Model for predicting the critical size of aggregates in nanofluids

Stable suspension of the nanoparticles in the base fluids is inevitable to have the nanofluids be operated properly. Here we report the theoretical model to find the critical size of aggregates in nanofluids for the first time. The concept of relaxation time τ _r is adopted, which reflects the probability of encountering the particles. The hydrodynamic diameter of the aggregates in nanofluids must be kept below the critical size to be stably suspended, which is in good agreement with the experimental results.