scholarly journals Experimental Air Impingement Crossflow Comparison and Theoretical Application to Photovoltaic Efficiency Improvement

2020 ◽  
Vol 12 (14) ◽  
pp. 5577
Author(s):  
Pablo Martínez-Filgueira ◽  
Ekaitz Zulueta ◽  
Ander Sánchez-Chica ◽  
Gustavo García ◽  
Unai Fernandez-Gamiz ◽  
...  
Keyword(s):  
Jet Impingement ◽  
Photovoltaic Cell ◽  
High Heat ◽  
Experimental Comparison ◽  
Back Surface ◽  
Rate System ◽  
Air Jet ◽  
High Heat Transfer ◽  
Solar Energy Harvesting ◽  
Air Impingement

The photovoltaic cell temperature is a key factor in solar energy harvesting. Solar radiation raises temperature on the cell, lowering its peak efficiency. Air jet impingement is a high heat transfer rate system and has been previously used to cool the back surface of photovoltaic modules and cells. In this work, an experimental comparison of the cooling performance of two different air jet impingement crossflow schemes was performed. Crossflow is defined as the air mass interacting with a certain jet modifying its movement. This leads to a change in its heat exchange capabilities and is related with the inlet-outlet arrangement of the fluid. In this work, zero and minimum crossflow schemes were compared. The main contribution of this work considered the consumption of the flow supplying devices to determine the most suitable system. The best configuration increased the net power output of the cell by 6.60%. These results show that air impingement cooling can play a role in increasing photovoltaic profitability. In terms of uniformity, on small impingement plates with a low number of nozzles, the advantages expected from the zero crossflow configuration did not stand out.

Experimental Investigation of Heat Transfer Augmentation by Different Jet Impingement Hole Shapes Under Maximum Crossflow

2016 ◽  
Author(s):  
Prashant Singh ◽  
Bharath Viswanath Ravi ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
High Heat ◽  
Absolute Pressure ◽  
Target Plate ◽  
Heat Transfer Augmentation ◽  
Plate Spacing ◽  
High Heat Transfer ◽  
Heat Loads

To achieve higher overall efficiency in gas turbine engines, hot gas path components are subjected to high heat transfer loads due to higher turbine inlet temperatures. Jet impingement has been extensively used especially as an internal cooling technique in the leading edge and mid-chord region of first stage vanes, which are subjected to highest heat loads. With the advent of additive manufacturing methods such as Direct Metal Laser Sintering (DMLS), designers are not limited to designing round or race track holes for impingement. The present study is focused on exploring new jet hole shapes, in an arrangement, typical of mid-chord region in a double wall cooling configuration. Transient liquid crystal experiments are carried out to study heat transfer augmentation by jet impingement on smooth target where the spent air is allowed to exit in one direction, thus imposing maximum crossflow condition. The averaged Reynolds number (based on jet hydraulic diameter) is varied from 2500 to 10000. The jet plate has a square array of jets with 7 jets in one row (total number of jets = 49), featuring hole shapes — Racetrack and V, where the baseline case is the round hole. The non-dimensional streamwise (x/dj) and spanwise (y/dj) spacing is 6 and the normalized jet-to-target-plate spacing (z/dj) is 4 and the nozzle aspect ratio (L/dj) is also 4. The criteria for the hole shape design was to keep the effective area of different hole shapes to be the same, which resulted in slightly different hydraulic diameters. The jet-to-target plate spacing (z) has been adjusted accordingly so as to maintain a uniform z/dj of 4, across all three configurations studied. Heat transfer coefficients are measured using a transient Liquid Crystal technique employing a one-dimensional semi-infinite model. Flow experiments are carried out to measure static pressures in the plenum chamber, to calculate the discharge coefficient, for a range of plenum absolute pressure-to-ambient pressure ratios. Detailed normalized Nusselt number contours have been presented, to identify the regions of high heat transfer augmentation locally, so as to help the designers in the organization of jet hole shapes and their patterns in an airfoil depending upon the active heat loads.

An Experimental Setup for Multiple Air Jet Impingement Over a Surface

2018 ◽  
Author(s):  
Flávia V. Barbosa ◽  
João P. V. Silva ◽  
Pedro E. A. Ribeiro ◽  
Senhorinha F. C. F. Teixeira ◽  
Delfim F. Soares ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Thermal Design ◽  
Test Facility ◽  
Experimental Setup ◽  
Optimized Design ◽  
Transfer Coefficients ◽  
Reflow Soldering ◽  
Air Jet ◽  
High Heat Transfer

Air jet impingement technology receives considerable attention due to its high performance for heat transfer enhancement in thermal equipment, providing high heat transfer rates. Due to its inherent characteristics of high average heat transfer coefficients and uniformity of the heat transfer over the impinging surface, this technology is implemented in a variety of engineering applications and industrial processes, such as reflow soldering, drying of textile, cooling of turbojet engine blades and fusion reactors. Multiple jet impingement involves several variables such as: jets arrangement, jet diameter, nozzle-to-surface distance, nozzle shape, jet-to-jet spacing, jet velocity and Reynolds number, among others. However, the total control of all these parameters is still one of the remarkable issues of the thermal design of jet impingement systems. In some industries that have implemented this technology in their processes, such as reflow soldering, the range of values of these variables are established through empiricism and “trial and error” techniques. To improve the process and to reduce time and costs, it is fundamental to define accurately all the process parameters in order to obtain an optimized design with a high degree of control of the heat transfer over the target surface. To perform an accurate and complete study of the multiple jet impingement variables for a specific application, the development of both experimental and numerical studies is fundamental in order to obtain reliable results. In that sense, this work reports the project and construction of a purpose-built test facility which has been commissioned, using a PIV system. This experimental setup is based on the oven used in the reflow soldering process. The optimization of the multiple jets geometry which is integrated in the experimental setup is herein described and discussed both experimentally and numerically. The numerical simulation of the jet impingement inside the oven was conducted using the ANSYS software, specially designed to predict the fluid behavior. Regarding the relevance of the multiple jet impingement, this work intends to improve the knowledge in this field and to give reliable and scientifically proved answers to the industries that apply this technology in their processes.

scholarly journals Air jet impingement to reduce hot strip wave on a run-out table

2018 ◽  
Vol 19 (6) ◽  
pp. 601 ◽  
Author(s):  
Young Yun Woo ◽  
Sang Wook Han ◽  
Jin Rae Cho ◽  
Young Hoon Moon
Keyword(s):  
Jet Impingement ◽  
Pilot Scale ◽  
Process Efficiency ◽  
Rolled Strip ◽  
Pressure Distributions ◽  
Air Jet ◽  
Hot Strip ◽  
Air Impingement ◽  
Moving Strip ◽  
Moving Direction

Traveling stability is necessary for a hot rolled strip on a run-out table before coiling in steel mills because it affects the process efficiency and the quality of the rolled products. This study proposes an air jet impingement system to reduce the hot strip wave that occurs during tensionless travel in a run-out table before the top end of the strip reaches the coiler mandrel. The finite element method was used to examine the pressure distributions on the moving strip associated with the parameters in the air jet systems. Experiments were carried out on a pilot-scale air jet impingement system to investigate the performance. The results show that the air impingement in the moving direction effectively reduces the strip wave, and the simulated results agree with the actual measurements and observations.

Effect of Acoustic Excitation on the Heat Transfer to an Impinging Air Jet

2007 ◽  
Author(s):  
Tadhg S. O’Donovan ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Excitation Frequency ◽  
High Heat ◽  
Cooling Capacity ◽  
Mean Flow ◽  
Transfer Coefficients ◽  
Air Jets ◽  
Air Jet ◽  
High Heat Transfer ◽  
Impingement Surface

Impinging air jets are known as a method of achieving particularly high heat transfer coefficients and are employed in many applications including the cooling of electronics, manufacturing processes such as grinding, etc. The current investigation is concerned with acoustically exciting an impinging air jet to enhance its overall cooling capacity. Distributions of the heat transfer to an axially impinging air jet for a range of Reynolds numbers (Re) from 10000 to 30000, non-dimensional nozzle to impingement surface heights (H/D) from 0.5 to 2 and excitation frequencies (f) that range from 0.5 to 1 times the natural frequency of the jet are presented. For this low range of nozzle to impingement surface spacings it has been shown that the heat transfer distribution exhibits a peak at the stagnation point and secondary peaks at a radial location that is both excitation frequency and Reynolds number dependent. Distributions of the fluctuating component of the heat transfer coefficient are also presented for the range of parameters tested. These have been used, along with spectral analysis of the heat flux signal, to discern whether local variations in heat transfer are due to changes in the local vortex flow or to changes in the mean flow structure of the impinging jet.

Numerical Simulation of the Flow Field of a Confined, Submerged Slot Jet Impinging on an Oscillating Surface: A Parametric Study

2016 ◽  
Author(s):  
Srivathsan Ragunathan
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Heated Surface ◽  
Jet Impingement ◽  
High Heat ◽  
High Heat Flux ◽  
Lower Wall ◽  
Local Skin ◽  
Submerged Jet ◽  
High Heat Transfer

Impinging jets are an attractive option for spot-cooling of high heat flux devices because of the stagnation region surrounding the point of impingement and the resulting high heat transfer. In small devices with a small jet (microjet) , however, the cooled region due to just a single jet is small. One way to potentially increase this area exposed to the impinging jet is by oscillating the heated surface. In the current paper, the flow structure and transport in a confined and submerged jet impingement arrangement impinging on a wall oscillating horizontally is numerically studied with respect to both parameters governing jet impingement :Jet Reynolds Number (from 40 to 200), distance from the jet inlet to the impinging wall (z/d ratios of 2 and 5) and an oscillation parameter (oscillatory peak Reynolds Numbers of 55 and 110). OpenFOAM v 2.2.2, an open-source CFD code based on the finite volume method is used to solve the problem. The Grid Convergence Index (GCI) is used to estimate discretization uncertainty and error bars on all of the parameters calculated. The flow structure in a confined submerged jet is made up of a double recirculation zone (mostly attributed to the confining top wall) the reattachment regions are associated with a secondary peak in the Nusselt Number. Heat transfer is not studied in this paper. The effect of the oscillating lower wall on the locations of the primary and the secondary recirculation zones are studied with respect to all the parameters mentioned above over a complete oscillation cycle. The local skin friction coefficients along different sections on the lower wall are computed along sections of the oscillating wall and compared to the case where there is no oscillation.The results are anticipated to have significant impact on the heat transfer enhancement possible in such an arrangement.

Heat Transfer Investigations in Multiple Impinging Jets at Low Reynolds Number

2010 ◽  
Author(s):  
Arvind G. Rao ◽  
Myra Kitron-Belinkov ◽  
Vladimir Krapp ◽  
Yeshayahou Levy
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbine Blades ◽  
Jet Impingement ◽  
High Heat ◽  
Geometrical Parameters ◽  
Transitional Region ◽  
High Heat Transfer ◽  
Low Reynolds

Jet impingement is a well established cooling methodology used for cooling turbine blades in gas turbine engines. Jet impingement results in high heat transfer coefficients as compared to other conventional modes of single phase heat transfer. Most of the research in jet impingement has been confined to high Reynolds number regime. In order to increase the applicability of this technique to non conventional applications like in a low pressure micro turbine combustors or turbine blades, the behavior of such systems in the low Reynolds number regime should be understood. The present paper is a continuation of earlier investigations on the heat transfer behavior of a large jet impingement array in the low Reynolds number regime, especially in the laminar and transitional region. More experiments have been conducted with different geometrical parameters of the array to analyze the effect of these parameters on the average heat transfer coefficient. Numerical simulations with existing CFD tools were carried out in order to understand the fluid mechanics inside such a complex system. The CFD model was validated with the experiments. Different turbulence models were used and it was found that the SST-k-ω model was the best for modeling jet impingement phenomena. It is anticipated that the results obtained from the present exercise will give better insights in optimizing the design of multiple jet impingement cooling systems for high heat density applications.

Novel PCM and Jet Impingement Based Cooling Scheme for High Density Transient Heat Loads

2010 ◽  
Author(s):  
Pritish R. Parida ◽  
Srinath V. Ekkad ◽  
Khai Ngo
Keyword(s):  
Phase Change Materials ◽  
High Efficiency ◽  
Cooling System ◽  
Jet Impingement ◽  
High Heat ◽  
High Heat Flux ◽  
Impingement Cooling ◽  
Small Areas ◽  
High Heat Transfer ◽  
Heat Loads

Breakthroughs in the recent cutting-edge technologies have become increasingly dependent on the ability to safely dissipate large amount of heat from small areas. Improvements in cooling techniques are therefore required to avoid unacceptable temperature rise and at the same time maintain high efficiency. Jet impingement is one such cooling scheme which has been widely used to dissipate transient and steady concentrated heat loads. With constantly increasing transient cooling needs, conventional pin-fin cooling and conventional jet impingement cooling are not meeting the requirements. Considerable improvements are therefore required to meet such stringent requirements without any significant changes in the cooling system. A combined cooling scheme based on jet impingement and phase change materials (PCMs) is presented as one such alternative to existing cooling systems. A high heat storage capability of PCMs in combination with a high heat transfer rates from impingement cooling can help overcome the existing heat distribution and transient cooling problems in high heat flux dissipating devices. Preliminary conjugate CFD simulations show promising results. Additionally, experimental validation of the simulation predictions has also been performed. A reasonably good agreement was found between the predictions and experiments.

Heat Transfer in a Confined Oblique Jet Impingement Configuration

2009 ◽  
Author(s):  
Florian Hoefler ◽  
Simon Schueren ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Impingement Cooling ◽  
Turbine Blade Cooling ◽  
Flow Recirculation ◽  
Nusselt Numbers ◽  
High Heat Transfer

Impingement cooling is widely used in cooling configurations for gas turbine components. Relatively high local heat transfer rates and the possibility of jet adjustment to specific geometries are advantageous for internal turbine blade cooling designs. In this paper a confined impingement cooling configuration is investigated. The assembly consists of four non-perpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The flow extraction is realized through two staggered rows of holes opposing the impingement holes wall. Heat transfer experiments were carried out using a transient liquid crystal technique for a series of jet Reynolds numbers between 10,000 and 75,000. The obtained local heat transfer data was evaluated regarding spatially resolved Nusselt numbers as well as line and area averaged values. The results include measurements of the discharge coefficients for the flow through the impingement holes. Numerical simulations of the flow field were carried out, complementary to the experiments. The simulations yield information for a better understanding of the main flow structures. The jets cause high heat transfer in the flow impinging regions with Nusselt numbers up to 180 for Re = 45,000. By contrast, for the same Reynolds number the Nusselt number drops below 20 in flow recirculation regions. For area-averaged Nusselt numbers, the correlation Nu ∝ Rex was found to be valid with slightly modified exponents for each passage wall.

Measurement Errors and Uncertainty Quantification of a 2D-PIV Experimental Setup for Jet Flow Characterization

2020 ◽  
Author(s):  
Flavia Barbosa ◽  
Carlos Costa ◽  
Senhorinha Teixeira ◽  
Jose Carlos Teixeira
Keyword(s):  
Heat Transfer ◽  
Uncertainty Quantification ◽  
Measurement Errors ◽  
Jet Impingement ◽  
Velocity Fields ◽  
Mean Velocity ◽  
Air Jets ◽  
Air Jet ◽  
High Heat Transfer ◽  
Wide Range

Abstract The study of the flow interaction and the heat transfer between air jets and a surface is of paramount importance in industrial processes that apply air jet impingement. To ensure a good performance of the process, high heat transfer rates and uniformization of the flow over the target plate are required. To perform this analysis, a PIV technique was implemented for the measurement of the flow velocity fields. However, as any real experiment, the values recorded by the PIV method are subjected to several errors that compromise the reliability and accuracy of the measurements. These errors can have different sources, from the installation and alignment to the particles seeding and calibration procedure. To maximize the accuracy of the experimental results, this paper focus on the identification of measurement errors and uncertainty quantification of an experimental set up specially built for the analysis of the interaction between air jets and a target surface. This work presents an analysis of the system, and the source of errors are identified, quantified and, when possible, corrected. The particle seeding is characterized and its efficiency for the flow tracking is analyzed. The setup was tested to fully characterize the flow field in terms of mean velocity profile and turbulence intensity over a wide range of Reynolds numbers and temperature. Several velocity fields are then measured until convergence of the flow quantities is reached. The combination of these measurements with high spatial resolution and low measurement errors allow to obtain accurate and precise measurements.

scholarly journals ANN-Based Stop Criteria for a Genetic Algorithm Applied to Air Impingement Design

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 16
Author(s):  
Ander Sánchez-Chica ◽  
Ekaitz Zulueta ◽  
Daniel Teso-Fz-Betoño ◽  
Pablo Martínez-Filgueira ◽  
Unai Fernandez-Gamiz
Keyword(s):  
Genetic Algorithm ◽  
Jet Impingement ◽  
Optimization Process ◽  
Second Step ◽  
Flower Pollination Algorithm ◽  
Training Process ◽  
Air Jet ◽  
Stop Criterion ◽  
Air Impingement ◽  
The Cost

Artificial Neural Networks (ANNs) have proven to be a powerful tool in many fields of knowledge. At the same time, evolutionary algorithms show a very efficient technique in optimization tasks. Historically, ANNs are used in the training process of supervising networks by decreasing the error between the output and the target. However, we propose another approach in order to improve these two techniques together. The ANN is trained with the points obtained during an optimization process by a genetic algorithm and a flower pollination algorithm. The performance of this ANN is used as a stop criterion for the optimization process. This new configuration aims to reduce the number of iterations executed by the genetic optimizer when learning the cost function by an ANN. As a first step, this approach is tested with eight benchmark functions. As a second step, the authors apply it to an air jet impingement design process, optimizing the surface temperature and the fan efficiency. Finally, a comparison between the results of a regular optimization and the results obtained in the present study is presented.

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