It was concluded after reviewing the literature that the existing medium theory (Maxwell model) cannot explain this anomalous increase of thermal conductivity of nano-particles that are suspended in fluid (nano-fluids). This new mechanism restricts the definition of nano-particles as particle that perfectly obeys the Gibbs rule of thermodynamics and act as a chemical actuator during heat transfer. This driving force for the chemical actuator is the microstructure phase change of the passive layer during heat transfer. The new mechanism require the presence of nano-convection (Brownian motion) in the vicinity of nano-particles surface, explain temperature and particles size dependency, require the presence of a shell or a sheath where chemical interaction occurs between the surface and the fluid and many others. The high rate of heat transfer of the nano-fluid is due to first, the bubbles formations inside the passive layer and their departure from grain boundaries and second due to nano-convection generated in the vicinity of the nano-particles of the nano-particles as result of the chemical actuation of the nano-particles. This nano-convection produces Brownian motion which increase rate of heat transfer.

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