Lesser particle momentum, high mobility and larger surface area are the features that made nanoparticles a prospect in the field of suspended particles.
In the terms of thermal conductivity, use of multi-walled carbon nanotubes (MWCNTs) as a suspended particle can increase the thermal conductivity by 20,000 times as compared to engine oil at room temperature.
If the proper dispersion of nano-fluid is achieved, they are expected to provide the following advantages over a simple liquid coolant.
Higher heat conduction of nanofluid
Nano-particles have larger surface area which increases the rate of heat transfer. Particles whose size is less than 20nm have 20% of their atoms on their surface which are readily available for heat transfer purposes.
Nano-particles due to their tiny size have high mobility and can bring about micro-convection which can increase the rate of heat transfer. The increased rate of heat transfer and micro-convection can also increase the rate of heat dissipation in fluid.
This is already known that increase of thermal conductivity in Nano-fluid rises significantly with the rise in temperature which can be related to the facts discussed above.
Stability of nanofluid
Nano-particles have small size and hence have less weight due to which the susceptibility of sedimentation is also less. Sedimentation, which is a major issue in suspended particles can be curbed using Nano-fluids and hence it makes Nano-fluids relatively more stable.
Micro-channel cooling without clogging using Nanofluids
Nano-fluids are not only a better option for heat transfer purposes in general, but they are also very ideal in the application of micro-channels where the heat load is very high.
A combination of Nano-fluids and micro-channels can provide large surface area and high thermal conductivity which cannot achieved with micro or meso-particles because they can clog in the micro-channels.
Nano-particles that have very few number of atoms are very small in size as compared to the size of micro-channels.
Reduced chances of erosion using Nanofluids
Nano-particles have less momentum due to their smaller size and lesser weight and hence they are not able to transfer high amount of momentum to the channel walls.
So, when the momentum is lower, the probability of erosion of pipelines, pumps and heat exchanger becomes less.
Reduction in pumping power using Nanofluids
To double the amount of heat transfer in the case of conventional fluid, pumping power should be increased by ten times.
It can also be shown that the rate of heat transfer is doubled in the same equipment when the thermal conductivity is tripled [15]. But, in the case of Nano-fluids the increase in pumping power is very nominal unless the fluid viscosity becomes very high with the introduction of Nano-particles.
Thus, large amount of pumping power can be saved if the volume fraction of Nano-particles is small. Nature, often, proves itself to be more thrilling than fascination.
According to Henry Becquerel, uranium ore absorbed sunlight and radiated it back until the concept of radioactivity was discovered and it was revealed that uranium emits radiations without absorbing sunlight.
In the similar fashion, Nano-fluids showed attributes that were beyond the expectations [16]. Four unique attributes of Nano-particles are given below.
a. Abnormal enhancement of thermal conductivity. Nano-particles show an abnormal increase in thermal conductivity. This abnormal increase in the thermal conductivity was the most significant feature and it was way beyond the expectations. None of theory was able to predict the increase that they had shown.
b. Nano-fluids have proved their self to be more stable as compared to the use of stabilizing agent .
c. Small concentration and Newtonian behavior. As discussed earlier, Nano-particles depicted a sharp increase in thermal conductivity even with the small concentrations of Nano-particles. This helped fluid to maintain its Newtonian behavior because the increase in viscosity was very less and increase in pressure drop was also very nominal.
d. Particles size dependence. In the case of micro-slurries, the thermal conductivity varied with size of particles. But in the case of Nano-particles, the thermal conductivity remained the function of concentration only. At large, increase in thermal conductivity was noticed with the decrease in particle size.
No comments:
Post a Comment