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    Wyświetlanie 1-18 z 18
    Tytuł:
    Application of computer image analyzes in the investigation of refrigerants condensation in minichannels
    Autorzy:
    Sikora, Małgorzata
    Bohdal, Tadeusz
    Powiązania:
    https://bibliotekanauki.pl/articles/240468.pdf
    Data publikacji:
    2019
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    condensation
    flow structures
    image analyze
    minichannels
    kondensacja
    struktury przepływu
    analiza obrazu
    minikanały
    Opis:
    The image analysis consists in extracting from the information which is available to the observer of the part that is important from the perspective of the investigated process. This process usually accompanies a considerable reduction in the amount of information from the image. In the field of two-phase flows, computer image analysis can be used to determine flow and geometric parameters of flow patterns. This article presents the possibilities of using this method to determine the void fraction, vapor quality, bubble velocity and the geometric dimensions of flow patterns. The use of computer image analysis methods is illustrated by the example of HFE 7100 refrigerant methoxynonafluorobutane condensation in a glass tubular minichannel. The high speed video camera was used for the study, and the films and individual frames received during the study were analyzed.
    Źródło:
    Archives of Thermodynamics; 2019, 40, 1; 103-114
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    An investigation of the thermal characteristics of the refrigerants zeotropic mixtures condensation in minichannels
    Autorzy:
    Bohdal, T.
    Sikora, M.
    Widomska, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/175244.pdf
    Data publikacji:
    2015
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    condensation
    heat transfer coefficient
    mass flux density
    minichannels
    vapor quality
    zeotropic mixture
    Opis:
    This paper describes the results of experimental investigations of heat transfer during the condensation of the homogenous R134a refrigerant and zeotropic mixtures R404A, R407C and R410A in pipe minichannels with internal diameters 0.31–3.30 mm. The values of the local and average heat transfer coefficient throughout the range of changes in the vapor quality 1–0 were determined. Based on the obtained results, the effect of vapor quality, mass flux density and channel diameter changes on heat transfer coefficient was illustrated. a pronounced effect of the refrigerant properties at the heat exchange efficiency during the condensation process in pipe minichannels was indicated. The results were compared with calculations according to the correlations proposed by other authors. On the basis of the experimental investigations, the authors proposed their own correlation for the calculation of local heat transfer coefficient, obtaining the results of compatibility tests in the range of ±20%.
    Źródło:
    Transactions of the Institute of Fluid-Flow Machinery; 2015, 128; 43-57
    0079-3205
    Pojawia się w:
    Transactions of the Institute of Fluid-Flow Machinery
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels
    Autorzy:
    Mikielewicz, D.
    Andrzejczyk, R.
    Jakubowska, B.
    Mikielewicz, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/240815.pdf
    Data publikacji:
    2014
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    two-phase pressure drops
    heat transfer coefficient
    boiling
    condensation
    dwufazowy spadek ciśnienia
    współczynnik przenikania ciepła
    wrzenie
    kondensacja
    Opis:
    In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced.
    Źródło:
    Archives of Thermodynamics; 2014, 35, 3; 17-37
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modeling of pressure drop during refrigerant condensation in pipe minichannels
    Autorzy:
    Sikora, M.
    Bohdal, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/240860.pdf
    Data publikacji:
    2017
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    minichannels
    pressure drop
    refrigerant
    condensation
    minikanał
    spadek ciśnienia
    chłodziwo
    kondensacja
    Opis:
    Investigations of refrigerant condensation in pipe minichannels are very challenging and complicated issue. Due to the multitude of influences very important is mathematical and computer modeling. Its allows for performing calculations for many different refrigerants under different flow conditions. A large number of experimental results published in the literature allows for experimental verification of correctness of the models. In this work is presented a mathematical model for calculation of flow resistance during condensation of refrigerants in the pipe minichannel. The model was developed in environment based on conservation equations. The results of calculations were verified by authors own experimental investigations results.
    Źródło:
    Archives of Thermodynamics; 2017, 38, 4; 15--28
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Heat transfer during condensation of refrigerants in tubular minichannels
    Autorzy:
    Bohdal, T.
    Charun, H.
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/239949.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    chłodzenie
    kompaktowy kondensator
    kondensacja w minikanałach
    wymiana ciepła
    compact condenser
    condensation in minichannels
    heat transfer
    refrigeration
    Opis:
    Abstract The present paper describes the results of experimental investigations of heat transfer during condensation of R134a, R404A and R407C in pipe minichannels with internal diameters 0.31-3.30 mm. The results concern investigations of the local heat transfer coefficient. The results were compared with the correlations proposed by other authors. Within the range of examined parameters of the condensation process in minichannels made of stainless steel, it was established that the values of the heat transfer coefficient may be described with Akers et al., Mikielewicz and Shah correlations within a limited range of the mass flux density of the refrigerant and the minichannel diameter. On the basis of experimental investigations, the authors proposed their own correlation for the calculation of local heat transfer coefficient.
    Źródło:
    Archives of Thermodynamics; 2012, 33, 2; 3-22
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pressure drop during condensation of refrigerants in pipe minichannels
    Autorzy:
    Bohdal, T.
    Charun, H.
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/240165.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    kompaktowy kondensator
    przepływ
    skraplanie
    skraplaniea w minikanałach
    spadek ciśnienia
    compact condenser
    condensation in minichannels
    pressure drop during flow in condensation
    Opis:
    The present paper describes results of experimental investigations of pressure drop during the condensation of R134a, R404a and R407C refrigerants in pipe minichannels with internal diameter 0.31-3.30 mm. The results concern investigations of the mean and local pressure drop in single minichannels. The results of experimental investigations were compared with the calculations according to the correlations proposed by other authors. A pressure drop during the condensation of refrigerants is described in a satisfactory manner with Friedel and Garimella correlations. On the basis of the experimental investigations, the authors proposed their own correlation for calculation of local pressure drop during condensation in single minichannels.
    Źródło:
    Archives of Thermodynamics; 2012, 33, 1; 87-106
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pomiary oporów przepływu podczas skraplania w minikanałach rurowych
    Measures of pressure drops during condensation in tulbar minichannels
    Autorzy:
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/153482.pdf
    Data publikacji:
    2012
    Wydawca:
    Stowarzyszenie Inżynierów i Techników Mechaników Polskich
    Tematy:
    skraplanie
    opory przepływu
    pomiary
    minikanały
    czynnik chłodniczy
    condensation
    flow resistance
    measures
    minichannel
    refrigerant
    Opis:
    Badanie i analiza oporów przepływu podczas skraplania czynników chłodniczych w minikanałach rurowych ma duże znaczenie dla poznania procesu skraplania. W artykule tym przedstawiono wyniki przeprowadzonych badań, które mają na celu ułatwienie projektowania, konstrukcji i eksploatacji kompaktowych wymienników ciepła. W wyniku analizy rezultatów badań autorka proponuje własną zależność pozwalającą na wyznaczenie średnich i lokalnych oporów przepływu w minikanałach.
    Nowadays, much attention is paid to miniaturization of devices while increasing their efficiency. The same is with heat exchangers which have to exchange a lot of heat from a small area. By using minichannels and phase transitions, miniaturization of heat exchangers with intensification of heat exchange is possible. Unfortunately, the decrease in internal diameter creates problems associated with an increased flow resistance, which is a negative phenomenon because it causes increases in energy consumption for refrigerant transportation. The understanding of the dependence between the flow resistance and the flow parameters, refrigerant properties as well as internal diameter of a minichannel can improve design, construction and exploitation of compact heat exchangers. It will also enable optimization of the heat transfer coefficient α and flow resistance (Δp/L) growth. For this purpose, investigations were performed on three different refrigerants: R134a, R404A, R407C in minichannels with an internal diameter of the range dw = 0.31 mm - 3.3 mm. Miniaturization of compact heat exchangers and use of environmentally friendly CFC substitutes also help to reduce harmful effects on the environment and costs due to the absorptivity of material decrease. Based on the analysis of the investigation results the author has developed own correlation describing change of the pressure drop on the minichannel length, depending on its internal diameter, flow parameters and refrigerant properties.
    Źródło:
    Pomiary Automatyka Kontrola; 2012, R. 58, nr 6, 6; 559-562
    0032-4140
    Pojawia się w:
    Pomiary Automatyka Kontrola
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badanie skraplania czynników chłodniczych w kanałach o małej średnicy
    Investigation of condensation of refrigerants in minichannels
    Autorzy:
    Bohdal, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/154355.pdf
    Data publikacji:
    2011
    Wydawca:
    Stowarzyszenie Inżynierów i Techników Mechaników Polskich
    Tematy:
    chłodnictwo
    skraplanie
    wymiana ciepła
    opory przepływu
    refrigeration
    condensation
    heat transfer
    pressure drop
    Opis:
    Przedstawiono wyniki badań skraplania proekologicznych czynników chłodniczych R134a i R404A w kanałach o średnicy wewnętrznej d = (0,31÷3,3) mm. Wyznaczono wartości lokalne współczynnika przejmowania ciepła i tarciowego spadku ciśnienia w całym procesie skraplania (x = 1 ÷ 0). Zilustrowano wpływ stopnia suchości pary czynnika oraz gęstości strumienia masy na intensywność wymiany ciepła i wartość oporów przepływu. Wyniki badań własnych porównano z wynikami obliczeń według zależności innych autorów. Uzyskano bazę wyników pomiarów procesu skraplania w minikanałach rurowych, która będzie wykorzystana przy opracowaniu własnych korelacji do określania współczynnika przejmowania ciepła i oporów przepływu w tych warunkach.
    The investigation results of environmentally friendly refrigerants R134a and R404A condensation in minichannels with internal diameter d = 0.31 ÷ 3.3 mm was shown. Author appointed local heat transfer coefficient and pressure drops in whole range of quality (x = 0 ÷ 1). Influence of quality and mass flux on intensify heat transfer and pressure drop was illustrated. The results of experimental investigations were compared to the results of calculation according to correlations proposed by other authors. Author got many ex-perimental results in this range, what was the essence to made owns correlations.
    Źródło:
    Pomiary Automatyka Kontrola; 2011, R. 57, nr 5, 5; 568-571
    0032-4140
    Pojawia się w:
    Pomiary Automatyka Kontrola
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The analysis of thermal and flow characteristics of the condensation of refrigerant zeotropic mixtures in minichannels
    Autorzy:
    Bohdal, T.
    Widomska, K.
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/240470.pdf
    Data publikacji:
    2016
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    minichannels
    condensation
    zeotropic mixture
    heat transfer coefficient
    pressure drop
    minikanał
    kondensacja
    mieszanina zeotropowa
    współczynnik przewodnictwa cieplnego
    spadek ciśnienia
    Opis:
    The paper presents the results of experimental heat transfer and pressure drop during condensation of the single component refrigerant R134a and zeotropic mixtures R404A, R407C, and R410A in tube minichannels of internal diameter from the range 0.31–3.30 mm. The local values and the average of heat transfer coefficient and pressure drop in the whole range of the change in mass quality were measured. On the basis of the obtained test results there was illustrated the influence of the change of mass vapor quality, the mass flux density, and the inner diameter of channel on the studied parameters. These results were compared with the calculation results based on the relations postulated by other authors. The discrepancy range was ± 50%. On the basis of given test results own correlation was developed to calculate the heat transfer coefficient and pressure drop of tested refrigerants which presents the obtained results in a range of discrepancy of ±25%.
    Źródło:
    Archives of Thermodynamics; 2016, 37, 2; 41-69
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badania eksperymentalne oporów przepływu podczas skraplania proekologicznego czynnika chłodniczego w minikanałach rurowych
    Pressure drop during condensation of refrigerant R134a in pipe minichannels
    Autorzy:
    Bohdal, T.
    Charun, H.
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1819601.pdf
    Data publikacji:
    2012
    Wydawca:
    Politechnika Koszalińska. Wydawnictwo Uczelniane
    Tematy:
    czynnik chłodniczy
    skraplanie
    wymienniki ciepła
    refrigerant
    liquefaction
    heat exchangers
    Opis:
    Wiele ośrodków światowych zajmuje się konstrukcją i eksploatacją kompaktowych urządzeń chłodniczych. Jest to zgodne z trendem zapoczątkowanym w XX wieku i nadal kontynuowanym, zmierzającym do stosowania urządzeń technicznych materiało- i energooszczędnych oraz przyjaznych środowisku. W przypadku sprężarkowych urządzeń chłodniczych problem dotyczy przede wszystkim budowy sprężarek i wymienników ciepła. Wymienniki ciepła powinny być tak zaprojektowane, aby przy użyciu stosunkowo małej ilości czynnika chłodniczego w instalacji można przekazać dużą gęstość strumienia ciepła, przy wysokiej efektywności energetycznej. Oznacza to, że zapotrzebowanie na energię napędową czynnika chłodniczego i chłodzonego powinno być możliwie małe, a to jest z kolei związane z małymi oporami przepływu w układzie kanałów wymiennika. Opracowanie prezentuje wyniki badań eksperymentalnych spadku ciśnienia w przepływie dwufazowym czynnika chłodniczego R134a (zamiennik R12) podczas jego skraplania w minikanałach rurowych skraplaczy kompaktowych.
    Many research centers all over the world are dealing with the structure and operation of compact refrigerating devices. This is in line with the trend of 21st century, which is moving towards the use of energy-saving and environ mentally friendly technical equipment. The present study covers the results of investigations of a pressure drop in a two-phase flow of the R134a refrigerant (an R12 substitute) during its condensation in pipe minichannels in compact condensers. The investigation results of environmentally friendly refrigerant R134a condensation in minichannels with internal diameter d = 0.1÷3.3 mm were presented. The authors established local and average pressure drops in the whole range of quality (x = 0÷1). The influence of the quality and mass flux on pressure drop was illustrated. The results of experimental investigations were compared to the results of calculation according to correlations proposed by other authors. The authors obtained many experimental results in this range, with was essential to make their owns correlation. The pressure drop in two-phase flow during condensation of refrigerant R134a is dependent on: the type of agent, process parameters and the structure of two-phase flow. In the literature there are no generalized maps of structures for two-phase flow of refrigerants, which significantly limits the choice of an appropriate correlation in the design of compact condensers. As a result of systematic experimental studies of condensing refrigerant R134a in smooth pipe minichannels (stainless steel) with an inside diameter d = 0.31÷3.3 mm a database of measurements of average and local values of pressure drop in pipe minichannels (within the range of parameters: ts = 30÷40°C, x = 0÷1, (w?) = 0÷1200 kg/(m2źs) was obtained. They have been used for development of on, author's correlation (8) for determination of pressure drop under these conditions.
    Źródło:
    Rocznik Ochrona Środowiska; 2011, Tom 13; 347-359
    1506-218X
    Pojawia się w:
    Rocznik Ochrona Środowiska
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modeling the instabilities of the condensation process of the R134a and 404A refrigerants in pipe minichannels in the conditions of periodic hydrodynamic disturbances
    Autorzy:
    Kuczyński, W.
    Denis, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/95362.pdf
    Data publikacji:
    2017
    Wydawca:
    Politechnika Koszalińska. Wydawnictwo Uczelniane
    Tematy:
    condensation
    minichannels
    modeling of instabilities
    kondensacja
    minikanały
    modelowanie niestabilności
    Opis:
    In the present paper, an attempt was made to model the periodic hydrodynamic instabilities of the condensation process of a refrigerant in pipe minichannels. For this purpose, a homogenous thermodynamic model with an equilibrium condition on both sides was used, which was based on the equations of the balance of the mass, momentum and energy. These equations were used for numerical modeling of flow disturbances with a phase change. This model takes into account the complexity of multiphase flows. The accuracy of the model calculations was verified by means of the experimental results obtained. A satisfactory compliance was found for this comparison, which confirms the usefulness of the computational model proposed for the determination of the influence of periodically generated hydrodynamic disturbances on the condensation process of R134a and R404A refrigerants in pipe minichannels.
    Źródło:
    Journal of Mechanical and Energy Engineering; 2017, 1, 2; 179-187
    2544-0780
    2544-1671
    Pojawia się w:
    Journal of Mechanical and Energy Engineering
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparative study of flow condensation in conventional and small diameter tubes
    Autorzy:
    Mikielewicz, D.
    Andrzejczyk, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/240398.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    kondensacja w przepływie
    minikanały
    wymiana ciepła
    flow condensation
    heat transfer
    minichannels
    Opis:
    Flow boiling and flow condensation are often regarded as two opposite or symmetrical phenomena. Their description however with a single correlation has yet to be suggested. In the case of flow boiling in minichannels there is mostly encountered the annular flow structure, where the bubble generation is not present. Similar picture holds for the case of inside tube condensation, where annular flow structure predominates. In such case the heat transfer coefficient is primarily dependent on the convective mechanism. In the paper a method developed earlier by the first author is applied to calculations of heat transfer coefficient for inside tube condensation. The method has been verified using experimental data from literature on several fluids in different microchannels and compared to three well established correlations for calculations of heat transfer coefficient in flow condensation. It clearly stems from the results presented here that the flow condensation can be modeled in terms of appropriately devised pressure drop.
    Źródło:
    Archives of Thermodynamics; 2012, 33, 2; 67-83
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Experimental investigations into the impact of the void fraction on the condensation characteristics of R134a refrigerant in minichannels under conditions of periodic instability
    Autorzy:
    Kuczyński, W.
    Charun, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/240014.pdf
    Data publikacji:
    2011
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    kondensacja
    minikanały
    okresowe niestabilności
    udział objętościowy
    condensation
    minichannels
    Periodic instabilities
    void fraction
    Opis:
    This paper present the results of experimental investigations of condensation of R134a refrigerant in pipe minichannels with internal diameters 0.64, 0.90, 1.40, 1.44, 1.92 and 3.30 mm subject to periodic pressure instabilities. It was established that as in conventional channels, the displacement velocity of the pressure instabilities distinctly depends on the frequency of their hydrodynamic generation. The void fraction distinctly influences the velocity of the pressure instabilities. The form of this relationship depends on the internal diameter of the minichannels and on the method of calculating the void fraction.
    Źródło:
    Archives of Thermodynamics; 2011, 32, 2; 21-37
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Condensation of refrigerant R407C in multiport minichannel section
    Autorzy:
    Bohdal, T.
    Charun, H.
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/240486.pdf
    Data publikacji:
    2016
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    condensation
    minichannels
    R407C refrigerant
    heat exchanger
    kondensacja
    minikanały
    czynnik chłodniczy R407C
    wymiennik ciepła
    Opis:
    Analysis of the state of-the-art in research of refrigerant condensation in miniature heat exchangers, so-called multiports, was made. Results of refrigerant R407C condensation in a mini condenser made in the form of two bundles of tubular minichannels from stainless steel with an inside diameter 0.64 mm and length 100 mm have been presented. Two exchangers consisted of four minichannels and 8 minichannels have been investigated. The values of average heat transfer coefficient and frictional pressure drops throughout the condensation process were designated. The impact of the vapor quality of refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A comparative analysis of test results for various refrigerants in both mini heat exchangers were made.
    Źródło:
    Archives of Thermodynamics; 2016, 37, 4; 3-18
    1231-0956
    2083-6023
    Pojawia się w:
    Archives of Thermodynamics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badanie niestabilności skraplania proekologicznego czynnika chłodniczego w minikanałach rurowych
    Investigation of the instability of the condensation of environmentally friendly refrigerant in pipe minichannels
    Autorzy:
    Bohdal, T.
    Charun, H.
    Kuczyński, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1819608.pdf
    Data publikacji:
    2011
    Wydawca:
    Politechnika Koszalińska. Wydawnictwo Uczelniane
    Tematy:
    czynnik chłodniczy
    skraplanie
    minikanały rurowe
    refrigerant
    liquefaction
    pipe minichannels
    Opis:
    Celem niniejszych badań było rozpoznanie tego problemu i stwierdzenie, czy zjawiska rozprzestrzeniania się niestabilności w mini-kanałach podczas skraplania mogą być porównywalne do tych, które są znane dla kanałów konwencjonalnych. Należy wskazać, że w skraplaczu chłodniczym pracującym w warunkach eksploatacyjnych zaburzenia mogą być generowane impulsowo (skokowo) [5] lub periodycznie [6]. Przykładowo, skokowe zamknięcie lub otwarcie zaworu na zasilaniu wężownicy skraplacza wywołuje typowe zaburzenia impulsowe, które mogą wywołać niestabilności związane np. z rozwojem lub zanikiem skraplania czynnika chłodniczego. W dalszej części opracowania przedstawiono wyniki badań eksperymentalnych wpływu zaburzeń generowanych periodycznie na proces skraplania czynnika chłodniczego w mini-kanałach rurowych skraplaczy kompaktowych.
    Under real conditions, the work of conventional and compact refrigerating machines and devices (with exchangers which construction is based on the use of mini-channels or micro-channels) is subject to a lot of disturbances which are the result of both external and internal impacts. Such phenomena occur very frequently in the operational practice. The cause of disturbances may be the start-up or the stoppage of the installation, a change of the heat load of the exchangers, opening or closing of the valves, the work of automatic control elements etc. Considering the above, investigations on the condensation of the refrigerant in the flow in pipe mini-channels in the conditions of external disturbances were conducted. The development or decay of condensation was produced through a unitary change of the parameters of the two-phase system, e.g. the pressure and the mass flux density in the pipe channel. It was confirmed that two-phase media exhibit wave properties, while the disturbances produced displaced with a finite velocity. It was demonstrated that in contrast with conventional channels, the value of the boundary velocity of the displacement of pressure disturbances is obtained in mini-channels with substantially lower frequencies of their generation. Investigations were conducted with the use of a compressor refrigerating cycle with the environmentally friendly R404A refrigerant.
    Źródło:
    Rocznik Ochrona Środowiska; 2011, Tom 13; 377-391
    1506-218X
    Pojawia się w:
    Rocznik Ochrona Środowiska
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ekologiczno-energetyczne aspekty badań eksperymentalnych procesu skraplania czynników chłodniczych w minikanałach rurowych
    Ecology and energy related aspect of experimental tests of the condensation process of refrigerants in pipe mini-channels
    Autorzy:
    Bohdal, T.
    Charun, H.
    Kuczyński, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1819808.pdf
    Data publikacji:
    2009
    Wydawca:
    Politechnika Koszalińska. Wydawnictwo Uczelniane
    Tematy:
    minikanały rurowe
    czynnik chłodniczy
    proces skraplania
    refrigerant
    pipe minichannels
    condensation prosess
    Opis:
    In the era of miniaturization of power equipment, application of compact systems is a very advantageous solution. Compact heat exchangers which are used in refrigerating systems do not only transfer a large density of the heat flux but also perform environment-friendly functions; a refrigerant occupies a small volume, and when there is no leak tightness, there is little threat to the natural environment. Application of heat exchangers with flux of single-phase mediums (water or air) is not sufficient any more. That is the possibility of utilization of phase changes of refrigerants (boiling and condensation) realized during flux in channels with small diameter. Conception of constructing so-called compact heat exchangers (evaporators and condensers) which are a part of cooling installation was created that way. However the designers of compact heat exchangers have to face today difficult problem of choice sufficient computational procedures in the range of the heat exchange and flow resistances in channels with hydraulic diameter smaller than 3 mm [13]. Wellknown in literature procedures, tested for conventional channels (d > 3 mm) theoretically and experimentally, do not have to and in most cases are not suitable for micro- and mini-channels. This causes need to find and point the best computational formulae to be used in compact exchangers. It should be underlined, that number publications, presenting description of heat exchange and flow resistances during boiling in the mini- and micro-channels is much larger, than for the case of condensation in such channels. Up to date knowledge about conventional channel proves that processes of boiling and condensation in flow cannot be treated as "symmetrical" phenomena. Also mechanism of energy transport and momentum in processes of boiling and condensation in flow both in conventional channels and in mini-channels. The basic part of the paper is constituted by the presentation of the author's own experimental research on heat exchange in the condensation process of R134 a refrigerant in pipe mini-channels with an internal diameter of 1.6÷3.3 mm. On the basis of a comparative analysis, the usefulness of Akers and Shah's correlations was stated for the determination of the heat transfer coefficient in this process. The range of divergence of experiment results and calculations according to Ackers correlation was significantly smaller and that is why this correlation may be recommended for designers. Experiments were conducted in the following range of parameters: saturation temperature tk = 35÷40°C, density of mass stream (wp) = 200÷600 kg/(m2źs) and density of heat stream q = 5÷50 kW/m2
    Źródło:
    Rocznik Ochrona Środowiska; 2009, Tom 11; 143-162
    1506-218X
    Pojawia się w:
    Rocznik Ochrona Środowiska
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Calculation method for flow boiling and flow condensation of R134a and R1234yf in conventional and small diameter channels
    Autorzy:
    Mikielewicz, D.
    Jakubowska, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/259535.pdf
    Data publikacji:
    2017
    Wydawca:
    Politechnika Gdańska. Wydział Inżynierii Mechanicznej i Okrętownictwa
    Tematy:
    heat transfer coefficient
    flow boiling
    conventional channels
    minichannels
    Opis:
    The paper presents the results of calculations performed using the authors’ model to predict the heat transfer coefficient during flow boiling for two refrigerants R134a and R1234yf. The experimental data from various past studies have been collected and the calculations have been conducted for the full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house flow boiling and flow condensation model. The importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels, as well as the influence of the reduced pressure were analysed. The obtained numerical results show good consistency with those recorded in the experiments.
    Źródło:
    Polish Maritime Research; 2017, S 1; 141-148
    1233-2585
    Pojawia się w:
    Polish Maritime Research
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pomiar parametrów geometrycznych i przepływowych struktur przepływu dwufazowego w minikanałach
    Measurements of geometrical and flow parameters of two-phase flow structures in minichannels
    Autorzy:
    Sikora, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/152930.pdf
    Data publikacji:
    2014
    Wydawca:
    Stowarzyszenie Inżynierów i Techników Mechaników Polskich
    Tematy:
    skraplanie
    struktury przepływu dwufazowego
    minikanały
    czynnik chłodniczy HFE-7100
    condensation
    flow patterns
    two-phase flow structures
    minichannel
    HFE-7100 refrigerant
    Opis:
    Przeprowadzono badania eksperymentalne skraplania czynnika chłodniczego HFE7100 w minikanale rurowym o średnicy wewnętrznej d = 2 mm. Podczas badań wykonano wizualizację występujących podczas procesu skraplania struktur przepływu. Dokonano pomiaru parametrów geometrycznych i przepływowych w celu identyfikacji struktur przepływu dwufazowego skraplania w minikanale. Przeprowadzono identyfikację zakresu występowania poszczególnych struktur przepływu podczas skraplania niskociśnieniowego czynnika chłodniczego HFE7100. Badania wykonano w całym zakresie procesu skraplania (x = 0 – 1).
    Identification of flow patterns can be made by two methods. The first one is a calculation method consisting in calculating flow parameters and comparing their values with the ranges given by other authors or flow maps. This method has a number of limitations associated with a small amount of existing flow patterns maps, and many restrictions on their use. The second method visualizes the flow and identifies it from photos. This method is more accurate. This paper presents a methodology and results of experimental identification of the two-phase flow structure by measurement of flow and geometrical parameters. The test stand was designed and built. An optical measurement system was used for recording, processing and image analysis. Preliminary measurements were made for a two-phase flow mixture of HFE – 7100 refrigerant. The results of visualization and measurement of parameters are shown in the figures presented in the paper.
    Źródło:
    Pomiary Automatyka Kontrola; 2014, R. 60, nr 10, 10; 872-875
    0032-4140
    Pojawia się w:
    Pomiary Automatyka Kontrola
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-18 z 18

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