Characterization of Impingement Heat/Mass Transfer to the Synthetic Jet Generated by a Biomimetic Actuator

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Zdeněk Trávníček ◽  
Zuzana Broučková
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Mass Transfer Rate ◽  
Jet Impingement ◽  
Flux Measurement ◽  
Impinging Jets ◽  
Synthetic Jet ◽  
Working Fluid ◽  
Naphthalene Sublimation Technique ◽  
Flexible Diaphragm

Two biomimetic synthetic jet (SJ) actuators were designed, manufactured, and tested under conditions of a jet impingement onto a wall. Nozzles of the actuators were formed by a flexible diaphragm rim, the working fluid was air, and the operating frequencies were chosen near the resonance at 65 Hz and 69 Hz. Four experimental methods were used: phase-locked visualization of the oscillating nozzle lips, jet momentum flux measurement using a precision scale, hot-wire anemometry, and mass transfer measurement using the naphthalene sublimation technique. The results demonstrated possibilities of the proposed actuators to cause a desired heat/mass transfer distribution on the exposed wall. It was concluded that the heat/mass transfer rate was commensurable with a conventional continuous impinging jets (IJs) at the same Reynolds numbers.

A Synthetic Jet Issuing From a Bio-Inspired Actuator With an Oscillating Nozzle Lip

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Zdeněk Trávníček ◽  
Zuzana Broučková
Keyword(s):  
Momentum Flux ◽  
Flux Measurement ◽  
Experimental Methods ◽  
Synthetic Jet ◽  
Operating Frequency ◽  
Working Fluid ◽  
Hot Wire ◽  
Synthetic Jet Actuator ◽  
Novel Variant ◽  
Flexible Diaphragm

A novel variant of a synthetic jet actuator (SJA) has been designed, manufactured, and tested. The novelty consists in a bio-inspired nozzle whose oscillating lip is formed by a flexible diaphragm rim. The working fluid is air, and the operating frequency is 65 Hz. The proposed SJA was tested by three experimental methods: phase-locked visualization of the nozzle lips, hot-wire anemometry, and momentum flux measurement using a precision scale. The results demonstrate advantages of the proposed SJA, namely, an increase in the momentum flux by 18% compared with that of a conventional SJA.

Flow and Heat (Mass) Transfer Characteristics in an Impingement/Effusion Cooling System With Crossflow

2003 ◽  
Vol 125 (1) ◽  
pp. 74-82 ◽  
Author(s):  
Dong Ho Rhee ◽  
Jong Hyun Choi ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Cooling System ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Jet Flows ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Transfer Characteristics

The present study is conducted to investigate flow and heat/mass transfer characteristics in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of two times of the hole diameter, and initial crossflow passes between the plates. Both the injection and effusion hole diameters are 10 mm, and the Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and six times of the hole diameter, respectively. To investigate the effect of crossflow, the flow rate of crossflow is changed from 0.5 to 2 times of that of the impinging jet, and the results of impingement/effusion cooling with crossflow are compared with those of the crossflow in the channel and of an array of impingement jets and the effusion cooling system. A naphthalene sublimation method is used to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The flow patterns are calculated numerically using a commercial package. With the initial crossflow, the flow and heat/mass transfer characteristics are changed significantly from the results without the crossflow. Jet flows ejected from the injection plate are deflected by the crossflow, so that the stagnation points of the impinging jets move downstream. The heat/mass transfer rates on the effusion (target) plate decrease as the velocity of crossflow increases, since the crossflow induces the locally low transfer regions formed at the mid-way between the effusion holes. However, the impingement/effusion cooling with crossflow presents higher heat/mass transfer rates than the array jet impingement cooling with the same initial crossflow.

Flow and Heat (Mass) Transfer Characteristics in an Impingement/Effusion Cooling System With Crossflow

2002 ◽  
Author(s):  
Dong Ho Rhee ◽  
Jong Hyun Choi ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Cooling System ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Jet Flows ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Transfer Characteristics

The present study is conducted to investigate flow and heat/mass transfer characteristics in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter, and initial crossflow passes between the plates. Both the injection and effusion hole diameters are 10 mm, and the Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effect of crossflow, the flow rate of crossflow is changed from 0.5 to 2 times of that of the impinging jet, and the results of impingement/effusion cooling with crossflow are compared with those of the crossflow in the channel and of an array of impingement jets and the effusion cooling system. A naphthalene sublimation method is used to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The flow patterns are calculated numerically using a commercial package. With the initial crossflow, the flow and heat/mass transfer characteristics are changed significantly from the results without the crossflow. Jet flows ejected from the injection plate are deflected by the crossflow, so that the stagnation points of the impinging jets move downstream. The heat/mass transfer rates on the effusion (target) plate decrease as the velocity of crossflow increases, since the crossflow induces the locally low transfer regions formed at the mid-way between the effusion holes. However, the impingement/effusion cooling with crossflow presents higher heat/mass transfer rates than the array jet impingement cooling with the same initial crossflow.

Heat Transfer Measurements for Array Jet Impingement With Castellated Wall

2021 ◽  
Author(s):  
Taehyun Kim ◽  
Eui Yeop Jung ◽  
Minho Bang ◽  
Changyong Lee ◽  
Hee Koo Moon ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Impinging Jets ◽  
Wall Jet ◽  
Impingement Cooling ◽  
Baseline Case ◽  
Rib Structure

Abstract Impingement cooling is one of the powerful cooling methods in high-temperature devices. For the gas turbine applications, impingement cooling is commonly applied in the transition piece of a combustor and in the leading edge, suction and pressure sides of a turbine blade/vane. In the suction side and pressure side, impingement cooling is applied as a form of an array jet. However, due to the small gap between the jet hole and target surface, the wall jet faces a crossflow inside of the gap. This crossflow has an adverse effect on the jets and deteriorates the heat/mass transfer performance. Therefore, several studies have been conducted to minimized the crossflow effect. The present study also investigated the effect of crossflow reduction in the gap by having a castellated hole plate. The heat/mass transfer was measured using the naphthalene sublimation method. Heat/mass transfer data are compared among three different cases. One is the baseline case which is simple array impinging jets. Others are the castellated cases with and without rib structures on the target wall. Jet-to-jet spacing (s/d) and jet-to-target spacing (z/d) are selected as geometrical variables. Also, the experiments were conducted for the Reynolds numbers (based on jet hole diameter) of 5,000, 15,000 and 30,000. The baseline case was named as B case, the castellated case without rib structure as C case and with rib structure as CR case. Both C and CR cases showed the crossflow reduction effect and resulted high and similar Nusselt number values.

Influence of Injection Type and Feed Arrangement on Flow and Heat Transfer in an Injection Slot

2001 ◽  
Vol 124 (1) ◽  
pp. 132-141 ◽  
Author(s):  
Hyung Hee Cho ◽  
Jin Ki Ham
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Cooling System ◽  
Transfer Coefficients ◽  
Counter Flow ◽  
Flow Paths ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Vertical Injection ◽  
Injection Type

An experimental investigation is conducted to improve a slot film cooling system used for the cooling of a gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal, inline, and counter-flow paths to the mainstream flow direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot wall with various injection types and coolant feeding directions. A numerical simulation is also conducted to help understand the flow patterns inside the slot for different injection types. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the injection hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The dimensionless temperature distributions at the slot exits differ little with blowing rates, injection types, and secondary flow conditions. In the results of heat/mass transfer measurements, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effects of jet impingement. The lateral distributions of heat/mass transfer coefficients with the inline and counter-flow paths are more uniform than the normal-flow path. The average heat/mass transfer coefficients with the injection holes are about two to five times higher than that of a smooth two-dimensional slot path.

Heat/Mass Transfer in a 4:1 AR Smooth and Ribbed Coolant Passage With Rotation in 90-Degree and 45-Degree Orientations

2004 ◽  
Author(s):  
S. Acharya ◽  
P. Agarwal ◽  
D. E. Nikitopoulos
Keyword(s):  
Mass Transfer ◽  
Test Section ◽  
Heat Mass Transfer ◽  
Rectangular Channel ◽  
Spanwise Direction ◽  
Degree Relative ◽  
Naphthalene Sublimation Technique ◽  
Rotation Numbers ◽  
Smooth Channel ◽  
Naphthalene Sublimation

The paper presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio rectangular channel with smooth or ribbed walls for Reynolds number in the range of 5,000 to 30,000, rotation numbers in the range of 0–0.12 and for two different orientations of the test-section (90-degree and 45-degree relative to the plane of rotation). Such passages are encountered close to the trailing sections of the turbine blade. Inline normal tips (e/Dh = 0.15625 and p/e = 11.2) are used and placed on the leading and the trailing sides. The experiments are conducted in a rotating two-pass coolant channel facility using the naphthalene sublimation technique. It is observed that for the 45-degree orientation of the test-section, all the walls show an increase in the heat transfer with rotation as opposed to the 90-degree orientation where the stabilized wall shows reduction and the destabilized wall shows enhancement. The spanwise mass transfer distributions in the smooth and the ribbed cases are also presented, and show significant variations in the spanwise direction for the smooth channel.

scholarly journals Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects

1998 ◽  
Author(s):  
K. Jung ◽  
D. K. Hennecke
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Long Distance ◽  
Naphthalene Sublimation Technique

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations. Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.

Effect of Plenum Crossflow on Heat (Mass) Transfer Near and Within the Entrance of Film Cooling Holes

1997 ◽  
Vol 119 (4) ◽  
pp. 761-769 ◽  
Author(s):  
R. J. Goldstein ◽  
H. H. Cho ◽  
M. Y. Jabbari
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
Duct Flow ◽  
Naphthalene Sublimation Technique ◽  
Film Cooling Holes

Convective heat/mass transfer near and within the entrance region of film cooling holes supplied with air from an internal duct (plenum) behind the cooling holes has been measured using a naphthalene sublimation technique. The experiments are conducted for duct Reynolds number, based on the duct inlet flow condition, of 1800 to 13,500, which results in a range of hole Reynolds numbers of 8000 to 30,000, close to actual engine operating conditions. The flow entering the hole can be considered a combination of flow along a 90 deg tube bend and a sudden contraction duct flow. The flow separates at the inner corner and a secondary flow is induced by the centrifugal force associated with the streamline curvature. The mass transfer coefficient for the duct wall (surface of film-cooled plate) with a cooling hole is three to five times higher than for a fully developed duct flow. With a smaller duct, the overall transfer coefficient on the hole entrance surface increases due to the higher duct Reynolds numbers, but the flow has less secondary flow effects within the smaller space. Generally, transfer coefficients on the hole entrance surface are largely unaffected by the duct end presence, but the transfer coefficient is larger downstream for a short distance from the center of the last hole to the duct end. In tests with multiple film cooling holes, the flow at the first hole is more of a curved duct flow (strong secondary flow) and the flow at the last hole is more of a sink-like flow. At the middle hole, the flow is a combination of both flows. The mass transfer rates on the inner hole surfaces are found to be the same for holes with corresponding positions relative to the duct end, although the total number of open holes is different.

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