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1
Content available Subatmospheric pool boiling of water at very low liquid levels
Hałon Tomasz, Kaczmarek Dominika, Lada Wiktoria, Zajączkowski Bartosz
Archives of Thermodynamics
|
2023
|
Vol. 44, no 4
447--461
EN
The paper discusses how the vapour bubbles growing during boiling under the near-triple point pressure influence the heat transfer coefficient when the refrigerant level is lower than the bubble departure diameter. The experiments were carried out for liquid levels of 0.57 to 1.89 cm, saturated pressure range between 0.9 and 4 kPa (saturation temperatures between 5.5 and 29◦C). Boiling occurred on a plain surface with wall heat flux densities between 0.43 and 5.93 Wcm−2. We determined boiling curves for the low-pressure process and analyzed the changes in wall superheat for different filling levels. The experimentally obtained heat transfer coefficient (HTC) was compared with the theoretical values produced by the most popular mathematical expressions used at higher pressures. We also prepared the boiling map, where we specified two boiling regimes: the regime of convection or small popping bubbles and the regime of isolated bubbles. The results indicate that the level of liquid can be neglected within the heat flux range analyzed in this study. The main mechanism of heat transfer under measured conditions is heat convection and conduction, rather than evaporation. The experimentally determined difference between the heat transfer coefficients for different levels of liquid is under 100 Wm−2K−1 (for the same heat flux and pressure at the wall).
2
Content available Pool Boiling Heat Transfer from Rough and Microstructure Coated Surfaces
Orman Łukasz J., Orman Katarzyna, Wojton Iwona
Rocznik Ochrona Środowiska
|
2020
|
Tom 22, cz. 1
514--525
EN
The paper presents the test results of pool boiling heat transfer on the rough surface and the surface covered with capillary – porous microstructure. The porous layer is made of copper fibers sintered in the reduction atmosphere. The volumetric porosity amounted to 68%, while its height 1 mm. Distilled water and ethyl alcohol were used as the working fluids. The experiments have been carried out under the atmospheric pressure. Enhancement of heat transfer in relation to the smooth reference surface has been recorded especially for the low range of superheats, which might be related to the density of active nucleation sites. Experimental results have been compared with selected models of boiling available in literature.
PL
Artykuł przedstawia wyniki badań wymiany ciepła przy wrzeniu na powierzchniach chropowatych i z porowatym pokryciem metalowo-włóknistym. Mikrostruktura porowata została wykonana z włókien miedzianych spiekanych w atmosferze redukcyjnej. Porowatość objętościowa wynosi 68%, a wysokość warstwy 1 mm. Badania prowadzono dla wody destylowanej i alkoholu etylowego jako cieczy wrzących pod ciśnieniem atmosferycznym. Zaobserwowano intensyfikację wymiany ciepła w porównaniu do powierzchni gładkiej, szczególnie w zakresie małych przegrzań, co może być związane z gęstością aktywnych centrów nukleacji. Wyniki badań eksperymentalnych porównano z wybranymi modelami wrzenia dla danych powierzchni.
3
Content available Phase change heat exchangers made of pin-fins for boiling enhancement
Orman Łukasz J., Radek Norbert, Pietraszek Jacek, Gontarski Dariusz
Quality Production Improvement - QPI
|
2019
|
Vol. 1, Iss. 1
433--439
EN
The paper deals with the important issue of boiling heat transfer enhancement using mechanical treatment of the heater surface. The surface has been modified in such a way that microfins have been produced. The application of such a structure leads to highly increased heat fluxes in relation to the smooth surface as has been presented and discussed in the paper. The experiments including distilled water and ethyl alcohol on the horizontal copper samples of 3 cm diameter have been considered. The heat flux value of microfinned surface was even nine times higher than the heat flux dissipated from the smooth surface without any coating. It proves a considerable enhancement of boiling with the application of the mechanically treated surfaces of heat exchangers.
4
Content available remote Passive methods of boiling heat transfer enhancement
Orman Ł. J., Radek N., Kapjor A., Karpisz D.
Technical Transactions
|
2018
|
Vol. 115, iss. 12
193--198
EN
The paper presents the issue of boiling heat transfer enhancement with the use of different passive techniques, namely the application of wire mesh coatings, capillary porous layers, pin – fins and laser treatment. Enhanced boiling heat transfer has been described as well as the research data of the authors that deals with microstructural coatings. The conducted experimental tests confirm the possibility of increasing heat fluxes transferred at the same superheat value due to the use of heat transfer enhancing techniques.
PL
W artykule przedstawiono zagadnienie intensyfikacji wymiany ciepła przy wrzeniu poprzez zastosowanie różnych pokryć tj. struktur siatkowych, kapilarno – porowatych, mikrożeber czy obróbki laserowej. Przybliżono zagadnienie intensyfikacji wymiany ciepła przy wrzeniu i opisano wyniki badań autorów, dotyczące intensyfikacji wrzenia na mikropowierzchniach strukturalnych. Przeprowadzone badania potwierdzają możliwości zwiększenia gęstości odbieranych strumieni ciepła przy tym samym przegrzaniu.
5
Content available Boiling heat transfer phenomenon from an isolated nucleation center
Orman Ł. J.
Structure and Environment
|
2016
|
Vol. 8, no. 1
59--63
EN
The paper discusses a method of boiling heat transfer investigation from a cavity of given geometrical dimensions. The testing method is described together with literature review on the subject. This experimental concept can be used to provide useful data on the creation and departure frequency of bubbles, thus giving more insight into the boiling phenomenon.
6
Content available remote Efficient surfaces for boiling heat transfer enhancement
Radek N., Orman Ł. J., Kapjor A., Sladek A.
Czasopismo Techniczne. Mechanika
|
2016
|
Y. 113, iss. 4-M
3--8
EN
The paper discusses the use of efficient surfaces for heat transfer enhancement during a nucleate boiling heat transfer. Distilled water under ambient pressure was the working fluid in the presented experiment. The application of a brass mesh of 0.63 mm aperture and 0.20 mm wire diameter on the surface of a copper heater led to considerable improvement in the value of heat flux at low temperature differences of a few Kelvin, where the enhancement ratio exceeded 2. Such modified surfaces could be used in the design of more efficient heat exchangers e.g. in refrigeration systems.
PL
Artykuł dotyczy wykorzystania wydajnych powierzchni do intensyfikacji wrzenia. Czynnikiem roboczym w badaniach była woda destylowana. Zastosowanie siatki mosiężnej o prześwicie 0,63 mm i o grubości drutu 0,20 mm na powierzchni wymiennikowej skutkowało znacznym wzrostem gęstości strumienia ciepła w obszarze małych przegrzań, gdzie stopień intensyfikacji wymiany ciepła przekroczył 2. Takie modyfikowane powierzchnie mogą być wykorzystywane do projektowania bardziej wydajnych wymienników ciepła, np. w systemach chłodniczych.
7
Zjawiska zmiany fazy w pasywnym odszranianiu fragmentów dróg
Tyburczuk A.
Logistyka
|
2015
|
nr 4
6313-6319, CD 2
PL
Praca dotyczy badań intensyfikacji wymiany ciepła przy wrzeniu na nieizotermicznych powierzchniach elementów wymiennikowych. W literaturze spotyka się wiele badań związanych z procesami wymiany ciepła przy zmianie fazy, które bardzo często dotyczą pokryć wytwarzanych różnymi technologiami. Główną wadą tych badań jest to, że głównie prowadzone są na powierzchniach izotermicznych. Rzeczywiste układy wymiennikowe są nieizotermiczne, na których proces wymiany ciepła zachodzi odmiennie. W niniejszej pracy przedstawiono badania wpływu wybranego pokrycia kapilarno-porowatego na wielkość wymiany ciepła na nieizotermicznych powierzchniach usytuowanych pionowo. Badania prowadzono na stanowisku pomiarowym, którego głównym elementem jest długie miedziane żebro, którego podstawę utrzymywano w stałej dla danej serii pomiarów temperaturze. Cieczą odbierającą ciepło był etanol pod ciśnieniem atmosferycznym. Omówiono metodykę pomiarów oraz przedstawiono wyniki badań. W oparciu o zmierzony kamerą termowizyjną powierzchniowy rozkład temperatury wyznaczono lokalne wartości odprowadzanego strumienia i współczynnika przejmowania ciepła, które pokazano w postaci krzywej wrzenia dla żebra o powierzchni gładkiej i pokrytej strukturą kapilarno-porowatą. Z porównania lokalnie odprowadzanych strumieni ciepła wynika, że największa różnica pomiędzy nimi występuje przy przegrzaniu 14 K i wynosi ponad 197 kW/m2. Otrzymane wyniki badań są niezbędne przy projektowaniu i wymiarowaniu wysokowydajnych wymienników ciepła pracujących przy zmianie fazy.
EN
The paper deals with boiling heat transfer intensification on non-isothermal heat exchanger surfaces. Multiple research related to heat transfer with phase change on coverings made in different technologies are reported in the literature. The disadvantage of that research is that the results are presented for isothermal surfaces mainly, while the real world heat exchanger units are usually non-isothermal and heat transfer processes differ from that on isothermal ones. The paper presents the results of investigations into a single fin operating in ethanol boiling under ambient pressure. Thermovision camera was used to measure temperature distribution for two specimens: with a smooth surface and mesh-capillary-porous structure superimposed to enhance heat transfer. The measurement system set up for the experiment makes it possible to make an assumption of one-dimensional phenomenon, that is to assume that the temperature change along the fin thickness is negligibly small and can be disregarded. Temperature distributions obtained with thermovision measurements indicate that mesh-capillary-porous covering clearly enhances heat transfer when compared to a smooth surface. On the basis of the axial temperature distribution measured with the thermovision camera, boiling curves has been determined. The maximum difference in the locally rejected heat flux at 14 K superheat is observed an equals 197,3 kW/m2 nearly.
8
Content available Nucleate pool boiling heat transfer from small horizontal smooth tube bundles
Krasowski K., Cieśliński J.
Transactions of the Institute of Fluid-Flow Machinery
|
2011
|
nr 123
85-97
EN
Measurements of boiling heat transfer coefficients in water, methanol and refrigerant R141b are reported for the bundles of smooth tubes that represent a portion of a flooded-type evaporator. Each bundle contained 19 instrumented, electrically heated tubes in a staggered triangular-pitch layout. The effect of heat flux, tube pitch and operating pressure is studied in the paper. Bundle factor and bundle effect are discussed as well. A correlation for prediction of a bundle average heat transfer coefficient is proposed.
9
Content available remote Intensyfikacja wymiany ciepła podczas wrzenia cieczy organicznych na gładkiej powierzchni rury w obecności pola elektrycznego
Bryszewska-Mazurek A., Mazurek W.
Przegląd Elektrotechniczny
|
2008
|
R. 84, nr 10
121-123
PL
W artykule przedstawiono wyniki badań doświadczalnych procesu wrzenia czynnika R-245fa w obecności pola elektrycznego. Badano odparowanie czynnika na wewnętrznej powierzchni pionowej rury cieplnej.
EN
The paper presents experimental results of R-245fa boiling under the electric field. The evaporation on an inner surface of the vertical heat pipe was investigated.
10
Content available remote On determining the temperature dependent heat transfer coefficient
Orzechowski T.
Archives of Thermodynamics
|
2003
|
Vol. 24, no 2
69-88
EN
The paper deals with analysis of a thermal field measured by means of a thermovision camera. A two-dimensional ill-posed problem of heat transfer was solved using a fin as an example. The quantity that needs to be found is the heat flux leaving the invisible inner surface of the fin. The method of heat functions was used for the calculations. The results of the numerical analysis of the problem are some local values of the transfer coefficients. The convergence of the calculation procedures was chacked by applying the heat balance to the considered area. Then, the optimal degree of the heat polynomials for such a problem was determined and the range of the method convergence was analysed. During the experiments, the heat transfer from the surface of a fin submerged in boiling water was observed. Values of heat transfer coefficients were determined and compared with the calculation results. A reasonable degree of congruence was found to exist between the calculation and experimental results.
11
Content available remote Hysteresis characteristics of boiling heat transfer from copper fibrous porous structures
Wójcik T.
Archives of Thermodynamics
|
2003
|
Vol. 24, no 2
37-54
EN
The paper presents an experimental study of boiling on heating surfaces covered with copper fibrous porous layers used as a filling of heat pipes. The knowledge of thermal characteristics of capillary-porous structures is indispensable in the design and construction of heat exchangers utilizing the concept of heat pipes. Experiments were carried out for pool boiling of distilled water, ethanol, refrigerant R-123 and refrigerant R-113 on lavers of 40, 70 and 85 % porosity. Porous surface significantly enhances heat transfer in comparison to a smooth one. Among four different types of hysteresis observed, a new one of h-type was discovered. It can be applied to control the temperature of the heating surface.
12
Content available remote Analysis of boiling heat transfer from a microstructure - covered fin
Orzechowski T.
Archives of Thermodynamics
|
2001
|
Vol. 22, nr 3-4
77-94
EN
The one-dimensional equation presented here concerns the transfer of heat in a fin covered with a structure intensifying the heat exchange. Stochastic parameters of the microstructure were determined using the normalised probability density function. The equation was solved for a regular coating in the form of rectangular microfins, assuming that there is power dependence of the heat transfer coefficient on wall superheat. Verifying experimental studies were carried out on a multilayer copper mesh structures with water boiling at atmospheric pressure. For a flat copper fin covered with a various number of mesh layers, the superficial distribution of temperature along the fin was registered by means of a THV-550 SW thermovision camera. The results were used to calculate the heat flux transported by the fin for three mesh layers with a different thickness and compared with results obtained for plain surface. Methodology of the analysis of results and calculation has been provided, too. It was found that the results of calculation were compatible with the results of experiment.
13
Content available remote Probabilistic model of boiling heat transfer in thin-layer porous structures
Poniewski M., Wiśniewski M., Wójcik T.
Archives of Thermodynamics
|
2000
|
Vol. 21, nr 3-4
55-73
EN
There were presented the results of theoretical analysis of boiling heat transfer on heating surfaces covered with thin-layered capillary porous structures. Heat transfer probabilistic model was proposed. It was then compared with experimental results of II type hysteresis. The results of investigations and modeling were obtained for metal, fibrous structures with non-homogeneous distribution of the porous layer cell dimensions. II type hysteresis, termed by the authors "controlled hysteresis", could be applied to surface temperature adjustment.
14
Propane pool boiling heat transfer on horizontal tube
Vasiliev L., Zhuravlyov A., Khrolenok V., Novikov M., Rak A., Mazyuk V.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika
|
1999
|
Z. 67
339--347
EN
An experimental investigation of propane boiling heat transfer was done on single horizontal smooth tubes and tubes with porous coverings. Three modes of heat transfer were determined on evaporation surfaces with increasing heat flux: free convection, a transitional mode (the average vapor bubble population was negligible) and developed boiling. The existence of the region length depends on saturation pressure, the kind of evaporation surface, and the direction of heat flux change. On heat flux reduction, a strong heat-flux hysteresis phenomenon was observed: the picture regarding changes of heat transfer regimes the same, but boiling extended into the region which was occupied by free convection. In the wide range of saturation pressures and heat fluxes, the intensity of heat transfer on the samples with porous coatings is high than that on the smooth surface samples. The research carried out showed that an application of metal porous covering with electric arc gas-thermal spraying allows one to increase significantly (3-5 times as high in the region of low heat loads, q < 8 kW/m2, and 2.5-3 times in the region of high heat fluxes, q > 8 kW/m2) the heat transfer intensity for propane boiling on horizontal tubes.
15
Heat transfer crisis on porous surfaces - experimental investigations and the outline of the maximum point process based model
Poniewski M. E., Wiśniewski M., Wójcik T. M.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika
|
1999
|
Z. 67
323--338
EN
The paper presented the results of experimental investigations into intralayer boiling crisis and accompanying phenomena. It was observed that the structural parameters of the porous covering affected the course of the process. Hysteresis phenomenon manifested itself when the heat flux initiating intralayer heat crisis was reached. The crisis mechanism hypotheses, the description of which was available in literature, were discussed. The maximum point process was selected as a tool of the mechanism modelling. There was presented the methodology of the calculations of intralayer boiling crisis occurrence probability which depends on physical and chemical properties of the surface and the liquid as well as the porous structure geometrical properties.
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