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1
Content available Assessment of the impact of jet impingement technique on the energy efficiency of air-cooled BIPV/T roof tile
Wajs Jan, Łukasik Jakub
Archives of Thermodynamics
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2024
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Vol. 45, no 2
5--18
EN
The paper concerns a numerical analysis of cooling of the hybrid photovoltaic (PV) modules dedicated to Building-Integrated Photovoltaic/Thermal (BIPV/T) systems. Attention was focused on the photovoltaic roof tiles, using a jet impingement technique, in which the intensification of heat transfer is ensured by streams of air hitting the heat exchange partition. A series of numerical simulations were carried out to assess an influence of the distance of the nozzle outlet from the absorber surface on the values of selected thermal-hydraulic performance indicators and the electrical parameters of the roof tile. The results confirmed the high effectiveness of the proposed method. The best effect was obtained for the case in which the relative distance of the nozzle from the partition to the nozzle diameter was equal to 1. For the mentioned configuration, an over 4 times increase in the value of the heat transfer coefficient was obtained in relation to the reference variant of cooling roof tiles. At the same time, the relative increase in the value of the generated electrical power was from 2.9 to 7.8%, depending on the value of the Reynolds number characterising the flow.
2
Content available Development and testing of data reduction software for measurements using pressure sensitive paints
Deitrick W. J., Stryczniewicz W.
Transactions on Aerospace Research
|
2018
|
Nr 4 (253)
83--97
EN
The paper concentrates on post-processing of data necessary for pressure measurements using Pressure Sensitive Paints (PSP). The purpose of the study was to develop and test procedures for extraction of the surface pressure distribution from the images captured during PSP tests. The core issues addressed were reduction of the influence of model movement and deformation during wind tunnel run and synchronization between conventional pressure tap measurements and PSP data, necessary for in-situ calibration. In the course of the studies, two approaches on image registration were proposed: the first based on geometric transformation of control points pairs with cross-correlation tuning and the second based on similarity finding and estimation of geometric transformation of the images. Performance of the developed algorithm was tested with use of experimental setup allowing for controlled movement of the imagined target with micrometer resolution. Both of the proposed approaches to PSP image resection proved to perform well. After testing of the software, the PSP system was used for determination of the pressure field on flat plate exposed to impinging jet. The presented procedures and results can be useful for research groups developing in-house PSP measurements systems for wind tunnel tests and internal flow investigations.
PL
W artykule przedstawiono procedury konieczne i wystarczające do przeprowadzenia pomiarów techniką farb czułych na ciśnienie. Celem pracy było opracowanie oraz sprawdzenie procedur wyznaczenia rozkładu ciśnienia na powierzchni ze zdjęć pomiarowych farb czułych na ciśnienie. Głównymi podjętymi tematami była redukcja wpływu przemieszczenia i deformacji modelu podczas dmuchu w tunelu aerodynamicznym oraz synchronizacja pomiędzy pomiarem ciśnienia a rejestracją zdjęć. W pracy zaproponowano dwie metody uzgodnienia pozycji modelu pomiędzy zdjęciami: pierwsza metoda oparta na transformacji geometrycznej punków kontrolnych z dodatkowym uzgodnieniem wykorzystującym korelację obrazów znaczników oraz drugą metodę opartą na odnajdywaniu podobnych cech obrazów i estymacji przekształcenia geometrycznego obrazów. Skuteczność algorytmów została sprawdzona przy wykorzystaniu stanowiska pomiarowego umożliwiającego wykonanie zdjęć obiektu testowego przesuwanego z rozdzielczością poniżej jednego mikrometra. Testy zaproponowanych rozwiązań potwierdziły ich skuteczność. Kolejnym krokiem, po testach opracowanego oprogramowania, było wyznaczenie rozkładu ciśnienia na płaskiej płycie poddanej strumieniowi sprężonego powietrza. Przedstawione procedury oraz wyniki mogą być użyteczne dla grup badawczych wdrażających technikę farb czułych na ciśnienie do pomiarów w tunelach aerodynamicznych oraz badań przepływów wewnętrznych.
3
Content available Numerical investigation of local heat transfer distribution on surfaces with a non-uniform temperature under an array of impinging jets with various nozzle shapes
Marzec K., Kucaba-Piętal A.
Journal of Theoretical and Applied Mechanics
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2017
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Vol. 55 nr 4
1313--1324
EN
Numerical calculations of heat transfer characteristics of an impingement cooling system with a non-uniform temperature on a cooled surface using ANSYS CFX have been performed. The influence of a surface heat flux qw(x) and a nozzle shape on the Nusselt number distribution on the cooled surface has been studied. The setup consisted of a cylindrical plenum with an inline array of ten impingement jets. Cylindrical, convergent divergent shapes of nozzles and linear temperature distribution on the cooled surface have been considered for various heat fluxes qw (x). Results indicate that geometry of the cylindrical nozzles resulted in the highest Nusselt numbers along the cooled surface. The line of the averaged Nusselt number has a trend to increase in the direction of the flow for the cooling system with increasing values of the surface heat flux q(x). This tendency can be observed for all presented shapes of jets. On the other hand, for decreasing functions of the heat flux qw (x), the Nusselt number distribution is more uniform. It can be observed for all types of nozzles. Very similar values of the Nusselt number occur especially for the non-uniform heat flux 5000-2500W/m². For constant values of the heat flux q(x) = 5000W/m², the line of the average Nusselt number has a trend to increase slightly in the direction of the flow. Numerical analysis of different mesh density results in good convergence of the GCI index, what excludes mesh size dependency. The presented study is an extension of the paper (Marzec and Kucaba-Piętal, 2016) and aims at answering the question how the Nusselt number distribution on the cooled surface is affected by various geometries of nozzles for a non-uniform surface heat flux qw (x).
4
Content available remote Pneumatic actuators with "bouncing" air-jet - part 2: Flow field in the cascade
Tesar V., Peszyński K.
International Journal of Applied Mechanics and Engineering
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2010
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Vol. 15, no 3
867-874
EN
Unusual actuators generating a fluid force action on a small body by issuing an air jet "reflecting" or "bounding back" from an impact on a wall were described in previous publication (Tesar and Peszynski, 2010). The seemingly impossible return from the wall is based on the unusual effect of the wall provided with perforations that allow a part of the jet to pass through. Upon the impingement, the jet is split in two parts, both having to change their directions. It is the part that remains above the wall, the "reflected" jet, that is of interest for the actuation. In particular, the phenomenon was used in shuttle-less loom to prevent the inserted weft from contact with the reed. The details of the flowfield inside the reed - or cascade of foils with passages between them play a critical role in the phenomenon. This was investigated by flow visualisation discussed in the second part of the paper.
5
Content available remote Pneumatic actuators with "bouncing" air-jet - part 1: Numerical solutions
Tesar V., Peszyński K.
International Journal of Applied Mechanics and Engineering
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2010
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Vol. 15, no 3
855-865
EN
An actuator generating a force action on a small body by an issuing air jet is based on the unusual, little known and seemingly impossible mechanism of the jet "reflecting" or "bouncing back" from an impact on a solid wall. Under usual conditions the bouncing back from the wall is not possible - the trick is the wall is provided with perforations that allow a part of the jet to pass through. On doing so it has to change its direction and this has to be compensated by the remaining part changing its direction too, into the opposite side as seen from the jet axis. This part forms the "reflected" jet. The phenomenon is investigated by flow visualisation and detailed flowfield computations presented in this paper - the first part of which discusses the computed results.
6
Content available remote The analysis of turbulent flow structure in a free jet
Bartoszewicz J.
International Journal of Applied Mechanics and Engineering
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2009
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Vol. 14, no 4
917-928
EN
The paper presents the results of numerical calculations and experimental investigations of free jets under variable turbulence in the jet outlet. The research concerns two cases: the issue of an unstimulated axisymmetric jet to stationary surroundings and the impinge of an unstimulated jet on a flat fixed surface. The results of the numerical calculations have been presented in graphs showing the impact of the changes in the initial turbulence on the structure of the turbulence in the jet. A comparison of the numerical calculations with own results of the experimental investigations has been made for selected cases.
7
Content available remote Effectivity of two-equation turbulence model in impinging jet in short nozzle to surface distance
Bartoszewicz J., Bogusławski L.
International Journal of Applied Mechanics and Engineering
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2009
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Vol. 14, no 2
337-347
EN
Results of numerical analysis of a turbulent flow in an impinging air jet have been presented. Numerical simulations of a turbulent flow will be compared with measurements data. Results of calculations for different turbulence models have been analyzed. The Phoenics program developed by CHAM Ltd. will be used for numerical calculation. Five different two-equation models of turbulence will be tested in a selected configuration. The impinging jet turbulent flow was measured in an open wind tunnel using constant temperature anemometer.
8
Content available Turbulent heat transfer in thin liquid films at low and high heat fluxes
Mikielewicz D., Mikielewicz J.
Journal of Theoretical and Applied Mechanics
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2007
|
Vol. 45 nr 3
603-619
EN
In the paper presented are considerations of turbulent heat transfer in thin liquid films at low and high heat fluxes. Postulated have been simple models of heat transfer for laminar and turbulent liquid films formed by impinging jets and exposed to nucleate boiling, namely under high heat fluxes, as well as without nucleate boiling, at low heat fluxes, as a simplified case. Turbulence in such case is strongly modified and difficult to be modelled. Turbulence model due to Prandtl has been applied where, in the case of high heat fluxes, the mixing length is strongly modified. In the case of high heat fluxes, incorporated into the model is a blowing velocity, which models the transverse transport of momentum caused by departing bubbles. Calculated have been the velocity and temperature distributions in the liquid film, which enabled determination of the corresponding heat transfer coefficient and the Nusselt number.
PL
W pracy przedstawiono rozwiązanie turbulentnej wymiany ciepła w cienkich filmach cieczowych przy małych i dużych strumieniach ciepła. Zaproponowano proste modele wymiany ciepła dla przypadków laminarnego i turbulentnego filmu cieczowego wytworzonego uderzającą strugą w warunkach dużych i małych strumieni cieplnych. W takich przypadkach turbulencja jest silnie modyfikowana i z tego względu trudna do modelowania. W pracy zastosowano model drogi mieszania Prandtla i w przypadku dużych strumieni cieplnych droga mieszania jest szczególnie mocno zmodyfikowana. W przypadku dużych strumieni ciepła wprowadzono do modelu tzw. prędkość wzdmuchu, która modeluje wymianę pędu w kierunku poprzecznym do przepływu wywołaną odrywającymi się od ścianki pęcherzykami. Wyznaczono rozkłady prędkości i temperatury w filmie cieczowym, które umożliwiły wyliczenie współczynnika przejmowania ciepła i liczby Nusselta.
9
Content available Experimental investigations of jet flows
Fornalik E., Szmyd J. S.
Journal of Theoretical and Applied Mechanics
|
2007
|
Vol. 45 nr 3
569-586
EN
The paper describes two kinds of jet flows: the confined and impinging jet flow. A triaxial thermoanemometer probe with a temperature sensor was used to study the confined jet flow. The time-average analysis of data resulted in a turbulence characteristic. It allowed the estimation of the budget of tur bule nt heat flux. The impinging jet flow was investigated by the Particle Image Velocimetry (PIV) method together with heat transfer analysis done with a liquid erystal film.
PL
Zaprezentowane zostały badania eksperymentalne dotyczące dwóch rodzajów przepływów strumieniowych: strugi pierścieniowej oraz strugi uderzającej. Czterowłóknowa sonda termoanemometryczna wykorzystana została w badaniach związanych ze strugą pierścieniową. Analiza danych pozwoliła na wyznaczenie wielkości charakteryzujących przepływ turbulentny, ze szczególnym uwzględnieniem bilansu turbulentnego strumienia ciepła. W badaniach strugi uderzającej pod działaniem przepływu krzyżowego do wyznaczenia pola prędkości wykorzystano metodę PIV (ang. Particle Image Velocimetry). Badaniom przepływu towarzyszyła analiza wymiany ciepła przy użyciu termoczułych ciekłych kryształów w postaci cienkiego filmu. Zaobserwowane zostały wiry, które w głównej mierze odpowiadały za intensyfikację wymiany ciepła, co zostało potwierdzone wyznaczonymi polami prędkości.
10
Content available remote Phenomenon of hydraulic jump formed on liquid layer by single-phase impinging liquid jet
Gumkowski S.
Transactions of the Institute of Fluid-Flow Machinery
|
2005
|
nr 117
81-90
EN
In the paper theoretical analysis of the phenomenon of impingement of a circular liquid jet upon a plate has been carried out. In the considered case, spreading of the liquid on a plate is caused by the inertia and gravity forces. For supercritical liquid flow, in certain conditions a hydraulic jump is formed. The circular hydraulic jump exhibits behaviour quite different from that commonly observed in planar jets. In the paper a new theoretical model of the phenomena of hydraulic jump has been formulated. Theoretical treatment have been compared with own and other available experimental data.
11
Usuwanie cząstek PM 2,5 z gazów w odpylaczach zderzeniowych
Warych J.
Inżynieria i Aparatura Chemiczna
|
2005
|
Nr 4
37--38
PL
Omówiono zasady działania i konstrukcję odpylaczy zderzeniowych w aspekcie ich przydatności do usuwania z gazów cząstek aerozolowych mniejszych od 2,5 urn stanowiących istotny problem toksykologiczny i procesowy. Wydzielanie cząstek PM 2,5 ze sprawnością większą niż 50%, a także zanieczyszczeń gazowych kwaśnych i alkalicznych z wysoką sprawnością rzędu 99, .. % w prezentowanych skruberach jest możliwe.
EN
Discussion on PM 2.5 particulates removal in the space of impinging jets collector has been presented. Separation efficiency of particulates over 50% was achieved in some configurations. The removal of another contaminants such as acid or alkali gases can be also processed with high efficiency.
12
Content available remote Distribution of heat generated by a local heat source
Gumkowski S., Gościk J.
Archives of Thermodynamics
|
2005
|
Vol. 26, no. 4
69-86
EN
In the paper, results of analytical investigations concerning distribution of heat generated by local heat source placed in a solid plate, have been presented. The analysis yields the conclusion that in the considered case, the distribution of heat depends mainly on the heat transfer coefficient between the surface and liquid layer flowing at that surface. As a result the qualitative formula was obtained, which can be helpful for accurate determination of heat transfer coefficient without commonly applied assumption about negligible conductive heat losses in the plate.
13
Modelowanie turbulencji w osiowosymetrycznej strudze uderzającej
Bartoszewicz J., Bogusławski L.
Zeszyty Naukowe Politechniki Poznańskiej. Maszyny Robocze i Transport
|
2004
|
Nr 57
65-70
PL
W artykule przedstawiono wyniki obliczeń numerycznych i porównano je z danymi eksperymentalnymi dotyczącymi analizy napływu niezawirowanej i niestymulowanej strugi osiowosymetrycznej na powierzchnię płyty usytuowanej w takiej odległości wylotu emitera, przy jakiej zanika rdzeń potencjalny strugi kołowej. Obliczenia numeryczne wykonano z użyciem pakietu Phoenics 3.1, umożliwiającego rozwiązanie układu równań transportu masy, pędu i energii na podstawie hipotezy Reynoldsa z wykorzystaniem modelu turbulencji Wilcoxa. Badania eksperymentalne prowadzono w otwartym tunelu aerodynamicznym z użyciem technik termoanemometrycznych.
EN
In the paper results of numerical analysis of turbulent flow in impinging jet are presented. Numerical simulation of turbulent flow compare with measurements and literature data. Calculations were conduced mode for different velocity at nozzle outlet. Obtained results indicat, that profiles of average velocities in impinging jet are in good agreement with measurements. Nevertheless, direct comparison of kinetic energy plots of turbulent fluctuations of velocity with experimental data shows rather essential differences. The flow and turbulent fluctuations of velocity were measured by use a constant temperature anemometer. For numerical simulation of turbulent flow the Phoenics code was used.
14
Content available remote Experimental investigations of hydraulic jump created by a two-phase impinging jet an a solid surface
Gumkowski S.
Transactions of the Institute of Fluid-Flow Machinery
|
2003
|
nr 112
119-124
EN
In the paper the results of experimental investigations concerning the hydraulic jump formed by an aerosol impinging jet have been presented. Results of carried out experiments yield that aerosol impinging jet enables to form significantly higher diameter of the hydraulic jump, as compared with single phase, liquid impinging jet. This is caused by shear stresses, between liquid layer, formed by liquid deposited from aerosol, and gas, which is the second component of aerosol.
15
Content available remote Liquid and liquid-gas cooling of machine elements
Mikielewicz J.
Transactions of the Institute of Fluid-Flow Machinery
|
2002
|
nr 110
21-45
EN
In the work presented are thermal and hydraulic problems concerned with the liquid films formed by impinging jets. Formulated has been a simple two-dimensional model of the flow and heat transfer in the film. The model is based on simplified equations of mass, momentum and energy balance. Solution of such set of equations enables determination of velocity profile in the film as well as local heat transfer coefficients.
16
Content available remote Visualization of heat transfer enhancement regions modified by the interaction of inclined impinging jets into crossflow
Fornalik E.
Machine Graphics and Vision
|
1999
|
Vol. 8, No. 4
597-609
EN
Visualization of heat transfer enhancement regions was made for a pair of jets obliquely discharged into a crossflow. The examination of interaction between the two oblique jets and the comparision of different flow patterns caused by the vertically and obliquely issued jets were provided. The temperatures of the target surface were visualized with thermochromic liquid crystal sheets. The colours of the liquid crystal image taken by a CCD camera were transformed accurately and effectively into the temperatures by meas of the neural network technique to obtain Nusselt number distributions on the target surface. Fluorescent dyes were added to the jet fluid to visualize the cross--sectional flow patterns with the light sheet of a laser. The moist important parameter used in the present study was the velocity ratio V R of the jet to the crossflow besides the crossflow Reynolds number.
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