Optimization Arrangement of Two Pulsating Impingement Slot Jets for Achieving Heat Transfer Coefficient Uniformity

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
S. D. Farahani ◽  
M. A. Bijarchi ◽  
F. Kowsary ◽  
M. Ashjaee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Objective Function ◽  
Uniform Distribution ◽  
Target Plate ◽  
Nusselt Numbers ◽  
Design Variables ◽  
Pulsating Jets

In this paper, an optimization was performed to achieve uniform distribution of convective heat transfer coefficient over a target plate using two impinging slot (air) jets. The objective function is the root mean square error (Erms) of the local Nusselt distribution computed by computational fluid dynamic (CFD) simulations from desired Nusselt numbers. This pattern search minimized this objective function. Design variables are nozzle widths, jet-to-jet distance, jet-to-target plate distance, frequency of pulsations (for pulsating jets), and the flow rate. First, an inverse design is performed for two steady jets for simplicity and the obtained errors for three different desired Nusselt numbers, NuD = 7, 10, and 13, were 20.73%, 20.08%, and 22.92%, respectively. Uniform distribution of heat transfer coefficient for two steady jets was not achieved. Thus, two pulsating jets are considered. The range of design variables for pulsating state is as same as steady-state and heat transfer rates increased about 400% over steady-state due to the effects of pulsations in inlet velocity. Thus, in the pulsating state, optimization must be performed for the desired Nusselt numbers around four-times NuD in the steady-state, i.e., NuD = 28, 40, and 52. The Erms reduced less than 0.01% and distribution of heat transfer coefficient for all cases was uniform. An experimental study using an inverse heat conduction method (conjugate gradient method with adjoint equation) has been performed and the experimental results for the case of NuD = 52 are presented. The estimated distribution of Nusselt number on the target plate with the numerical distribution has around 3.2% relative error with optimal configuration.

Heat Transfer Coefficient Measurements on the Film-Cooled Pressure Surface of a Transonic Airfoil

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Paul M. Kodzwa ◽  
John K. Eaton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Wide Band ◽  
Heat Fluxes ◽  
Pressure Surface ◽  
Lift Off ◽  
Transonic Airfoil

This paper presents isoenergetic temperature and steady-state film-cooled heat transfer coefficient measurements on the pressure surface of a modern, highly cambered transonic airfoil. A single passage model simulated the idealized two-dimensional flow path between blades in a modern transonic turbine. This set up offered a simpler construction than a linear cascade but produced an equivalent flow condition. Furthermore, this model allowed the use of steady-state, constant surface heat fluxes. We used wide-band thermochromic liquid crystals (TLCs) viewed through a novel miniature periscope system to perform high-accuracy (±0.2 °C) thermography. The peak Mach number along the pressure surface was 1.5, and maximum turbulence intensity was 30%. We used air and carbon dioxide as injectant to simulate the density ratios characteristic of the film cooling problem. We found significant differences between isoenergetic and recovery temperature distributions with a strongly accelerated mainstream and detached coolant jets. Our heat transfer data showed some general similarities with lower-speed data immediately downstream of injection; however, we also observed significant heat transfer attenuation far downstream at high blowing conditions. Our measurements suggested that the momentum ratio was the most appropriate variable to parameterize the effect of injectant density once jet lift-off occurred. We noted several nonintuitive results in our turbulence effect studies. First, we found that increased mainstream turbulence can be overwhelmed by the local augmentation of coolant injection. Second, we observed complex interactions between turbulence level, coolant density, and blowing rate with an accelerating mainstream.

scholarly journals Local Heat Transfer Coefficient and Adiabatic Wall Temperature Measurement Beneath Arrays of Staggered and Inline Impinging Jets

1994 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
Terry V. Jones ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Channel Height ◽  
Published Data ◽  
Target Plate ◽  
Adiabatic Wall

Recent work, Van Treuren et al. (1993), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000–40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is confined on three sides and spent flow is allowed to exit in one direction. Local values are averaged and compared with previously published data in related geometries. The current data for a staggered array is compared to those from an inline array with the same hole diameter and pitch for an average jet Reynolds number of 10,000 and channel height to diameter ratio of one. A comparison is made between intensity and hue techniques for measuring stagnation point and local distributions of heat transfer. The influence of the temperature of the impingement plate through which the coolant gas flows on the target plate heat transfer has been quantified.

SURFACE HEATER FABRICATION USING MICRO-LITHOGRAPHY FOR TRANSPIRATION COOLING HEAT TRANSFER COEFFICIENT MEASUREMENTS

2021 ◽  
pp. 1-23
Author(s):  
Zheng Min ◽  
Sarwesh Narayan Parbat ◽  
Qing-Ming Wang ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Target Surface ◽  
Transpiration Cooling ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Adiabatic Cooling

Abstract Transpiration cooling is able to provide more uniform coolant coverage than film cooling to effectively protect the component surface from contacting the hot gas. Due to numerous coolant ejection outlets within a small area at the target surface, the experimental thermo-fluid investigation on transpiration cooing becomes a significant challenge. Two classic methods to investigate film cooling, the steady-state foil heater method and the transient thermography technique, both fail for transpiration cooling because the foil heater would block numerous coolant outlets, and the semi-infinite solid conduction model no longer holds for porous plates. In this study, a micro-lithography method to fabricate a silver coil pattern on top of the additively manufactured polymer porous media as the surface heater was proposed. The circuit was deliberately designed to cover the solid surface in a combination of series connection and parallel connection to ensure the power in each unit cell area at the target surface was identical. With uniform heat flux generation, the steady-state tests were conducted to obtain distributions of a pair of parameters, adiabatic cooling effectiveness, and heat transfer coefficient (HTC). The results showed that the adiabatic cooling effectiveness could reach 0.65 with a blowing ratio lower than 0.5. Meanwhile, the heat transfer coefficient ratio (hf/h0) of transpiration cooling was close to 1 with a small blowing ratio at 0.125. A higher HTC ratio was observed for smaller pitch-to-diameter cases due to more turbulence intensity generated at the target surface.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Jet Impingement ◽  
Thermochromic Liquid Crystal ◽  
Transient Techniques ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the airflow to the passage walls. The geometry is similar to gas turbine applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow direction are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient Thermochromic Liquid Crystal (TLC) method was used to measure the heat transfer on the passage walls. Due to the nature of the experiment, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, additional measures were taken to qualify this assumption. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient which was made for the transient TLC experiments. Nusselt number evaluations from all techniques show a good agreement, considering the respective uncertainty ranges. For all sites the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

Impingement Cooling in Narrow Rectangular Channel With Novel Surface Features

2016 ◽  
Author(s):  
Sarwesh Narayan Parbat ◽  
Sin Chien Siw ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Rectangular Channel ◽  
Jet Impingement ◽  
Test Case ◽  
Target Plate ◽  
Surface Features ◽  
Baseline Case ◽  
The Heat Transfer Coefficient

This paper describes a detailed experimental investigation of narrow jet impingement channel with surface features. Three novel surface features: aerofoil shaped dimple cavities on the target plate, chevron elements extending between the jet issuing plate and the target plate and 45 degree wedges mounted on the jet-issuing plate, are proposed. The narrow rectangular channel is 254 mm × 57.2 mm × 19.1 mm (10” × 2.25” × 0.75”) in dimensions and consists of five jets with a constant diameter, D of 9.525 mm (0.375”). The inter-jet spacing and jet-to-target plate distance is 4D and 2D, respectively. Three test cases with different novel surface features are proposed, and the effect of these surface features on the distribution of heat transfer coefficient on the target plate is characterized using the transient liquid crystal technique. In the first test case, dimpulated surface features are introduced on the target plate. The second case consists of chevron elements which extend between the jet issuing plate and the target plate, while the third case has 45 degree wedges mounted on the jet-issuing plate. The smooth jet impingement channel is used as a baseline case for comparison of the heat transfer coefficient distribution on the target plate. The Reynolds number is defined based on the jet diameter, D and bulk velocity of the jet. The experiments were performed at Reynolds number ranging between 61,000 to 98,000. In order to gain a better insight of the flow field within the channel for each of these features, a steady state numerical simulation was performed for each case using the commercially available software, ANSYS CFX. The boundary conditions for these simulations were set as close to the experimental conditions as possible. For turbulence closure, the Shear Stress Transport (SST) model was used which has been shown to be reasonably accurate with moderate computational costs. The numerical results are in favorable trend compared to the values obtained through experimentation. However, in certain regions, the SST turbulence model has overpredicted the heat transfer coefficient values. The results show that the first test case with dimpulated surface features exhibits the highest heat transfer enhancement among all the tested configurations. This enhancement is approximately 25 percent higher than that of the baseline case. The presence of the chevron elements has minimized the deflection of the jets due to crossflow, but, inhibited the spreading of the impinging jets on the target plate. This, in turn, has reduced the local heat transfer performance quite substantially. In case of the 45 degree wedges, the heat transfer enhancement was augmented at the downstream, which was ultimately caused by the diversion of the crossflow towards the target plate.

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

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
C. Camci ◽  
B. Gumusel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
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.

Combined Effect of Grid Turbulence and Unsteady Wake on Film Effectiveness and Heat Transfer Coefficient of a Gas Turbine Blade With Air and CO2 Film Injection

1997 ◽  
Vol 119 (3) ◽  
pp. 594-600 ◽  
Author(s):  
S. V. Ekkad ◽  
A. B. Mehendale ◽  
J. C. Han ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Leading Edge ◽  
Combined Effect ◽  
Grid Turbulence ◽  
Free Stream Turbulence ◽  
Nusselt Numbers ◽  
Unsteady Wake

Experiments were performed to study the combined effect of grid turbulence and unsteady wake on film effectiveness and heat transfer coefficient of a turbine blade model. Tests were done on a five-blade linear cascade at the chord Reynolds number of 3.0 × 105 at cascade inlet. Several combinations of turbulence grids, their locations, and unsteady wake strengths were used to generate various upstream turbulence conditions. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Air and CO2 were used as injectants. Results show that Nusselt numbers for a blade with film injection are much higher than that without film holes. An increase in mainstream turbulence level causes an increase in Nusselt numbers and a decrease in film effectiveness over most of the blade surface, for both density injectants, and at all blowing ratios. A free-stream turbulence superimposed on an unsteady wake significantly affects Nusselt numbers and film effectiveness compared with only an unsteady wake condition.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

1998 ◽  
Vol 120 (1) ◽  
pp. 92-99 ◽  
Author(s):  
D. R. H. Gillespie ◽  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Plate

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Steady State Heat Transfer Within a Nanoscale Spatial Domain

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Kirill V. Poletkin ◽  
Vladimir Kulish
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Spatial Domain ◽  
Thermal Waves ◽  
Steady State Heat ◽  
Steady State Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper, we study the steady state heat transfer process within a spatial domain of the transporting medium whose length is of the same order as the distance traveled by thermal waves. In this study, the thermal conductivity is defined as a function of a spatial variable. This is achieved by analyzing an effective thermal diffusivity that is used to match the transient temperature behavior in the case of heat wave propagation by the result obtained from the Fourier theory. Then, combining the defined size-dependent thermal conductivity with Fourier’s law allows us to study the behavior of the heat flux at nanoscale and predict that a decrease of the size of the transporting medium leads to an increase of the heat transfer coefficient which reaches its finite maximal value, contrary to the infinite value predicted by the classical theory. The upper limit value of the heat transfer coefficient is proportional to the ratio of the bulk value of the thermal conductivity to the characteristic length of thermal waves in the transporting medium.

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