Frantisek Marsík

Frantisek Marsík
The Czech Academy of Sciences | AVCR · Institute of Thermomechanics

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100
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453
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Publications

Publications (100)
Article
Full-text available
The high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) based on the polybenzimidazole (PBI) membrane doped with phosphoric acid (H3PO4) presents a promising route in the development of fuel cell technology. The higher operating temperature of 160-200 °C results in an increased tolerance of the platinum catalyst to the carbon monoxid...
Conference Paper
Swirling flows are important for technical applications that require high heat transfer and enhanced fluid mixing such as cyclone cooling applications. However, the flow in such systems is unstable and thus vortex breakdown may occur. In order to improve the physical understanding of this phenomenon a numerical analysis of convergent vortex tubes i...
Article
Accelerated stress testing is one of the most used approaches to characterize the performance and the degradation of the membrane electrode assembly (MEA) in low-temperature hydrogen polymer electrolyte membrane fuel cells (PEMFC). A standard JRC on/off testing procedure was used to characterize two sets of commercial MEAs, by ElectroChem and by Pa...
Article
The current work presents a concept that deals with the production of entropy generated by non-equilibrium processes in consequence of mass and energy transfer. The often used concept of endoreversible thermodynamics is based on the non-realistic conjecture that the entire entropy production is realized at the system boundary. In this contribution,...
Article
Full-text available
This paper presents an experimental and numerical analysis of swirl flow in a circular tube. Swirl flow is important for technical and natural processes, where high heat transfer and good fluid mixing are needed. Flow and vortex structures respecting redistribution of momentum and possible occurrence of vortex breakdown are taken into account. The...
Chapter
Thermodynamics of open systems offers a new concept for description of real material objects including the living systems. The second law of thermodynamics can be interpreted as an evolution law of all material systems, which are in interaction with surroundings. The most important quantity is entropy, which is defined by balance of entropy. The pr...
Article
Full-text available
The well-known Gouy-Stodola theorem states that a device produces maximum useful power when working reversibly, that is with no entropy production inside the device. This statement then leads to a method of thermodynamic optimization based on entropy production minimization. Exergy destruction (difference between exergy of fuel and exhausts) is als...
Article
Objective: The human motion system reacts to both hypo and hyperactivity loads by changes to the rheological properties of tissues. This study deals with changes to the axial system (AS) compartment. Using the appropriate methodologies and mathematical-physical methods, these changes can be identified and quantified. Methods: This study describe...
Article
Full-text available
Correctly dosed physical activity is the basis of a vital and healthy life, but the measurement of physical activity is certainly rather empirical resulting in limited individual and custom activity recommendations. Certainly, very accurate three-dimensional models of the cardiovascular system exist, however, requiring the numeric solution of the N...
Article
Full-text available
Exergy analysis, which provides means of calculating efficiency losses in industrial devices, is reviewed, and the area of its validity is carefully discussed. Consequently, a generalization is proposed, which holds also beyond the area of applicability of exergy analysis. The generalization is formulated within the framework of classical irreversi...
Article
A case study concerning validation of wind speed measurements made by a laser wind sensor mounted on a 190 square foot floating platform in Muskegon Lake through comparison with measurements made by pre-existing cup anemometers mounted on a met tower on the shore line is presented. The comparison strategy is to examine the difference in measurement...
Conference Paper
Full-text available
Efficiency of hydrogen fuel cells is analyzed using a non-equilibrium theory of mixtures based on classical irreversible thermodynamics 1 . The efficiency depends on energy of fuel and on a function (map of efficiency losses) revealing how much efficiency is being lost at each point of the fuel cell. It is shown that the losses are not only given b...
Article
Full-text available
We provide an extensively discussed formulation of theory of mixtures of inter-acting fluids. This careful discussion leads to clarification of questions whether kinetic energy of diffusion should be defined to be part of internal energy or not, whether potential energy should be included into internal energy or not, how studying time-reversal pari...
Article
Full-text available
Energy conversion in fuel cells is performed by electrochemical and transport processes in the polymer electrolyte membrane, gas diffusion layers, catalyst layers, and in the pipes transporting hydrogen, oxygen, water and air into and out of the fuel cell. All these processes are analyzed from the point of view of phenomenological thermodynamics, w...
Article
Full-text available
Bone remodelling is a fundamental biological process that controls bone microrepair, adaptation to environmental loads and calcium regulation among other important processes. It is not surprising that bone remodelling has been subject of intensive both experimental and theoretical research. In particular, many mathematical models have been develope...
Conference Paper
Full-text available
The well-known Magnus effect is the phenomenon responsible for the curved streamlines around rotating cylinders or balls. In other words, the phenomenon causes the curved motion of spinning balls and missiles. A related application is the Flettner rotor ship, which was designed to use the Magnus effect for propulsion. More generally, the Kutta-Jouk...
Conference Paper
Full-text available
Efficiency of hydrogen fuel cells is analyzed using a non-equilibrium theory of mixtures based on classical irreversible ther-modynamics. The efficiency is expressed in terms of processes taking place inside the fuel cells revealing which processes are responsible for efficiency losses. This provides a new method of optimization. It is shown that e...
Article
It is common knowledge that efficiency of fuel cells is highest when no electric current is produced while when the fuel cell is really working, the efficiency is reduced by dissipation. In this paper the relation between efficiency and dissipation inside the fuel cell is formulated within the framework of classical irreversible thermodynamics of m...
Article
A thermoacoustic standing-wave prime mover with a quarter-wave resonator has been investigated experimentally. The working fluid is air at the barometric pressure. The holographic interferometry and hot-wire anemometry have been used. A special optical setup, based on a Michelson interferometer, has been developed and used. The setup exhibits a dou...
Article
The problem of vortex shedding behind a heated cylinder for diluted gasses can be solved by reducing to an isothermal case by means of introducing some effective temperature Teff and based on the similarity condition ReC,∞ = ReC,eff. Different situation occurs for liquids. At first sight the similarity should exist since the cylinder cooling stabil...
Article
The aim of this study was to simulate different types of cervical vertebra loading and to find out whether mechanical stress would concentrate in regions known in clinical practice as predilection sites for osteophyte formation. The objective was to develop a theoretical model that would elucidate clinical observations concerning the predilection s...
Article
The present study utilizes a recently developed literature model for the bone remodelling process to predict the evolution of bone density following Duracon total knee arthroplasty (TKA). In this model, which is based on chemical kinetics and irreversible thermodynamics, bone is treated as a self-organizing system capable of exchanging matter, ener...
Article
The Classical Nucleation Theory (CNT) in its multicomponent form is presented as a reliable tool for the investigation of homogeneous nucleation in cavitation processes in aqueous systems. Several cases are considered, starting form the most simple case of a void cavity emerging at negative pressure, then treating the case of a bubble composed of w...
Article
The aim of this article was to present a new thermodynamic-based model for bone remodeling which is able to predict the functional adaptation of bone in response to changes in both mechanical and biochemical environments. The model was based on chemical kinetics and irreversible thermodynamic principles, in which bone is considered as a self-organi...
Article
Full-text available
Understanding of the bone remodelling process has considerably increased during the last 20 years. Since the ability to simulate (and predict) the effects of bone remodelling offers substantial insights, several models have been proposed to describe this phenomenon. The strength of the presented model is that it includes biochemical control factors...
Article
Remodelling is a dynamic process occurring during growth and it includes sensing of environmental changes, tissue resorbance, i.e. the removal of existing old bone, and formation of new tissue. The biomechanical remodelling process is relatively well formulated for bones and can be divided into three stages: (1) bone resorption based on the osteocl...
Article
The influence of rotation on the stability of coaxial flow between steady cylinders is still an open question. The pattern of a swirling annular jet depends strongly on the quality of the issuing flow. Our new approach to the fluid flow stability problem is based on the attenuation of the kinetic energy of disturbances. This concept follows from th...
Article
This paper offers a theoretical explanation of the coupling effect phenomenon between mechanical loading and chemical reactions based on linear nonequilibrium thermodynamics and also discusses the classical method of obtaining restrictions on the phenomenological coefficients. The question whether static or dynamic loading influences biochemical pr...
Chapter
The aim of the present study is to predict the functional adaptation of bone in response to changes in mechanical loading using a new biothermodynamic model for bone remodeling. In our approach, which fits into the framework of open systems, changes in the density are governed by balance of mass and balance of entropy supplemented by additional mas...
Article
A simplified thermodynamic analysis is applied to elucidate the basic feature of fuel cells operation, i.e., the transformation of chemical energy into electricity. To be able to handle this problem analytically we propose a simple model of the chemical reaction kinetics at the electrodes and diffusion in the polymer electrolyte membrane (PEM). The...
Article
The objective of this article is to give an overview of available experimental techniques and theoretical fundaments of the classical theories of homogeneous binary nucleation. The principles of the experimental setups are reviewed, ranging from low-nucleation-rate (≤103 nuclei/(cm3⋅s)) devices, i.e., thermal-diffusion cloud chamber, expansion cham...
Article
The authors have studied venous problems of the brain for a long time. In this study they show venous complications and problems together with biomechanical and hemodynamic studies. They studied histobiomechanical aspects of bridging veins and the connection between bridging veins and sinuses, described in sinuses chorda Willisi. The authors develo...
Article
The effect of altered shape of the spinal subarachnoidal spaces (SAS) in stenosis on cerebrospinal fluid (CSF) dynamics is not well understood and clinical consequences remain unknown. In cervical spinal canal there is pulsatile motion of the CSF strongly related to intracranial pressure-volume dynamics [Otáhal, 2007]. Stenosis of the spinal canal...
Article
Full-text available
INTRODUCTION Transportation of the cerebrospinal fluid (CSF) in the craniospinal system is possible due to finely tuned resistance and compliance of the spinal canal. In previous modelling study of the CSF transportation we have shown that main source of the hydrodynamical resistance and compliance of the craniospinal system is cervical part of spi...
Article
Full-text available
This research is aimed to the determination of the changes in the cardiac energetic output for three different modes of cardiac rhythm pacing. The clinical investigation of thirteen patients with the permanent dual-chamber pacemaker implantation was carried out. The patients were taken to echocardiography examination conducted by way of three pacin...
Article
The pulsatile nature of the CSF movement is a result of the cardiac-related pulsations in blood volume in cranial region. According to Monro–Kellie Doctrine, the net inflow of arterial blood during systole is compensated by an equal outflow of venous blood and by caudal displacement of the CSF. Knowledge of the distribution of physical properties (...
Article
This paper focuses on the wake flow behind a heated circular cylinder in the laminar vortex shedding regime. The phenomenon of vortex shedding from a bluff body is an interesting scientific and engineering problem. Acquisition of reliable experimental data is considered an indispensable step toward a deeper physical understanding of the topic.An ex...
Article
In this study, the authors show venous complications and problems related to biomechanical and hemodynamic studies. They studied histobiomechanical aspects of bridging veins and the connection between bridging veins and sinuses, described in sinuses chorda Willisi.The authors developed the special program for modeling in the cardiovascular system a...
Article
Full-text available
Nucleation processes in the binary water-sodium chloride system are investigated in the sense of the classical nucleation theory (CNT). The CNT is modified to be able to handle the electrolytic nature of the system and is employed to investigate the acceleration of the nucleation process due to the presence of sodium chloride in the steam. This phe...
Article
A zero-net-mass-flux actuator was used to generate a synthetic air jet. The local mass transfer in the jet impingement configuration was investigated using the naphthalene sublimation method. Based on the heat/mass transfer analogy, the mass transfer data have been converted to the corresponding heat transfer data. The results have been compared wi...
Conference Paper
Conference on Mechanics of Biomaterials & Tissues, Waikoloa, December 11-15, 2005, Hawaii, USA.
Article
Temporal evolution of laser generated cavitation bubbles and shock waves were studied. Q-switched Nd-Yag laser pulses at 1064 nm are focused into the liquid. An Imager 3 CCD camera with multi exposure mode allows recording of 10 images with minimal exposure delay of 100 ns and minimal exposure time of 100 ns. Illumination is provided by xenon flash...
Article
Full-text available
The uptake of the drugs by human organisms has long been one of the primary concerns of pharmacological research. The numerical model of the human cardiovascular and respiratory system with the baroreflex and chemoreflex regulation including the physiologically-based pharmacokinetic model and also the model of the drug-cardiac cell channels interac...
Article
The numerical simulation of the Korotkoff sounds is realized by a 14 segment hemodynamic model of the cardiovascular system developed in the Institute of Thermomechanics, Czech Academy of Sciences. The cardiovascular system is modeled by four segments of the pulsating heart and by 10 vascular segments of pulmonary and systemic circuits connected wi...
Article
A two-dimensional air impinging jet with a passive control has been studied experimentally, and smoke visualization, measurement of mean flow characteristics, and mass transfer experiments have been performed. Investigated flow field is intrinsically bistable, and two flow patterns exist under the same boundary conditions. The both patterns differ...
Article
Our objective is a better understanding of the role of physical properties of real fluids in the thermodynamics of cavitation in impure water. An extension to the classical homogenous nucleation theory suitable for mixtures is presented in attempt to address the discrepancy between the theoretical predictions and practical observations of cavitatio...
Article
The classical theory of homogeneous bubble nucleation is reconsidered by employing a phenomenological nucleation barrier in the capillarity approximation that utilizes the superheat threshold achieved in experiments. Consequently, an algorithm is constructed for the evaluation of the superheat temperatures in homogeneous boiling (tensile strengths...
Article
The aim of this investigation is to reconsider the classical theory of homogeneous condensation and bubble nucleation by using real properties of fluids and non-equilibrium (dissipative) effects. To find out the influence of a chemical composition on the surface tension and consequently on the nucleation work and further to elucidate how the nuclea...
Article
At elevated temperatures, droplet growth becomes very fast. We present a new method to generate a nucleation pulse using a shock tube. This method is particularly suitable for nucleation and growth studies at high-temperature conditions, because the falling edge of the nucleation pulse is very sharp. A comparison of the wave-based methods to genera...
Article
The basic rheological parameters of synovial fluids - shear stress and first normal stress difference were measured as a function of shear rate. In addition, the concentration of hyaluronic acid as a main component of synovial fluid was measured. Pathological synovial fluids were investigated (n = 120 samples) from various joint diseases, i.e. infl...
Article
The homogeneous nucleation with subsequent spontaneous condensation of water, pentanol, and ethanol vapors in a carrier gas are investigated experimentally and theoretically in the expansion part of a shock tube. The precise pressure and M CW measurements give additional information about the wetness, so that the nucleation and condensation rates w...
Chapter
This chapter experimentally and theoretically investigates the homogeneous nucleation with subsequent spontaneous condensation of the vapors of water, molecular mass Mv, in a carrier gas, Ar and He with molecular mass Mc,, in the expansion part of a shock tube. The amount of condensate produced in the condensation wave (CW) is evaluated by the prin...
Article
This study analyses forward problem of electrocardiology. Premature beats originated from subepicardial layer of myocardium were simulated in order to analyse their shape dependence on the site of origin. The equation governing the propagation of the electrical wave through human thorax together with transition and boundary conditions is derived un...
Article
A theory of embedded shock formation by homogeneous condensation in the centered rarefaction wave of a shock tube is presented. The necessary and sufficient conditions for the existence of such embedded shock waves are exhibited in a parabolic approximation to the family of intersecting characteristics. In particular the coordinates of the embedded...
Chapter
The onset of condensation of an argon-steam mixture in the expansion fan in a shock tube driver is experimentally measured by a Mach-Zehnder interferometer. The effect of a high expansion rate is determined and compared to the classical Volmer theory and the new DillmannMeier theory. The expansion of steam from states above of the saturation curve...
Article
A general equation for muscle energy balance is derived, describing irreversible macroscopic processes of energy transformation in a muscle as a whole, and the interaction of the muscle with its surroundings. The formulation of the equation stems from the balances of mass, mechanical energy, internal energy and entropy. The equation involves isoton...
Article
The expansion of steam from states in the upper surroundings of the saturation curve to states under this curve is simulated by the finite volume method. Main attention is given to the description of the condensation rate and droplet growth in molecular free flow.The dissipative properties of the numerical procedure are tested and compared with the...
Article
The influence of an artificial viscosity on the stability of numerical solution of transonic flows with shock waves is investigated. The variational principle with dissipation introduced through a physical viscosity is derived, and a simplified relation describing the stabilizing influence of the dissipative process is presented. The numerical solu...
Chapter
The mechanism of transonic instability on isolated profiles and on circular cylinder is described. The role of a circulation around the profile is decisive. The instability period is determined as the time needed for the movement of the disturbances around the leading edge. The resonance of this disturbances with the fluctuations in separated flow...
Article
Traditionally, optimal shape design has been treated as a branch of the calculus of variation and more specially of optimal control. This subject interfaces with no less than four fields: optimization, optimal control, partial differential equations and their numerical solutions, which is the most difficult aspect of the subject. In this paper, we...
Article
Dissipative processes which take place in thermoviscoelastic materials stabilize these materials with respect to small fluctuations of temperature, deformation and velocity. The limit of the stability for one-dimensional model of thermoviscoelastic body and for simple shear flow of Newtonian fluid is shown explicitly.
Article
The generalized thermodynamic stability criterion is used to derive the stability limits of transonic fluid flow. The important role of dissipation for the stability of hyperbolic problems is shown physically, numerically and experimentally. In the numerical procedure, dissipation is described by a so-called numerical viscosity μ n , which is propo...
Article
The generalized thermodynamic stability criterion is used to derive the stability limits of transonic fluid flow. The important role of dissipation for the stability of hyperbolic problems is shown physically, numerically and experimentally. The dissipation in numerical procedure is defined by numerical viscosity μ n , which is proportional to the...
Article
Numerical experiments show strong oscillations of the solution in regions with great gradients. The stability of the numerical procedure (FEM - implicit time stepping scheme) is investigated and the stability condition is derived. The instability arises for the Courant number equal to (m/(2π))2. Numerical experiments show that the most dangerous va...
Article
A draft of a new method for the simulation of the coarsening of carbides under spatially non-homogeneous conditions was elaborated. For calculations the time and the local variations in the concentration of the carbide-forming elements, the temperature, the mechanical stress etc. can be considered. The method can be used to solve approximately exam...
Article
1. Respiration Oxygen-uptake by respiration in organisms decomposes macromolecules such as carbohydrate, protein and lipid and liberates chemical energy of high quality, which is then used to chemical reactions and motions of matter in organisms to support lively order in structure and function in organisms. Finally, this chemical energy becomes he...
Article
The method of the local potential is applied to the flow past an arbitrary body. First, the derivation of the local potential is derived for the general case from a stability condition on the fluctuations of the macroscopic quantities describing a macroscopic body. Then the local potential is derived for the flow of a perfect compressible fluid. Th...
Article
Full-text available
The classical theory of homogeneous bubble nucleation is reconsidered by employing a phenomenological nucleation barrier in the capillarity approximation that utilizes the superheat threshold achieved in experiments. Consequently, an algorithm is constructed for the evaluation of the superheat temperatures in homogeneous boiling (tensile strengths...