The paper presents the results of systematic measurements of the thermal conductivity coefficient of nanofluids at room temperature. In total, more than fifty various nanofluids based on water, ethylene glycol, and engine oil containing particles of SiO2, Al2O3, TiO2, ZrO2, CuO, and diamond were studied. The nanoparticles volume concentration ranged from 0.25 to 8% and the particles size ranged from 10 to 150 nm. It is shown that the thermal conductivity of nanofluids is not described by the classical theories (Maxwell's and so forth). The nanofluid thermal conductivity coefficient is a complicated function not only of the particle concentration, but also the particles size, their material, and type of base fluid. Measured thermal conductivity coefficients almost always exceed the values calculated by the Maxwell's formula, though nanofluids with sufficiently small particles may have thermal conductivity coefficients even lower than those predicted by the Maxwell theory. However, in all cases, the nanofluid thermal conductivity coefficient enhances with increasing particle size. It is convincingly shown that there is no direct correlation between the thermal conductivity of the nanoparticle material and the thermal conductivity of nanofluid containing these particles. The base liquid also significantly influences the effective thermal conductivity of the nanofluid. It has been confirmed that the lower the thermal conductivity of the base fluid, the higher the relative thermal conductivity coefficient of the nanofluid.

The paper presents the results of experimental study of rheological behavior of nanofluids based from consideration of several tens of nanofluids based on water, ethylene glycol and engine oil, containing particles of different oxides and diamond. The sizes of nanoparticles ranged from 5 to 150 nm, while their volume concentration ranged from 0.25 to 8%. At that, no dispersants were used when preparing tested nanofluids. It is shown that in some cases, when increasing nanoparticle concentration, rheological behavior of nanofluids becomes non-Newtonian and is well described by power-law fluid models or Herschel-Bulkley fluids. The influence of nanoparticle size and material, as well as the nature of the base fluid on the rheological behavior of nanofluids have been studied.

No abstract

Проведено экспериментальное исследование зависимости числа Прандтля для наножидкости от концентрации, размера и материала наночастиц. Исследуемые наножидкости были приготовлены на основе дистиллированной воды и наночастиц оксидов кремния, алюминия, титана и циркония. Объемная концентрация наночастиц изменялась в диапазоне от 1% до 8%. Диаметр наночастиц варьировался от 10 до 150 nm. Установлено, что с ростом концентрации наночастиц число Прандтля для наножидкостей возрастает. При этом показано, что значение числа Прандтля существенно зависит от размера частиц. С увеличением размера частиц число Прандтля для наножидкостей уменьшается.

No abstract

No abstract

The experiment investigation of turbulent forced convection of nanofluids with SiO2 and

No abstract