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Abstract
When the size of fluidic devices is scaled down, inertial effects start to vanish such that the governing equation becomes linear. Some microfluidic devices rely on the nonlinear term related to the inertia of the fluid, and one example is fluid rectifiers (diodes) e.g. related to some micropumps. These rectifiers rely on the device geometry for their working mechanism, but on further downscaling the inertial effect vanishes and the governing equation starts to show symmetry properties. These symmetry properties reduce the geometry influence to the point where fluid rectifiers cease to function.
In this context it is natural to look for other sources of nonlinearity and one possibility is to introduce a nonNewtonian working fluid. NonNewtonian properties are due to stretching of large particles/molecules in the fluid and this is commonly seen for biological samples in “labonachip” systems. The strength of nonNewtonian effects does not depend on the device size. Furthermore a nonNewtonian working fluid removes symmetry properties such that geometry influence is reintroduced, and indeed nonNewtonian effects have been used in experimentally realized microfluidic rectitifiers[1].
The rectifiers in [1] have the simplest thinkable nonsymmetric geometry, but the relation between the geometry and the corresponding working behavior is nonintuitive. This indicates that we will be able to enhance the performance of these devices by changing the design. For this purpose we use the method of topology optimization, which is a kind of design optimization where nothing is assumed about the topology of the design. We will apply a highlevel implementation of topology optimization using the density method in a commercial finite element package[2].
However, the modeling of nonNewtonian fluids remains a major scientific challenge, but progress continuous and it is now possible to model systems in a parameter regime where actual devices work. Presently we have implemented a stateoftheart model of a nonNewtonian fluid and used this model for topology optimization of a nonNewtonian rectifier. In this way we have found designs that are topologically different from previously experimentally realized nonNewtonian rectifiers.
NonNewtonian microfluidics is not at all restricted to rectifiers. The project outlook thus relates to optimization of bistable fluid devices, as experimentally demonstrated in [3]. Due to the nonintuitive nature of nonNewtonian microfluidics, there is even the possibility of finding new devices with the help of topology optimization: That is rather than improving existing devices, we can imagine a novel device, then define an objective function and finally investigate the feasibility of the device idea using topology optimization.
In this context it is natural to look for other sources of nonlinearity and one possibility is to introduce a nonNewtonian working fluid. NonNewtonian properties are due to stretching of large particles/molecules in the fluid and this is commonly seen for biological samples in “labonachip” systems. The strength of nonNewtonian effects does not depend on the device size. Furthermore a nonNewtonian working fluid removes symmetry properties such that geometry influence is reintroduced, and indeed nonNewtonian effects have been used in experimentally realized microfluidic rectitifiers[1].
The rectifiers in [1] have the simplest thinkable nonsymmetric geometry, but the relation between the geometry and the corresponding working behavior is nonintuitive. This indicates that we will be able to enhance the performance of these devices by changing the design. For this purpose we use the method of topology optimization, which is a kind of design optimization where nothing is assumed about the topology of the design. We will apply a highlevel implementation of topology optimization using the density method in a commercial finite element package[2].
However, the modeling of nonNewtonian fluids remains a major scientific challenge, but progress continuous and it is now possible to model systems in a parameter regime where actual devices work. Presently we have implemented a stateoftheart model of a nonNewtonian fluid and used this model for topology optimization of a nonNewtonian rectifier. In this way we have found designs that are topologically different from previously experimentally realized nonNewtonian rectifiers.
NonNewtonian microfluidics is not at all restricted to rectifiers. The project outlook thus relates to optimization of bistable fluid devices, as experimentally demonstrated in [3]. Due to the nonintuitive nature of nonNewtonian microfluidics, there is even the possibility of finding new devices with the help of topology optimization: That is rather than improving existing devices, we can imagine a novel device, then define an objective function and finally investigate the feasibility of the device idea using topology optimization.
Original language  English 

Publication date  2012 
Number of pages  1 
Publication status  Published  2012 
Event  The 2011 Fluid•DTU Summer School: The 2011 Fluid•DTU Summer School Complex Motion in Fluids  Krogerup Højskole, Krogerup, Denmark Duration: 7 Aug 2011 → 13 Aug 2011 http://www.fluid.dtu.dk/English/Events/Summer_School_2011.aspx 
Course
Course  The 2011 Fluid•DTU Summer School 

Location  Krogerup Højskole 
Country/Territory  Denmark 
City  Krogerup 
Period  07/08/2011 → 13/08/2011 
Internet address 
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 1 Guest lectures, external teaching and course activities at other universities

The 2011 Fluid•DTU Summer School
Kristian Ejlebjærg Jensen (Speaker)
9 Aug 2011Activity: Talks and presentations › Guest lectures, external teaching and course activities at other universities
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