On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows

Surface Temperature ◽

Transfer Coefficient ◽

Wall Temperature ◽

Convective Heat Transfer Coefficient ◽

Internal Heat ◽

Reference Temperature ◽

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.

High Resolution Heat Transfer Measurements on the Stator Endwall of an Axial Turbine

Journal of Turbomachinery ◽

10.1115/1.4028431 ◽

2014 ◽

Vol 137 (4) ◽

Cited By ~ 17

Author(s):

Benoit Laveau ◽

Reza S. Abhari ◽

Michael E. Crawford ◽

Ewald Lutum

Keyword(s):

Heat Transfer ◽

High Resolution ◽

Surface Temperature ◽

Transfer Coefficient ◽

Mass Flow ◽

Wall Temperature ◽

Adiabatic Wall ◽

Axial Turbine ◽

In order to continue increasing the efficiency of gas turbines, an important effort is made on the thermal management of the turbine stage. In particular, understanding and accurately estimating the thermal loads in a vane passage is of primary interest to engine designers looking to optimize the cooling requirements and ensure the integrity of the components. This paper focuses on the measurement of endwall heat transfer in a vane passage with a three-dimensional (3D) airfoil shape and cylindrical endwalls. It also presents a comparison with predictions performed using an in-house developed Reynolds-Averaged Navier–Stokes (RANS) solver featuring a specific treatment of the numerical smoothing using a flow adaptive scheme. The measurements have been performed in a steady state axial turbine facility on a novel platform developed for heat transfer measurements and integrated to the nozzle guide vane (NGV) row of the turbine. A quasi-isothermal boundary condition is used to obtain both the heat transfer coefficient and the adiabatic wall temperature within a single measurement day. The surface temperature is measured using infrared thermography through small view ports. The infrared camera is mounted on a robot arm with six degrees of freedom to provide high resolution surface temperature and a full coverage of the vane passage. The paper presents results from experiments with two different flow conditions obtained by varying the mass flow through the turbine: measurements at the design point (ReCax=7.2×105) and at a reduced mass flow rate (ReCax=5.2×105). The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are derived from measurements at 14 different isothermal temperatures. The experimental data are supplemented with numerical predictions that are deduced from a set of adiabatic and diabatic simulations. In addition, the predicted flow field in the passage is used to highlight the link between the heat transfer patterns measured and the vortical structures present in the passage.

High Resolution Heat Transfer Measurements on the Stator Endwall of an Axial Turbine

Volume 5B: Heat Transfer ◽

10.1115/gt2014-26105 ◽

2014 ◽

Author(s):

Benoit Laveau ◽

Reza S. Abhari ◽

Michael E. Crawford ◽

Ewald Lutum

Keyword(s):

Heat Transfer ◽

High Resolution ◽

Surface Temperature ◽

Transfer Coefficient ◽

Mass Flow ◽

Wall Temperature ◽

Adiabatic Wall ◽

Axial Turbine ◽

In order to continue increasing the efficiency of gas turbines, an important effort is made on the thermal management of the turbine stage. In particular understanding and accurately estimating the thermal loads in a vane passage is of primary interest to engine designers looking to optimize the cooling requirements and ensure the integrity of the components. This paper focuses on the measurement of endwall heat transfer in a vane passage with a 3D airfoil shape and cylindrical endwalls. It also presents a comparison with predictions performed using an in-house developed RANS solver featuring a specific treatment of the numerical smoothing using a flow adaptive scheme. The measurements have been performed in a steady state axial turbine facility on a novel platform developed for heat transfer measurements and integrated to the nozzle guide vane row of the turbine. A quasi-isothermal boundary condition is used to obtain both the heat transfer coefficient and the adiabatic wall temperature within a single measurement day. The surface temperature is measured using infrared thermography through small view ports. The infrared camera is mounted on a robot-arm with six degrees of freedom to provide high resolution surface temperature and a full coverage of the vane passage. The paper presents results from experiments with two different flow conditions obtained by varying the mass flow through the turbine: measurements at the design point (ReCax = 7,2.105) and at a reduced mass flow rate (ReCax = 5,2.105). The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are derived from measurements at 14 different isothermal temperatures. The experimental data are supplemented with numerical predictions that are deduced from a set of adiabatic and diabatic simulations. In addition, the predicted flow field in the passage is used to highlight the link between the heat transfer patterns measured and the vortical structures present in the passage.

ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels ◽

Flow Boiling in Transparent Heated Microtube

10.1115/icnmm2008-62314 ◽

2008 ◽

Author(s):

Osamu Kawanami ◽

Shih-Che Huang ◽

Kazunari Kawakami ◽

Itsuro Honda ◽

Yousuke Kawashima ◽

...

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Wall Temperature ◽

Flow Boiling ◽

Flow Behavior ◽

High Heat Flux ◽

Experimental Conditions ◽

In the present study, a detailed investigation of flow boiling in a transparent heated microtube was performed. The transparent heated tube was made by electroless gold plating method. The enclosed gas-liquid interface could be clearly recognized through the tube wall, and the inner wall temperature measurement and direct heating of the film were simultaneously conducted by using the tube. The experimental conditions were: tube diameter 1 mm, mass velocity 100 kg/m2s, inlet liquid sub-cooling 20 K and heat flux up to 384 kW/m2 in the open system. Flow fluctuation was minimized by employing a twin plunger pump. Among our experimental results, we observed a high-frequency fluctuation of the inner wall temperature and a sharp peak for the heat transfer coefficient with high heat flux conditions, which have not been reported in previous experiments. This abrupt increase in the heat transfer coefficient coincided with a slight rapid axial growth of an elongated bubble found in the observation of the flow behavior. Hence, in low heat flux conditions, the fluctuations of temperature and heat transfer coefficient are strongly suppressed except for the instances when there is no bubble in the tube.

Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽

10.3390/en14010180 ◽

2020 ◽

Vol 14 (1) ◽

pp. 180

Author(s):

Asif Ali ◽

Lorenzo Cocchi ◽

Alessio Picchi ◽

Bruno Facchini

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Linear Regression ◽

Surface Temperature ◽

Transfer Coefficient ◽

External Surface ◽

Internal Surface ◽

Regression Method ◽

Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

Nanoparticle aggregation kinematics on the quadratic convective magnetohydrodynamic flow of nanomaterial past an inclined flat plate with sensitivity analysis

10.1177/09544089211056235 ◽

2021 ◽

pp. 095440892110562

Author(s):

AS Sabu ◽

Joby Mackolil ◽

B Mahanthesh ◽

Alphonsa Mathew

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Sensitivity Analysis ◽

Heat Source ◽

Transfer Coefficient ◽

Flat Plate ◽

Inclined Plate ◽

The Impact ◽

The study focuses on the aggregation kinematics in the quadratic convective magneto-hydrodynamics of ethylene glycol-titania ([Formula: see text]) nanofluid flowing through an inclined flat plate. The modified Krieger-Dougherty and Maxwell-Bruggeman models are used for the effective viscosity and thermal conductivity to account for the aggregation aspect. The effects of an exponential space-dependent heat source and thermal radiation are incorporated. The impact of pertinent parameters on the heat transfer coefficient is explored by using the Response Surface Methodology and Sensitivity Analysis. The effects of several parameters on the skin friction and heat transfer coefficient at the plate are displayed via surface graphs. The velocity and thermal profiles are compared for two physical scenarios: flow over a vertical plate and flow over an inclined plate. The nonlinear problem is solved using the Runge–Kutta-based shooting technique. It was found that the velocity profile significantly decreased as the inclination of the plate increased on the other hand the temperature profile improved. The heat transfer coefficient decreased due to the increase in the Hartmann number. The exponential heat source has a decreasing effect on the heat flux and the angle of inclination is more sensitive to the heat transfer coefficient than other variables. Further, when radiation is incremented, the sensitivity of the heat flux toward the inclination angle augments at the rate 0.5094% and the sensitivity toward the exponential heat source augments at the rate 0.0925%. In addition, 41.1388% decrement in wall shear stress is observed when the plate inclination is incremented from [Formula: see text] to [Formula: see text].

Heat Transfer Measurements Downstream of Trenched Film Cooling Holes Using a Novel Optical Two-Layer Measurement Technique

Journal of Turbomachinery ◽

10.1115/1.4031919 ◽

2015 ◽

Vol 138 (3) ◽

Cited By ~ 3

Author(s):

Peter Schreivogel ◽

Michael Pfitzner

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Film Cooling ◽

Slight Reduction ◽

Superposition Method ◽

Cooling Effectiveness ◽

Cylindrical Holes ◽

A new approach for steady-state heat transfer measurements is proposed. Temperature distributions are measured at the surface and a defined depth inside the wall to provide boundary conditions for a three-dimensional heat flux calculation. The practical application of the technique is demonstrated by employing a superposition method to measure heat transfer and film cooling effectiveness downstream of two different 0.75D deep narrow trench geometries and cylindrical holes. Compared to the cylindrical holes, both trench geometries lead to an augmentation of the heat transfer coefficient supposedly caused by the highly turbulent attached cooling film emanating from the trenches. Areas of high heat transfer are visible, where recirculation bubbles or large amounts of coolant are expected. Increasing the density ratio from 1.33 to 1.60 led to a slight reduction of the heat transfer coefficient and an increased cooling effectiveness. Both trenches provide a net heat flux reduction (NHFR) superior to that of cylindrical holes, especially at the highest momentum flux ratios.

Casing Convective Heat Transfer Coefficient and Reference Freestream Temperature Determination Near an Axial Flow Turbine Rotor

Journal of Heat Transfer ◽

10.1115/1.4003757 ◽

2011 ◽

Vol 133 (8) ◽

Author(s):

C. Camci ◽

B. Gumusel

Keyword(s):

Heat Transfer ◽

Steady State ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Convective Heat ◽

Convective Heat Transfer Coefficient ◽

Axial Flow ◽

Reference Temperature ◽

Steady State Heat Transfer

The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steady-state heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The freestream reference temperature, especially in the tip gap region of the casing, varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the freestream temperature is not as straightforward as constant freestream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local freestream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and freestream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5% and 8% of the convective heat transfer coefficient.

ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels: Parts A and B ◽

Two Phase Heat Transfer of Ammonia in a Mini/Micro Channel

10.1115/fedsm-icnmm2010-30302 ◽

2010 ◽

Author(s):

M. Hamayun Maqbool ◽

Bjo¨rn Palm ◽

R. Khodabandeh ◽

Rashid Ali

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Mass Flux ◽

Experimental Results ◽

Working Fluid ◽

Internal Diameter ◽

Vapour Quality ◽

Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.

Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

Journal of Heat Transfer ◽

10.1115/1.3580115 ◽

1969 ◽

Vol 91 (1) ◽

pp. 27-36 ◽

Cited By ~ 86

Author(s):

B. S. Shiralkar ◽

Peter Griffith

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

High Heat ◽

Supercritical Pressure ◽

Heat Fluxes ◽

Bulk Temperature ◽

Operating Pressure ◽

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.