Depends on the Reynolds number - not only your velocity, but also your viscosity and your length scale determine if your flow is turbulent or laminar.
So check out your Reynolds number. If you are doing an experiment, Re=2000-3000 should be sufficient. If you do numerical simulations, it depends a little bit on your code and how you trigger turbulence.
In the case a Newtonian fluid is used it is indeed the Reynolds number one has to estimate. In the case of a viscoelastic fluid, turbulent motion may be triggered when the Weissenberg (Wi) number exceeds unity. This is the so called Elastic Turbulence. To estimate Wi in a microchannel one can simply multiply the largest relaxation time of the viscoelastic solution with a scale of the velocity gradients (a rough estimate is simply the average velocity divided by half channel width).
It depends on the Reynolds number you choose...Possibly 2500 plus will give a turbulent flow as i believe u deal with Newtonian fluid...All the best
The laminar-turbulent transition occurs in the range of Reynolds numbers from 2000 to 3000 for both micro- and macro-channels. But for the flow in micro-channels two factors have to be taken into account: the value of the Knudsen number (Kn) and the relative value of the roughness.
Namely, for a gases at pressures up to about 10 - 20 atm, the corresponding Kn of the micro-currents lies in the range: 10 ^ (- 2)
Dear rishnayan Haldar
It is still a questionable issue. Some experimental results concerning microchannels are different from our knowledge about macro-channels. For example, Wu and Little (1983;1984) obtained that the transition from laminar to turbulent flow occurs at Re = 400-900 for different geometries. On the other hand, Peng et al. (1994a;b) indicated that the flow would be fully turbulent at 400-1500 and higher Reynolds numbers.
Wu, P.Y. and Little, W.A., Measurement of Friction Factor For The Flow of Gases in Very Fine Channels Used For Microminiature Joule-Thompson Refrigerators, Cryogenics, 1983, 23(5), 273-277.
Wu, P.Y. and Little, W.A., Measurement of Heat Transfer Characteristics of Gas Flow in Fine Channels Heat Exchangers Used For Microminiature Refrigerators, Cryogenics, 1984, 24(5), 415-420.
Peng, X.F., Peterson, G.P. and Wang, B.X., Frictional Flow Characteristics of Water Flowing Through Micro-Channels, Experimental Heat Transfer, 1994a, 7, 249-264.
Peng, X.F., Peterson, G.P., and Wang, B.X., Heat Transfer Characteristics of Water Flowing Through Micro-Channels, Experimental Heat Transfer,1994b, 7, 265-283.
GL
Maziar
- Badges
- Science topic
- Similar topics
- Philosophy
- Philosophy Of Science
- Reasoning