with invicid predictions. Heat transfer coefficients were measured and compared to a TEXSTAN boundary layer code prediction. The influence of Reynolds number and Mach number on the airfoil external heat transfer coefficient were also studied and is presented in the paper.

Streamline Modeling of Manifold Microchannels in Thin Film Evaporation

2013 ◽  
Author(s):  
Raphael Mandel ◽  
Amir Shooshtari ◽  
Serguei Dessiatoun ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Mass Fluxes ◽  
Flow Length

Manifold microchannels utilize a system of manifolds to divide long microchannels into an array of parallel ones, resulting in reduced flow length and more localized liquid feeding. Reducing flow length is desirable because it enables the simultaneous enhancement of heat transfer rate and reduction of pressure drop. Furthermore, localized feeding reduces potential for localized dryout, increasing the operational heat flux. Because of the failure of the available conventional heat transfer correlations to predict the thermal performance of manifold microchannels operating in two phase mode, a “streamline” model was created. The heat transfer surface area was divided into parallel, non-interacting streamlines, and the quality, void fraction, film thickness, heat transfer coefficient, heat flux, and pressure drop was calculated sequentially along the streamline. The mass flow rate through each streamline was adjusted in order to obtain the specified pressure drop, and the value of this pressure drop was adjusted in order to obtain the desired microchannel mass flux. Finally, the average wall heat transfer coefficient was calculated, and temperature profile in the fin was adjusted to correspond with the analytical 1-D temperature distribution of a thin fin with an average wall heat transfer coefficient and specified base superheat. The average wall heat transfer coefficients predicted by the model was then compared to the available experimental data with sufficiently good agreement with a wide variety of geometries and working fluids at low mass fluxes.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

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