Mass transfer phenomena in biofilm systems

2000 ◽  
Vol 41 (4-5) ◽  
pp. 357-360 ◽  
Author(s):  
S. Wäsche ◽  
H. Horn ◽  
D.C. Hempel

Mathematical models allow the simulation of microorganism growth and substrate transport in biofilm systems. Nevertheless there is still a lack of knowledge about the mass transfer of substrate in the boundary layer between biofilm and bulkphase. Several biofilms were cultivated under different substrate and hydrodynamic conditions in a biofilm tube reactor. Oxygen concentration profiles were measured with oxygen microelectrodes in the biofilm and in the boundary layer. The thickness of the concentration layer was found to depend on surface structure which depends on the substrate loading and the hydrodynamic conditions during the growth phase of the biofilm. Biofilm density and maximum substrate flux were also influenced by growth conditions. An empirical function for the concentration layer thickness was formulated for biofilms grown under different conditions to describe transport phenomena in the boundary layer.

1998 ◽  
Vol 37 (4-5) ◽  
pp. 139-147 ◽  
Author(s):  
Harald Horn ◽  
Dietmar C. Hempel

The use of microelectrodes in biofilm research allows a better understanding of intrinsic biofilm processes. Little is known about mass transfer and substrate utilization in the boundary layer of biofilm systems. One possible description of mass transfer can be obtained by mass transfer coefficients, both on the basis of the stagnant film theory or with the Sherwood number. This approach is rather formal and not quite correct when the heterogeneity of the biofilm surface structure is taken into account. It could be shown that substrate loading is a major factor in the description of the development of the density. On the other hand, the time axis is an important factor which has to be considered when concentration profiles in biofilm systems are discussed. Finally, hydrodynamic conditions become important for the development of the biofilm surface when the Reynolds number increases above the range of 3000-4000.


Author(s):  
P. Sudarsana Reddy ◽  
A. Chamkha

Purpose In recent years, nanofluids are being widely used in many thermal systems because of their higher thermal conductivity and heat transfer rate. The higher thermal conductivity depends on many parameters such as size, shape and volume and the Brownian motion and thermophoresis of added nanoparticles. The purpose of this paper is to analyze the influence of the Brownian motion and thermophoresis on natural convection heat and mass transfer boundary layer flow of nanofluids over a vertical cone with radiation. Design/methodology/approach Using similarity variables, the non-linear partial differential equations, which represent momentum, energy and diffusion, are transformed into ordinary differential equations. The transformed conservation equations are solved numerically subject to the boundary conditions by using versatile, extensively validated, variational finite-element method. Findings The sway of significant parameters such as magnetic field (M), buoyancy ratio parameter (Nr), Brownian motion parameter (Nb), thermophoresis parameter (Nt), thermal radiation (R), Lewis number (Le) and chemical reaction parameter (Cr) on velocity, temperature and concentration evaluation in the boundary layer region is examined in detail. The results are compared with previously published work and are found to be in agreement. The velocity distributions are reduced, while temperature and concentration profiles elevate with a higher (M). With the improving values of (R), the velocity and temperature sketches improve, while concentration distributions are lowered in the boundary layer region. The temperature and concentration profiles are elevated in the boundary layer region for higher values of (Nt). With the increasing values of (Nb), temperature profiles are enhanced, whereas concentration profiles get depreciated in the flow region. Social implications In recent years, it has been found that magneto-nanofluids are significant in many areas of science and technology. It has applications in optical modulators, magnetooptical wavelength filters, tunable optical fiber filters and optical switches. Magnetic nanoparticles are especially useful in biomedicine, sink float separation, cancer therapy, etc. Specific biomedical applications involving nanofluids include hyperthermia, magnetic cell separation, drug delivery and contrast enhancement in magnetic resonance imaging. Originality/value To the best of the authors’ knowledge, no studies have assessed the impact of the two slip effects, namely, Brownian motion and thermophoresis, on the natural convection of electrically conducted heat and mass transfer to the nanofluid boundary layer flow over a vertical cone in the presence of radiation and chemical reaction; therefore, this problem has been addressed in this study. Comparison of the results of this study’s with those of previously published work was found to be in good agreement.


2016 ◽  
Vol 8 (2) ◽  
pp. 119-128 ◽  
Author(s):  
M. Ali ◽  
M. S. Alam ◽  
M. Z. U. Chowdhury ◽  
M. A. Alim

The present paper is an investigation of steady MHD free convection, heat and mass transfer flow of an incompressible electrically conducting fluid over a stretching sheet in a rotating system under the influence of an applied uniform magnetic field with Hall current. The governing equations are transformed to a system of non-linear ordinary differential equations which are then solved numerically by the shooting method. The numerical results concerned with the primary velocity, secondary velocity, temperature and concentration profiles, effects of various parameters on the flow fields are investigated and presented graphically. The results presented graphically illustrate that primary velocity field decrease due to increase of rotational and magnetic parameter but reverse results arises in case of Hall and heat generation parameter while secondary velocity decrease for stretching parameter and increase for Hall, rotational and magnetic parameter. The thermal boundary layer decreases for the increasing values of mentioned parameter. Also, concentration profiles decreases for increasing the values of magnetic parameter, rotational parameter, reaction parameter and Schmidt number but increases for heat generation and Dufour number. Finally, the numerical values of the skin friction, wall temperature gradient and concentration gradient are also shown in a tabular form.


2002 ◽  
Vol 46 (1-2) ◽  
pp. 249-252 ◽  
Author(s):  
H. Horn ◽  
S. Wäsche ◽  
D.C. Hempel

The hydrodynamic conditions and the substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the substrate conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, substrate conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.


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