Basin stability approach for quantifying responses of multistable systems with parameters mismatch

Acknowledgement This work is funded by the National Science Center Poland based on the decision number DEC-2015/16/T/ST8/00516. PB is supported by the Foundation for Polish Science (FNP).Peer reviewedPublisher PD

Surface effects in flow boiling of R134a in microtubes

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierThe inner surfaces of microtubes may be influenced strongly by the process of making them due to manufacturing difficulties at these scales compared to larger ones, e.g. the surface characteristics of a seamless cold drawn tube may differ from those of a welded tube. Accordingly, flow boiling heat transfer characteristics may vary. In addition, there is no common agreement between researchers on the criteria of selecting tubes for flow boiling experiments. Instead, tubes are usually ordered from commercial suppliers, in many cases without taking into consideration the manufacturing method and its effect on the heat transfer process. This may explain some of the discrepancies in heat transfer characteristics which are found in the open literature. This paper presents a comparison between experimental flow boiling heat transfer results obtained using two different metallic tubes. The first one is a seamless cold drawn stainless steel tube of 1.1 mm inner diameter while the second is a welded stainless steel tube of 1.16 mm inner diameter. Both tubes have a heated length of 150 mm and the flow direction is vertically upwards. The tubes were heated using DC current. Other experimental conditions include: 8 bar system pressure, 300 kg/m2 s mass flux, about 5K inlet sub-cooling and up to 0.9 exit quality. The results are presented in the form of local heat transfer coefficient versus local quality and axial distance. Also, the boiling curves of the two tubes are discussed. The results show a significant effect of tube inner surface morphology on the heat transfer characteristics

Heat transfer correlation for flow boiling in small to micro tubes

This article is available open access under a Creative Commons license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Copyright © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.There is a large discrepancy in the open literature about the comparative performance of the existing macro and microscale heat transfer models and correlations when applied to small/micro flow boiling systems. This paper presents a detailed comparison of the flow boiling heat transfer coefficient for R134a in stainless steel micro tubes with 21 macro and microscale correlations and models. The experimental database that was used in the comparison includes the data for 1.1 and 0.52 mm diameter tubes, mass flux range of 100–500 kg/m2 s and system pressure range 6–10 bar obtained in the course of this study. The effect of the evaporator heated length on the comparative performance of the correlations and models was investigated using three different lengths of the 1.1 mm diameter tube (L = 150, 300 and 450 mm). This comparative study demonstrated that none of the assessed models and correlations could predict the experimental data with a reasonable accuracy. Also, the predictability of most correlations becomes worse as the heated length increases. This may contribute in explaining the discrepancy in the comparative performance of the correlations from one study to another. A new correlation is proposed in the present study based on the superposition model of Chen. The database used in developing the correlation consists of 5152 data points including the current experimental data and data obtained previously with the same test rig, fluid and methodology for tubes of diameter 4.26, 2.88, 2.01 mm. The new correlation predicted 92% of the data within the ±30% error bands with a MAE value of 14.3%

Wyznaczanie orientacji włókien w papierze drogą analizy obrazu realizowaną w systemie on-line

A paper web produced under industrial conditions always exhibits an anisotropy in its mechanical properties measured in the machine and cross directions. Proper and fast information about current paper anisotropy would significantly increase the efficiency of web quality control systems and allow to produce paper with greater precision. The main objective of the work presented was to determine the possibility of measurement of paper anisotropy. The method proposed is based on the image analysis of the orientation and location of special markers – luminescent fibres – which were introduced to the structure of the paper. Studies have shown that the method of image analysis provides a detection of fibres with a satisfactory level of efficiency, thus allowing accurate examination of the anisotropy of the paper samples analyzed. On the basis of experiments, it was also found that the method of image analysis proposed allows to detect fibres with an accuracy appropriate for the problem under consideration. The invention presented has already been registered in a Patent Office as submission no. P.411294.Celem pracy było określenie możliwości wyznaczenia zorientowania włókien celulozowych w papierze co pozwoliłoby określić anizotropię wytwarzanego materiału. Parametr ten jest niezwykle istotny w technologii papieru ze względu na ścisłą zależność między anizotropią a właściwościami mechanicznymi wytworów papierowych. Pomiar orientacji włókien realizowano drogą analizy obrazu, gdzie analizowanymi obiektami były wprowadzane do struktury papieru znaczniki – sztuczne włókna celulozowe o właściwościach luminescencyjnych. Cechą charakterystyczną tych włókien były ich właściwości zbliżone do właściwości naturalnych włókien celulozowych. Dzięki temu włókna luminescencyjne nie zmieniały właściwości papieru a przy tym zachowywały się w sposób podobny do pozostałych włókien występujących w masie papierniczej. Efekt luminescencji pojawiał się w chwili oświetlenia tych włókien światłem UV, co pozwalało na uzyskanie wyraźnego obrazu badanych obiektów. Na podstawie uzyskanych wyników stwierdzono, że zaproponowane: metoda pomiarowa oraz zastosowany algorytm analizy obrazu umożliwiły określenie zorientowania włókien w badanych strukturach papierniczych oraz pozwoliły na wyznaczenie anizotropii tych struktur. Wyniki zostały potwierdzone laboratoryjnymi badaniami wytrzymałościowymi badanych papierów. Na tej podstawie zaproponowano również sposób realizacji układu pomiarowego dla maszyny papierniczej, w którym byłaby zastosowana ta metoda. Rozwiązanie zostało już zgłoszone w Urzędzie Patentowym RP i zarejestrowane pod numerem P.411294