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This paper aims to study the convective heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal tube heated under constant heat flux condition. Consideration is given to the effects of particle concentration and Reynolds number on heat transfer enhancement and the possibility of nanofluids as the working fluid in various heat exchangers. It is found that (i) significant enhancement of heat transfer performance due to suspension of nanoparticles in the circular tube flow is observed in comparison with pure water as the working fluid, (ii) enhancement is intensified with an increase in the Reynolds number and the nanoparticles concentration, and (iii) substantial amplification of heat transfer performance is not attributed purely to the enhancement of thermal conductivity due to suspension of nanoparticles.

The Fe₃O₄ nanoparticles coated by citrate (citric acid, CA) were prepared by chemical co-precipitation method. Via Stokes polarimeter, the variation of retardance in water-based CA coated Fe₃O₄ ferrofluids (FFs) with different molarities of CA solutions was measured and compared. Next, the verification of the sample with the second high retardance using orthogonal test of L₉(3⁴) in our previous study was executed. Further, the heating performance of this CA coated FF sample with high magnetic retardance and response in the alternating magnetic field was investigated. When the concentrations of CA coated FFs were 2mg/ml and 50mg/ml, under the external alternating magnetic field with applied apparent current of 300A, after heating 76s and 16s, the temperature of the CA coated FFs is greater than 45°C, respectively, reached the requirements for the magnetic inductive heating treatment of medicinal cancer tumor.