Elzbieta Fornalik-Wajs

Transients and turbulence pockets in thermal convection of paramagnetic fluid subjected to strong magnetic field gradients

We performed combined experimental and numerical studies of the flow and heat transfer of a paramagnetic fluid inside a differentially heated cubical enclosure subjected to various strong non-uniform magnetic field gradients. Two different heating scenarios are considered: unstable (heated from below) and stable (heated from above) initial thermal stratification. In contrast to the previously reported studies in literature, which observed solely laminar flow regimes, we investigated also appearance and sustenance of the periodic- and fully transient-flow motions for the very first time. This was consequence of using significantly stronger magnetic field strength (up to 10 T experimentally, and up to 15 T numerically) than those used in previous studies (up to 5 T). Detailed comparison between experiments and numerical simulations are performed and generally very good agreements were obtained.

An analysis of unsteady thermal convection of paramagnetic fluid in cubical enclosure under strong magnetic field gradient

The experimental studies of the flow and heat transfer of a paramagnetic fluid inside a cubical enclosure in a configuration heated from below and subjected to various strong non-uniform magnetic field gradients are presented. In contrast to the previously reported studies in literature, which observed solely laminar flow regimes, the appearance and sustenance of the periodic- and fully transient – flow motions for the very first time were investigated. This was consequence of using significantly stronger magnetic field gradient (up to 900 T2/m) than those used in previous studies (up to 200 T2/m). The fluid flow was studied at two Rayleigh numbers: 7.89105 and 1.86106. Non-monotonic behaviour of flow with increase of imposed magnetic field gradients was observed for both cases. Detailed analysis (Fast Fourier Transform) of temperature time series has been reported.

Thermal performance of a prototype plate heat exchanger with minichannels under boiling conditions

To solve the problem and to meet the requirements of customers in the field of high heat fluxes transfer in compact units, a new design of plate heat exchanger with minichannels (minichannels PHE) was proposed. The aim was to construct a compact heat exchanger of high effectiveness for the purpose of household cogeneration ORC system. In this paper the experimental analysis of an assembled prototype of such compact heat exchanger was described. The attention was paid to its thermal performance and the heat transfer coefficients under the boiling conditions. Water and ethanol were chosen as working fluids. The maximal value of transferred heat flux was about 84 kW/m2, while of the overall heat transfer coefficient was about 4000 W/(m2K). Estimated values of heat transfer coefficient on the ethanol (boiling) side reached the level of 7500 W/(m2K). The results are promising in the light of future applications, for example in cogeneration ORC systems, however further systematic investigations are necessary.

Local Nusselt number evaluation in the case of jet impingement

Jet impingement still is one of demanding cases regarding computational fluid dynamics, due to its highly turbulent behaviour, with occurrence of turbulent-laminar transition. Even recently developed methods exhibit some drawbacks - RANS based simulations lack accuracy, LES and DNS based ones require too much computational time. Hybrid methods also exist, but their development and validation is in progress. Nevertheless, CFD application can play major role in the investigation of jet impingement phenomena. While the flat surface impingement is widely discussed in the literature, there is lack of data regarding non-flat surfaces - the ones that might exist for example in the heat exchangers. In the following paper, the numerical simulation of both flat and non-flat surfaces single jet impingement is presented, with the aim of precise description of the turbulence models impact on the thermal and hydrodynamic results. Choice of turbulence model is crucial for sufficient calculation outcome. Only the complex analyses, shown in the article, including the turbulence and momentum budgets comparison between particular models, can reveal significant and meaningful differences.

High Performance Tubular Heat Exchanger with Minijet Heat Transfer Enhancement

ABSTRACT In the paper, the original cylindrical heat exchanger with minijets (MJHE) was introduced. The systematic experimental analysis of the prototype heat exchanger was described with special attention paid to such parameters as the heat transfer effectiveness, heat transfer rates, overall heat transfer coefficients, and pressure drop. The heat transfer coefficients were determined based on Wilson plot method, the most suitable approach for heat transfer coefficient determination in exchangers of complex geometry. The thermal-hydraulic characteristics of the in-house manufactured prototype of MJHE in water–water and gas–water configuration are also presented. The experimental results were compared with the predictions from well-known correlations found in the published research papers dedicated to the free-surface and submerged types of jets.

XXI Fluid Mechanics Conference

This Conference Volume contains the papers presented at the 21st Fluid Mechanics Conference (XXI FMC) held at AGH – University of Science and Technology in Krakow, Poland, 15–18 June 2014, and accepted for Proceedings published in the Journal of Physics: Conference Series. The Fluid Mechanics Conferences have been taking place every two years since 1974, a total of forty years. The 21st Fluid Mechanics Conference (XXI FMC) is being organized under the auspices of the Polish Academy of Sciences, Committee of Mechanics. The goal of this conference is to provide a forum for the exposure and exchange of ideas, methods and results in fluid mechanics. Conference topics include, but are not limited to Aerodynamics, Atmospheric Science, Bio-Fluids, Combustion and Reacting Flows, Computational Fluid Dynamics, Experimental Fluid Mechanics, Flow Machinery, General Fluid Dynamics, Hydromechanics, Heat and Fluid Flow, Measurement Techniques, Micro- and Nano- Flow, Multi-Phase Flow, Non-Newtonian Fluids, Rotating and Stratified Flows, Turbulence. Within the general subjects of this conference, the Professor Janusz W. Elsner Competition for the best fluid mechanics paper presented during the Conference is organized. Authors holding a M.Sc. or a Ph.D. degree and who are not older than 35 years of age may enter the Competition. Authors with a Ph.D. degree must present individual papers; authors with a M.Sc. degree may present papers with their supervisor as coauthor, including original results of experimental, numerical or analytic research. Six state-of-the-art keynote papers were delivered by world leading experts. All contributed papers were peer reviewed. Recommendations were received from the International Scientific Committee, reviewers and the advisory board. Accordingly, of the 163 eligible extended abstracts submitted, after a review process by the International Scientific Committee, 137 papers were selected for presentation at the 21st Fluid Mechanics Conference, 68 papers were accepted for Proceedings published in the Journal of Physics: Conference Series. The total number of submitted and accepted papers for this years conference represents a significant increase over previous Fluid Mechanics Conferences, and has expanded its initial national character and borders which speaks to the great vitality of fluid mechanics. We hope that these proceedings will be used not only as a document of the event but also to assess achievements and new paths to be taken in fluid mechanics research. Finally, we would like to congratulate the winners of the 2014 Professor Janusz W Elsner Competition Ruri Hidema from Japan, Fernando Tejero from Spain and Lukasz Laniewski-Wollk from Poland. Acknowledgements We would like to express grateful appreciation to our colleagues from the Polish Academy of Sciences, Committee of Mechanics, as well as to the International Scientific Committee i.e. Members and the Advisory Board. Their advice and efforts have helped us to overcome the problems normally associated with organising international meetings. Special thanks goes to the reviewers for their work in encouraging the submission of papers and the subsequent review of all papers. Their contribution cannot be overestimated. The 21st Fluid Mechanics Conference was organised by AGH University of Science and Technology, the Polish Academy of Sciences the Committee of Mechanics and the AGH-UST Foundation. Proceedings was published in the Journal of Physics: Conference Series. The demanding work involved could not have been done without the contribution of so many individuals from all institutions as well as numerous external co-workers. Without their extremely valuable help such a meeting would have been impossible. Thank you all so much! Details of the committees are available in the PDF